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I know the Boeing 777 and 787 run on Fly-By-Wire. I was wondering:

  1. Do they have the Alpha Floor or Flight Envelope protections Airbus aircraft have?
  2. Do they have force feedback/force feel? The 737, for example, is connected using physical cables that move the flight control surfaces, so you can feel the yoke trying to move and when there is turbulence, it will actually shake a bit. This can't be felt with an Airbus sidestick. Can you feel this in Boeing Fly-By-Wire aircraft?
  3. When banking (without any pitch input), will the aircraft start to descend, or does the system counteract it like in an Airbus? In non Fly-By-Wire aircraft, they will start to descend a bit when banking, but Airbus Fly-By-Wire counteracts it by adjusting stabilizer trim.
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    $\begingroup$ A B737 actually has artificial feedback provided by the “feel and centering unit”, because the hydraulic power drive does not otherwise transfer the force back. I believe it is additionally connected with cables for case of hydraulic failure, which provides some additional feedback, but it is far from direct feedback. $\endgroup$
    – Jan Hudec
    Jan 23 at 0:02
  • $\begingroup$ @JanHudec Didn't know that, thanks. $\endgroup$
    – tizmataz77
    Jan 28 at 0:04
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1. Do they have the Alpha Floor or Flight Envelope protections Airbus aircraft have?

The Alpha Floor protection on an Airbus overwrites the thrust setting commanded with the thrust levers to TOGA. Boeing does not do this. The autothrottles (if armed) will engage to prevent a stall, but the computer never overwrites the actual thrust lever position in the cockpit:

With the autothrottle armed, the autothrottle automatically activates if not autopilot or F/D is active or and autopilot or F/D is in VNAV XXX, ALT, V/S, or G/S, and:

  • speed less than FMC calculated value for one second
  • thrust below reference thrust
  • airplane altitude above 100 feet RA on approach, or airplane barometric altitude 400 feet above airport on takeoff

Note: During a descent in VNAV SPD, the autothrottle may activate in HOLD mode and will not support stall protection.

(Boeing 777 FCOMv2 4.20.9 - Automatic Flight - System Description)

Also, unlike an Airbus, this protection can be disabled by simply disarming the autothrottle using the switch on the MCP.

The Boeing 777 and 787 do however have Flight Envelope Protections. These also work a bit differently than in a modern Airbus, where sidestick inputs are simply ignored or limited by the computers. In a Boeing, the flight envelope protection will use artificial forces on the yokes to provide the following:

Flight Envelope Protection

The flight envelope protection system reduces the possibility of inadvertently exceeding the airplane's flight envelope. The flight envelope protection system provides crew awareness of envelope margins through tactile, aural, and visual cues. The protection functions do not reduce pilot control authority. The protection functions are described later in this section and include:

  • stall protection
  • overspeed protection
  • roll envelope bank angle protection.

(Boeing 777 FCOMv2 9.20.5 - Flight Controls - System Description)

It says that the pilot control authority is not reduced because the pilots can always overpower the simulated forces on the yoke and command the aircraft to go beyond the protected flight envelope.

Essentially, the philosophy for the control authority differs:

  • Airbus will not let you do control inputs that might get you killed.
  • Boeing will stop you from accidentally making control inputs that might get you killed, but you can overwrite them.

See also:

2. Do they have force feedback/force feel?

Yes, unlike an Airbus sidestick the Boeing 777 and 787 simulate the forces on the yoke and therefore provide force feedback:

The primary flight control system uses conventional control wheel, column, and pedal inputs from the pilot to electronically command the flight control surfaces. The system provides conventional control feel and pitch responses to speed and trim changes.

(Boeing 777 FCOMv2 9.20.1 - Flight Controls - System Description)

You won't see the yoke shake in turbulence like on a 737, but you will see or feel the autopilot inputs as the yoke moves.

See also: How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?

3. When banking (without any pitch input), will the aircraft start to descend, or does the system counteract it like in an Airbus?

It will counteract like an Airbus, up to 30° bank angle, so you can fly a turn by rotating the control wheel only:

The PFCs also provide compensation for flap and speedbrake configuration changes, and turns up to 30° of bank. The PFCs automatically control pitch to maintain a relatively constant flight path. This eliminates the need for the pilot to make control column inputs to compensate for these factor. For turns up to 30° of bank, the pilot does not need to add additional column back pressure to maintain altitude. For turns of more than 30° of bank, the pilot does need to add column back pressure.

(Boeing 777 FCOMv2 9.20.10 - Flight Controls - System Description)

The PFCs here are the three Primary Flight Computers.

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  • $\begingroup$ Note that what Airbus is missing is position feedback, not force feedback, because in normal law the force produced by the surface, not its displacement, is what is proportional to the side-stick command. $\endgroup$
    – Jan Hudec
    Jan 22 at 23:57
  • $\begingroup$ @JanHudec You are right of course that the sidestick deflection is proportional to the force, but there is no force feedback, which would require some information to be fed back to the sidestick (minor semantic nitpick). $\endgroup$
    – Bianfable
    Jan 23 at 10:59
  • $\begingroup$ Well, it is a force feedforward, really. The point is that the force on the actual control surface more closely matches the command given with the side-stick, while the position varies with speed (the real reference value of course comes from the ADIRU). So while there is no feedback at all, saying there is no force feedback is misleading in that it suggests the force applied by the pilot does not correspond to the response of the aircraft where in fact it does. $\endgroup$
    – Jan Hudec
    Jan 23 at 12:59
  • $\begingroup$ Thanks, very nice answer @Bianfable $\endgroup$
    – tizmataz77
    Jan 23 at 19:15

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