Monthly Archives: September 2016

Douglas C-47b G-APBC British Midland

Why airplane windows are round

Why are airplane windows rounded?

You may have wondered why airplane windows are round. Yes, it does look more sleek perhaps

Jet Airliner Window

Today we are used to all our airliner windows being oval.

and gives a streamlined impression. To be honest as far as streamlining goes it matters not whether the windows are square, round or some other shape, as they are flush with the fuselage metal and the air goes past them just as happily. So, is there another reason for rounded windows?

The answer, of course, is yes. Every feature of an aircraft exists for a very specific reason. Designs of various components are normally in place to respond to certain conditions that exist in various phases of flight to which the aircraft will be exposed. These can be anticipated conditions which designers are aware of, or they can be the result of lessons learned in the school of hard knocks.

The design of aircraft windows falls into the school of hard knocks category.

In the early days of aviation when passengers were first being carried, windows were found to be required as people would tend to become quite claustrophobic in a windowless tube. In spite of the weight penalty incurred by adding slabs of perspex at regular intervals along the side of the fuselage, designers resigned themselves to the necessity if they were to carry more than just cargo.

The early airliner windows resembled those you might find on a bus.  They were usually rectangular in shape and came in various sizes depending on who’s aircraft you were in. Passengers would have the opportunity to enjoy the view and assure themselves that they were indeed flying right side up.

This worked like a dream, everyone was happy, passengers enjoyed the flying experience quite happily entering this metal or canvas tube to be taken aloft and deposited at some distant location. This applied to propeller airliners and worked well in their operating range of altitudes to a maximum of the mid 20,000s of feet.

Junkers_Ju52.3m_G-AHOF_BEA_Ringway

A German made Junkers J-52 airliner with traditional square windows. This was not a problem for low-flying propeller aircraft.

Enter the jet age

In the early 1950s, there was a new sound in the sky. Jet engines were used for the first time on passenger transport aircraft. The de Havilland Comet was a radical new concept in passenger travel. With its four jet engines buried in the wing roots, it was a very sleek looking aircraft for the period. The Comet offered faster travel times as compared to its propeller predecessors partly due to its ability to fly higher in thinner air, which propeller engines were not capable of doing.

Comet Prototype at Hatfield with square windows

The jet age came to passenger air travel in the form of the de Havilland Comet. The prototype is seen here at Hatfield, England with square windows.

For a year, the Comet enjoyed huge success. It was popular with passengers as the higher altitude flights meant not only faster travel times but also smoother flying due to the Comet’s ability to fly above most of the turbulent weather, that propeller aircraft were forced to fly through

The cause of these accidents had investigators baffled. With all the pieces of wreckage retrieved, they could ascertain that the aircraft suffered catastrophic structural failure. Eventually, they were able to pinpoint the source of the break up to a point in the roof of the fuselage. It took some time before they finally worked out the route cause.

Effects of high altitude flying.

As mentioned earlier, propeller aircraft are limited to how high they can fly. This means that the effect of high altitude flying is not really a factor in their day to day operation. Let’s look, however, at jet airliners. These aircraft fly much higher, often twice as high as their propeller driven cousins.

We know that we as humans can only survive below a certain altitude if we are not to succumb to the effects of hypoxia. This in simple terms means we need to have a certain amount of oxygen in the air we breathe or we will lose consciousness and eventually perish. Airliner manufacturers are aware of this situation and have as a result come up with pressurisation in aircraft cabins when it is anticipated that this aircraft will climb above the acceptable altitude.

In the past, most airliners have offered a cabin pressure which is approximately equivalent to the pressure at 10,000 feet above sea level. In today’s more modern aircraft such as the Airbus A350 or Boeing 787 Dreamliner, the pressure offered is closer to that found at 6,000 feet above sea level.  Obviously the lower the pressure altitude, the more comfortable it is for the passengers as it is closer to what they are used to on the ground.

Let’s look at what this does to the aircraft fuselage. An aircraft such as an A350 takes off from sea level and commences its climb to a cruise altitude of let’s say 35,000 feet above sea level. As it climbs out, the air inside and outside the aircraft are of equal pressure. On passing 6,000 feet, the pressurisation system kicks in. As climb continues, the cabin pressure is held at that which was found at 6,000 feet. On the outside, however, the pressure continues to fall the higher the aircraft climbs. On reaching the cruise altitude of 35,000 feet, the pressure differential between outside and inside is almost 6 times. There is almost 6 times more air pressure inside the aircraft then outside.

Todays aircraft are made from various metal alloys and have a very high strength to weight ratio. This notwithstanding, there is still some anticipated growing and shrinking of the fuselage each time the aircraft climbs and descends. Each takeoff, climb and descent and landing is known as a cycle. Aircraft with very high cycle amounts are those that are used on short domestic hops as opposed to those doing long trans-continental or trans-oceanic flights. These aircraft are rigorously checked for any cracks or metal fatigue resulting from many cycles where the fuselage is subject to many expansion and contraction events.

Before the advent of the jet age, the understanding of the effects of cycles and metal fatigue were not understood as they had not applied to airliners that had been used thus far. It was not until the Comet flew much higher and endured many cycles that things unravelled. The Comet still flew fairly short hops by today’s standards, much like the propeller aircraft of the day. A trip from London to Singapore would involve many stopovers such as; London, Rome, Cairo, Karachi, Calcutta, Rangoon, Singapore. That is 6 cycles for one trip.

Square Windows

As mentioned above, investigators of the Comet crashes were able to pinpoint the source of the structural failure to a point in the fuselage roof. It seemed as if a crack had opened up along one of the joins between pieces of the aluminium skin. After some time and testing, it was found that the crack had started at the corner of one of the windows.

Window section of Fuselage of de Havilland Comet Airliner G-ALYP which was the third Comet built. On 10 January 1954 after taking of from Rome enroute London Heathrow, the aircraft broke up near the island of Elba on the Italian coast.

Window section of Fuselage of de Havilland Comet Airliner G-ALYP which was the third Comet built. On 10 January 1954 after taking off from Rome en route London Heathrow, the aircraft broke up near the island of Elba on the Italian coast. From this, investigators made the shock discovery of the effects of metal fatigue on square windows.

The Comet was designed with square windows just like its propeller-driven ancestors. Unlike its propeller-driven ancestors, the Comet experienced a much more extreme difference in pressures as it flew much higher. Tests showed that structural pressures would always find the weakest point, which in this case was the corner of a square window. Instead of pressure being absorbed evenly throughout the structure it found the window corner was the weakest point which became the focus of the pressure.

Dan-Air London Comet 4C G-AYWX

The de Havilland Comet with rounded windows continued on to a successful 30 years of service. Here we see the larger Comet 4C model which included round windows and wing pods for additional fuel.

The Comet was grounded for two years while the research was conducted and corrections were made to the design. Whilst the Comet mark one never flew again and sales were severely affected for the following versions, it still went on to have a successful 30 years of life with rounded windows.

So why do we have rounded windows on aircraft? It is to maintain structural integrity and distribution of the considerable forces applied to the fuselage evenly.

Mystery of MH370

Where is MH370 two years on?

