motopolitico
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How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:08 am

I know this may well be an exercise in futility, but given the apparent situation of BA038, dual engine failure 40 seconds from landing, and a FO who appears to have pushed his aircraft to the limit to get it across the fence, would an A330 in a similar situation with Airbus' envelope protection have fared better or worse?
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PhilSquares
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:20 am



Quoting Motopolitico (Thread starter):
I know this may well be an exercise in futility, but given the apparent situation of BA038, dual engine failure 40 seconds from landing, and a FO who appears to have pushed his aircraft to the limit to get it across the fence, would an A330 in a similar situation with Airbus' envelope protection have fared better or worse?

Considering the aircraft are both FBW, I don't think it would have made any difference at all. ?????
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DH106
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:33 am

Yes, but as I understand it Airbus has a 'hard' envelope protection whilst Boeing allows pilots the final say - exceeding the envelope if commanded. Assuming similar glide ratios it boils down to:

1) the margin (if any) that Airbus allows at the envelope limits
2) how 'accurately' the F/O flew the B777 at it's perfomrance limits
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motopolitico
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:46 am

Ah! I hadn't considered differing glide characteristics. There's clearly a lot more to the question than I thought when I asked it. I guess what I really meant to ask was how would BA038 have done if the T7 had had Airbus-style hard envelope protection. I suppose the world will never know.
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Rj111
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 12:08 pm

I think it's quite important to establish all the facts of the incident first before we speculate on how an Airbus would have performed.
 
DH106
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 12:13 pm



Quoting RJ111 (Reply 4):
I think it's quite important to establish all the facts of the incident first before we speculate on how an Airbus would have performed.

Definitely agreed.
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Starlionblue
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 12:57 pm



Quoting RJ111 (Reply 4):
I think it's quite important to establish all the facts of the incident first before we speculate on how an Airbus would have performed.

As long as it's understood we're speculating with incomplete information, I don't think it's really a problem.

So here's my speculative answer.
As far as flying characteristics, an 330 would have behaved the same way after the "lack of power-up". Envelope protection would only have come into play is the aircraft had been entering a stall.

If the aircraft had been entering a stall, the 777 would have activated the stick shaker (right?) and the trusted the pilots to do the right thing. The 330 would have prevented the stall altogether by lowering the nose.

It's also important to remember that Airbus envelope protection is there to make the aircraft safer. Preventing a stall at low altitude ensures the plane hits the ground wings level and controlled (as in the notorious Mulhouse 320 crash) as opposed to flipping end over end. Envelope protection is not a suicide pact. It is not the case of a French computer suddenly intoning (cue French movie villain voice): "I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"

Anyway...
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 5:55 pm



Quoting Starlionblue (Reply 6):
"I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"

 bigthumbsup 
Good summary. I suspect that your conclusion is correct; the pilot in the 777 did not exceed the envelope that an Airbus would have enforced; if he had the 777 would almost certainly have stalled and crashed. The only situation I can envision where the envelope protection of the Airbus could stand in the way of a successful outcome would be a violent maneuver to avoid a collision. But there may arise some other situation, which is what Boeing feels. They do not consider themselves smart enough to foresee every situation, and thus leave ultimate control to the pilot.
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DH106
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 7:56 pm



Quoting SEPilot (Reply 7):
I suspect that your conclusion is correct; the pilot in the 777 did not exceed the envelope that an Airbus would have enforced; if he had the 777 would almost certainly have stalled and crashed

Do we know the B777 didn't in fact stall ?
I'm speculating , but it may well have stalled from quite a low height and 'just' carried over the fence. The initial grooves at the point in the earth of the runway undershoot seemed quite deep to me which might imply a fairly high vertical descent speed at touchdown and the state of the gear afterwards seems to reinforce this - the left gear looked as though it had been fairly brutally forced up through the wing rather than just drag damage from running over rough unprepared ground.
I'm not taking anything away from the skill of the F/O here - it was certainly a disaster averted.
Be interesting to see what the report says..
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 8:34 pm



Quoting SEPilot (Reply 7):
the pilot in the 777 did not exceed the envelope that an Airbus would have enforced;

There is also no guarantee that the Airbus FBW system would have enforced anything - the aircraft would have been in an unknown state, and Airbus FBW (like Boeings) has several modes of operation, one of which includes 'get out of the pilots way and play no part other than to pass messages between pilot and control surfaces' (Direct Law).
 
