Flying Machines 10 Airbus A320

The Airbus was the last aeroplane I flew before I retired and also, as it turned out, the aircraft I flew most hours in. The Airbus is a bit different and is usually difficult to explain quickly to those who have flown the older aircraft. It took me a few years to fully come to like the systems after the much simpler Boeing 737. I will try to explain how it works at the end of this page.

The A320 was designed as a completely new way of looking at an airliner; a complete break with the previous generation of aircraft. Some things are fixed, such as the need for at least two engines and the physical size of the aeroplane, although Airbus went for a larger diameter fuselage than the Boeing 737 which makes the cabin a bit more spacious. The control system was revolutionary in an airliner replacing the large control wheels (that were really only needed on aircraft without power controls) with small sidesticks similar to a computer game. The most efficient place to put engines has evolved to forward and below the wing, unfortunately this leads to a powerful nose-up trim change when power is increased. On earlier aircraft this has been handed to the pilots to sort out with large changes in control and trim with every power change. On the airbus the flight control computers allow for this and there is no change and no re-trimming. There are lots of other examples of the computers solving what had been piloting problems.

The cockpit is spacious and very comfortable without any of the strange steps and changes in floor level that are a feature of the B737. The instrument panel is particularly uncluttered as it consists mainly of six screens, two side by side for each pilot and two stacked vertically in the centre. There are, of course a few extra items, but almost everything that the pilot needs to know is on those six screens.

The centre lower screen is devoted to systems diagrams and the ECAM. The ECAM make choices of display throughout the flight and, particularly if there is a problem, displays the correct page. The lower part is the electronic check list that deals with non-normal situations.

Everything is simplified, for example in many aircraft the flap settings are named after the degrees that the flaps are extended; in the Airbus the flap settings are 0, 1, 2, 3 and Full, so there is no need to learn meaningless numbers. In general you take off with flap 1 and land with flap 3 or Full.

In Normal control law the pilot moves the sidestick to indicate what he wants and seven flight control computers then move the aircraft’s control surfaces to achieve that. In essence fore and aft movement of the stick controls “G” and side to side movement controls rate of roll; if you leave the stick central the aircraft will continue in one “G” flight at the angle of bank it was at when the stick was centralised. If the aircraft is disturbed from this by outside factors (gusts), it will return itself to where it was. If you pull the stick fully back it will pull 2.6 “G” whatever the speed or angle of bank, if you push it fully forward it will go to another limit that I have forgotten (but is irrelevant because you don’t go there). If you push the stick fully to one side it will roll at the maximum rate and will maintain that angle of bank when you let go.

There are, of course, some limits to this. If the angle of bank is greater than 45 degrees, it will return to 45 degrees when you let go. At 67 degrees of bank it won’t roll any further (effectively at more than 45 degrees of bank the stick position controls angle of bank). In pitch it will not exceed 25 degrees nose up or 15 degrees nose down. If you approach Vno (maximum normal operating speed) it will pitch up to prevent an exceedence and as you approach the stall speed it will first of all increase the power to TOGA (full power) and if you still pull back it will control the attitude to keep the wing below stalling angle of attack. There are other limits, but let’s not get too technical.

If the aircraft has not got enough information from the sensors, or any control computers fail it reverts to Alternate Control Law which is much the same as normal except you lose the protections. It will let you know that you are approaching a limit, but will not do anything about it. For example if you get near the stall it will continuously shout “Stall Stall!” at you and put the word “STALL” in red in the centre of the primary flying display. This means two things, you are about to, or have stalled and the aircraft is in alternate law. This is roughly the state the Air France A330 was in when it crashed in the Atlantic.

The next stage down is Basic Law. In basic law fore and aft movement of the stick controls the elevators directly and side to side the ailerons and roll spoilers; it becomes a “normal” aeroplane. If everything fails the aircraft defaults to Mech Law. The only controls available to the pilot are the rudder and the pitch trimmer through the variable incidence tailplane. The aircraft is controllable in this state and I have landed the simulator like this. Mech law is really intended to keep the aircraft under control while the crew reset computers.

As a result of the above, the aircraft is generally nice to fly with none of the pitch/power couples of other aircraft.

The control of the engines is also computer controlled; there is no direct connection between the throttle levers in the cockpit and the engine FADEC, they are computer input levers. Manual control of power is possible, but the aircraft is really designed to be flown with auto throttle. The levers have a detent at idle. There are three different idle power settings, Ground Idle and Flight Idle, triggered by the weight on switches, are obvious, but there is also an Approach Idle that comes in when Flap 1 is selected. Moving the levers rearwards from idle moves the engines into reverse (locked out in the air, of course). Forward movement of the levers causes an increase in engine power as you would expect, but towards the forward end of the movement there are three detents. The furthest forward is TOGA (take off and go around, full power), aft of that the second detent is Flex (reduced power for take off) or MCT (Maximum Continuous Thrust); What you get when you put the throttles there depends on what the aircraft is doing. The rearmost detent is Climb Power, when the throttles are in this detent auto throttle is automatically selected.

In practice the throttles are put in the Flex detent for take-off and brought back to Climb at the first power cut-back where they remain for the rest of the flight until they are moved back to idle in the landing flare. The throttle levers do not move as the auto throttle does its job; they are basically engine control switches.