Here we are, 2 years down the taxi way from one of aviation’s biggest mysteries. Two years ago 239 passengers and crew settled in for a routine flight from Kuala Lumpur to Beijing. The Boeing 777 belonging to Malaysia’s national flag carrier, Malaysia Airlines, lifted off into the balmy Malaysian night and flew into history. Now on the second anniversary of the aircraft’s disappearance, we seem no closer to finding an answer.

Like MH370, a Malaysia Airlines Boeing 777 lifts off.

Like MH370, a Malaysia Airlines Boeing 777 lifts off.

Now on the second anniversary of the aircraft’s disappearance, we seem no closer to finding an answer.

it sends inconceivable in today’s high tech world that we can lose a big airliner so utterly and completely. It goes to show that we haven’t quite got the ability to track the movement of everything that goes on in our world.
Since that fateful night two years ago, there have been so many theories of cover-ups, lies, and deception. Was it done by a rogue pilot? Was the aircraft deliberately flown below the radar to enable it to be hijacked elsewhere? Was the aircraft flown in the shadow of a Singapore Airlines flight to enable it to be flown to Central Asia undetected.

The initial search area for MH370.

The initial search area for MH370 centred on the logical areas around the Malaysian Peninsula.

We’ve heard of an oil rig worker seeing a ball of fire crash into the sea in the distance in the South China Sea.

We’ve heard of inhabitants of an island in the Maldives, where large airliners are rarely seen, reporting a low-flying large jet flying overhead hours after the disappearance of the Malaysian Airlines Boeing 777. This prompted a theory about the jet being flown to a small atoll called Diego Garcia which lies just south of the equator in the middle of the Indian Ocean  and belongs to Great Britain.

It just goes to show that we do not take readily, as humans, to unexplained situations and work to fill the void with theories of what we think the likely train of events may have been. It also serves to show we are quite willing to believe some fairly far-fetched theories to fill the void of actual knowledge.

But as usual, it seems fact is stranger than fiction. Of all the far-fetched scenarios, who came up with one where the airliner found its way into the southern reaches of the Indian Ocean? No one as far as I can recall.

I must admit that when I first heard of it, I was amazed why someone would believe such a far-fetched story. Of all the stories I had heard, this seemed to be the most fanciful.  A flight that was headed north ends up being further south than it was ever intended to go north.

The current search areas determined by satellite pings as well as fuel range limits of MH370.

The current search areas determined by satellite pings as well as fuel range limits of MH370.

Those engine ping handshakes that gave the arc of area where the aircraft is supposed to have been, were obviously conclusive enough for several governments to throw in millions of dollars’ worth of search time and resource. While it is admirable that governments are seen to be caring about those poor souls who perished, and those who are left behind wondering what became of their loved ones. I am often left wondering why the Southern Indian Ocean scenario was so readily accepted so quickly and that governments were so quick to be prepared to throw millions at the project.

I am not trying to promote any of the conspiracy theories. I do find it strange that not one floating object such as seat squabs, neck pillows and other floating objects have never been found. These objects are more susceptible to wind-driven effects, as opposed to the flaperon found on Reunion and the alleged horizontal stabiliser piece found in Mozambique that would have floated below the surface and been more influenced by ocean currents.

There are of course many kilometres of uninhabited coast lines around the Indian Ocean, but something should turn up somewhere and be found. If the flaperon and other piece were ripped off the aircraft, I feel it safe to assume the fuselage did not stay intact to contain all the loose objects that should have floated away.

I just hope that something is found soon. The friends and relatives need closure and aviation needs to know what happened and how it happened so steps can be taken to remove the likelihood for the future.

Aviation because safer as we learn from accidents and incidents and build process to prevent it happening again.

I don’t pretend to be an expert in any way shape or form and would love to hear the opinion of others. Feel free to join the discussion below.

Plane Spotting and Plane Spotters

Plane Spotting

Very few of us can resist watching and taking in the sound of raw power as a jet liner makes its take off run and claws its way into the sky. Plane spotting or plane watching is a pass time enjoyed by many. You don’t have to be a plane spotter as such but just someone who has a few minutes to spare as you head past the airport, or a parent giving your kids the thrill of the beauty of flight. The planes themselves are a marvel to watch as they make their precision landings and powerful take offs. But this also stirs the imagination around where they are going and where they are coming from, conjuring up images of far-flung places.

Access to airfields for plane spotting

Every airport is different, some are easily accessible for plane spotters, while others present quite a challenge. With the extra security around air travel these days, airfield operators are keen to keep as much distance between the public and operating aircraft as possible.

Mangere Airport

Some airports, like Auckland’s’ Managere Airport are challenging as they are surrounded by water. Sometimes going off the airport location can give you a better vantage point.

The first thing to do is to familiarise yourself with the airfield. If it is your hometown you may already know all the locations that are appropriate for getting good views of the runway. If you are not familiar, then Google Maps is a good way of getting a feel for the best places to try. It may be a little hit and miss at first as you might find some of the roads indicated on the map are private access roads and not for public use. Be sure to comply with all access rules as security is taken very seriously today and heavy fines could apply.

Best views for plane spotting

As I said, some airfields offer more choices of locations for plane spotters due to the nature of the topography of the countryside in which they are located. Maybe they are surrounded by industry with warehouses blocking the view, or maybe they protrude out into the water with no way of getting close. Whatever the situation, there is usually some location that offers the opportunity to catch sight of air traffic coming and going.

Where to be to watch taking off aircraft.

Where to be to watch taking off aircraft.

When you do have a choice of locations, you need to decide which phase of the landing and take-off phase you want to see. Do you want to be in the middle where you can see taking off aircraft rotate and begin to climb out as well as landing aircraft completing their landing roll. Do you want to be at the end of the runway where you can either having taking off aircraft climbing over you or landing aircraft descending over you? Each time you go and plane spot, you can choose a different experience and if you are so inclined, add to your photo collection.

Where to be to watch landing aircraft.

Where to be to watch landing aircraft.

Conditions to help you choose your plane spotting location.

As we know, aircraft operations are very weather dependent. Aircraft fly in almost all weathers, however, it is how they fly that changes. The wind plays a critical part of how the airfield is used due to the fact that aircraft must take off and land into the wind. This reduces the length of runway they require, as the air is already moving over their wings before they even start their take-off roll. This will perhaps affect the location you choose to plane spot.  For instance, if you stand at the upwind or windward end of the runway on a windy day, you may possibly not see many aircraft up close. The arriving aircraft will stop more quickly as their speed across the ground is slower on landing. Taking off aircraft may be quite high by the time they cross over you, as their rate of climb will appear much steeper. A location closer to the downwind end of the runway would be better.

The angle of the sun is also another aspect to consider. Even if you are not photographing the planes, you will be more comfortable with the sun behind you than having to look into it. Aircraft rise into the sky and as you follow them with your eyes you will likely look directly into the sun. Be aware of the orientation of the runway you want to visit. If it runs north/south then try to be on the east side in the morning and the west side in the afternoon. If you are photographing the aircraft then you will ensure that the detail and colourful liveries of the airliners are nicely represented instead of that disappointing shot turning out to be little more than a silhouette.

Plane Spotting Photography

Like any kind of photography, the sky is the limit on what you could spend on getting the best equipment. This is great for those who live and breath aircraft and perhaps make an income through flight photography. These are the enthusiasts who have huge telescopic lenses, tripods and all sorts of other paraphernalia.