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:26 pm



Quoting Starlionblue (Reply 6):
"I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"

What's next, livestock being catapulted over the wall?  mischievous 
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Starlionblue
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RE: How Might Have An A330 Have Responded In BA038?

Fri Feb 15, 2008 11:57 pm



Quoting Moo (Reply 9):

There is also no guarantee that the Airbus FBW system would have enforced anything - the aircraft would have been in an unknown state, and Airbus FBW (like Boeings) has several modes of operation, one of which includes 'get out of the pilots way and play no part other than to pass messages between pilot and control surfaces' (Direct Law).

It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems. Assuming the engines were the only affected system, the aircraft would have remained in Normal Law.
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RE: How Might Have An A330 Have Responded In BA038

Sat Feb 16, 2008 12:09 am

Quoting PhilSquares (Reply 1):

Considering the aircraft are both FBW, I don't think it would have made any difference at all. ?????

The 777 has a slightly different manual reversion should certain FBW be lost. What that means is that there are a few cables running to certain control surfaces. However at this point it isn't believed that the FBW system was lost, so that point is not important.

Quoting Starlionblue (Reply 6):
If the aircraft had been entering a stall, the 777 would have activated the stick shaker (right?) and the trusted the pilots to do the right thing. The 330 would have prevented the stall altogether by lowering the nose.

It takes about 70lbs of back pressure to make a 777 stall. The computer will let you do it, but you have to put a lot of work into stalling a 777. 70lbs of force means that you basically have your feet up and are pulling with all your might. The stick shaker of course is going off along with visual and verbal master alarms and cautions. I've never been in a 777 when it has stalled, but I hear it is made to be very difficult.

[Edited 2008-02-15 16:38:39]
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474218
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 12:23 am



Quoting PhilSquares (Reply 1):
Considering the aircraft are both FBW, I don't think it would have made any difference at all. ?????

FBW means that electrical signals are used to tell the flight control servos where to position the control surface (by supplying hydraulic fluid to the actuators) rather than controls cables. So FBW nothing to do with the incident.

Quoting Starlionblue (Reply 11):
It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems. Assuming the engines were the only affected system, the aircraft would have remained in Normal Law.

There is nothing "Normal" about loosing forward thrust when the wing is as dirty as BA038's.

Quoting RoseFlyer (Reply 12):
The 777 has manual reversion should FBW be lost.

I need a explanation of how this is possible?
 
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RE: How Might Have An A330 Have Responded In BA038

Sat Feb 16, 2008 12:29 am

Quoting 474218 (Reply 13):
Quoting RoseFlyer (Reply 12):
The 777 has manual reversion should FBW be lost.

I need a explanation of how this is possible?

I'm not exactly sure how it works, but I'll ask around when I'm at work on Monday. What I do know is that Boeing's Fly By Wire on the 777 is different than the Airbus model and that there are differences in how the backup systems work. I think I chose my words incorrectly since it does not have manual reversion in the sense of the 737. I could be wrong though since I'm not an expert on the 777. What I have been told is from a coworker who worked on the early design of the 777.

[Edited 2008-02-15 16:36:46]
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 12:50 am



Quoting 474218 (Reply 13):
I need a explanation of how this is possible?

Direct linkages that bypass the FBW system entirely. I know a 777 has to spoilers hooked up for non-FBW roll control, and I think either the elevator or the elevator trim can be manually actuated as well.

Does anyone know what an A330 would do if it lost both engines? Does the envelope protection stay engaged, or will it go back to another mode (normal mode, direct mode--whatever it is you avionics experts call it).
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474218
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 1:23 am



Quoting Dw747400 (Reply 15):
Direct linkages that bypass the FBW system entirely. I know a 777 has to spoilers hooked up for non-FBW roll control, and I think either the elevator or the elevator trim can be manually actuated as well.

