DozyWannabe

Until it doesn't (just because it hasn't gone wrong yet doesn't mean it won't). One of the things I used to find amusing about the A v B debate were the B people who swore up-and-down that Boeing's latest models weren't entirely computer-reliant, and the presence of the moving yokes proved it.

They'd overhauled the ailing MD by the early-mid '90s. In any case the point still stands, because the MD/Boeing merger would have produced a company that consistently outsold Airbus year-on-year if Airbus themselves hadn't done something about it.

[EDIT : I'm sure I've said this before, but as an aside, I wonder what would have happened if Boeing had elected to shrink the 757 rather than stretch the 737 for their (then) next-gen narrowbody. ]

rudderrudderrat

Hi DozyWannabe,
http://www.davi.ws/avionics/TheAvion...ook_Cap_11.pdf
"11.3 Design Philosophy.

More will be said of these specific features later. What should be noted, however, is that none of these features limit the action of the pilot. 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. Envelope limiting prevents the pilot from commanding the airplane beyond set limits. For example, the 777 bank angle protection feature will significantly increase the wheel force a pilot encounters when attempting to roll the airplane past a predefined bank angle. This acts as a prompt to the pilot that the airplane is approaching the bank angle limit. However, if deemed necessary, the pilot may override this protection by exerting a greater force on the wheel than is being exerted by the backdrive actuator. The intent is to inform the pilot that the command being given would put the
airplane outside of its normal operating envelope, but the ability to do so is not precluded. This concept is central to the design philosophy of the 777 Primary Flight Control System."

It seems to have the benefit of computer assisted warning - but not interference.

DozyWannabe

It's a different approach certainly, and one that seems to work just as well. As I'm sure you're aware, you have to put the A320 a fair amount out of whack attitude-wise before the non-alpha related protections kick in.

The point I was making (albeit not very clearly) was that those early nay-sayers were adamant that an entirely computer-controlled flight control system could not be trusted under any circumstances, and were labouring under the misapprehension that the 777 didn't have one.

jcjeant

Hi,

DW:
Seem's to me that it will be better if:
An entirely computer-assisted flight system controlled by the pilot ....

DozyWannabe

Which is true of both Airbus and Boeing's FBW systems. Unlike Boeing, Airbus's system does have hard limits, but I'd be prepared to bet you could count the number of times those limits have been encountered in 24 years of service on your fingers and toes. For example, the bank angle limit is 67 degrees - any further and you'll risk a spiral dive and structural damage. Those limits are not there to inhibit pilots, they're there to prevent structural damage and loss of control.

rudderrudderrat

Hi DozyWannabe,
That was the design concept - but sometimes the programmers haven't anticipated every possible eventuality. There have been several heavy landings where the ELAC computers prevented the authority the pilots wanted.
Accident of an Iberian Airbus A320 in Bilbao

I bet the LH A320 crosswind landing pilots wish they had full aileron control once the landing gear touched the runway. I know they should not have been there in the first place (X wind outside limits) - but reducing the maximum amount of available aileron control on touch down doesn't make sense to me.

DozyWannabe

@rudderrudderrat

If there's a case to change it, they will. It wouldn't have been the programmers making that call in any case, it would have been the aeronautical engineers and the test pilots*. Even the best and most experienced of us codemonkeys have to stick to the specification we're given. A good software engineer will tell you how to implement a specification in the best way, but they can't change the spec themselves.

I suspect that even with a conventional airliner, the engineers would push back on changing a behaviour that manifested itself outside of the operational limits - those limits are there for a reason after all.

[* Just to reiterate the point in general - Software Engineers do not define the limits within a FBW control system. That is the remit of the aero engineers and test pilots. ]

RR_NDB

Hi,

Why Airbus SAS (former AI) introduced SS in commercial aviation?

bubbers44

23,000 hrs flying in my career has never required a computer to protect my bank limit. Maybe we just need to train pilots, not computer operators. AF447 had computer operators because they rarely flew the aircraft. They just monitored the autopilot. If we continue to use autopilot monitor people to fly we need an absolutely fool proof automated airplane that will never disconnect, no matter what. Is that what we want? Why?

