Habsheim

[CONF iture]

Originally Posted by Chris Scott

Before I read the captain's memoir, I may be able to explain (1), and I've some observations on (2).

Thanks for such first hand information, I am satisfied with point (1) - It is the minimum the BEA should have mentioned.
Point (2) is more delicate - Your information seems accurate to me, but the correlation with the CVR data, and also the Asseline's account, would need that crucial missing piece of info that BEA kept out of our sight ...

Take your time to go through MA account, but we'll need to look deeper as there is so much more to be discussed ...

[Machinbird]

Originally Posted by Owain

Yes, thanks for that link and graph. I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back.

I read the alpha graph to indicate that the aircraft quickly approached its 22 degree pitch limit and the down elevator bunt maneuver was to keep it from overshooting. The time ticks are relatively large 20 second increments.

Much more maneuvering g available in the example than at Habsheim.

I'm wondering whether these systems calculate limiting pitch angle based on excess thrust available at the instant? I'll have to read the report more carefully.

A33Zab, thank you for your post, which, although not directly relating to AI products, is still highly relevant.

[Chris Scott]

Quotes from OK465:
"But the current [Airbus] software is probably many FCS software iteration revisions from 1988."

Yes! I wish all our contributors would bear that in mind, particularly when interpreting data from later accident reports... Why would it not have changed? The guys at St Martin-du-Touch would have been constantly striving for improvement, as well as accommodating the new birds.

"I was young then."

Really?

[HazelNuts39]

The guys at St Martin-du-Touch would have been constantly striving for improvement, ...

... and more than a runway separated them from the guys at 1 Rond Point Maurice Bellonte.

[Linktrained]

The flight had been briefed to be at 100 ft along R/W 34 L.
Perhaps due to the realignment with grass R/W 34 R the aircraft used some of its potential energy (now only height and airspeed, with flight idle having been set at 12.44.14) the descent to 46 ft became inevitable. This required more of a climb than had been planned - or an earlier selection of TOGA by a few seconds ( 10 ?).


Many pilots must have learned a valuable lesson since seeing what happened.


PS. Some could be younger, too !

[HazelNuts39]

Originally Posted by rudderrudderrat in post#228

Vs1g was demonstrated in flight test in ALT LAW.

In your post #266 you quoted from the preamble of the FAA Special Conditions for the US type certification of the A320. Development testing is not certification testing. In the Special Conditions it is evident that certification tests to determine Vs1g are conducted in normal law, the AoA protection system operating normally, except that alpha-floor must be disengaged.

Special Condition 6. Flight Envelope protection, (b) Angle-of-Attack Limiting, under (1)(i), states: Conditions associated with the determination of the stalling speed are those provided in § 25.103 of the FAR.

Relevant sections of FAR § 25.103 as amended by the special conditions read:

(a) VS is the reference stalling speed with--
(1) Stalling speed determined at not greater than IDLE thrust (NOTE: automatic go-around thrust application feature must be disengaged);
(2) (...)
(b) The stalling speed VS is the minimum speed obtained as follows:
(1) From a stabilized straight flight condition at any speed not less than 1.16 Vs (or speed at AOA protection onset, if greater) nor more than 1,30 Vs, apply elevator control to decelerate the airplane so that the speed reduction at the stall does not exceed one knot per second.
(2) (...)

In short: Vs is the speed obtained in normal law when the sidestick reaches the aft stop, i.e. Vs = V(alpha-max)

[CONF iture]

Originally Posted by Owain Glyndwr

Yes, thanks for that link and graph. I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back. Hmmmm!

Is it surprising to you ?

[Chris Scott]

Me: "The guys at St Martin-du-Touch would have been constantly striving for improvement, ..."
HN39: "... and more than a runway separated them from the guys at 1 Rond Point Maurice Bellonte."

Yes, the rather uninspiring Airbus premises - did they even exist in 1988? As you know, the south side of la ville de Blagnac has changed almost beyond recognition since the late 1980s, partly because of the creation of the rocade. (And, more recently, the north side of l'aeroport de Blagnac went completely bonkers - but that's another story.)

[HazelNuts39]

For me St Martin-du-Touch were the premises of Aerospatiale Engineering and Production facilities, and I was assuming that Airbus was responsible for FCOM, FCTM, pilot training and Customer Services in general, and of course, marketing and sales.

[Owain Glyndwr]

Originally posted by Confiture
Is it surprising to you ?

No not at all.

[CONF iture]

If I wanted to confuse and discourage a reader, I would probably do that :

1. Publish the photocopy of a copy of a copy ... of the original
2. Not include the seconds of the GMT
3. Add a TGEN for which I would not specify the origin
4. Publish a limited amount of FDR data
5. Publish those data for only a short period of that short flight

[HazelNuts39]

Hi Chris,

In your post #133 you wrote:

My interpretation is that 329.0s = 12:45:33 (see explanation offered in my previous post).