So the 777 has control cables, bell-cranks and push rods, just like a non-FBW aircraft, except they are only used for back-up?
 
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 1:44 am



Quoting Starlionblue (Reply 6):
t is not the case of a French computer suddenly intoning (cue French movie villain voice): "I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"

What a strange person!

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zeke
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 2:13 am



Quoting Motopolitico (Thread starter):
Yes, but as I understand it Airbus has a 'hard' envelope protection whilst Boeing allows pilots the final say - exceeding the envelope if commanded. Assuming similar glide ratios it boils down to:

1) the margin (if any) that Airbus allows at the envelope limits
2) how 'accurately' the F/O flew the B777 at it's perfomrance limits

Because of the envelope protection that is on the Airbus, it has a lower stall buffet than similar aircraft, it is one of the reasons why the Airbus FBW outperforms the Boeing FBW on maneuvers like a CFIT recovery. With the engines still developing thrust, as it was in this case, it would be possible to fly a A330 in landing configuration at stall speed without a risk the aircraft from stalling. One would not fly the aircraft so slow, as flying at that speed would actually increase your descent rate, and reduce performance.

Quoting RJ111 (Reply 4):
I think it's quite important to establish all the facts of the incident first before we speculate on how an Airbus would have performed.

Agreed 100%

Quoting Starlionblue (Reply 11):
It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems. Assuming the engines were the only affected system, the aircraft would have remained in Normal Law.

It is not an unknown state with all engines failed, with an all engine flame out you are in direct law because of the loss of electrical buses and hydraulics, the FBW protections are not in place, Airbus has a QRH procedure for this (unlike the 777). With engines still developing thrust as it appears in this accident, a A330 in a similar case would still be in normal law as the electrics and hydraulics are normally powered.

Quoting RoseFlyer (Reply 12):
The 777 has a slightly different manual reversion should certain FBW be lost. What that means is that there are a few cables running to certain control surfaces. However at this point it isn't believed that the FBW system was lost, so that point is not important.

It is difficult to say what would be lost with a dual engine flame out, Boeing does not have a procedure for dual engine flame out on the 777 in their QRH or FCOM 3. With engines still developing thrust, nothing would have been lost at all on a 777 or A330.
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PhilSquares
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 2:13 am



Quoting 474218 (Reply 13):


Quoting PhilSquares (Reply 1):
Considering the aircraft are both FBW, I don't think it would have made any difference at all. ?????

FBW means that electrical signals are used to tell the flight control servos where to position the control surface (by supplying hydraulic fluid to the actuators) rather than controls cables. So FBW nothing to do with the incident.

Am I missing something??????

Just for the record, THERE IS NO MANUAL REVERSION on the 777. By manual reversion I am talking about what exists on the 737/727. There is a manual backup very similar to the 320, but it's not manual reversion
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ex52tech
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 4:45 am



Quoting Starlionblue (Reply 11):
It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems

My question here is .........Is the A330 being powered by the APU, which would have allowed for the hydraulics to be powered by the electric pumps, or are we on just the emergency bus here?
How does the protection system work on just battery power? I do not recall if that situation came up when I went to A320 school many years ago.
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474218
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 5:23 am



Quoting PhilSquares (Reply 19):
There is a manual backup very similar to the 320, but it's not manual reversion

What I want to know is how the "manual back up works". How is the servo actuated in the manual back-up mode, are there cables? From what I have read the 777 has three separate channels in the flight control system which, did away with the requirement for a mechanical back-up. Is this wrong?
 
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Starlionblue
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 6:27 am



Quoting Zeke (Reply 18):
Quoting Starlionblue (Reply 11):
It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems. Assuming the engines were the only affected system, the aircraft would have remained in Normal Law.

It is not an unknown state with all engines failed, with an all engine flame out you are in direct law because of the loss of electrical buses and hydraulics, the FBW protections are not in place, Airbus has a QRH procedure for this (unlike the 777). With engines still developing thrust as it appears in this accident, a A330 in a similar case would still be in normal law as the electrics and hydraulics are normally powered.