For most of us, this is not the case. We love to watch aircraft and even like to build up a nice collection of photos of the aircraft we have seen. So long as your camera has a reasonable zoom lens on it and you are not 5 kilometres from the runway, then you have a reasonable chance of capturing some great snaps.

The other thing that can help you is to be sure your camera has a good megapixel rate. I will be honest, many of my earlier pictures were done on my phone which sports 13 megapixels. How this helps is that even if you zoom can’t get you close enough, the density of the picture can go some way to making up for it, in fact quite a long way. Once you have your picture on screen you might find your aircraft occupies a quarter or maybe even less of the picture. By cropping it and zooming in you may find that you still end up with quite a nice picture.

The picture below of the QANTAS A330 was such a picture. It was quite a long way off, but because the megapixels were quite high I was still able to crop and zoom in to feature this aircraft. To do this I simply used the default Windows Picture viewer which as an edit function. Not rocket science, nor in any way costly.

You might also notice that I didn’t adhere to my own advice as relates to the sunlight. The colours would have been more vibrant had I been on the other side of the aircraft. On this occasion I been there very early to capture dawn pictures, which put me on the western side of the airfield in the morning.

QANTAS A330 climbing out at Sydney

A QANTAS Airbus A330 climbs out from runway 34L at Sydney Airport

Alternative places for plane spotting.

It may sound a little strange, as where else would you go to spot planes other than an airfield? As nice as it would be to get some good views of aircraft in level cruise, it is not really possible. Any land formation high enough would be avoided by aircraft like the plague.

There are other locations you can consider though when looking to snap or just watch aircraft. Sometimes these locations can be near the airport and will give you the ability to watch these aircraft in a slightly different phase of flight. For example, I went to the car park of a well known Swedish furniture store which is on the flight path of aircraft departing to the north. As the crow or aircraft flies, it is less than a kilometre from the runway threshold and a little to the west.

Singapore Airlines Airbus A380-841 Registration 9V-SKA was the worlds first commercial A380 delivered 16 Oct 2007 seen here climbing out from Sydney.

Singapore Airlines Airbus A380-841 Registration 9V-SKA was the world’s first commercial A380 delivered 16 Oct 2007 seen here climbing out from Sydney.

This enabled me to capture aircraft in the post takeoff climb configuration during and just after landing gear retraction. Being slightly to the west of the runway centre line meant that I was able to get a bit of a side view rather than just seeing the underbellies of the departing airliners.

Perhaps in your location, there might be a hill or building that can give you a bit of elevation alongside the approach or departure track of aircraft into and out of your local airfield.

When should I go plane spotting?

The object of the exercise is to go to the airfield at such a time when there will be a lot of aircraft movements. Your location will determine how challenging or easy this is. If you live near London Heathrow for example, then you would be hard pressed to go when it isn’t busy. If you live somewhere that is a little more off the beaten track then it may take a little more research before you go out.

Like any kind of movement of people, airports often have peak and quiet times. Obviously, you want to go in the peak time if possible so you can view the most number and biggest variation of aircraft. Most airfields these days have an online arrivals and departures information website. Use this to get a feel for the best times to go and do some plane spotting.

How can I monitor air traffic once I am at the airfield?

It used to be that the only way to monitor air traffic was by the use of a multi band radio scanner. Don’t get me wrong, this is still a great way to monitor where the air traffic is as you listen to communications between air traffic controllers and aircraft flight crews. As well as the information on where the aircraft are. It adds a bit of a human touch as you can actually listen to the pilots of the aircraft you are watching.

Today we have access to mobile phone apps that allow you to track all the aircraft as if you were an air traffic controller yourself. Using such an app you can monitor the aircraft as they approach the airfield and line up for landing. This way you can be prepared for aircraft that you hope to capture on film. Examples of these include; Flightradar24 and Flightaware.

I hope that this item on plane spotting has helped you in some way. I would love to hear your plane spotting experiences, perhaps you have favourite spots that you can recommend to others.

Thank you for stopping by.

Air India boeing 787-8 dreamliner

Long Haul Flights

Getting to far flung parts of the world has been a challenge to mankind for as long as history stretches back. Knowledge of riches and resources beyond what can be found locally has driven us to find new ways and routes to far distant corners of the planet. What virtually anyone can achieve on today’s long haul flights in a matter of hours would have taken months, if not years in the not so very distant past.

Whether it was the Vikings setting off for lands unknown, the Chinese doing the same, or the Portuguese circumnavigating the Earth. We have always been driven to new horizons by the prospect of the exotic worlds that lie beyond and how they could enrich our lives.

We still live by those same principles. Instead, however, of intrepid explorers setting off for journeys that may take them from their homes for years at a time, or forever, in many cases. We have business travellers completing those same journeys in a matter of hours and making trade deals. We have holiday makers making those same journeys to find the sun, or a great shopping deal not available at home.

Those journeys are now so common as to seem mundane to many. While travelling over routes that were once only for the brave and those willing to risk life and limb, we now quibble over the quality of food, the entertainment system or how much leg room we have. How quickly we adapt.

Today we are seeing records tumble every few weeks as airlines propose and begin ever longer “non-stop” routes. These are made possible by the latest long range airliners, such as the Airbus A350, the Boeing 787,  Airbus A380 and the Boeing 777. Emirates launched their super long range route of Dubai to Auckland, initially with the Airbus A380 but now with the Boeing 777-200LR (LR=Long Range), a distance of 14,200 kilometres. That is around 16 hours, depending on the wind.

The Emirates flight is impressive but that record is set to tumble as Qatar Airways are about to launch a Doha to Auckland non-stop flight which is 300 odd kilometres longer than the Emirates flight. Also announced are United Airlines non-stop flights from San Francisco to Singapore, Singapore Airlines flights from Singapore to Los Angeles.

So how did we get around the world before the advent of today’s modern airliners?

The simple fact was, that travel was for the rich in most cases. Yes, there was the opportunity to travel relatively cheaply by ship if you travelled in the lowest class. This kind of travel was usually once in a lifetime as you emigrated from one country to another. Long distance aviation was another story.

The difficulty for early international travel was to create an aircraft that could carry a usable payload for a long enough range. There has always been the trade-off between carrying enough fuel to reach the destination versus carrying enough payload (passengers) to make the trip profitable for the airline.

Flying Boats

During the 1930s on both sides of the Atlantic, aircraft makers like Boeing and Short Brothers

Boeing 314 Clipper

Boeing 314 Clipper

decided that the future of long-range passenger air travel lay with the flying boat. These large chunky machines were generally powered by four propellers affixed to a huge wing atop the fuselage. Inside the accommodations were laid out as if the travellers were on a first class sea journey.  Cabins could be set up for seating during the day-time, and as sleepers for night-time. There were even dining rooms so meals could be taken in a civilised fashion.

