How an instrument landing system(ILS) can autoland aircraft.

At the end of a flight, there is always that feeling of excitement. The flight was pleasant enough, with some nice views along the way, but now you are ready to get off and rejoin planet Earth. You look out of the window and glimpse the layout of the world you are about to become part of, perhaps seeing some expected landmarks.

Now that you are lower it becomes more interesting as there is more to see close up. The usual hubbub of activity and announcements as the crew prepares the cabin for landing is going on around you as you continue to enjoy the view. Gradually, however, more clouds are appearing and your view becomes more and more interrupted until eventually, all you see are variations of white and grey. You wonder to yourself, can the pilots see any better than I can? How are they going to land this thing without any visibility? I assume this aircraft uses an instrument landing system(ILS) to get us down. Maybe even autoland.

We've all no doubt heard about instrument landing systems and the ability to autoland an aircraft. But what does it mean?

Why do we need ISL and autoland?

Some parts of the world have a greater need to be able to autoland an aircraft. For example, the United Kingdom and much of North-West Europe are very prone to thick fog. This is mainly due to the cooler air condensing over the warmer waters of the Gulf Stream. In the U.K. the thickness of these fogs, famously the "London Fogs", was further exacerbated by soot in the air and visibility was literally down to a few feet.

This has improved since the Clean Air Act came into force which forbade the burning of smoke-producing fuel. Driven by these conditions the U.K. Government created a unit to investigate the feasibility of an autoland system in the mid-1940s. The flight delays and cancellations caused by these weather conditions were very disruptive and costly.

The Sud Aviation Caravelle was the first aircraft to be certified to Cat III autoland on 28 December 1968. These categories are determined by the number of backup autopilots an aircraft has. Generally, three are required as backups in case one or more fail.

So what do we know about how an aircraft can be brought to the ground safely using technology? Well, we need several different pieces of technology on the aircraft as well as on the ground. Let's look at the ground first.

At most major airports, some or all of the runways will be equipped with an ILS or Instrument landing System. This system very basically comes with two radio beams. One of those beams is located beyond the far end of the runway and is responsible for sending a signal directly down the centreline of the runway. This beam is used for directing the aircraft horizontally left or right until it is lined up with the runway centre line.

The second of the two beams is located next to the touchdown point of the runway, so the point where the aircraft wheels should first settle on the runway. This beam is directed up at an angle of 3 degrees, as this is the angle at which aircraft approach a runway to land. This beam is the benchmark for letting aircraft know whether they are too high or too low in their approach.

The Hawker-Siddeley HS.121 Trident followed the Caravelle with a (CAT IIIA) and CAT IIIB in 1975.

How does ILS work?

You are perfectly correct if you observed no beams in the sky on your last approach in the fog or any other time for that matter. That is why pilots have an instrument on their panel called a VOR or Very high-frequency Omni-directional Range.

This is a very important instrument and one of its many uses is to show a representation of the ILS radio beams as two needles. The horizontal needle will move up and down to represent the horizontal 3-degree glideslope. The other vertical needle will move left and right to represent the aircraft's position relative to the runway centre line. The pilots can then orient the aircraft correctly for the approach and "fly the needles" for a safe landing.

In addition, some airfields may have marker beacons along the approach path to the runway so as to back up the ILS information as far as the centreline and distance to go is concerned. There is usually an outer, middle and inner marker and these will light up on the instrument panel to confirm the progress toward the runway.

The ILS is a great system for getting aircraft lined up and approaching at the correct angle and heading for landing. If a pilot is flying the aircraft, however, they will expect some visual clues to start presenting themselves while the aircraft is still at a height where last-minute corrections can be made or the landing can be aborted.

Put yourself in the pilot's seat of a Boeing 747 on approach to Heathrow. It's foggy, and Tower Bridge was the last thing you saw before you popped into cloud and then fog. You dutifully fly the needles nicely lined up and as your altitude decreases you slow the aircraft, drop the undercarriage and run out all the flaps. The aircraft's manoeuvrability now takes on the attitude of a breeze block, so you need to be sure you are on the centreline and glideslope as the ability to correct your position is severely diminished.