Indeed as you say the "engines out" and the "engines idling" scenarios are quite different. AFAIK BA038 had engines idling, so in an equivalent 330 it would have been normal law unless I'm much mistaken.

Quoting 474218 (Reply 13):
Quoting Starlionblue (Reply 11):
It would not have been in an unknown state. Direct Law is only used if you lose quite a few control systems and power systems. Assuming the engines were the only affected system, the aircraft would have remained in Normal Law.

There is nothing "Normal" about loosing forward thrust when the wing is as dirty as BA038's.

It's called "Normal Law". I didn't invent the name. It is not a reference to flight circumstances. It is a mode of the Airbus flight control systems.

Quoting BuyantUkhaa (Reply 17):

Quoting Starlionblue (Reply 6):
t is not the case of a French computer suddenly intoning (cue French movie villain voice): "I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"

What a strange person!

Did you not watch "Monty Python's Quest for the Holy Grail"?!? If you haven't, you owe it to yourself to go rent or buy it and have a nice evening of hysterical laughter. Big grin KELPkid's comment is in reference to the same scene.
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PhilSquares
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 7:41 am



Quoting Zeke (Reply 18):
Because of the envelope protection that is on the Airbus, it has a lower stall buffet than similar aircraft, it is one of the reasons why the Airbus FBW outperforms the Boeing FBW on maneuvers like a CFIT recovery.

Are you sure about that? On the Airbus you get Alpha Prot at a AOA less than the stall AOA. However, on the 777 you can pull up to the max energy line and be right on the stick shaker. That is where the wing is being max performed. My understanding was on Airbus you could never get there. In a situation as you described, CFIT, the Boeing would give a little bit better AOA.
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mandala499
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 8:15 am



Quoting DH106 (Reply 2):
Yes, but as I understand it Airbus has a 'hard' envelope protection whilst Boeing allows pilots the final say - exceeding the envelope if commanded. Assuming similar glide ratios it boils down to:

Yes but as Roseflyer wrote...

Quoting RoseFlyer (Reply 12):
It takes about 70lbs of back pressure to make a 777 stall. The computer will let you do it, but you have to put a lot of work into stalling a 777.

And according to a friend who flies the 777... "you can tell the computer to buzz off, but you do that by having a fight against it!"  Smile

Quoting Dw747400 (Reply 15):
I know a 777 has to spoilers hooked up for non-FBW roll control, and I think either the elevator or the elevator trim can be manually actuated as well.



Quoting PhilSquares (Reply 19):
Just for the record, THERE IS NO MANUAL REVERSION on the 777. By manual reversion I am talking about what exists on the 737/727. There is a manual backup very similar to the 320, but it's not manual reversion

I agree that it isn't manual reversion, it's a manual back up... ie: you can't select it, it gets selected when everything else screws up... Manual reversion I think you can select it or induce it (I wouldn't bother unless I'm a test pilot getting bored with my career).

If I was informed correctly, for the 777 it's roll by spoilers or differential thrust and pitch by trim (the electric switches on the yoke, or the STAB TRIM tab on the pedestal... no elevator no rudder... On the bus, again if I was informed correctly, it's rudder, trim wheel and thrust...

It does sound like the Bus manual back up require more than a handful, but then again, I haven't read the manuals on those sections for those aircraft.

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zeke
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 8:40 am



Quoting PhilSquares (Reply 23):
Are you sure about that? On the Airbus you get Alpha Prot at a AOA less than the stall AOA. However, on the 777 you can pull up to the max energy line and be right on the stick shaker. That is where the wing is being max performed. My understanding was on Airbus you could never get there. In a situation as you described, CFIT, the Boeing would give a little bit better AOA.

Compare the two CFIT recovery procedures, the Airbus is full back stick to go to Alfa Max (with auto speed brake retraction), on the 777 you pitch attitude of 20°, retract speed brakes, and only then rotate up to the pitch limit indicator or stick shaker or initial buffet.