Little wonder that a trip from the UK to Australia would cost as much as an average annual salary. The cabin may have been first class, but it was quite an adventure never the less. One of the reasons for choosing to land and take off from water was the ability to fly to places, or via places, where no adequate runway was prepared. These lumbering behemoths may have been able to lift a luxurious cabin and it’s occupants into the sky, however, their range was severely limited by today’s standards. At little better than 1,000 kilometres, they had to hop their way across the globe which made for very long journey times. For example a trip from Sydney to Singapore which today takes between 7 and 8 hours, involved a journey time of four full days with three overnight stop-overs. This was not too dissimilar to travelling by ship where you got to see some of the world on your way.

Land Based Propeller Airliners

War always brings advances in technology and for aviation this was certainly the case. A new generation of land-based propeller airliners emerged making use of advances in engine reliability as well as many more airfield that were now available.

War always brings advances in technology and for aviation this was certainly the case. A new generation of land-based propeller airliners emerged making use of advances in engine reliability as well as many more airfield that were now available.

These airliners started to resemble what we see today as far as cabin layout is concerned. Gone was the cavernous and opulent interior of the flying boat to be replaced by a more practical cabin seating both economy and first class passengers in most cases. Airliners of this age were more streamlined and were capable of higher speeds than the lumbering flying boats.

A preserved Super Constellation "Connie" come in to land. The long nosewheel and curved fuselage was designed to keep the longer propeller blades clear of the ground, whilst the triple lower tail enabled it to still be stored in the standard hangars of the day.

A preserved Super Constellation “Connie” come in to land. The long nose-wheel and curved fuselage was designed to keep the longer propeller blades clear of the ground, whilst the triple lower tail enabled it to still be stored in the standard hangars of the day.

Perhaps the pinnacle airliner of this age was the Lockheed Super Constellation, a very sleek aircraft almost resembling a dolphin in shape. With a cruising speed of 295 knots (547 KPH) she had a maximum range of 4,700 Nautical Miles (8,700 Kilometres). For the princely sum of around 2.5 times the average annual salary, one could travel from Sydney to London in no less than 64 hours. The journey would involve 8 stops, such as; Darwin, Singapore, Calcutta, Karachi, Cairo, and Tripoli. The journey, lasting 3 days, would involve overnight stops in Singapore and Cairo.

Engine reliability was still an issue and it was not uncommon for delayed propeller airline to arrive with only 3 or its 4 engines running.

In addition, these aircraft were all susceptible to weather conditions. The Super Constellation had a service ceiling of 24,000 feet which means it was not able to climb above weather as we expect today’s jets to do. This could lead to delays as pilots awaited weather systems to pass over, manoeuvring around them if they were already airborne

A New Sound in the Sky

The late 1950s saw the introduction of the Jet Airliner age. Aircraft like the Boeing 707 and the Douglas DC8, each with four jet engines mounted beneath their swept back wings, started to be the mainstay of intercontinental travel. With a much higher speed than the propeller  airliners, these jets dramatically cut down travel times. The Sydney to London trip could be done in half the time at around 30 hours.

The jet airliner age brought faster speeds as well as the ability to fly above most of the weather.

The jet airliner age brought faster speeds as well as the ability to fly above most of the weather. This QANTAS Boeing 707 sported the V Jet insignia were the V stands for vanna, the Latin for fan. It was powered by the newer generation fan jets.

The problem of range, was still there though. These jet flights, while being faster, still required multiple stopovers along the way to refuel. The Sydney to London route would require 5 to 6 stops along the way.

Enter the Jumbo

In 1969 passenger aviation changed dramatically. Boeing launched their most audacious design yet, the Boeing 747. This aircraft, dubbed, the Jumbo Jet enable several hundred passengers to be carried all on one aircraft. One result was a drop in the cost of flying which brought it within reach of the common person.

Pan Am Boeing 747 May 1985. Pan Am was the driving force behind the development of the Boeing 747.

Pan Am Boeing 747 May 1985. Pan Am was the driving force behind the development of the Boeing 747.

Whilst the size and carrying ability of the 747 was impressive, one of the great features that attracted airlines was its range ability and speed. It could fly further and faster than the DC8 and 707 at a cheaper seat / mile cost. This opened up the ability for intercontinental airlines to offer faster and cheaper journey times to far away destinations. If we go back to our Sydney to London route, the early 747s reduced the stopovers to 2 which were typically Singapore and somewhere in the Persian Gulf like Bahrain. The journey time was now in the low 20 hours.

There was even a shorter version of the 747, 747SP (Special Performance)  which had an increased ranged due to the reduced weight. This was requested by Pan Am and Iran Air so that they could service some of their longer non-stop routes such as New York to the Middle East and Tehran.

It’s Twins!

Jet engine technology has now reached a point of reliability where a shut down during flight is almost unheard of. An aviation standard called ETOPS (Extended Operations or Engines Turn Or Passengers Swim) governs the certification of twin jet airliners to fly long distances over water or remote territory. These certifications have been gradually granted to the large twin jets we see in our skies today.

It took a while to gain acceptance that twin jets could be used on long over water intercontinental routes. Airbus had an each way bet with their A330 and A340 models. They are essentially the same airframe, but one has four engines and one has two. Their adage was, “four engines for long haul”. The A340 proved popular at first and boasted a long range model that flew some of the longest routes in the world. It was quipped that it was a flying tanker with a few passengers along for the ride.

Once ETOPS approval was given to the large twin-jets such as the; Airbus A330, Boeing 777 and more recently the Boeing 787 Dreamliner and Airbus A350, the economics of the four-engined airliner just didn’t stack up anymore.

Today

Today it seems to be the age of the twin-engined airliner which is capable of meeting and surpassing the performance, reliability and economics of all previous airliners. What used to take 6 weeks by ship, 4 days by flying boat or 3 days by Super Constellation is now possible in around 17 hours.

Airbus A350 History started with test aircraft tirlessly chekcing and testing new systems.

Airbus A350 XWB is the new high tech twin jet airliner from Airbus.

When we expect to be able to go and explore any part of the world in the few weeks holiday we are allocated, or go and close a business deal on the other side of the world, this is a huge step forward.

On the other side of the coin, one has to wonder what is lost when you no longer stop along the way. Have we lost the adventure that makes travel exciting? Will we no longer look forward to the journey itself as we complain about the food and watch the same shows we watch in our own living room?

It seems long haul flights have become as exciting as a trip to the mall.

A330 QANTAS ready for interior fit out

How Safe is Flying?

How safe is flying today?

How safe is flying? I used to get asked this a lot while I was training for my private pilots’ licence. My favourite response always used to be. “Well, the most dangerous part is the drive to the airport.”

Seriously though, it is a very good question. How safe is flying in those gigantic machines along with a few hundred other people coming along for the ride. Let’s face it, this isn’t a perfect world and things go wrong. When airliner accidents happen, they of course go spectacularly wrong. Larger aircraft, carrying more passengers flying faster. It seems a miracle any get through at all. But they do. In fact, travelling by air is one of the safest methods of transport available today.

As an example, in peak times there can be 5,000 commercial aircraft flying over the U.S.A. at any one time. Similar numbers are also over Europe and Asia. These flights all happen every day with little incident.

Air Crash Investigations

Air safety is no accident. Let’s turn that around. Ok, we know accidents happen, we see it on the news and of course those popular TV programs like Air Crash Investigation. It may seem like a lot of people taking ghoulish interest in a tragic event. The actuality is that accidents contribute more to air safety than almost anything else. When an accident happens, no matter how minor or major, investigators will examine the details until they are 100% sure of what the cause was. This can be a pains-taking process and sometimes takes a year or more.