As you pop out of the cloud, you expect to see the Hatton Reservoir ahead of you but there it is over to the right. You are nicely lined up for the Southern Perimeter Road, landing on which is not approved. So you go round and try again.

So what happened there? Well, two things really. Firstly, as you get closer to the ground, the accuracy of the radio beam signals is diminished due to ground and other factors. The second was the fact that the aircraft flying more slowly near the ground is far less manoeuvrable as the lessened effect of flight controls due to less air passing over them. The controls become sloppy and need more exaggerated movements to achieve the same result. Any last-minute corrections to go over further to the right would be met with disaster as there would be no time to get the aircraft correctly lined up again in a stable descent.

So this was the problem. ILS is a great system, but not good enough to land in near-zero visibility conditions.

This brings us to the aircraft systems that are used in concert with the ILS signal to achieve a safe landing in visibility conditions that in the past would have required the pilot to seek out their alternative landing airport.

An older-style analogue VOR instrument shows the needles neatly crossed in the middle to show the aircraft is in the correct space horizontally and vertically.

Autoland and the radio altimeter.

Autoland is a system that takes control of the aircraft's approach and landing using autopilot. During the autoland process, the autopilot will still use the ILS as described above to fly the needles, however, in addition, it will also reference the radio altimeter. What is that I hear you ask. Well, as you probably know the standard altimeter is little more than a barometer measuring air pressure. The higher up we go the less air pressure becomes at a fairly uniform rate, so we assign different heights with air pressure. This works fairly well when you measure in thousands of feet, however, you need something a little more accurate when you are flying near the ground.

A radio altimeter is very much like a boat or submarine depth sounder, it sends down a radio signal directly beneath the aircraft and then listens for the remnants of the signal to come back and then measures the change of phase between the sent signal and the returned signal. This gives the height above the ground directly below the aircraft. The radio altimeter is only used at the beginning and end of the flight as beyond 2,500 feet it becomes ineffective. Above that height, the instrument will have a flag pop up saying Off so that it doesn't confuse pilots during flight.

On approach using autoland.

So back to our intrepid crew landing a 747 at Heathrow. Tower Bridge disappears behind us again for our second attempt.

This time you've made an early decision that autoland might be the way to go. You select this setting on the autopilot panel and as speed reduces you run out the flaps again and dangle the Dunlops. You now have the best seat in the house while you watch the aircraft line up precisely on the needles, horizontally and vertically. At 2,500 feet the radio altimeter leaps into action and your co-pilot starts reading out the steadily decreasing altitude. You picture Kew Gardens below you and start further reducing speed. By Hounslow, you need to be in a steady flight configuration at around 1,000 feet.

ILS coupled with autoland enables aircraft to continue operating in all types of weather.

This is where the radio altimeter earns its right to be on the instrument panel.

Because of its high accuracy, you will be depending on it to flare the aircraft for a soft landing at the correct moment. The flare is when the aircraft nose is raised just prior to touching down. This serves to arrest its downward movement to something that the landing gear can cope with when slammed down onto the ground.

This is one of the trickiest parts of flight and one that pilots train and train for. Flare too early and you can stall over the runway and come down like a ton of bricks. Flare too late and well, the same effect really. Being able to flare at the correct moment is made much easier if you can see the ground.

We won't be able to see the ground which is why we are using our trusty autoland.

Through 1,000 feet and you constantly scan your instruments to check for anything that looks out of place. Meanwhile, you are subconsciously taking in your co-pilot reading off the altimeter readings.

Still pea-soup out there. Approach speed now we are on short finals. Then you hear your co-pilot calmly call out THIRTY FEET! Right on queue, the aircraft nose raises higher to bleed off the speed for the touchdown.

As the spoilers pop up and brakes come on with reverse thrust the autoland will still use the ILS to maintain the aircraft on the centreline of the runway until such time it is manually disconnected.