The study found that the airbus gave predictable, repeatable results, on the Boeing it varied with pilot technique (Boeing says you should use smooth, steady control to avoid a pitch attitude overshoot and stall), but they concluded at the end of the day the difference was minor.
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Jetlagged
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 2:32 pm



Quoting PhilSquares (Reply 23):
However, on the 777 you can pull up to the max energy line and be right on the stick shaker. That is where the wing is being max performed.

Stick shaker does not occur at Clmax. So in flying on the shaker you are not at maximum lift. Airbus is similar, you climb at what is effectively stick shaker speed.
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 4:34 pm



Quoting Moo (Reply 9):
and Airbus FBW (like Boeings) has several modes of operation, one of which includes 'get out of the pilots way and play no part other than to pass messages between pilot and control surfaces' (Direct Law).

When is Direct Law invoked? Does the pilot select it or is it automatically selected under certain circumstances. If so, when?
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OldAeroGuy
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 5:28 pm



Quoting RoseFlyer (Reply 12):
The computer will let you do it, but you have to put a lot of work into stalling a 777. 70lbs of force means that you basically have your feet up and are pulling with all your might.

It's not quite pulling with all your might. The current 777 Chief Pilot is female and weighs about 55 kg. She has been able to stall the 777 quite readily.

Quoting 474218 (Reply 13):
Quoting RoseFlyer (Reply 12):
The 777 has manual reversion should FBW be lost.

I need a explanation of how this is possible?



Quoting Dw747400 (Reply 15):
Direct linkages that bypass the FBW system entirely. I know a 777 has to spoilers hooked up for non-FBW roll control, and I think either the elevator or the elevator trim can be manually actuated as well.



Quoting 474218 (Reply 16):
So the 777 has control cables, bell-cranks and push rods, just like a non-FBW aircraft, except they are only used for back-up?

If FBW is lost on the 777, pitch is controlled by electric Stab Trim (no mechanical cables). The only mechanical cables are to the hydraulic actuators on a left/right spoiler pair. There is no true manual reversion as on the 737 or MD80.

Quoting Zeke (Reply 18):
One would not fly the aircraft so slow, as flying at that speed would actually increase your descent rate, and reduce performance.



Quoting PhilSquares (Reply 23):
However, on the 777 you can pull up to the max energy line and be right on the stick shaker. That is where the wing is being max performed. My understanding was on Airbus you could never get there. In a situation as you described, CFIT, the Boeing would give a little bit better AOA.



Quoting Jetlagged (Reply 26):
Stick shaker does not occur at Clmax. So in flying on the shaker you are not at maximum lift. Airbus is similar, you climb at what is effectively stick shaker speed.

The best steady state horizontal glide distance from a given height will be obtained at the speed for best L/D. On an A330 or 777, this speed is very close to 1.23*Vstall.

However, it is possible to extend this distance somewhat by flaring near the ground and trading kinetic energy (speed) for potential energy (height). The best case would be to contact the ground at zero sink rate with the wing at stall angle of attack. Pilot technique would have to be spot on to obtain such a result.

Since the BA038 incident conditions would have had either an A330 or 777 in Normal FBW mode, it is possible that the Boeing system that does not limit angle of attack to sticker shaker or below could have provided slightly more glide distance than the Airbus system. The difference would be marginal and real world pilot technique would probably over shadow the difference.
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DH106
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 5:38 pm



Quoting Zeke (Reply 18):
Quoting Motopolitico (Thread starter):
Yes, but as I understand it Airbus has a 'hard' envelope protection whilst Boeing allows pilots the final say - exceeding the envelope if commanded. Assuming similar glide ratios it boils down to:

1) the margin (if any) that Airbus allows at the envelope limits
2) how 'accurately' the F/O flew the B777 at it's perfomrance limits

Twas me you actually quotede Zeke - not Motopolitico

Quoting PhilSquares (Reply 23):
Are you sure about that? On the Airbus you get Alpha Prot at a AOA less than the stall AOA. However, on the 777 you can pull up to the max energy line and be right on the stick shaker. That is where the wing is being max performed. My understanding was on Airbus you could never get there. In a situation as you described, CFIT, the Boeing would give a little bit better AOA.