The reason for this painstaking process is prevention. By investigating and determining the cause of an accident, processes or new methods in construction can be put in place to prevent a similar accident from occurring in the future. In this way, no accident is ever without benefit for future fliers. These benefits will manifest themselves as; new training procedures, new maintenance procedures or new construction procedures.

B Checks must be done in the aircraft hangar, whilst C and D checks must be done at a purpose built aircraft maintenance centre. How safe is flying depends on these being done.

B Checks must be done in the aircraft hangar, whilst C and D checks must be done at a purpose built aircraft maintenance centre.

Aircraft Maintenance

Aircraft maintenance is a key component to the safety of flying. Each aircraft has strict guidelines set down by the manufacturer on how the specific aircraft should be maintained. In addition, there are strict guidelines set down by aviation authorities such as the FAA (Federal Aviation Authority) in the U.S. or EASA (European Aviation Safety Agency) in Europe as well as other national aviation bodies in other countries. These bodies set the minimum standard of maintenance procedures for aircraft in that country as well as those flying into that country.

These procedures are constantly being updated with new findings from accidents, incidents or new technology that comes into the industry. All this is in place to ensure that when you and I get on a plane, we can count on doing so in full safety.

Aircraft maintenance service intervals can be broken into 4 categories or checks plus the daily pre-flight inspection. The timing of each of these checks is generally determined by the amount of hours an aircraft has flown and/or the amount of flight cycles an aircraft has endured. A flight cycle is one take-off and one landing. Therefore a flight from Melbourne to London via Bangkok is 2 flight cycles.

How Safe is Flying is Determined By Aircraft Maintenance Checks

Daily Inspection

Prior to every days’ first flight, a visual inspection of the aircraft is carried out. This inspection is a methodical walk around performed by one of the pilots and is a check for any superficial damage or anomalies on the aircraft. The visual inspection looks for any outwardly obvious damage or inconsistencies that might render the airliner unsafe for flight that day.

  • The wings and skin are checked for damage caused by bird-strike or other foreign objects.
  • Moving parts such as flaps, ailerons and elevators are checked for any foreign objects that may impede their free movement.
  • Tyres and are checked for splits or excessive wear.
  • Brakes are checked for  foreign objects or cracking
  • Air intake ports are checked for foreign objects
  • Pitot and Static air intake tubes are checked for any blockage

These checks are continued throughout the day before every flight. You can rest assured that the pilots want to have a safe aircraft every bit as much as you do. Nobody likes surprises once you are in the air.

Airlines very carefully schedule the various maintenance checks to coincide with their due date whilst minimising time out of service for aircraft.

Airlines very carefully schedule the various maintenance checks to coincide with their due date whilst minimising time out of service for aircraft.

Like your car requires servicing according to the manufacturer’s manual, aircraft also have a stringent schedule for mandatory checks and servicing. Airlines must have very detailed documented procedures for every step of aircraft maintenance which must be followed to the letter and signed off. As part of their certification to be allowed to fly into and out of various countries, airlines must be able to show their maintenance procedures and how they are followed to ensure passenger safety. In this way the question, how safe is flying? can be answered, as safe as we can possibly make it.

Airliner maintenance and safety checks can be broken down into 4 different levels. These are commonly known as the; A, B, C and D checks.

A Check

Other than the Daily Inspection, the A Check is the lightest check and is performed the most often. Depending on the aircraft type and the kind of use it gets, the A Check is performed every 300 – 600 flight hours or every 200 – 300 flight cycles. Remembering that a flight cycle equals one take-off and one landing. If the aircraft is used on short domestic flights, for example, it is more likely the cycles will be the determining factor as these will build up more quickly versus the flying hours.

The A Check itself is generally carried out overnight while the aircraft is not in service to minimise any loss of revenue. Around 20 – 50 man hours are involved in this check and it can be carried out at the airport gate.

B Check

The B Check is a more intense check and needs to be performed in an aircraft hangar. The check is performed around every 6 months and depending on the aircraft type may require 120 – 150 man hours. A Checks can be incorporated into the B Check so that the aircrafts’ removal from flying schedules is minimised.

C Check

The C Check is a much more intense check and requires a lot more space. For this reason, it must be carried out at a designated maintenance base. Depending on the aircraft type, this check is required to be carried out every 20 to 24 months which is also influenced by the number of flying hours. Around 6,000 man hours will be required which may keep the aircraft out of service for 1 to 2 weeks. A much more in-depth check of the airframe is carried out while many components are removed for inspection or replacement.

This check is designed to capture any problems with corrosion and cracking before they become a problem, as well as replacing or servicing smaller components.

Early detection is the purpose of most of the check performed during maintenance checks.

Early detection is the purpose of most of the checks performed during maintenance periods.

D Check

The D Check is by far the most intensive check performed on aircraft and is also known as the HMV (Heavy Maintenance Visit). This check is carried out around every 6 years and can take the aircraft out of service for 2 months. Like the C Check, the service must be carried out at a purpose built maintenance base with the appropriate facilities. The work can involve around 50,000 man hours and essentially is a total strip down of the aircraft. Often even the paint has to be removed to allow a detailed inspection of the aircraft skin, looking for cracking and corrosion.

Airlines will often use this opportunity to refresh or update the livery of the aircraft as well as refurbishing and updating the cabin interior.

The cost of performing a D Check is huge. Depending on the aircraft type, a ball park figure of 1 million US dollars is not unusual. For this reason, the number of maintenance bases in places like the US are few. Many airlines will fly their aircraft to locations where labour costs are lower to perform this check. This doesn’t mean the work is inferior, as the same stringent documented work processes are in place and supervised.

As a rule of thumb, an airliner generally has 3 D Checks in its working life. After the third, the aircraft value has diminished to the point where it is likely to be worth less than the cost of doing the next scheduled D Check. At this point, the airline normally decides to retire the aircraft.

Air safety is no accident, but a painstaking very highly controlled process.

Air safety is no accident, but a painstaking very highly controlled process.

Conclusion

How safe is flying? When we look at the number of flights that are achieved without incident every day, we can see that the expectation of arriving at our destination in one piece is almost a given. Almost, because nothing in life is guaranteed. The same could be said for walking or driving down to our corner store. There is an element of risk in simply being alive.

The airline industry, and in this I include airlines, airliner manufacturers and airport operators, take safety extremely seriously. Their reason for their existence depends on the public being comfortable with the answer to, how safe is flying? Flight, for most people, is the only time in their lives that they will be in an environment that is totally hostile to their being. Too cold, not enough air to breath, too far to fall and too fast. Air travel has to be seen to be going the extra mile to provide a safe environment.

By learning from every accident that occurs and using that knowledge in maintenance procedures or flight training procedures, bit by bit accident likelihood is being reduced.

Being on a commercial airliner is now one of the safest places to be.

I would love to hear your views or experiences around how safe is flying today. By all means, leave those comments below. Thank you for stopping by and reading how safe is flying..

QANTAS Airbus A380 842 Named Nancy Bird Walton

What is the average plane speed of a modern airliner?