Another flight managed to operate on schedule regardless of the visibility conditions.

Is this finally the end of the Boeing 747 Jumbo?

Just over 50 years ago on 09 February 1969, Boeing made history as the world's largest jet airliner, the Boeing 747 named City of Everett, climbed off the new purpose-built runway into Seattle's grey sky. Thus began our love affair with what was to be dubbed the Jumbo Jet.

US carrier Pan Am was the launch customer for the Jumbo and scheduled their first service from New York to London for 7:00 pm on 21 January 1970. The service was to be flown by an aircraft named Clipper Young America. On departure from the terminal in New York, however, there were technical difficulties around one of the engines overheating. The aircraft returned to the terminal and a replacement aircraft was flown in. The replacement 747 which was called Clipper Victor, was substituted and renamed Clipper Young America. The first commercial service of the 747 Jumbo departed New York finally at 1:52 am on 22 January.

Pan Am under the stewardship of Juan Trippe was a force to be reckoned with during that time and their need for a larger aircraft than the Boeing 707 and Douglas DC-8 was a driving force in the eventual design outcome of the 747. Boeing was not completely convinced that a passenger aircraft of this size had a market. To this end, they created a design that would work well for freight airlines, which is where they saw the biggest market potential. This is of course why we have the distinctive bubble on top of the fuselage where the flight deck is located. The bubble enabled the 747 to be produced with a nose door for loading cargo with clear access to the fuselage unencumbered by a flight deck blocking the access. This may well have been a stroke of genius as we now see Boeing still producing the 747-8F, the freighter version.

Including the current 747-8, there have been 1,555 Boeing 747s delivered since that historic flight back in 1969. The 747, "Queen of the Skies", changed the world of travel and became the symbol of air travel. Appearing in songs and movies and just generally winning our hearts, the 747 has been a favourite for many years.

KLM Boeing 747-400 departing from Amsterdam. KLM has been retiring their 747s and don't anticipate the type to ever fly again under a KLM tail.

50 years is a long time in technology. Of course, the various models of the 747 have all come out with improvements and technology updates, but other technologies have also improved and eclipsed the need for a very large four-engined airliner.

Whilst Boeing is seeing a tapering off in interest in the passenger Jumbo, they at least still have the cargo version which has around 17 outstanding air-frames still to be delivered. Spare a thought for Airbus and the Airbus A380. You could say they came a little late to the Jumbo, or Super Jumbo party. By the time the first A380s were being delivered, the aviation scene was already changing, with newer technology large twin-engine airliners such as the Boeing 777, Boeing 787, Airbus A330, and Airbus A350 taking on long haul services. ETOPS certifications enabled these giant twins to fly the routes previously reserved for the 4 engined giants. The writing was on the wall.

Lufthansa Boeing 747-8 (D-ABYU) at Frankfurt Airport. Lufthansa was the launch customer for the Boeing 747-8i (International) and currently have not announced plans to retire these newer aircraft.

These changes were already well underway before the current economic market created by Covid-19 took its toll on travel. Airlines that still carried the Boeing 747 in their fleets already had firm plans in place to retire the type in the very near future. This, in many cases, was projected to happen over the first years of the 2020s, however, the effects of Covid-19 on global travel have prompted these airlines to bring forward their 747 retirement plans.

For example, Virgin Atlantic will be retiring its 7 747s very shortly. Consider that its 747 fleet has an average age of 20 years, whereas the rest of its fleet, excluding these 747s, has an average age of 9 years. This represents a significantly higher cost in maintenance for aging older technology aircraft. Lufthansa has also brought forward the retirement of 5 of its 13 Boeing 747-400s. It is worth noting that Lufthansa is one of the few airlines that bought the newer Boeing 747-8i. At the time of writing, this aircraft would still be retained by the airline. British Airways which has a large fleet of 28 747s will be working toward complete retirement of the type by 2024.

British Airways have 28 Boeing 747-400s in its fleet and are working toward retiring them all by 2024.