Yes, but as Zeke has alluded to with his CFIT explanation - you're not looking for max AOA/CL (max lift) performance here but best glide - i.e. best L/D ratio which occurs at an AOA well, well below the stall - so really the Airbus envelope protection doesn't affect the glide range.
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RE: How Might Have An A330 Have Responded In BA038?

Sat Feb 16, 2008 11:47 pm



Quoting OldAeroGuy (Reply 28):
If FBW is lost on the 777, pitch is controlled by electric Stab Trim (no mechanical cables). The only mechanical cables are to the hydraulic actuators on a left/right spoiler pair. There is no true manual reversion as on the 737 or MD80.

That is just as I though, no manual revision, thanks OldAeroGuy.
 
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RE: How Might Have An A330 Have Responded In BA038?

Sun Feb 17, 2008 12:43 am



Quoting Zeke (Reply 18):
It is not an unknown state with all engines failed, with an all engine flame out you are in direct law because of the loss of electrical buses and hydraulics, the FBW protections are not in place, Airbus has a QRH procedure for this (unlike the 777).

The 777 QRH's I've seen have an All Engines Inoperative set of procedures. Maybe you were looking at a version your airline had edited.
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zeke
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RE: How Might Have An A330 Have Responded In BA038?

Sun Feb 17, 2008 1:03 am



Quoting OldAeroGuy (Reply 31):
The 777 QRH's I've seen have an All Engines Inoperative set of procedures. Maybe you were looking at a version your airline had edited.

All of our manuals are tailored, but I would not think we would remove that. Can you let me know the exact title, I have access to the manuals from a few other airlines as well that I can have a look at.
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Jetlagged
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RE: How Might Have An A330 Have Responded In BA038?

Sun Feb 17, 2008 4:07 am



Quoting OldAeroGuy (Reply 28):
There is no true manual reversion as on the 737 or MD80.

The MD80 flight controls are manual all the time!  Wink

Manual reversion on a 777 sized aircraft would be very difficult to arrange, FBW or not. The 747 is not FBW, but has no manual reversion.

Quoting SEPilot (Reply 27):
When is Direct Law invoked? Does the pilot select it or is it automatically selected under certain circumstances. If so, when?

Direct Law is automatically selected. The way the system transitions to Direct Law is too complex to express in words here, but it is based on failures detected with the EFCS, IRS, etc. In pitch, between Normal Law and Direct Law there is Alternate Law, which is a bit like Normal Law but offers simpler protections. In roll there is only Normal and Direct Law.

On an A320 you can switch to Direct Law (with gear down) by turning off both the FACs. With gear up, switching off the FACs puts you in Pitch Alternate, Roll Direct.
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OldAeroGuy
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RE: How Might Have An A330 Have Responded In BA038?

Sun Feb 17, 2008 4:40 pm



Quoting Jetlagged (Reply 33):
Quoting OldAeroGuy (Reply 28):
There is no true manual reversion as on the 737 or MD80.

The MD80 flight controls are manual all the time!

Then why is there a hydraulic line running to the elevators?

http://www.md80.it/OLDFILES/schemi/FlightControls/two.JPG

The MD80 and the 737 use hydraulic power as the prime mover of the elevators but have tabs as a backup if the hydraulics fail. With hydraulics operating, these tabs follow the main surface movement but they are not the prime mover.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
DH106
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RE: How Might Have An A330 Have Responded In BA038?

Sun Feb 17, 2008 10:32 pm



Quoting OldAeroGuy (Reply 34):
Then why is there a hydraulic line running to the elevators?

I think the MD-80 has an emergency stall recovery push-down elevator function, which is probably what the hydraulic line is for. Normally the elevators are manually activated tab driven.
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SEPilot
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RE: How Might Have An A330 Have Responded In BA038?

Mon Feb 18, 2008 1:50 pm



Quoting Jetlagged (Reply 33):
Direct Law is automatically selected.

Thanks for the explanation.
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Jetlagged
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RE: How Might Have An A330 Have Responded In BA038?