Average Plane Speed

How often have you sat aboard a jet airliner and wondered about the average plane speed and how it is arrived at? Why is it that different speeds are used at different stages of the flight and why do they climb to different altitudes each time you fly?

To answer this we have to look at the various factors that determine the answer.

Atmosphere

The atmosphere in which you will be flying is a very fluid environment and just like the sea, has established currents. Also like the sea, it has varying pressures with the highest pressure being at the Earth’s surface and that pressure decreasing the further we get from the surface until we reach the near vacuum of space.

 

The currents or winds and the changing pressure plays a huge part in the planning of flights and the way they are carried out. Some winds are a constant feature of the atmosphere. On the surface, we know of the Trade Winds that blow along the Equatorial regions. These winds were counted on by the early sailing ships and were so named as they blew the early traders to and from their destinations.

Air_India_Boeing_787_Dreamliner_Taking_off_Sydney_To_Delhi_15Sep13

Air India Boeing 787 8 climbs out on a Sydney gray day.

Like the early traders, we still count on the wind to aid us in reaching our destinations more quickly. Since the advent of jet airliners in the 1950s which could fly much higher than their propeller ancestors, it was found there are very strong winds at those higher altitudes which were named the Jetstream. When flying with the Jetstream, one can easily add significant speed to the flight and reduce the flying time to the destination. The winds move slightly with the seasons but can be counted on to the extent that airlines schedule their flights taking into account a faster flight with the Jetstream and slower flight against the Jetstream.

Measurement of Aircraft Speed

When we ask the question, how fast is an aircraft going? There are several answers that can be given and it can be very dependent on the stage of flight the aircraft is in.

Average plane speed and Take-off

We are sitting on the runway in a shiny new Boeing 777 about to apply full power and commence our take-off run. We’ve done our calculations and with the weight of cargo and fuel, we expect the airliner to become airborne at, for example, 152 knots(nautical miles per hour).

Emirates Boeing 777-300 climb out at Sydney_692x240

Hold on a minute, what does that mean exactly?

Ok, the additional information we need is that the local wind on the runway is blowing in your face and you will take off into the wind. When you are taking off, you don’t care about how fast the wheels are spinning on the ground, you care about how fast the air is moving over your wings. For instance, if the wind is blowing in your face at 20 knots, you only need to achieve 132 knots ground speed before you can expect the aircraft to start flying. This makes for a shorter take-off run as you started with a bonus of 20 knots before you even applied engine power. If you decided to take-off with the wind in the other direction, you would start off with 20 knots of wind going the wrong way over your wings and therefore would require a longer take-off run. The result is you would take the tops off the car park shuttle buses on the perimeter road which is not approved.

So we have established that speed through the air is the governing factor of flight. This is measured and expressed as KIAS or Knots Indicated Air Speed. Simplistically this is measured by air rushing into a forward facing tube called a pitot head or pitot tube which channels the air into a bladder inside the Air Speed Indicator. The higher the pressure which is driven by the forward movement of the aircraft, the higher the bladder causes the dial to read. It is a little more complex than that but it gives the idea at least.

Fight Phase diagram

A breakdown of the basic phases of an airliner’s flight.

 

Climb Out

Now in the climb out phase, air traffic control will be aware of the flight plan you have lodged, however, their first priority is to get you into a traffic flow that will clear you from the airport area without banging into other flight traffic. You will be given an assigned altitude, compass heading and speed. At busy airports, this can be a long involved process and you may find yourself tracking all over the countryside, possibly even in the opposite direction to your intended destination.

During this phase of flight, the rule of thumb all over the world is that you must remain under 250 KIAS (Knots Indicated Air Speed). Remember this is your speed through the air and not across the ground, so if the same wind you had on the runway is still blowing at this level you will have a ground speed of 230 Knots if you fly against it, but if you turn around and fly with the wind you will be doing 270 knots ground speed.

The speed restriction is there to enable a safer control of aircraft in a constricted space. In some  cases, if it is not busy, air traffic control may release you from the speed restriction and allow you to go off on your merry way.

Philippine Airlines Airbus A340-313X Registration RP-C3487 climbs out of Sydney

A Philippine Airlines Airbus A340-313X climbs out of Sydney. She is restricted to 250 KIAS and is under Sydney departure control.

 

Climb to Cruise Altitude

So long as the sky above you is not too congested you should get your clearance to climb to your desired cruise altitude and start on your actual journey. As we pass through 10,000 AMSL (Above Mean Sea Level) we can increase our speed from 250 KIAS to that recommended in our particular airliners manual. The rule of thumb is 300 KIAS.

You may wonder why we need to bother to climb to those high altitudes. Isn’t the view nicer down here where you can see something? There are a couple of answers to that:

Firstly, at higher altitudes, we can fly above most of the weather. This is a winner for the passengers who expect to have mostly smooth flying when they get on an aircraft. In the pre-jet days, aircraft were much more susceptible to the vagaries of the weather as they had to fly through storm clouds and the like which was very uncomfortable.

Secondly, the higher you climb, the thinner the air. This means an aircraft can pass though it with less air resistance and therefore can fly faster using less fuel. This not only makes the airline accountant happy, but also enables a long range aircraft to achieve that range. For example, if I loaded up my Boeing 777 with enough fuel to get from Singapore to London and then only flew at 10,000 feet of altitude. I would expect to be looking for an emergency landing site somewhere in Afghanistan as my fuel was about to run out.

United Boeing 777 taxi for 34L at Sydney_4_692x201

A United Airlines Boeing 777-200ER taxis to runway 34L at Sydney. The 777 replaced the 747 on the US Australia routes as of 01 April 2014. The trans Pacific route is one of the worlds longer routes and demands careful balance between fuel and payload.

 

Initial Cruise

The logistics of managing a long range flight are quite complex. The object of the exercise is to take as much payload as we can and carry it over the distance required. Obviously for long range flights we need a significant amount of fuel which will make up a large proportion of our weight at take-off and initial climb out. You may have noticed on long haul flights you have been on, that you might climb to an altitude around 30,000 feet to start with and then after a few hours you may then climb to a higher altitude possibly approaching 40,000 feet.  There are two reasons for this:

Firstly, in the initial stages of flight with full fuel tanks the aircraft is too heavy to climb economically and safely past the early 30,000s. Doing so would burn more fuel trying to achieve the higher level. It could also put the aircraft in an unstable flight phase where a stall might be possible.

Secondly, pilots may change the altitude of the aircraft during flight from time to time to either make use of more favourable tail winds or to avoid unfavourable head winds.

 

Speed in the Cruise Phase of Flight

Once your aircraft reaches a certain height, the effectiveness of the ability to measure speed as KIAS (Knots Indicated Air Speed) begins to diminish. The air is now so thin that it can no longer provide accurate readings on the Air Speed Indicator.  This is where speed starts to be measured differently.

Most aircraft and modern airliners particularly, have their speed controlled by the autopilot. A speed is selected, 300 KIAS for example, and the aircraft happily flies with the auto pilot applying or reducing thrust to maintain the desired 300 KIAS. When the aircraft achieves an altitude of around 25,000 feet, and this varies slightly from aircraft to aircraft, the speed is automatically changed from KIAS (Knots Indicated Air Speed) to a Mach number.

 

What is a Mach Number?