Stall recovery was quite simple, lower the nose and add power not pull up into a deep stall at 38,000 ft. We need qualified pilots back in the cockpit now. Not a 300 hr new guy that will only monitor the autopilot for thousands of hours then become a captain. Does anybody disagree? UAS is an abnormal, not an emergency. Every jet has a checklist to keep you flying with no airspeed. pitch and power for weight and altitude. Or just use the altimiter since it is working.

mm43

Which begs the question, "How do you get 'hands on' experience?"

This post by Good Business Sense in R&N is possibly food for thought.

Diesel8

Aguadalte,

Wasn't slagging on you, just asking.

Besides, glad you found your logbooks so easily, last I looked for mine I wound up in the dark attic!

CONF iture

The statement is strong I agree. Still, I did not want to write the killer, but just one element in the puzzle that lead to the final result.
I gave my opinion below but we can discuss further.

http://www.pprune.org/6727692-post1024.html

http://www.pprune.org/6812692-post343.html

Lyman

"That’s even worse Lyman, under Normal Law, the system logically thinks it’s time to cancel autotrim by reaching Alpha Prot or slightly above, but when the situation has degraded and Alternate Law is active, the system thinks it’s smart to autotrim all the way whatever the Alpha …" CONFiture.

And to me, the sequence of events should be seen in its logical context... Once climbing, the THS stopped trimming @ ~3 degrees. That would indicate that NORMAL Law obtained...(overspeed react, a/c?)

At 2:10:22 "....ALTERNATE LAW..." PNF

Once slowed, with AoA increasing, the THS re-invigorated, then the a/c STALLED.

By the evidence, and knowing the controls LAW profile, one could conclude that the a/c was reacting to an actual overspeed at 2:10:07. The STALLWARN could have been triggered by an A0A at or above STALLWARN trigger (bug).

Once slowed by ( 'elevators only' climb, ) the a/c switched to ALTERNATE2 and the THS started cranking again....

Other than ruffling feathers, I have not seen that this could not be so.

In the case of controls LAW, the evidence points to overspeed followed by Law degrade, then STALL, with an active THS.

Not knowing the length of time the a/c takes to suss/WARN Overspeed, or ALTERNATE LAW, it is conceivable the direction and fortitude of the airmass, plus controls input (to include THS), could easily cause: climb/upset/STALL......

In any case, the aircraft seems to be telling us that @ Alpha Prot (STALLWARN) the THS is stopped. And that once degraded into Alternate2 in the climb, the THS starts trimming UP once again.

As above....

mm43

[BEA]"The flight control law switched from normal to alternate at about 2 h 10 min 05. The alternate law adopted was alternate 2B and it did not change again subsequently."

The PNF took 17 secs to note and verbalize the LAW change.The aircraft was effectively stalled before the THS passed 5°NU.

A33Zab

This is Lyman's logic!.......very well corrected by mm43

Compare for differences and similarities:

F-GLZU A340-300 22 july 2011:

Avherald Link

BEA reort (French)

mm43

Yes! No wonder the BEA want to know what is being said in these cockpits.

HazelNuts39

Find the differences to the AIRPROX incident to A340 TC-JDN on 2 october 2000:
The turkish pilots responded slightly earlier to the zoom climb. (Turkish 18s, AF 90s).

Isn't it strange that pilots immediately respond to an overspeed warning, but fail to notice a zoom climb that (if it hadn't been protected) would have brought the airplane close to stalling?

P.S. Another notable difference is a change in the control law, which now leaves high AoA protection mode with SS in neutral during 0.5 seconds when the AoA is below AlphaProt.

aguadalte

mm43:
Yes...but the question is: did they have enough pitch command to put the nose down when the THS reached more than 13º nose up?
(please, before replying that the aircraft could have been manually trimmed by them, please consider that apart from direct law flight sim situations, (done my flight sim check today) FBW pilots may have the chance to never touch a trim wheel during their whole life...)