Mon Feb 18, 2008 2:34 pm



Quoting DH106 (Reply 35):
I think the MD-80 has an emergency stall recovery push-down elevator function, which is probably what the hydraulic line is for. Normally the elevators are manually activated tab driven.

Correct. This thread describes it all in detail: MD-80 Elevator Controls (by TWAMD-80 Jul 12 2003 in Tech Ops)
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OldAeroGuy
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RE: How Might Have An A330 Have Responded In BA038?

Mon Feb 18, 2008 4:36 pm



Quoting DH106 (Reply 35):
Quoting OldAeroGuy (Reply 34):
Then why is there a hydraulic line running to the elevators?

I think the MD-80 has an emergency stall recovery push-down elevator function, which is probably what the hydraulic line is for. Normally the elevators are manually activated tab driven.

Thanks for correcting my mis-understanding. I thought the 737 and DC9/MD80 flight control systems were similar since they are of the same airplane design generation.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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RE: How Might Have An A330 Have Responded In BA038?

Tue Feb 19, 2008 4:35 pm



Quoting Zeke (Reply 32):
Can you let me know the exact title, I have access to the manuals from a few other airlines as well that I can have a look at.

Don't have a copy of the QRH at hand, but you might try "Dual Engine Failure".
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
BAE146QT
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RE: How Might Have An A330 Have Responded In BA038?

Tue Feb 19, 2008 6:44 pm



Quoting Starlionblue (Reply 6):
The 330 would have prevented the stall altogether by lowering the nose.

From what we have been told, that's what the FO did anyway. So the answer might be, "The same outcome would probably have occurred in the Airbus. The nose would be pushed down to increase range. The difference being who it was that performed that action."

But I'm not sure that the situation would be so obviously critical to a computer when the crew noticed it.

It might be that human analysis meant that the FO acted faster than the computer(s) would have done because he had a better view of the future than the aircraft could. He KNEW that he had to get the aircraft into the airport. The computer might not be so critical about outcome, other than preventing the imminent stall when it sensed it. The outcome MIGHT be the same, but the reasons could be different.

So an interesting question would be, "Would the computer have realised what was happening in time to perform the same manoeuvre that the human did at the same time, or would it only act when things had gone pear-shaped, leaving the aircraft to land in Hounslow?"

Incidentally, when I first saw this thread I read "A330" as "A380".
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DH106
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RE: How Might Have An A330 Have Responded In BA038?

Tue Feb 19, 2008 9:25 pm



Quoting BAe146QT (Reply 40):
So an interesting question would be, "Would the computer have realised what was happening in time to perform the same manoeuvre that the human did at the same time, or would it only act when things had gone pear-shaped, leaving the aircraft to land in Hounslow?"

Lot of 'if's there.
Why wouldn't the pilot of the A330 also lower the nose in the same situation? The computers would only do so to prevent an imminent stall.
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RE: How Might Have An A330 Have Responded In BA038

Tue Feb 19, 2008 10:16 pm



Quoting Starlionblue (Reply 6):

"I don't wanna talk to you no more, you empty headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!"



Quoting KELPkid (Reply 10):
What's next, livestock being catapulted over the wall?  mischievous 

Only if catapulted by guys in medieval armor, with British accents ...

Quoting BAe146QT (Reply 40):
Incidentally, when I first saw this thread I read "A330" as "A380".

We'd have probably felt the earth shake on this side of the pond, in that case ...

- litz
 
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Starlionblue
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RE: How Might Have An A330 Have Responded In BA038

Tue Feb 19, 2008 11:32 pm



Quoting DH106 (Reply 41):

Quoting BAe146QT (Reply 40):
So an interesting question would be, "Would the computer have realised what was happening in time to perform the same manoeuvre that the human did at the same time, or would it only act when things had gone pear-shaped, leaving the aircraft to land in Hounslow?"

Lot of 'if's there.
Why wouldn't the pilot of the A330 also lower the nose in the same situation? The computers would only do so to prevent an imminent stall.

