Aviation Explained

Answers to some of the things that you thought about but maybe didn't know who to ask...

Starting a plane is not the same as starting a car. There is no key but on modern jets it is a simple process: there are two switches - one on an overhead panel called the 'Autostart Switch' and the other one is behind the thrust levers on the central control panel called the ‘Fuel Control Switch’. A pilot flicks the first to 'Start' and the second to ‘Run’, then the FADEC (the Full Authority Digital Engine Control - a computer program) does the rest by starting the engine rotating, opening the fuel valve and, at the right time, starting the igniters. It's pretty much what happens in your central heating system every time you, or your thermostat turns it on.

Do you need a key to start the engine on an airplane?

The runway speed depends on the type of plane. A Boeing 777 reaches 180 Knots - just over 200 miles an hour - before it has enough airspeed for lift to be able to overtake gravity allow takes off. When the plane hits this speed on the runway a co-pilot will call 'Rotate'. At this call, the pilot pulls back on the control column and it's up, up and away!

What speed does a plane get up to on a runway?

The engine provides the thrust which hurtles the plane down the runway but it can only push the plane forwards not upwards, something called lift does that: At the call 'Rotate', a pilot pulls back on the control column and the tail of the plane (which is basically an upside down wing) is pulled downwards. When the tail comes down, the angle of the wings is altered and the air flowing under and over the wings at different speeds creates lift and lifts the plane into the air.

How does something as heavy as a plane get off the ground?

Hmm- yes and no - pilots do talk to each other about the weather along their route but they do it via Air Traffic Control wherever possible. So, a pilot will radio Air Traffic Control and say, 'I'm trying to find out what the ride's like up ahead?' Air Traffic Control will locate another plane close by and call that pilot up and ask him whether he's encountered any 'chop' or 'turbulence'. The pilot will hear the other pilot's reply but won't talk to him directly. A plane's radio only covers a 200-250 mile radius when talking to a ground station though so over oceanic airspace or other remote regions a pilot may not be able to reach Air Traffic Control. Here he'll call on the 'Inter-pilot Frequency', give his rough co-ordinates and ask for information from any other planes in the vicinity. He will hear directly from other pilots in this instance.

Do pilots talk to each other in the air?

They look just like long, thin, straight clouds heh? Which is exactly what they are. They are called contrails, which is a shortened version of the phrase 'condensation trail'. They form when warm exhaust from the jet engines cool, which it does very quickly in the cold and dry air at high altitude. Basically, they are man-made clouds.

What are those white streaks a plane leave behind?

35,000 feet is a common average cruising altitude for jet turbine aircraft. It the magic point where maximum efficiency and minimum drag intersect. As a plane climbs the temperature around it drops which is great news as a jet engine is more efficient at colder temperatures. The air also gets thinner, so there is less drag. Above 35,000 feet the temperature tends to stop dropping but the air continues to get thinner which means the engine produces less power.

Why do commercial airplanes typically fly at 35,000 feet?

Passengers tend to think that if they feel a bump as the plane touches down the pilot has landed badly but this is not necessarily the case. Pilots refer to a firm touch down as a 'positive landing'. Because a plane cannot brake in the air, a pilot will perform a positive landing on a short runway rather than floating the plane along the runway for a softer touch-down, which would risk running out of runway before the plane could stop. Remember, the wheel brakes do not work unless the wheels are on the runway! The weather also plays a part in determining how hard the pilot comes in to land. On a wet runway a pilot would perform a positive landing to reduce the risk of hydroplaning.

Are hard landings bad landings?

Before landing a pilot 'flares' the plane by pitching up the nose of the aircraft. This increases the angle of attack on the wings which increases the amount of lift being produced thus slowing the rate of descent and ensures a comfortable landing. The impact on the tyres is not much more than you'd feel on the soles of your feet if you jumped off a five foot high wall.

Why don't tyres burst on touchdown?

Absolutely. Each engine on the airplane is big enough and powerful enough to keep the plane flying if the other fails mid-flight. The pilot would need to descend to around 20,000 feet though where the air was dense enough for that one engine to produce enough power to keep flying.

Can a plane fly on 1 engine?

Have you ever tried to keep your focus for 15 hours straight?! A computer does not lose concentration or need to take a break so the autopilot can do the mundane task of flying the aircraft whilst the pilots monitor the flight, talk on the radio (and eat their breakfast!). Airplanes are not currently set up for automatic take-off though and the auto-pilot is only used to land if the visibility is so bad that a manual landing would be unsafe (because the pilot cannot see the runway!).

Why do planes have autopilot?

Special measures need to be put in place at an airport to allow an aircraft to perform an automatic landing. The plane uses a system called an Instrument Landing System (ILS). The ground ILS equipment sends out a radio signal to guide the plane towards the landing area of the runway. Vehicles and other aircraft near the runway can disrupt this signal which would confuse the aircraft's onboard sensors and autopilot so the airport has to keep the area around the runway clear. ILS systems will slowly be phased out in the future to be replaced with a system using GPS (Global Positioning System) equipment which is not affected by vehicles or other aircraft.

If a plane can land itself, why do a manual landing?

There are 3 primary controls: elevators and rudder, which are both on the tail and ailerons, which are on the wings. The elevators pitch the nose up and down, the rudders turn the nose right and left and the ailerons roll the aircraft left or right.

What do you use to control the plane in the air?

Carrying fuel increases the weight of the aircraft which in turns requires more energy to create the required lift to make the plane fly. Carrying more fuel than is required makes the journey more costly than it needs to be. Companies want to reduce costs wherever possible so an aircraft will always carry the minimum amount of fuel which helps minimise the 'gallons per mile' of the flight. That said, for safety purposes an aircraft must always carry extra fuel in case it is kept in a holding pattern prior to landing and also an extra amount sufficient to reach an 'alternate' airport in case it needs to divert.

Does an airplane only carry enough fuel for the journey?

Pilots only really dump fuel in a 'non-normal' situation. If a passenger got sick for example, the plane would need to land at the nearest airport. The plane could be too heavy for the before-schedule landing so fuel would be dumped to reduce the landing weight. Fuel dumped by an aircraft that is more than 4,000 feet above the ground tends to evaporate before it hits the ground.

Why do planes sometimes need to dump fuel and where does that fuel go?

It allows passengers eyes to adjust to the low light outside the aircraft. If there is a problem during the take off or landing and the passengers have to evacuate the plane then their eyes will already be accustomed to the dark helping them better to see once they get outside the aircraft.

Why do cabin lights get dimmed before take-off and landing at night?

There are actually three panes in every cabin window, an inner, a middle and an outer. The outer window is the actual window which keeps the cabin air inside. The middle one acts like double glazing to insulate the aircraft against the freezing air temperature outside. The inner window is there so that passengers don't touch the freezing cold middle pane or scratch or damage it in any way. The hole in the middle pane allows the pressure to equalise between the various windows. It also stops condensation building. Modern aircraft no longer have window shades, windows are dimmed at the touch of a button.

Why is there a little hole in the cabin windows?

At 35,000 feet the air temperature outside the aircraft is -55 degrees Celsius (-70 Fahrenheit). The fuel - called Jet A-1 - which is carried in the wings, turns to wax at -47 degrees Celsius and cannot flow through the pipes to the engine. The friction of the air passing over the airplane however warms up the outside of the plane so the aircraft skin is at only about -20 degrees Celsius. At this temperature the fuel is fine.

Why doesn't the fuel freeze in the air?

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