Turbine D

Hi Dozy,

Have been reading the ongoing back and forth on A vs B, sidesticks vs yokes, FBW control, etc. I know you are knowledgable on Airbus control systems and defend Airbus practices when challenged. So in that there is not much going on relative to AF447, I though it might be good to put some things in perspective, A vs B.

Boeing designed the 767 & 757 aircraft in tandem with the idea of shared cockpit design features so that pilots could obtain a common type rating to operate either aircraft. Boeing continued to selected conventional control systems for both aircraft.

Airbus had a difficult time initially selling A300 aircraft as a replacement for either the MD-10/11 or the Lockheed Tri-Star and decided on a new approach to the soon to be A-320 which would compete against the Boeing 737. For this airplane and those that followed, a FBW system was designed and the yokes used in the A-300 were replaced with sidesticks.

Boeing finally decided to introduce a FBW system for the new 777 aircraft being considered. In the design of the Boeing 777, Boeing changed the way it went about designing aircraft. On previous aircraft, Boeing pretty much selected the design and presented the aircraft to the customers. For the 777, eight major airlines had a role in the development of the aircraft. The airlines were, All Nippon Airlines, American Airlines, British Airways, Cathay Pacific, Delta Airlines, Japanese Airlines, Qantas and United Airlines. It was the first aircraft completely designed entirely on a computer. It was decided to retain conventional control yokes rather than change to sidestick controllers. Along with traditional yoke and rudder controls, the cockpit featured a simplified layout that retained similarities to other Boeing aircraft. However, the FBW concept used was slightly different than what Airbus designed for the A320. The differences are in philosophies.

Airbus designed its FBW jets with built-in protections or hard limits. Boeing, on the other hand, believed pilots should have the ultimate say, meaning the pilot can override onboard computers and therefore built-in soft limits. So here is the issue. Should pilots or a computer have the ultimate control over a commercial jetliner as the plane approaches its design limits in an emergency? There were and are strong arguments by pilots on both sides of the debates. Some pilots are of the opinion that computer protection of the A320 and subsequent designed aircraft are very good whereas other pilots support the Boeing philosophy that they must have the final say in controlling the aircraft. There are valid arguments both ways.

One argument was the Boeing 757 Cali Columbia crash where the pilot didn't retract the speed brakes after receiving a terrain avoidance warning. In a A320 the retraction would have been automatically accomplished by the computers. On the other hand, the A320 Habsheim crash was the result of the pilot going below a 50 ft threshold in which the computers assumed the pilot was trying to land. The plane did exactly what it was suppose to do according to the computers and landed in the treetops. The first five accidents involving A-320 aircraft were the result, in one way or another, of misunderstandings between the computers and the flight crews. Obviously this has improved through pilot training, familiarity with the computer control systems, and refinements of the computer control systems by Airbus. Over time, there have been 50 incidents on A320 aircraft involving "glass cockpit blackout". The most serious occurred on a United Airlines aircraft where half of the ECAM displays, all radios, transponders, TCAS and attitude indicators were lost. Due to good weather and daylight conditions the pilots were able to land at Newark airport without radio contact.

I should point out that the Boeing 777 FBW aircraft have suffered only two hull-loss accidents and 6 other "occurrences" with 1,009 aircraft currently flying. Neither hull-loss accidents involved the FBW system. One was BA's mishap landing at Heathrow (engine problems) and the other was an onboard fire in the cockpit due to a faulty oxygen tube while the plane was at the gate in Egypt, there have been no fatalities.

Personally, I would fly on any aircraft in commercial service that either A or B have produced. Each are different in some respects but both share very good safety records when you take away the outlying causes such as hijackings and deliberate crashes. I flew on A320s back and forth to the West coast of the US last week, uneventful, pleasant flights and a nice comfortable seating arrangement by Delta Airlines.

Just trying to be fair and balanced when it comes to a statement like this:


The merger of Boeing and MD had nothing to do with the commercial aircraft side of the ledger. IMHO, it had everything to do with the military side of the ledger as MD was near or at bankruptcy. The US DOD arranged a "shotgun wedding" to save the production of several lines of military aircraft from folding. At the time, there was no redeeming value on MD's commercial side of the ledger.

PJ2

Turbine D - a fine post, thanks.