autopilot

It’s just the autopilot that’s flying the plane!

Tim Takeoff
17.07.2018
1 picture
5 minutes

It’s really just the autopilot that’s flying the plane! The men and women in the front row of seats are just sitting and twiddling their thumbs. Or are they?

You hear this generalisation time and time again. Certainly it might also be rather calming for many passengers to visualise that an imaginary robot is flying however many tonnes of metal through the air. No doubt the ‘human’ pilots will be sitting with a cup of coffee and biscuits in front of their monitors watching the autopilot as it works. Most people feel sure that at least take-off and landing is done manually. Landing gear up, autopilot on! Isn’t that the reality?

Up and down, left and right

To provide a little clarity about this myth, it’s worth mentioning that nowadays there are not just one or two, but a total of more than four basic automatic flight control systems on board aircraft.

All of them work redundantly and simultaneously with each other. They, in turn, are precisely monitored by yet another computer. Should one of these systems have an ‘off day’ and deliver unusual figures, it will be isolated and disabled. The remaining systems then take over its job. This creates a cycle, which controls, monitors and corrects itself and only asks for help when it doesn’t know what to do next.

Input = Output

And so we’ve already reached a crucial point: knowledge. An automatic system, let’s simply call it a computer, can naturally only calculate and evaluate all processes the more knowledge you feed it. Translating this principle to our ‘friendly’ autopilot means that the pilot is responsible for feeding sufficient information into the entire system before the flight. Not just the current flight route, but also weights, centre of gravity, fuel, spare fuel, emergency procedure in the event of engine failure, speed, wind … the list goes on. And the more precisely these figures are entered, the more exactly can the complex computer system calculate and execute the flight. This factor is particularly crucial in the selection of the right cruising altitude, among other things. Today, the remaining airspace and flight paths are becoming much more closely intertwined, which is why aircraft are reliant on extreme precision when it comes to automatic flight control. Vertical clearances of approximately 1000 feet, which translates to around 300 metres, need to be flown precisely at cruising height at speeds approaching supersonic speed…

Digital support

There are also various restrictions by air traffic control. These figures may also have to be adapted at any time during the flight to adjust to new instructions and situations. In most aircraft, pilots have a primary flight computer for this, in which they can program and alter all the parameters. Every airline has therefore already stored a wealth of key information in a kind of database for its flight routes, to which the computer has access at all times. Modern jets even have a function with which data can be sent by satellite from the ground to the on-board computer, a factor that can be useful if you need new data for wind or flight route in the air – data that would take a lot of time to input manually. However, ultimately it is still the crew that decides what data is accepted and what is not. During the flight, the pilot monitors all these systems and is prepared at all times to take back control in the event of an emergency. Read more here on the responsibilities of a pilot.

Great, well we’ve discussed up and down, and left and right.

Faster or slower?

A fourth system, essentially the autopilot’s right hand man, controls the thrust lever during the flight: it’s known as automatic thrust or “autothrottle”.

Today it’s even used during take-off. Using state-of-the-art programs, the crew calculates the sequence before take-off right down to the last detail: the length of the runway, temperature, wind, air pressure, weight and centre of gravity, to mention but a few. Several precise speeds are calculated should there be a need to abort or continue take-off. The aircraft also needs an optimum take-off thrust for this, which can be reduced in the event of more favourable conditions, such as a longer runway or low weight, helping to reduce wear and emissions, including noise emissions. A precise take-off thrust is calculated to achieve this and so pilots rely on the automatic thrust system for take-off for maximum precision.

During the flight, all the systems work for and with each other like a well-oiled machine. If the aircraft needs to climb to a certain altitude, then the autopilot gives the automatic thrust system a target altitude to be reached. This, in turn, calculates the thrust needed in a fraction of a second and transmits these figures to the engines. Having said that, passenger comfort does not suffer because of this, as the thrust is neither too sudden nor too jerky. Technology that cannot fail to impress!

The “button”

Should one of the systems report that it cannot cope with the current situation, the crew has the option of taking back control of the aircraft at any time. Both the autopilot and also the automatic thrust can be disabled separately at the press of a button, so that the pilot can always manually land the aircraft using the automatic thrust if he or she needs to. This might be necessary possibly in very turbulent weather or due to stringent requirements due to local conditions.

Should the weather conditions fall below what is possible with the human eye, then the computers also need to “keep up”. Today there are a dozen or so procedures for getting an aircraft onto the ground even in poor visibility. The automatic systems can do this – up to a certain degree – fully independently, thanks to ground and satellite-based assistance.

The pilot’s job is to be suspicious at all times. The autopilot is only as good as its operator and demands the highest attention at each phase of the flight. Any discrepancies need to be identified quickly and systematically to get the autopilot back on track. If need be, with real “manual work” as well.

Cover picture Unsplash – imcockpit

by Tim Takeoff

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