Flight mode, why do we need to use this when we fly?

Air travel is something that a great many of us get to do reasonably frequently.  For some, it is too often, for others it is not often enough. Whichever it is, we are all familiar with the various announcements that are made on-board, particularly this one…

“At this time, make sure your seat backs and tray tables are in their full upright position and that your seat belt is correctly fastened. Also, your portable electronic devices must be set to ‘airplane’ mode until an announcement is made upon arrival. Thank you.”

Your new pilot, the kid with the game controller.

Most of us dutifully obey the instruction and reach for our device(s) switching them either off, or to the particular phone makers version of Flight or Airplane mode. It wasn’t so many years ago that the devices had to be turned off completely from the moment you arrived at your seat until such time as the aircraft reached a certain altitude. We were led to believe that our mobile devices would interfere with the aircraft’s systems and it was very much in our own interests to keep those devices switched off. I always used to have visions of some 10-year-old kid in row 36 who managed to get his game controller linked to the flight controls and then take us through some barrel rolls and loop de loops.

Things have changed a little now. Your mobile phone can be left on, with most airlines, for the whole flight and the only concession you have to make is to ensure it is in Flight Mode for the duration of the trip. This is of course only for devices weighing under 1Kg. Not because they emit a stronger signal or anything, but because they can become seriously dangerous projectiles in the event of the aircraft performing extreme manoeuvres.  So you will be asked to stow those during take off and landing.

…because they can become seriously dangerous projectiles in the event of….

Ok, so back to the Flight Mode question. Why do we still need to use flight mode during the course of the flight? Various sources indicate that the effect of a mobile phone or cell phone on an aircraft’s flight instruments is fairly negligible. Aircraft instrumentation is state of the art as you would expect from a unit costing tens if not hundreds of millions. There are so many systems with many kilometres of wiring throughout the aircraft that need protecting from each other, never mind your mobile device. These systems are fully shielded so that attenuation or interference from outside sources cannot corrupt signals sent around the systems.

So does that mean we can go ahead and just ignore the request for flight mode from the crew then?  Not quite. There is still a relatively old technology used by the flight crew. The radio. No, not the one tuned to the football, but the one used in the all-important communications with air traffic control. The giving and receiving of instructions is still done using the good old radio waves.  Mobile devices depend on microwave towers or other ground stations to provide them with the required signal to enable them to provide you with information and other services you depend on. As you can imagine, these towers get harder and hard to find as you are cruising 11 kilometres up, perhaps over sea or desert.  Your phone, being the faithful servant that it is, tries harder by cranking up the signal strength to as much as 8 watts in an effort to enable you to view those all-important food and puppy shots.

So what, I hear you say. Well, cast your mind back to the days when mobile/cell phones switched from analogue to digital signal. When you got your new digital-enabled phone, you found the signal and call quality was nice and crisp. However, if you were ever on a call near someone with an analogue phone, you knew all about it.  It sounded like your ear was being ripped apart. This is what it can be like for the pilots, maybe not quite as extreme, but an annoyance never the less.

Let’s face it, if the use of mobile/cell phones was of major concern to flight safety then you can rest assured that leaving the responsibility of ensuring the devices were turned off would not be left to the travelling public.  There is no doubt that on every flight you will find a number of devices have been left on during a flight either due to forgetfulness or laziness.

Whether it is safety critical or not, we want our pilots to be as relaxed as possible. We want them to be able hear and be heard when they talk to the ground without the possibility of interference blurring any flight direction instructions.  So complying with the flight mode instruction still carries as much weight as it ever did.

What Does Flight Mode Do?

The control centre on your mobile or cell phone.

The flight mode function on your phone or other radio-equipped device is the main control switch to turn off all radio enabled functions on your device. On your typical mobile/cell phone, this includes the voice/text, data (3g, 4g etc), Bluetooth and Wifi. You also have GPS but this doesn’t actually send anything, it sits there and listens for satellite signals and then translates them into something you understand by showing it on a map. Without data, however, you won’t get your map presentation so having GPS can be as useful as an ashtray on a motorbike.

For a few years now several airlines have been trialing and are supplying Wifi onboard their aircraft. What this means is that you have the ability now to connect to the aircraft’s onboard Wifi service and enjoy surfing the net and checking your email in the same way you can do at an internet cafe. “So hang on”, I hear you say, “I had to put my phone in Flight Mode, so how can I connect using Wifi?” Very good question and by the way, bravo for putting your phone in flight mode. As I said, Flight Mode is a master switch for turning off all radio related functions on your cell, mobile, tablet or laptop. Once they are all off you can turn individual functions back on. So seat belts on, Flight Mode on and then wait for the announcement that Wifi service has commenced and turn just Wifi on.

