Sidestick safety concern [closed]

Question

I read about several aircraft crashes throughout aviation history and the investigations on wikipedia and also checked out some episodes of the documentary "Air Crash Investigation".

While of course I can only make conclusions of what I read, hear and see it appears, that problems related to communication are one typical reason to contribute to such disasters.

Something that attracted my attention is that the sidesticks used in the aircrafts of Airbus seem to be involved in not less than three crashes including Air France Flight 447.

Though there is the general distinction pilot flying (PF) and pilot not flying (PNF) failures, malfunctions and the triggered warnings tend to create a situation of stress and strain in the cockpit as comprehensible. Confusion comes up not seldom in such situations.

My point finally is, that

1. Sidesticks are smaller than yokes. To apply a control input one only needs to turn one's wrist while a yoke requires you to use both of your arms to make the big aircraft turn. I wonder if the inhibition threshold therefore is somehow lower to make extreme, exaggerated inputs in case of a sidestick?

2. Secondly, and this is the major question, as it appears, the sidesticks make it much harder, to be aware of the currently applied control input (especially) for the other pilot. While the yokes of both pilots are physically connected and both pilots have direct feedback of the currents state at any given time, the sidesticks

   • give no feedback to the other sidestick
   • are smaller, which makes it harder to see the current state their in already by the size alone
   • are more distant than yokes making it again harder to see for the other pilot, as this A380 cockpit shot shows

Question:

1. How is the general assessment of those sidesticks concerning safety?

2. Is there any feedback to the pilots which stick is giving what input?

3. Has there been any development in improving this situation?

4. What are the accidents/incidents sidesticks more or less contributed to confusion/lack of information?

Answer 1

Sidesticks are smaller than yokes. To apply a control input one only needs to turn one's wrist while a yoke requires you to use both of your arms to make the big aircraft turn.

Side-sticks are used together with control laws. In an Airbus Normal Law (and Alternate Law which differs only by not providing the flight envelope protections), the system automatically trims for 1 G wing loading (which equals constant flight path angle) and zero roll rate and the side-stick deflection commands wing loading in pitch and roll rate in roll. The springs are sufficient to provide all feedback there is to provide as the deflection and the force both correspond to the command given.

Due to the way side-sticks work, extended deflection is rarely necessary, nor are very fine adjustments normally needed to stabilize the plane on desired flight path, because the computer handles that.

Secondly, and this is the major question, as it appears, the sidesticks make it much harder, to be aware of the currently applied control input (especially) for the other pilot.

Feedback, on any kind of control, is provided by position and force. The other pilot can only feel the position. This allows them to notice that the other pilot pulled up, but not whether it is dangerously close to stall, because the stick position is biased by aircraft balance and, if horizontal stabilizer is used for trim (which all airliners do), also by trim. So the information it provides is rather limited.

On Airbus the side-sticks are not connected, so even this limited information is not available. But they have an advantage too. If the pilot flying is incapacitated or confused, the pilot monitoring can push a “control priority” button on the side-stick and the computer then only responds to their side-stick, so they don't have to fight with the other pilot on the controls.

How is the general assessment of those sidesticks concerning safety?

I've not seen any specific study. But they were approved and I am not aware of any accident on Airbus where similar accident wouldn't have happened with other type with traditional control column.

Is there any feedback to the pilots which stick is giving what input?

If both side-sticks are giving input, there is aural and visual warning “dual input”. If one pilot presses the “control priority” button, there is an announcement “control priority left/right” and visual indication. There is no direct indication of what the command is, but the pilots are looking for what the plane is doing anyway and they can usually judge from that. There is also indicator of control surface positions.

Has there been any development in improving this situation?

I am not aware of any aviation authority thinking there is a problem to fix. Manufacturers are coming up with new schemes they consider good, but that may be as much marketing as genuine improvement.

What are the accidents/incidents sidesticks more or less contributed to confusion/lack of information?

I can't think of any where it could be said the situation would have been significantly better if the controls were linked. If both pilots are confused, the connection would not help much and if only one is confused, the other can use the control priority to take over.

Even AF447, where some dual input was involved, is not really unique. There have been several crashes where pilots didn't realize a stall and didn't attempt recovery all the way from cruise level down to the ground (the most recent one) and all the others happened in planes with mechanically connected control column.

Answer 2

Regarding question 2:

There is no tactile or visual feedback (i.e. no sidestick movement when autopilot engaged). There may be visual cues on Airbus aircraft from the Side Stick Priority lights in front of each pilot on the glareshield. There is also an aural warning if sidestick priority is taken.

Regarding question 3:

The next generation of sidestick controls for fly-by-wire commercial aircraft are called Active Sidesticks and will provide visual and tactile feedback. They can already be found on the Gulfstream G500 and G600 aircraft.

This article from Aviation Week & Space Technology provides details.