AF 447 report out

[toffeez]

NIPPI

After how many deliveries do unlinked sidesticks (and the non moving thrust levers, too) stop being downright ridiculous?

With 6800 of these planes now in service, I think the design has earned a bit of credibility.

[HazelNuts39]

Originally Posted by AZR

Is that an "Airbus" design or an "Industry" design, i.e. same situation or comparable airliners (Boeings, Bombardier, Embraer...) ?
This is, I think, a question that was never answered.

It is not a simple question to answer, because it does depend not only on the 'cutoff airspeed', but also on the behaviour of the airspeed measuring system at high angles of attack. The actual airspeed in AF447 probably never went below 100 kCAS. The indicated airspeed went below 60 kt and even to negative values because at extreme AoA the pressures from which it is derived differed so much from the true static and total pressures. That is hardly 'by design', and other airliners may well be different in that respect.

[NIPPI 2000]

After how many deliveries do unlinked sidesticks (and the non moving thrust levers, too) stop being downright ridiculous?

With 6800 of these planes now in service, I think the design has earned a bit of credibility.
.

I would like to see your delivery of your arguments to one of the relatives of the people on board of A447. You could tell them, how good and save this design is - with, after all, 6800 AB FBW flying.

Just do it, after they have been told, that maybe, just maybe, with interconnected SS they might have had a different outcome.

Kids, face it. Airbus went that route because it was more economical and simpler to design non moving Thrust Levers and non connected SS. The present design is not safer - but Airbus (and the relevant authorities around the world) thought it was safe enough.

[HazelNuts39]

Whatever the merits of linked vs unlinked SS are, IMHO the facts do not suggest that the outcome of AF447 would have been different with linked SS,

Up to the point where the airplane stalled, the PNF was aware of what the airplane was doing and that the PF was doing it. If he had felt a need to feel the movements of the SS, feeling those erratic movements would not have added anything to his understanding.

After the airplane stalled, the PNF's understanding of that fact was no better than the PF's and his response to the excessive rate of descent was no different from the PF:

02:11:21 But we've got the engines what's happening?
02:12:13 We're pulling
02:13:40 Climb, climb, climb, climb.

[cessnapete]

fantom

The core issue?
BEagle got it right first time.
Plus at all times during the event, the crew had two fully functioning engines, a standby horizon and compass, and a groundspeed readout?????

[thermostat]

I'm quite sick and tired of people who should know better blaming Airbus for this crash. Had there been a different crew flying that night, they would have landed safely. I've said before and will state again:-
a. You don't flying a heavy 'plane (close to coffin corner, at high altitude) into a storm
b. You set up the radar at top of climb
c. You must know the memory items for loss of airspeed drill (and others)
d. You must understand what super-cooled water is and how it can affect your 'plane.
e. As someone pointed out, even if they did nothing, the aircraft is stable enough to right itself. However if you deliberately hold back pressure when you shouldn't, well.............
f. There is no harm in circumnavigating a storm, even if it means making a fuel stop. That's why the pay pilots big bucks, to be SAFE not stupid

This a very sad accident that should never have happened, and I hope by now most of you have learned some valuable lessons from it. I flew the A320 for over 10 years and never encountered any serious problems handling it. If you don't understand your airplane, don't try to fly it. Find something else to do with your life..
Thermostat.

[CONF iture]

Originally Posted by HN39

It will do just that, except when the pilot ignores the stall warning and continues to pull until the AoA exceeds 40 degrees.

At 40 deg AoA the airplane is still stalled so the warning has to keep going.

Originally Posted by A33Zab

With linked SS, PNF should remove his hand to not obstruct the SS movement.
When it is required to take over, he now first have to visually locate the deflected position of the stick, grab the stick and initially fight the other stick input. (and not forget to push the button to disconnect the adjacent SS)

Valuable time is lost and forward facing philosophy interrupted in critical phases.

Such assessment on linked SS is inaccurate.
For the PM the thumb and one finger around the base of the SS would be all it takes to know exactly how the PF is soliciting the other SS.
Valuable time is certainly not lost, but gained.

In AF447 linked SS could have contributed to another outcome but in the majority of airborne time it is completely useless and in critical phases it can be distracted or even dangerous (as described above)

Certainly not useless, distracting or dangerous, but a pure mine of information.
Much improved Situation Awareness.

[BEagle]

I would like to see your delivery of your arguments to one of the relatives of the people on board of A447. You could tell them, how good and save this design is - with, after all, 6800 AB FBW flying.

It's a perfectly good and safe design, provided it isn't being used by people who haven't a clue about what they're doing, who don't have a disciplined flight deck environment and who don't even have a positive handover/takeover control procedure.

PILOT ERROR cause the A447 accident - nothing more, nothing less.

[Cool Guys]

PILOT ERROR cause the A447 accident - nothing more, nothing less.

I dont think anyone disagrees with you. It is pretty clear the accident was due to pilot error. The comments advocating linked sidesticks are about reducing the posibilty of similar accidents by making the controls less susceptable to pilot error, less susceptable to training deficiencies, less susceptable to failures, such a pitot tube blocking, causing confusion etc.

Even in a "perfectly good and safe design" there is always room for improvement.

[Oakape]

Even in a "perfectly good and safe design" there is always room for
improvement.

You have to wonder though, if it's all the 'improvements' that have got us here in the first place. To a certain extent anyway.