The Wifi signal is much weaker than your main mobile or cell call signal as it only needs to talk to a device mere metres from your seat to get a connection. This is not going to scream in the pilot’s ear so everyone is happy.

Personally, I have mixed feelings about on-board Wifi. I’ve always seen flying as a few hours you can step off the planet and leave yours and responsibilities behind with a good excuse for doing so. You know what I mean, let them miss you a little. Now I’m sure that corporate travellers will be expected to connect up and be available online or get that project completed because all resources are available. No peace for the wicked.

Flight Mode as we have seen is not going to make or break your flight as far as we can tell, but let’s show some consideration for the pilots who have to talk over the interference. Your phone charge will last a lot longer in Flight Mode, so everybody is happy.

Fly safely and LIKE us if you do.


Aircraft Noise

The emotive topic of aircraft noise.

Aircraft noise can be a very emotional subject for those who are affected by it in their day to day lives. Yes, like other aircraft enthusiasts, I love being next to an airport taking in the sights and thrilling at the gut-shaking sounds of powerful jets. However,  I have also lived with those same jets passing near my home. The disruptive effect on your day to day life cannot be overstated.  Not being able to speak to someone else in the room or listen to your favourite TV show gets very frustrating. In the 1980s I lived in Fulham, London.  Twice every evening our windows literally rattled as first the Concorde from New York arrived followed sometime later by the one from Washington DC. Thrilling at first, but it gets old rather quickly.

So what is being done about it? What is the solution?

Aircraft noise in most countries is taken very seriously. Its disruptive characteristics have a negative effect on those exposed to it at close hand. Loss of quality of life, loss of productivity by those who have disturbed sleep among other things.

Enter the Jeg Age.

In the early days of passenger air travel, piston driven propellor engines were the only form of propulsion. Whilst they were relatively noisy, they didn’t produce sounds in the high-frequency range that jets do.  When the jet age began with aircraft like the Boeing 707 and the Douglas DC8, a whole new ball game started. These early jets, compared with today, were fuel hungry and extremely noisy. Their engines were what you call pure jets, consisting solely of the jet engine turbine. The result was that the high pressure ignited fuel-air mixture was forced out of the tailpipe into still air. The friction caused between the fast travelling air meeting the still air was significant and caused a large amount of the roaring sound that resulted.

Aircraft and particularly engine makers have for decades been working diligently to find ways to reduce the sound footprint of a jet engine. The most significant breakthrough was the bypass engine. The concept is to take the aforementioned pure jet, the jet turbine, and encase it in a second nacelle. The nacelle is the outer casing of the engine. Inside the front of this nacelle is a large fan. This fan sucks in air from the front of the engine and feeds some of it into the jet engine turbine, the rest of it flows around the jet turbine and is ejected back around the flow coming out of the exhaust tailpipe of the jet turbine.  As well as adding to the thrust of the engine, the bypass airflow also serves to encapsulate the exhaust from the jet turbine. This serves to reduce the friction between the jet turbine exhaust and the still air, as well as dampening the sound.

New methods and materials used in the construction of engine nacelles and the engines themselves have also been instrumental in reducing jet engine noise. Boeing for example have

Boeing 737-9 MAX CFM LEAP-1B engine. The chevroned rear of the nacelle like the Boeing 787 ensures a smooth laminar airflow over the engine casing.

adopted a new configuration for the trailing edge of their engine nacelles which can be seen on the Boeing 787,  Boeing 747 8  and the new 737 Max aircraft models. The nacelle trailing edge is finished in a chevron configuration, like a sawtooth. This means there is a longer linear trailing edge which allows the air from the engine and the still surrounding air to merge together over a larger area, spreading that shock over a larger amount of air particles. The smoother the transition through the air of an aircraft, the greater its fuel economy and the less noise it makes.

Aircraft design improvements around noise reduction are not just limited to creating quieter engines. When Airbus Industrie began their initial design of the giant A380, one of the design requirements was to make it as quiet as possible. The engines, of course, were designed to be state of the art and provide noise reduction to strict specifications. Airbus, however, also looked at another factor. An aircraft has a much larger noise footprint when it flys close to the ground. That stands to reason, an aircraft flying low over your house makes much more noise than one flying twice as high. So what Airbus undertook to do was to design the aircraft so that it was capable of a steeper climb out. That is to say that the A380 is designed to be able to climb more steeply after take-off, thereby spending less time closer to the ground while departing a city.

Flying Quieter

It is not only what you are flying in that makes a difference. Airports located near built-up areas are continually being pressured to find ways to reduce their noise footprint. As our urban areas continue to sprawl, airports that may once have been located in the countryside now find themselves being surrounded by new housing and industry. It is tempting to think, well they knew the airport was there already so how can they complain? The truth of the matter is, many of our cities are getting overcrowded and whatever land is available must be used.

