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B777 Flight Envelope Protections

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B777 Flight Envelope Protections

Old 17th Oct 2015, 10:35
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B777 Flight Envelope Protections

Hi there,

Does anyone have any links where I can understand the flight envelope protections on the B777 a little better?
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Old 21st Oct 2015, 00:17
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What would you like to know specifically?
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Old 22nd Oct 2015, 13:54
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I'll hijack this thread for a second since he doesn't respond, I'd like to know if it's possible to set autopilot to go to the airport that is not reachable (e.g. does autopilot take into account fuel levels), also is it possible to set it to go to x,y coordinate without entering waypoints but just tell it to go straight there? Again with or without fuel constraint.

Will autopilot automatically engage if it feels the plane is without human control and is going to stall or spiral down and what would it do in that case, go to the nearest airport and circle around or something else?
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Old 22nd Oct 2015, 14:51
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I'd like to know if it's possible to set autopilot to go to the airport that is not reachable (e.g. does autopilot take into account fuel levels)

The autopilot doesn't know anything about the aircraft's fuel state. The autopilot is just the "muscles" moving the controls to point the aircraft where it's told to go. The pilots can directly control the autopilot or they can set up the Flight Management System to guide it. The FMS will give you an "Insufficient Fuel" message anytime it thinks you will burn into the amount of reserve fuel you entered into the FMS during preflight.


also is it possible to set it to go to x,y coordinate without entering waypoints but just tell it to go straight there? Again with or without fuel constraint.

Think about it, what's the difference? Go to a waypoint a mile away or 10,000 miles, the FMS doesn't care. Again, it will give you the "Insufficient Fuel" message if it thinks you'll burn reserve fuel getting there.

Will autopilot automatically engage if it feels the plane is without human control ...

No



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Old 22nd Oct 2015, 15:01
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Hi,

Airbus has 5 types of protections, load factor, bank angle, pitch attitude, high speed and high angle of attack, and the in-depth explanations are explained in the FCTM/

But I can't find anything similar for Boeing and its flight envelope protections.

Pls advise.
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Old 22nd Oct 2015, 15:15
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Ah, maybe because Boeing doesn't have any? You can pulled the yoke back and generate G-loads until the aircraft stalls, roll the aircraft inverted, pitch the nose straight up or straight down, and go way past Vmo.
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Old 22nd Oct 2015, 15:57
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The 777 doesn't really have the ", I won't let you do that philosophy". It does have protections, but they're more of a subtle "I don't think you ought to do that..." and in any event the pilot can always override them.

In "Normal" flight control mode the Triple will drop lots of hints that you're getting close to the edge of the envelope; couple of examples - it will start to increase the control wheel force to resist roll inputs if the AOB starts to become extreme, and you can't continue trimming back if the airspeed gets too low, but the system won't stop you from grossly over banking, or stalling the aircraft, if that's what you really really insist on doing.
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Old 22nd Oct 2015, 16:02
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What wiggy said. and to spell it out, there's Bank angle protection, Turn compensation, Stall and overspeed protection, Pitch control and stability augmentation, Thrust asymmetry compensation.

http://www.davi.ws/avionics/TheAvion...ook_Cap_11.pdf

The 777 design utilizes envelope protection in all of its functionality rather than envelope limiting. Envelope protection deters pilot inputs from exceeding certain predefined limits but does not prohibit it
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Old 22nd Oct 2015, 16:52
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It's been a couple of years but I believe the 777 has max AOA protection. BA 038 would be an example of this. BA038 slowed until max AOA, at which point the autopilot disconnected to maintain max AOA without stalling.
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Old 22nd Oct 2015, 17:01
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also have a look at https://www.google.com/patents/US5722620
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Old 23rd Oct 2015, 06:17
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I believe the 777 has max AOA protection
Not that I'm aware of, I'd better check the FCOM again....(see the edit)

It does have what is decribed in the FCOM as "Stall protection" which limits the speed below which the aircraft can be trimmed and also increases control column force when flying near stall speed.

I'd have to check the BA38 report again but as I understand it the autopilot disengaged due to it running out of authority. I suspect what then happened was the aircraft might have pitched in reponse to being out of trim, rather than there being some form of active AOA protection

(Edit to add: Just checked the current FCOM. The pitch envelope has stall protection and over speed protection. "Stall protection" is as I paraphrased above. So unless Boeing are hiding features from the operators the 777 has no direct AOA protection.)

Last edited by wiggy; 23rd Oct 2015 at 09:04. Reason: Confirmation of FCOM contents
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Old 23rd Oct 2015, 10:50
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Google "b777 fbw controls" and you'll find some good articles including a very good synopsis of the flight control system by Gregg Bartley (Boeing)
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Old 23rd Oct 2015, 14:39
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wiggy - you're correct. Poor recall on my part.
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Old 24th Oct 2015, 16:51
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misd-agin It's been a couple of years but I believe the 777 has max AOA protection. BA 038 would be an example of this. BA038 slowed until max AOA, at which point the autopilot disconnected to maintain max AOA without stalling.
Slips are showing again as someone had opined earlier.
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