Yeah. The pilot would have behaved the same way, but the plane would have been there to catch a stall if needed. Of course a well trained pilot won't stall the plane anyway. However it could be argued that with a FBW Airbus the pilot could have flown closer to a stall since he would have known about the "safety net".

All quite academic of course.
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OldAeroGuy
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 2:26 am



Quoting Litz (Reply 42):
Quoting KELPkid (Reply 10):
What's next, livestock being catapulted over the wall?

Only if catapulted by guys in medieval armor, with British accents ...

I thought the cow was catapulted by guys with French accents.

Quoting Starlionblue (Reply 43):
However it could be argued that with a FBW Airbus the pilot could have flown closer to a stall since he would have known about the "safety net".

Since Airbus FBW won't allow you to fly past stall warning speeds and Boeing FBW will, I don't think you can say that an Airbus could have been flown closer to stall. The latest AARB report indicates BA038 touched down at 108 kts. This would be very close to stall speed for the 772ER at Flap 30 and the landing weight for BA038.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 4:15 am



Quoting OldAeroGuy (Reply 44):
Since Airbus FBW won't allow you to fly past stall warning speeds and Boeing FBW will, I don't think you can say that an Airbus could have been flown closer to stall. The latest AARB report indicates BA038 touched down at 108 kts. This would be very close to stall speed for the 772ER at Flap 30 and the landing weight for BA038.

Fair point. So it's all still pretty academic.  Wink
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DH106
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 6:55 am



Quoting OldAeroGuy (Reply 44):
Since Airbus FBW won't allow you to fly past stall warning speeds and Boeing FBW will, I don't think you can say that an Airbus could have been flown closer to stall. The latest AARB report indicates BA038 touched down at 108 kts. This would be very close to stall speed for the 772ER at Flap 30 and the landing weight for BA038.

I believe the report is published by the British AAIB, not AARB.

Didn't the captain take the flaps in a notch - to reduce the 'drag flap' when he realised the engines weren't responding?
So as I pointed out in Reply #8 the 777 may well have been stalled/stalling as it touched down.

Your point about not being able to fly the A330 "that close to the stall" - true in terms of AOA as Airbus applies a margin as we've discussed ad nausium. But if you were to look at an AOA / CL plot - there'd be a round out at the top representing the stall which would show that the performance difference in terms of CL denied by the Airbus envelope AOA margin would be negligible.
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Jetlagged
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 12:13 pm



Quoting OldAeroGuy (Reply 44):
Since Airbus FBW won't allow you to fly past stall warning speeds and Boeing FBW will, I don't think you can say that an Airbus could have been flown closer to stall. The latest AARB report indicates BA038 touched down at 108 kts. This would be very close to stall speed for the 772ER at Flap 30 and the landing weight for BA038.

Below 100 feet RA the Airbus is in a form of direct law anyway so presumably could have been stalled in over the last few feet, just as the 777 appears to have been.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
BAE146QT
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 5:40 pm

Thanks all who picked up my question and analysed/answered it.

Please understand that I asked the question not because I have a prejudice one way or the other, but because really I had no idea what would happen. Of course DH106's answer puts it to bed - the pilot would/should have acted the same way, regardless of the bird. Jetlagged's last post just puts the cherry on top.

Questions of what would have happened had the plane been entirely computer controlled would be a fascinating exercise in machine intelligence, forethought, prediction and self-preservation, but I hope that it's a long time before they need answering.

Like, some time after I'm dead.  Wink
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Longhornmaniac
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RE: How Might Have An A330 Have Responded In BA038?

Wed Feb 20, 2008 10:09 pm



Quoting Starlionblue (Reply 22):
Did you not watch "Monty Python's Quest for the Holy Grail"?!? If you haven't, you owe it to yourself to go rent or buy it and have a nice evening of hysterical laughter. Big grin KELPkid's comment is in reference to the same scene.

My dear friend, you must have missed the rest of his post...

Quoting BuyantUkhaa (Reply 17):

If the BA777 weighs the same as a duck... (see signature)

A WITCH!!!!!!!!!!!!

This has been a really interesting read...

Cheers,
Cameron
Cheers,
Cameron

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