A Mach number is an expression of speed relative to the speed of sound. For example, Mach 1 equals the speed of sound. Mach 0.5 is half the speed of sound, Mach 2 is twice the speed of sound. On top of that we need to add the complexity of the air temperature.  The speed of sound is not a constant value, but depends on the air it travels through for its’ speed. To illustrate this let’s take it to its’ extreme.

We know that in the sea, or water in general that sound travels long distances. Whales can communicate over long distances with their songs. The water molecules are dense and therefore will transmit the sound readily. At the opposite end of the spectrum, we can go into space and find that that it is almost silent. In the near vacuum there are few molecules available to help conduct sound.

This is why when you ask, what is the speed of sound? The answer will be 761.1 miles per hour / 661 knots / 1,225 kilometres per hour, with the qualifier being, at 15 degrees Celsius at sea level. This relates to the pressure of air which is governed by the altitude and by the temperature.

Using this knowledge we can understand that the higher you fly, the lower the speed of sound becomes.  If you look at the speed of sound at sea level and compare it with that at around 40,000 feet, you would see that it is around 90 knots slower at that height than at sea level. The fact that the temperature is much colder at 40,000 feet, around minus 56C, means that it is not as slow as it might be if the temperature was the same as at sea level.

British_Airways_Concorde_G-BOAC_03

Concorde is the only airliner to date that has achieved supersonic flight or flight that is beyond Mach 1. The design is very specific and the cost to run was enormous. The sonic boom generated by the shock waves ensured that this aircraft could only ever be used over water.

The only airliner to achieve greater than Mach 1 is the Concorde which was capable of Mach 2. This airliner was specifically designed to fly through the sound barrier as it used to be known. It took many attempts to break through this so called barrier as it calls for a totally different aircraft design. As an aircraft approaches the sound barrier, shock-waves start to build up on various surfaces of the aircraft. These have an adverse affect on the aircrafts’ forward movement and can negate any advantage of flying more economically through thinner air. If you persist on going faster still and get closer to the speed of sound, you will start to feel the aircraft start to buffet more and more violently until you reach a catastrophic failure of the air-frame and the aircraft breaks up.

Every aircraft comes with a Do Not Exceed speed, which indicates the air-frame is not built to sustain the possible pressures of those high speeds.

 

Transitioning to Mach Number

We are climbing through the mid 20,000s of feet of altitude and our auto pilot throttle control clicks over from KIAS to Mach.  It may be around Mach .50 or so depending on conditions and how many knots we were doing. Each airliner will have a maximum allowable Mach number and a cruise Mach number.  The cruise mach number is used to maximise the performance so we get the most economical flight results as well as keeping our aircraft within safe operating parameters. Too fast and we could bring on the buffeting which could break up the aircraft. Too slow and we could bring on a stall as the wing struggles to provide lift in the thinner air.

Typically most airliners operate in the Mach 0.71 to 0.85 range depending on the design.  To see the average plane speed for any of our featured aircraft be sure to look in the menu at the top of the page and select the Specs page for your desired airliner.

With the current flight information systems that most airlines offer, it is possible to see how fast you are flying and lots of other interesting statistics as you travel along. I always get a kick when we have a following wind to see how high the ground speed can get up to. Getting over 1,000 KPH always feels like a bonus to me.

Thanks for stopping by to find out a bit more about average plane speed. As you can see it is quite a complex answer to what appears to be a straight forward question.

I’d love to hear about your flight experiences, how fast have you gone? how high have you gone?

what-causes-turbulence

What causes turbulence, things that go bump in the flight?

What Causes Turbulence?

What causes turbulence you wonder as you sit there with your seat-belt hanked in as tight as a drum. Your white-knuckled hands gripping the armrests as if your life depended on it. There is no doubt that extreme in-flight air turbulence can be a very frightening experience. A large airliner shaking, dropping and rising can feel very dramatic, especially when our only view of the world is the inside of the cabin with no reference to the outside world in most cases.

Understanding what causes turbulence may go some way to alleviating the fear of it when it happens. Most of us, me included, always hope for a calm turbulence-free flight every time we board. In most cases, we are rewarded with just that, a calm flight with a few minor bumps along the way. But why does it happen?

Air Movement

The air in the atmosphere that surrounds us is fluid, just like the waters in the oceans, lakes and rivers. Like the waters in those environments, it never stops moving. External effects like the

plane in towering cumulonimbus

What causes turbulence? Thermal activity resulting in towering cumulo-nimbus clouds are areas of high likelihood of turbulence.

heat of the sun and the spinning of the Earth ensure that the air is constantly in motion. It is always rushing from one place to the next, never still. You experience this yourself in the winds you feel. If you are on the coast you will be aware of sea breezes in the afternoon caused by the sun heating the land. The warmed air over the land rises and cooler air from over the water rushes in to take its place, creating that sea breeze.

Air movement is affected by large global influences, such as ocean or continental temperatures as well as local influences such as mountain ranges.

Consider your aircraft moves through the air much like a boat on the water.  It is subject to waves and eddies in the same way and moves with them, up and down, side to side, etc.. This is what we experience in the aircraft cabin.



4 Types of Air Turbulence

There are 4 basic types of air turbulence. In most cases these are predictable and pilots are aware of the situation before they commence the flight. Obviously when turbulence is known to exist, all possible will be done to avoid or at least minimise the exposure of the aircraft and passengers to the effects. This is not always possible.  Let’s have a look at the different types.

What causes turbulence? – Thermal

turbulent-conditions-building

What causes turbulence? As the day heats up, warm moist air rises and creates unstable air as it mixes with cooler drier air above. This creates up and down draughts that can be quite violent.

As we mentioned earlier, the heat of the sun is a large cause for air movement in the atmosphere. Air rises as it starts to warm and pushes its way through cooler air in the upper atmosphere. This can lead to unstable moist air mixing with dry cooler air and creating up and down draughts. These are the kind of conditions experienced particularly in warmer climates where the heating can be quite extreme. In most equatorial regions where humidity is high on the surface, the thermal effect is quite evident by the formation of woolly clouds which may start towering into the upper atmosphere. This is where you can expect thunderstorms to start forming.

When you experience the aircraft dropping or rising, it is because it is flying through an air stream that is going up or down. They are sometimes called up draughts and down draughts. It may feel like the aircraft has stopped flying and is simply dropping out of the sky. In reality, the aircraft is still flying through the air, as it was in the still air, but that packet of air itself is moving. Of course, if the change from still to moving air is quick enough, the effects can be quite startling as gravity takes a while to catch up, if indeed it can. For this reason, you are always advised to keep your seat belt loosely fastened during flight. The aircraft may fly into a down-draught which can cause it to descend faster than gravity can pull you with it. In extreme cases food trolleys and cabin crew have been thrown against the ceiling during undetected turbulence.

What causes turbulence? – Ground Effect

As the air moves across the Earths surface, it may move unimpeded over oceans and fairly flat land. However, we know the Earths’ surface is not all flat. It is dotted with mountain ranges on a

wave clouds

What causes turbulence? Mountains have a significant effect on the air passing over them. Some of these effects can persist a long way down wind of the mountain itself.

large scale or man-made objects on a smaller scale. All of these features can contribute to creating varying levels of air turbulence. If you have ever been to the beach or even a river and watched the water pass over and around rocks, you will have a picture of how air also behaves around obstructions. The water gets all confused and turbulent at it meets and passes the obstacle. It can then take quite a bit of distance before the water stabilises back to a smooth flow again.

