It’s true that planes basically fly themselves — until they don’t.
We are living in an age of automation. Self driving cars, connected fridges, even smart trash bins. Then why does every commercial flight have not one, but two pilots flying the airplane?
The answer is quite simple: safety.
Are pilots really losing their skills?
A few years ago, the news of “pilots losing their manual flying skills” was everywhere. It was fueled by a few prior accidents where pilot skills were a contributing factor:
The Air France 447 flight, crashed in the Atlantic due to conflicting airspeed information being displayed to the pilots, ultimately due to a faulty airspeed sensor and the lack of training and information available at the time on manual flying with no airspeed indications.
The 2013 Asiana accident at San Francisco, where the pilots “landed” the airplane short of the runway, impacted the sea barrier and broke up in two parts, killing 3 of the 300 occupants. Media blamed the “inexperienced” pilots, but between the contributing factors, as found by the investigation, was an obscure throttle management mode on the Boeing 777 which didn’t protect the pilots from slowing down too much in a very critical phase of flight.
There has been in fact some evidence that pilots were at risk of losing some cognitive skills related to non-automatic flying; companies have since started to improve their training and operating practices to mitigate this risk. Automation is still prominent, and is there to help pilots in flying increasingly complicated machines. However, it’s not there to fully replace them.
Autopilot
Autopilot is a broad term that encompasses a series of automated tasks that the airplane performs without the pilots directly touching or moving the controls. The most basic form of autopilot, found in many small propeller aircraft, provides only a “straight and level flight” mode: based on a gyroscope (an instrument that remains parallel to the ground regardless of the airplane’s orientation) it acts on the ailerons to cancel any bank angle (or roll), and on parts of the horizontal stabiliser to modify the pitch so that the airplane doesn’t climb or descend. Some basic autopilots will also let the pilots climb or descend at a steady rate.
The next autopilot upgrade lets the airplane follow a specific route. Most routes are flown between VOR stations, which let the airplane follow a track leaving the station or going towards it. The autopilot can be instructed to follow this track by steering the plane towards the navigation aid’s signal. Modern autopilots will also follow GPS tracks, but commercial flight is still largely based on radio navigation.
Your airplane dealer may want to offer you also a nice upgrade, which lets you control the airplane’s throttle. Unsurprisingly this is called auto-throttle, and it works by changing the engines’ power so the airplane’s speed matches what the pilots programmed into it. In most aircraft it physically moves the throttles, to provide feedback to the pilots that it’s doing its job correctly (or not).
Approach and landing
Autopilots take a lot of workload off the pilots in some phases of flight, letting them concentrate on monitoring parameters, following and planning the route, and talking to air traffic control to maintain separation from other aircraft. There are phases of flight however when the workload gets higher, such as approach and landing. Here the aid of the autopilot is even more helpful to let the pilots concentrate on following the appropriate approach path and lining up with the runway, maybe in poor or no visibility conditions, with bad weather and heavy turbulence.
Autopilots found in all commercial aircraft have also an “approach mode”. Most airports are fitted with variations of a system called ILS (Instrumental landing system), which guides the airplane down to the runway starting from a certain altitude, following both a vertical profile (ensuring adequate clearance with the surrounding terrain) and a lateral profile (to be properly lined up with the runway). The autopilot here has full control of the aircraft: follows a descent path, maintains a certain speed, and stays on a certain ground track. Pilots will take over by disconnecting the autopilot below a certain altitude, when the airplane is very close to the navigation aid and the autopilot corrections might be too abrupt.
There are various categories of ILS systems, and the most precise ones (called “CAT3”) can allow fully automatic landing and rollout at a certain exit. This is very helpful in some regions, as it lets the plane land in zero visibility where it would be literally impossible for a human pilot to manually land. However auto-land is used sparingly as pilots will still need to take over if an autopilot malfunctions or if the airport doesn’t support autoland.
Something’s wrong! Who’s wrong?
I have spoken about a singular autopilot so far; in fact commercial aircraft are fitted with more than one autopilot (usually two or three). Say one autopilot, based on the data from some sensors, thinks the airplane is upside down. What ensures that the correct response is to turn the airplane upside down again? The sensors may be faulty. For this reason, different autopilots use data from different sensors to determine the airplane’s desired response. The autopilots commands are then checked and averaged to provide the actual input to the flight controls. If one autopilot starts acting erratically, it gets expelled by the decision pool and the pilots are informed of this situation. If the other two autopilots start disagreeing, the pilots can then take over manually. All autopilots functioning and agreeing is a necessary condition for automatic landing and roll-out, as the data needs to be very precise to allow it.
Fly by wire
Amongst other aids offered to pilots, is fly by wire. This is a topic that can spark heavy cult-like discussion in aviation circles, with some heavily opposing the approach (typical of Airbus) of no direct mechanical link between the controls and the control surfaces, and other manufacturers who still have a physical link (normally hydraulic) to provide control in case of an electrical failure. It has to be said that no accidents have been caused primarily by a total loss of control due to the loss of electrical power (MH370 conspiracy theorists stay away: that airplane has full mechanical backup).
Sometimes this is pointed out as the cause for the Air France 447 crash, blaming the lack of feel for the controls on the pilots. The Aviation Herald has a comprehensive coverage of the crash and of the final report, which was written by several air investigation professionals: it was not due to the lack of feel for the stall conditions through the controls, but due to the lack of specific training that would have allowed the pilots to better recognise the condition via e.g. aircraft vibrations.
In a fly by wire airplane, such as the Airbus A320, there are various control laws which change the way the airplane responds to pilots’ inputs. These different modes provide safety in case certain systems degrade their performance or fail. These are described in detail on a Skybrary page, in brief:
- normal law lets the pilots adjust the aircraft’s orientation in space — with the stick centered, the plane maintains the pitch angle and roll angle via automatic adjustments. This control law also prevents pilots to overload the airplane or slow it down too close to stall speed;
- alternate law, which engages when some failures are encountered, removes some protections and the effect of controls is not canceled once the stick is centered; this also deactivates some protections;
- direct law, which is a degraded version of alternate law, relates the airplane’s control surface movement (such as ailerons) directly to the stick inputs, and all flight envelope protections are lost.
On top of that it’s not true that pilots have no control left in the extremely unlikely case where all electrical systems fail at once. The trim wheels, which control small tabs at the end of the horizontal stabiliser, are still mechanically connected (via a cable) to these surfaces. This lets the pilots control the nose up — nose down attitude (pitch). Lateral control is provided by the rudder pedals, and engine power can let the plane adjust speed and altitude whilst pilots troubleshoot the problem.
These are broadly the systems that are allegedly making pilots lazy, but are in fact making your flights safer and smoother, and your pilots less stressed and tired. If you really do want a manual flight experience, you can book a trial lesson at your local airfield. It’s a rewarding and awesome experience, and you’ll surely realise very soon why pilots do love their autopilot systems.