[FlexibleResponse]

Quote:
Originally Posted by FlexibleResponse View Post
5. With the subsequent control law reversion, the aircraft was then doomed to a no-stall-recovery situation with the Stabilizer stuck full up (as the Stab autotrim feature was lost with control law reversion). One of the pilots should have re-trimmed the Stabilizer sufficiently nose down with manual inputs using the pitch trim wheel to allow recovery. This did not happen...why?
I'm sorry but that's just wrong. The Stab autotrim feature was never lost in AF447

AlfaZuluRomeo is correct. According to the Accident Report, a reversion to Alternate Law 2B was caused by airspeed "inconsistency" and this mode did not inhibit the THS Autotrim. The THS autotrimmed to 13 deg nose up in response to the PF's aft stick control movements and remained at that value due to the AOA averaging 35 deg during the descent until impact with the sea.

Unusual Attitude Law Reversion was never activated as none of the discrete values were reached.

[DozyWannabe]

Originally Posted by CONF iture

At 40 deg AoA the airplane is still stalled so the warning has to keep going.

We went through this in the Tech Log threads - how can the warning keep going if the data required to provide its correct operation is unavailable? You can't just latch it on, because that runs the risk of the warning continuing to sound after the aircraft is out of the stall regime and causing confusion that way.

[Capn Bloggs]

Originally Posted by DWB

You can't just latch it on, because that runs the risk of the warning continuing to sound after the aircraft is out of the stall regime and causing confusion that way.

Obviously you don't latch it on and forget it.

If all the vanes are flopping around in the breeze regardless of the speed, for goodness sake the aircraft must be in a non-flying ie stalled condition. Make the stall warning sound until it is flying again, not switch off below 60KIAS because some boffin thinks "that can't happen". This is not a hard concept to grasp.

[DozyWannabe]

For one thing, it's very hard to detect a "flopping around in the breeze" situation using either analogue or digital means. For another, you're talking about a single failure mode - it might work in an AF447-type scenario, but it won't work in other scenarios - say, if the vane itself fails structurally, or if the cable connecting the vane to the transducer unit fails for whatever reason. This is one of the oldest conundrums in engineering - making sure that an alteration that solves one issue doesn't inadvertently create more problems (as Boeing have been experiencing with their battery issues).

Additionally, this isn't an issue of 'some boffin think[ing] "that can't happen"'. The AoA vanes were supplied with a specification that said they will not function correctly below 60kts IAS - therefore the *aero engineers* wrote the systems specifications to disregard output below that value. According to A33Zab, Boeing's engineers wrote the same specification below 50kts IAS.

[Lonewolf_50]

One approach to cockpit warnings is that it is better to have a warning, and be able to override it, than not have the warning. Dozy, I understand what you are saying based on the spec, and as we noted previously, you can use a weight on wheel switch to inhibit the stall warning when on the ground.

We have discussed this over and over, and the hamster is getting awfully tired.

[HazelNuts39]

Dozy,

I'm not a systems expert but how about, in the case of loss of all AoA data, the stall warning system retaining the last valid value of AoA until that parameter is valid again? There also should be an ECAM message suggesting selection of FPV to allow comparison of FPA and pitch attitude.

[DozyWannabe]

@LW_50:

I get what you're saying, but this isn't a case of Stall Warning being inhibited, it's a case of the data being unusable. You can override the SW, but if the failure is of a nature whereby it comes straight back on, it could cause problems.

@HN39:
Retaining the last valid value can cause the same issue - sure, in a scenario like AF447 the values can come back, but in other failure scenarios (damaged vane or cable) SW could be stuck on and cause problems, because the value will never be valid again.

[Lonewolf_50]

And not having the warning can cause problems. See AF447. (Though that wasn't their only problem, not by a damned sight.)

It's a lose lose situation, other than the fact that there are multiple AoA probes on the A330. We went over that as well. We could even run the hamster for a while on the AoA indicator in the C/P ... but that got us nowhere other than "who uses it?" "if they aren't scanning primary, what else won't they scan?" and "it could cause problems."

Nothing new here, and that poor hamster is exhausted.

This all may shed some light on why the general training standard is prevent stall in large transport aircraft. Doing so renders a few of these problems moot.

[CONF iture]

10000 feet a minute is a good breeze enough for all AoA probes to indicate a pretty similar value. If the probes mechanical limit is at 85 deg I believe 40 to be in their range of operation.

The stall warning has to keep going.

[DozyWannabe]

Originally Posted by Lonewolf_50

And not having the warning can cause problems.

Agreed - however...

The AF447 scenario was not a case of the Stall Warning suddenly disappearing after sounding briefly, the warning sounded for almost a *minute* with no apparent acknowledgement by the crew. The AoA readings became invalid because the aircraft had been pulled into an attitude so extreme that the sensors could no longer keep up.

This is what would be considered in engineering terms an extreme edge case, and thus far it has happened precisely once. If a technical solution was simple to implement without serious knock-on effects, it would be done - but the fact is that it is an extremely difficult problem to solve.

[EDIT : Additionally, while it may seem logical to assume that a warning in the face of uncertain data is better than none, I can't help but think of Birgenair 301 - where the captain fixated on a false Overspeed warning to the exclusion of all else and ended up stalling the aircraft. ]

This all may shed some light on why the general training standard is prevent stall in large transport aircraft. Doing so renders a few of these problems moot.

Well, arguably that training standard was at the root of the problems because it was implemented at the expense of stall recognition and recovery, and as such the standards have been changed in the wake of the accident.

At the end of the day, we're not talking about a stall warning that stopped sounding in an unreasonably short period of time after stall was initiated, we're talking about an aircraft that was pulled even deeper into the stall while the warning was sounding - until it was so far outside the flight envelope that it exceeded even the theoretical limits of instrument behaviour.