At high altitude, there is little effect, but sooner or later an aircraft has to descend or take off and possibly come into the affected area of ground effect turbulence. Some parts of the world are more susceptible to ground effect than others. For example, airfields located near mountain ranges, particular if they are downwind of those mountains. The air having passed over the mountain ranges swirls and eddies as it rolls down the downwind or leeward side. Like our rock in the stream of water, the air may be disturbed for tens of kilometres or more before it reverts to a steady and stable stream of air.

Another feature of ground effect turbulence is the up draught. Let’s look at our mountain range again. As the wind or packet of air contacts the mountains, it suddenly has nowhere to go. The air behind it is pushing it against the mountains and it finds the only way to go is up. This air can be pushed upwards at high force as the pressure of the air on contact with the mountains increases because the air behind keeps pushing it. This means the upward draught can go much higher than the mountains themselves which can result in something that feels like the aircraft has been punched from below.

A combination of thermal and ground effect can also produce significant turbulence. The way the sun heats different types of land can produce instability. Even over flat land with no hills nearby, the sun can heat fields that have been ploughed quite differently from those that have green crops growing on them. These fields in turn will heat the air above them which then begins to rise. Ploughed fields are usually mixed in with wooded areas and fields that have green crops, so you will find different parcels of land will heat air at different rates and some not at all. This creates an unstable air mass with some air rising faster than other cooler air and the swirling and eddying begins as they contact each other.

What causes turbulence? – Shear or Wind Shear

Shear, or wind shear is when two packets of air that border each other are travelling at different speeds and/or directions. This can be horizontally or vertically.

Flying within either of the air packets is no problem at all. The transition from one to another, on the other hand, can be uncomfortable and in some cases quite dangerous.

First, let us look at shear in a horizontal situation. Let’s say the air at 20,000 feet is travelling east at 20 knots, however, the air at and above 21,000 feet is travelling east at 70 knots. Where the two layers of air meet will be an area of turbulence as the air moving at 20 knots tries to slow the air above down to its speed and the 70 knot air tries to speed the 20 knot air up to its speed. There will be eddies and disturbances between the layers much like our rock in the stream.  Tumbling waves of air which will make for a bumpy transition.

aircraft on approach to land

What causes turbulence? Wind shear at low altitudes is dangerous for aircraft. Many airports have equipment to warn if such conditions exist in the area.

Still in our horizontal shear transition, the second factor that has to be watched for is the aircraft’s’ airspeed. Often the difference in speed between the two air packets can be quite high. This can present a problem. An aircraft has parameters around the speed that it needs to be flown. To slow, and the aircraft stalls and ceases to fly. Too fast, and the maximum air-frame speed might be exceeded. This needs to be avoided as bits could start to fall off which means a lot of paperwork and explanations to the next crew who need to fly this aircraft. Aircraft measure their speed through the air, irrespective of what that air is doing. So if the aircraft is doing the correct speed in the first air packet, then it transitions to the second, it will suddenly be flying faster or slower than before until it stabilises to the new air mass. In our example above with the 20 and 70 knot air packet speeds. An aircraft climbing from one to the other at 300 knots in the 20 knot air packet will suddenly be doing 250 knots when it enters the 70 knot packet.

The other form of shear, or wind shear is the vertical type.  This is when packets of air are rising or falling at significantly different rates. This type of shear is quite dangerous at lower altitudes as aircraft do not have as much separation from the ground to recover. Most airports have equipment in place to detect such events in the immediate locality to ensure safe departures and arrivals. These shears can be caused by thermal activity as described above, including thunderstorms which are often preceded by a micro-blast containing extremely strong and volatile winds. Some have strong enough down-draughts that a jet airliner can’t out-climb them.

What causes turbulence? – Aerodynamic

Boeing 777 wake turbulence

What causes turbulence? The effects of wake or aerodynamic turbulence are beautifully illustrated here as this aircraft passes through clouds.

Aerodynamic or wake turbulence is the disturbed air left behind an airplane. If you have ever looked behind a moving boat or ship, you will be familiar with the wake it leaves behind. Waves travelling outwards the further away it gets. If another boat of equal or lesser size crosses this wake, it can be quite a rough ride for it.

So it is with aircraft. As wings move through the air and create lift, they also create drag which causes a wake of disturbed air. For this reason, very strict protocols exit for air traffic controllers when they direct aircraft at or near airports. There is a system of minimum time separation for aircraft taking off and landing which relates to the size of the leading and the following aircraft. For example, a business jet flying directly behind an Airbus A380 would likely have its wings ripped off. Drastic, but you get the picture.

What causes turbulence and how is it avoided.

Like most things, preparation and avoidance are the best tools when it comes to dealing with turbulence. In most cases, weather forecasters are able to predict when and where turbulent conditions may exist. This information is passed on to the pilots and flight planners. They will, where possible, plan flights to avoid these areas, or at least aim for the most moderately affected areas.

snowy weather station

What causes turbulence? Weather forecasting is a very important factor in ensuring the safest flight plans can be made to avoid turbulence.

Communication between pilots and between pilots and air traffic control is a very important way of creating awareness of turbulence areas. Weather forecasting can tell you so much, but sometimes un-forecast conditions can exist. The sharing of that information will enable aircraft that follow behind to either be prepared or perhaps even detour around the affected area.

Weather radar is another way to see ahead and be warned of possible adverse weather. Large airliners have a forward facing radar built into the nose of the aircraft. This radome, which is a shortening of the words, radar dome, is a forward facing radar that looks at the weather ahead. Most weather patterns involve some sort of moist air and from this, the radar can see where there might be adverse weather conditions ahead, particularly thunderstorms. Based on this information the pilot can decide to fly around, under or over a particular weather situation, providing air traffic control requirements allow for this.

CAT or Clear Air Turbulence is harder to detect. This is the kind of turbulence that catches everyone unawares. There is no moisture that helps detect its existence and it is a very good reason to keep that seat belt on loosely during the whole flight.

What Causes Turbulence – Conclusion

Like water, the air is a very fluid environment. In most parts of the world, most of the time, we can traverse this environment without incident. We have to accept, however, that it is still a natural environment that can be unpredictable and also hostile to us.

By understanding what conditions can cause turbulence, we are better able to predict when and where it might occur. In addition, we have technology in place that can sense many types of turbulent air and enables us avoid those areas. Not all turbulence can be predicted or sensed before being encountered, so there will always be the risk of experiencing some turbulence.

Although it may appear that your aircraft is a fragile contraption, the strength built into it is extraordinary. During the certification testing of a new airliner, one of the tests is to break the aircraft’s’ wings.  That involves bending the wings to an insane level until they break. The pass mark is for the wing to be able withstand at least twice as much pressure as the worst imaginable turbulence. Most airliners pass this with a very generous amount of leeway.

Understanding what causes turbulence is one of the many things that keeps flying safe.

We would love to hear any experiences you might have had with in-flight turbulence. How did it make you feel? Was it dramatic? Feel free to comment below.