QANTAS for its part was looking to retire its last 6 747s by the end of 2020. The current travel climate has caused them to re-evaluate that schedule. Of the 6 mentioned, 3 have now already made their way to the aircraft graveyard in the Mojave Desert, California. The remaining 3 were scheduled to operate routes to Johannesburg, Tokyo, and Santiago until the end of 2020. It is now widely believed that the remaining 3 will follow their sisters to Mojave this month, June 2020. Foreward QANTAS schedules show that the aforementioned routes will now be flown by the Boeing 787 Dreamliner. The "Flying Kangaroo" on a 747 tail, once a very common site will be no more. By the end of the year, the only place you will be able to see a QANTAS 747 will be at HARS(Historical Aircraft Restoration Society) at Shellharbour Airport, just south of Sydney. Well worth a visit.

QANTAS Boeing 747-438. Once such a common site in our skies, soon to be no more.

I know I've had some of my most epic and memorable flights on the 747. Down the back or up the front is always a wonderful experience. Whether it be a brand new 747-200B of Air New Zealand or a really tired old QANTAS 747-400, you always felt like you were on a real airliner, the grand old Queen of the Skies. I know I will miss seeing them and being able to get on one.

Do you have any special memories of 747 flights you have taken? Feel free to share them below.

Coronavirus (COVID-19) and Modern Airliners.

If there is one thing there is an abundance of at the moment, it is ever-changing information about COVID-19 and how it is affecting our lives. The situation merits all the superlatives being thrown at it at the moment and literally changes by the hour. So what has this got to do with Modern Airliners or any airliners for that matter?

You would have to have arrived from Mars to not know the extreme measures that are being taken by governments to try and reduce the effect of COVID-19. Obviously, the priority is to reduce the number of people that are infected and thereby reduce the death toll from this pandemic. The second concern, and perhaps nearly as important as the first, is the economy. I hate saying that as it sounds like life isn't worth very much. The economy, however, is what makes people's lives what they are today. It provides jobs, it keeps people fed, clothed, and under shelter. Ensuring this continues will prevent the loss of life through on flowing effects of the pandemic.

We have seen border closures in many countries around the world in the last few days. Even if the borders aren't closed, there are travel restrictions and simply the fear of, "if I travel will I be able to get home again?" In living memory for most people today, this is not a concept that they have ever experienced and it may take a few who ignore the warnings to get caught out before others see the seriousness of the issue.

Ok, what has this got to do with Modern Airliners?

I thought you'd never ask. All around the world airlines have felt the impact of the above border closures and travel restrictions. Most have severely trimmed back their services to try and stem back the money bleed. Flying empty aircraft is a very costly business and is to be avoided at all costs. Initially, Australian flag carrier QANTAS grounded 10 out of its 12 Airbus A380s as these aircraft require a high occupancy rate to break even, financially. This grounding has been quickly followed by many other of its aircraft for the same reason, as further route capacity reductions or cancellations take place. This is just one example of what is happening to carriers all over the world. The immediate result has been that many travellers who have been urged to and have chosen to, repatriate themselves are finding that they are part of a very large group that is being affected by the reduction of airline capacity.

QANTAS grounded 10 out of its 12 Airbus A380s.

So what of the airlines themselves? Airlines are a very important part of the world economy. They are the catalyst that enables world economies to work at all. For this reason, it is of paramount importance for a country to ensure its national or other carriers remain in business. I know here in Australia, the government has given an economic stimulus to the airlines to enable them to survive this major upheaval. Oil prices falling off a cliff earlier this month has not been enough to make up for the drop in customers for the airlines. Even though it is estimated this could save airlines in the order of B$28 (US) over 2020. We have to face the fact that we are going to see a mass extinction event of smaller airlines.

Depending on how quickly the COVID-19 pandemic can be contained, IATA estimates that revenue losses for passenger transport would run at B$63 - B$113 (US). Impact by market according to IATA looks something like this.