As our cities get bigger and spread around airport areas, more people are finding themselves living with aircraft noise. Of course, airports provide cities with the lifeblood of their economies. Having an airport near the centres of business encourages companies to base themselves in those cities.

Many airports have adopted various noise abatement procedures to help reduce the noise impact of their operations. For example, they can adopt air traffic control procedures that vary the approach paths to the airport. That way fewer aircraft will fly over more suburbs rather than a few suburbs bearing the full brunt. Aircraft can be guided over water or forested areas as much as possible. During off-peak times secondary runways can be used to allow those living under the main runway(s) approach path to have a break.

The way aircraft are controlled in the landing phase can also make a difference. In the landing phase, most aircraft generate a significant amount of noise due to the configuration of flaps and additional engine thrust required to compensate for the extra drag caused by the extension of flaps. Traditionally most approach patterns for landing at an airport have consisted of stepping the aircraft down to lower altitudes as it gets closer to the airfield. For example, it gets cleared down to 10,000 feet where it flies for a while, then down to 5,000 feet where once again it flies for a while.

The Continuous Descent Approach ensures that the landing aircraft stays as high above the ground as possible during the whole landing approach phase. Thereby it minimises the noise footprint over populated areas it passes over by being higher above them.

During this time it is overflying populated areas at these relatively low altitudes generating noise. A new approach, literally, is the constant glideslope. This means the aircraft is not asked to start descent until it is clear all the way to the runway. It means the aircraft will descend at a constant rate all the way to the ground and not spend any time flying over the ground at lower altitudes waiting to get further clearance to descend. Like the A380s take-off above, the aircraft will spend the minimum amount of time close to the ground where it is the noisiest.

Curfew is an option adopted by many airports. This restricts the operations of jet aircraft to certain hours of the day. For example, there may be no jet operations permitted between 10 pm and 6 am. This ensures that there is a quiet time when most people are trying to sleep. Curfew can cause problems for airlines. Flight delays for aircraft travelling to the curfew airport can be further exacerbated if that delay means they may arrive after curfew comes into effect. If they were only delayed by an hour to start with, they may find that the curfew will add a further 8 hours to the delay as they need to now arrive after 6 am.

Another scenario affecting airline competitiveness is where we have two airlines, one based in city A where there is a curfew and one in city B where there is no curfew. Both airlines want to maximise the number of flights they can do between cities A and B to profit from carrying more passengers. The airline operating from city B with no curfew has the advantage as they can start operating earlier and finish later.

Here we can see that the airline that operates out of the airport with a 10 pm to 6 am curfew is compromised by having to start later and finish earlier than its competitor based at the non-curfew affected airport. In this comparison, the airline from the non-curfew airport can do 3 return trips against its competitor’s 2.

By leaving at 4 am for example and arriving just after the 6 am curfew the airline from the non-curfew city is already halfway through their first return trip before the airline from the curfew city has even started. Similarly, the non-curfew city airline can depart on their last leg just before 10 pm curfew whilst the curfew city airline needs to conclude their last flight by 10 pm.

Another innovation to make airports quieter is the provision of electrical services for aircraft at the terminal gates. You may have noticed when you are at the airport that even though a jet might be stationary at the gate, you can still hear a jet engine whine. This is caused by what is known as the APU or Auxilary Power Unit. The APU is a small jet engine that usually sits in the tail cone of a jet aircraft. It doesn’t provide any thrust as its sole purpose, as the name implies, is to provide power to the aircraft whilst its main engines are not running. This power is what is used to run lighting, air conditioning and other electrical functions whilst the aircraft is parked. The APU may be much smaller than the main engines, however, its noise output is still significant. If you live next to an airport the jet noise is constant. To alleviate this type of noise, many airports are providing land-based power which an aircraft can plug into instead of firing up their noisy APUs before shutting down main engines. A significant amount of noise is avoided as well as unnecessary pollution.

Friendly Neighbour

It is accepted that airports are not the best of neighbours. Some airports, however,  make an effort to try and make life better for those who live close.  I use an example from Sydney, Australia, which is the largest city in Australia and a very important commercial hub. Sydney’s Kingsford Smith International airport is located around 7 kilometres from the city centre which is handy for travellers but also ensures many parts of the city are exposed to aircraft noise. Sydney city undertook to compensate the worst affected suburbs by providing the homes with soundproof double glazed windows. This, of course, helped those residents immensely, but at what cost?  Well, subscribing to the concept of user pays the users of the noisy aircraft paid. A levy of A$3.60 was applied to each ticket that involved an arrival or departure in Sydney. Once the expense of the double glazing was covered the levy was removed.

It is doubtful we will ever completely resolve the issue of aircraft noise, but finding ways to reduce it and manage it better goes a long way to improving the lives of those who are subjected to it. Finding ways to observe noise abatement helps us all.

Boeing 797 a Middle of Market Solution

The use of the 797 designation could be a nice round off for a 60-year cycle since the introduction of the Boeing 707. But why do we need another Boeing model and what is Middle of the Market?

Middle of the Market(MoM) is a term Boeing coined back in 2005 which described their then MoM solutions, the Boeing 757 at the top end of the single-aisle market and the Boeing 767 at the bottom end of the twin-aisle market. Those two venerable workhorses have been out of production for some time now which is why Boeing is concerned about this sector of the market.

So where does Middle of the Market lie? One could be forgiven for thinking that the 737 is growing bigger in the form of the 737 MAX and there is a smaller 787, the 787-8. However, let’s take a closer look at how those two aircraft compare.

Aircraft  Max Take-off Weight  Range  Configuration  Passengers
Boeing 737 MAX-9 88,300 Kg (194,700 lb) 6,510 km (3,515 nmi) 2 Class 178
Boeing 787-8 227,900 Kg (502,500 lb) 13,621 km (7,355 nmi) 2 Class 335
 Gap  139,600Kg (307,800 lb) 7,111 Km (3,840 nmi)  – 157

Looking at the figures above you can get an appreciation for the large gap between the largest 737 and the smallest 787.  To service this section of the market, airlines have to either underutilise their 787s or schedule more frequent services with their 737s. Neither option is very financially desirable which is why Boeing is looking at a completely new design for this niche in the market.

Sources indicate, and Boeing themselves have made announcements at the last Paris Airshow, that they expect to begin design work on what has unofficially been named the Boeing 797 or the MoM in 2018. The expected Entry Into Service (EIS) is 2024-2025 however, some sources indicate this could slip to 2026.

So what will the anticipated new model be like?

This view shows the distinctive Boeing 737 MAX winglet. Two smaller winglets mean that there is less weight required than for a more robust single longer span. In addition, it means that a significant addition wing surface is added whilst still being able to fit into Gate size C at airport terminals. Will we see this design feature included in the Boeing 797 design

General design requirements call for an aircraft that can manage a range up to 9,630 Km (5,200 nmi), around 10 hours flying. This will enable the aircraft to be used on routes such as the North Atlantic where it would be small enough to operate into and out of smaller city airports, avoiding the traditionally overcrowded main hubs. For passengers, the benefit will be to be able to fly to far off destinations from their home airport without inconvenient connections along the way.

The carrying capacity will, of course, depend on the carrier’s choice of configuration of the passenger cabin. The passenger carrying range is targeted for 220 – 270.

The new design will require a new range of engine with thrust in the 45,000-50,000 lbs range. Boeing has specified a requirement for a geared turbofan. This is where a gearbox sits between the big fan at the front of the engine and the internal turbine. This enables greater control over the engine with the ability to maximise the efficiency of engine speeds at different stages of flight. CFM, which is 50% co-owned by G.E. and Safran, have indicated they will be competing with Rolls Royce to produce such an engine, whilst Pratt and Whitney will offer an upgraded version of their GTF engine.

Boeing is confident in this sector of the market and estimates that they will be able to sell 4,000 797s over a period of 20 years. Airbus for their part are confident that their current offerings of the Airbus 321 NEO and A330 NEO will cover them, however, they haven’t ruled out the possible addition of an A322 to the Airbus family.
Construction of the B797 is likely to draw on lessons, new techniques and new materials that have gone into the development of the 787 as well as the 737 Max. The wings and fuselage will be made primarily from carbon fibre materials, as is the larger 787. We may also see the split winglets which are a feature of the 737 Max. These will increase the wing lifting area, giving better fuel economy without the penalty of greater wingspan. The benefit of maintaining a lesser wingspan is to enable the aircraft to fit into smaller gate areas at smaller airports thus enabling the concept of flying between more regional centres.

No doubt as design decisions are laid down, we will get a much clearer idea of how the latest Boeing offering will look. Meanwhile, 2026 seems a long way off. To bridge the gap, Boeing is seriously considering reintroducing the 767 300ER as an interim measure. It is a decision that has been on again, off again, but apparently, it is currently in an on again phase. The last off again phase was due to the production of the 787 being lifted from 12 to 14 per month, but we assume this roadblock has been removed.

Let us see what the future brings.

If you know any more about the Boeing 797 or MoM, please feel free to comment below.