Region	Percent Change	US Dollar Change
Australia, China, Japan, Malaysia, Singapore, South Korea, Thailand, and Vietnam.	-23%	-49.7 Billion
Rest of Asia Pacific.	-09%	-7.6 Billion
Austria, France, Italy, Germany, Netherlands, Norway, Spain, Switzerland, Sweden, United Kingdom.	-24%	-37.3 Billion
Rest of Europe.	-09%	-6.6 Billion
Bahrain, Iraq, Iran, Kuwait, Lebanon, United Arab Emirates.	-23%	-4.9 Billion
Rest of the Middle East.	-09%	-2.3 Billion
Canada and US	-10%	-21.1 Billion

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It doesn't make for good reading, does it?

So what will happen to the grounded aircraft? It is hard to know what to plan for. How long will the pandemic last, what will the world look like when it is all over? Will we need the same capacity as before? One thing we can be sure of is that things will eventually bounce back. They may be different in some ways, but the economy will pick up again as people come back from isolation.

We may find, however, that the need for people to work from their homes during the pandemic, will lead to more technology being thrown into the online world to make things possible that currently are not. People's perceptions of travel may change. If you go back to 9/11, people became fearful of flying. Not to mention the added hassles of extra security whenever you did so.

Cruising became a much more attractive alternative for holidaymakers, as there was a much lower likelihood of terrorist attacks, or at least so it was sold. I fear that many people are losing their appetite for being on a cruise ship after what has happened to several ships since COVID-19. So maybe air travel will regain its popularity again.

So, about those aircraft. Airlines like British Airways(BA) and Lufthansa(LH) have the biggest remaining fleets of Boeing 747s. If you discount the age of Lufthansa's Boeing 747-8s which are around 6 years old now, the average age of the BA and LH 747s is around 21 years. Will they consider retiring them early? An older aircraft becomes a lot more expensive to maintain and if there is no income being generated from this aircraft, its financial burden becomes too heavy.

Airlines like British Airways(BA) and Lufthansa(LH) have the biggest remaining fleets of Boeing 747s.

So with all these aircraft grounded, what about new aircraft orders? That is the on-flow effect that will hurt plane makers like Boeing and Airbus. There will be the airlines that disappear and their orders cancelled. Then there are airlines like Cathay Pacific, for example, that have approached Boeing and Airbus about delaying their orders.

Boeing for its part has approached the US government for a B$60 stimulus package. The aviation industry must survive and it is worth noting that Boeing estimates that 70% of its revenue flows onto its 17,000 suppliers. The aviation industry is a huge employer and its demise can not be allowed to happen. Similarly, Airbus and its many suppliers are in the same boat.

Apparently, the story is not all doom and gloom. Dr. Steve Wright of the University of the West of England, Bristol(UWE Bristol) believes that the aviation industry will survive. Jobs will be lost, mainly at the customer-facing level, and of course those smaller airlines. Aviation seems to go through an 11 to 12-year cycle. Events such as 9-11 and the global recession of 2008 knocked the industry about, but it recovered. It will again. Meanwhile, Dr. Wright says, the development of new aircraft still goes on. In 5 years' time, we will still see the fruits of technology research that is going on right now.

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 decreases the further we get from the surface until we reach the near vacuum of space.

The currents or winds and the changing pressure play 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.

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 a 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).

An Emirates Boeing-777-300 takes off in Sydney.

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 you the idea at least.

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 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.

A QANTAS Airways Boeing 747-438 Registration VH-OJT delivered 26 Oct 1999 climbs out at 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 airliner 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 through 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.

A United Airlines Boeing 777-200ER taxis to runway 34L in Sydney. The 777 replaced the 747 on the US-Australia routes as of 01 April 2014. The trans-Pacific route is one of the world's longest routes and demands a 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 of 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 a 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 a flight from time to time to either make use of more favourable tailwinds or to avoid unfavourable headwinds.

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 autopilot. A speed is selected, 300 KIAS for example, and the aircraft happily flies with the autopilot 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, and 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.

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 effect on the aircraft’s 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-20,000 feet of altitude and our autopilot 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 keep 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 straightforward question.

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

Boeing 747 8, are we falling out of love?

Our love affair with the Boeing 747 goes back 4 decades to those heady days of aviation when fuel was cheap and Juan Trippe and the boys at Pan Am asked Boeing to build them a much bigger airplane.  Never has an airliner captured the imagination of the public, appeared in so many movies, and made travel possible as much as the venerable Queen of the Skies.  We have seen her grow through 5 main variants, the 100, 200, 300 400, and SP.

Of all these, the 747 400 has been the most successful.  We know her well with her stretched upper deck bubble and winglets.  Never a real beauty but certainly majestic, she was seen at every major airport in the world.  With 442 produced she was the flagship of many of the world’s airlines.

It has now been 10 years since the last 747 400 Jumbo jet was handed over to China Airlines.  A decade.  It is also a decade since Airbus entered the Jumbo airliner market with their A380 Super Jumbo.  Of course, the A380 had been in development for many years already and perhaps its coming prompted orders for the 747 400 to diminish in anticipation.

Two Boeing 747 400s of Air France, one climbing out while the the other taxis.

So where was Boeing?  

The 747-400 program was winding down, but it seemed like there wasn't a successor waiting in the wings to take over.  There were a few attempts at tempting the market with a full two-decker version and a few other variations, but nothing concrete that the market wanted.  As we know, in the end, a significantly stretched version of the old 747 shape was decided upon and flew for the first time 5 years after the last 747 400 was delivered.  

The Boeing 747 8 comes in two versions; the Boeing 747 8 Intercontinental and the Boeing 747 8 Freighter. Boeing was hedging their bets by appealing to two arms of the market, just as they did with the first 747 which is why we have the bubble cockpit on top.  This allows a nose door to be installed for straight-through cargo access to the main deck.

So, why are we falling out of love with our Jumbo?  

Well, more particularly, why are airlines falling out of love? The correct question might be why haven't airlines fallen in love with the Boeing 747 8?  Sales have  been very soft, certainly for the 747 8 Intercontinental, the passenger version.  But, let's not think it's all about Boeing.  Airbus have also been experiencing a challenge with their A380 sales, with not one new customer being added in the last 3 years.  They need to build and sell 30 aircraft a year to make it an economically viable product.  This challenge is further exacerbated by the fact that second hand A380s are starting to come onto the market with airlines like Malaysia Airlines and Thai International talking of selling some of their 3 year old aircraft.  This will seriously undermine the prices of new aircraft.

An Airbus A380 in flight in Dubai in November 2006.

So what are airlines doing about their long haul high volume routes?  It's almost as if they are hedging their bets to see which way technology goes.  We know that the skies are starting to belong to the big twins.  Airliners such as the Boeing 777, Boeing 787, Airbus A350, and Airbus A330 are now becoming the mainstay of many of the world’s airlines.  But still, they seem to want a Jumbo in their fleets.

In the last few years we have seen major airlines like British Airways, Virgin Atlantic, Thai International and QANTAS to name but a few, go through major refurbishment programs on their 747 400s.  QANTAS for example has completed a $250 million program to update and upgrade the interiors of 9 of its 747 400s.  The selling point being, that now the 747 400 seats are just like those on their Airbus A380s.

So are airlines waiting to see what happens with the Jumbo market?  When you consider that the list per unit price for a Boeing 747 8 Intercontinental is US$357.5 million and the cost of an Airbus A380 is US$318 million it makes sense to spend $250 million and have 9 airliners.

Lufthansa was the launch customer for the Boeing 747-8I. The passenger version of the 747-8 is known as the 8I where I stands for Intercontinental.

It seems the end of the age of the Jumbo four-engined airliner may be not far off.  Airbus and Boeing will pull the rug at some stage if they can't sell them and concentrate on their cash cows; the Boeing 777, Boeing 777X, and the Airbus A350 XWB.

We would love to hear about your experiences travelling on a newly refurbished Boeing 747 400.  Do they feel new, do you feel this is money well spent by the airline?