I don't know if that issue was resolved. Recently I stumbled by chance upon a document entitled: The A320 Habsheim accident - An Airbus Industrie response to allegations ... .

On page 17 under "The CVR timing" Airbus writes:
CVR time 12H 44'31'' equated to DFDR time TGEN 266
TGEN is the timing in seconds from the start of the DFDR reading made by the investigators.

Does that help?

[Chris Scott]

Hi HN39,

"On page 17 under "The CVR timing" Airbus writes:
CVR time 12H 44'31'' equated to DFDR time TGEN 266"

Thanks for drawing that CVR timing reference to my attention, which I had not noticed in the 1991 Airbus document. It certainly confirms your interpretation of the co-ordination between the GMT references and the "TGEN" time frames which you had used in your graph, and contradicts (by one second) my own as used in my post #122 of Dec 18, which I also used in #130 and #133.

So the BEA definition of t=0 at 1245:39 clearly occurs at DFDR time-frame 334.0 secs. IIRC, that is the last time frame in which none of the (sequentially recorded?) data was corrupted.

And the GMT minute is not updated until the time frame (TGEN) 1 second after the beginning of the minute, i.e., the first 1245 GMT (at TGEN 296.0) represents 1245:01, and the last 1244 GMT (at TGEN 295.0) represents 1244:60, which would be 1245:00.

[HazelNuts39]

RE:: Sequentially recorded?

The same document on page 12 has following Note:

The graphical representations of the DFDR data were prepared by Airbus Industrie from the data in the appendices of the Final Report. Recording times are adjusted to reflect the exact time at which each parameter is recorded. There remains a small potential error (up to 0.3 seconds) due to the variable delay between reading and recording a parameter.

[CONF iture]

Originally Posted by Chris Scott

And the GMT minute is not updated until the time frame (TGEN) 1 second after the beginning of the minute, i.e., the first 1245 GMT (at TGEN 296.0) represents 1245:01, and the last 1244 GMT (at TGEN 295.0) represents 1244:60, which would be 1245:00.

Why suddenly changing the norm ... ?
Why simply not publishing the extensive FDR time reference ... seconds included ?

"TGEN is the timing in seconds from the start of the DFDR reading made by the investigators."

Is it really too much asking than expecting the investigators to specify which GMT H:M:S has been selected ?

Yes, and I'm still inclined to the theory that TGEN 000.0 seconds is most likely to be the instant that TOGA was selected on T/O.

It would be surprising that TOGA or FLEX has been selected before any takeoff clearance, but again, FDR data would tell more ... if only published.

[rudderrudderrat]

Hi Chris Scott,
Sorry for the delay in finding this info.

Post #270: I note Owain Glyndwr's quick response that reversion to Pitch Alternate may not have been necessary during the certification flights. Experience suggests he is usually right,...

You and Owain are correct. Please see http://sfte2013.com/files/78988645.pdf, slide 35

"Test Conduct - Stalls for certification
in FBW aircraft
• Initially performed at forward CG
• Must be performed in Normal Law
– In case a stall occurs despite the protections
– Airbus - Normal Law modified with higher limiting AOA"

edit.
Hi Owain Glyndwr,

I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back. Hmmmm!

Could than be explained by the FBW computers sensing the rate of speed decay, knowing the rate of pitch change available, and anticipating the change in attitude necessary to avoid exceeding aMax?

Hi HN39,

In short: Vs is the speed obtained when the sidestick reaches the aft stop, i.e. Vs = V(alpha-max)

The above presentation suggests the aircraft is actually taken beyond CL Max, and its behaviour is observed in both Normal law and "Additional stalls performed with degraded control laws" (slide 35) to determine VS1g.

[HazelNuts39]

Hi rudderrudderrat,

Thanks for the link to an interesting paper. For the purpose of our discussion I think a few points are worth mentioning:

-- The presentation is dated 29 October 2013
-- It presents the views of Boeing and Airbus FTP's and FTE's, not necessarily that of the airworthiness authorities
-- The first bullet is "Stall Definition and Requirements", but the paper does not contain a discussion of that subject
-- The paper does not distinguish the tests conducted to determine the stall speeds from those to verify the stall characteristics or to identify aerodynamic characteristics such as the CLalpha curve

The A320 Special Conditions are dated 1988 and state clearly that Vs1g must be determined in normal law with alpha-floor disengaged. Consequently, Vs1g for the A320 is the speed obtained when the airplane is decelerated at 1 kt/s, the sidestick reaches the aft stop and is held there a few seconds. The published stall speeds and the cl-alpha observed in the accident (t-6 122 kt alpha=13.5) suggest that Vs1g corresponds to alpha-max of 17.5 degrees.

[Owain Glyndwr]

Hi rrr

Could than be explained by the FBW computers sensing the rate of speed decay, knowing the rate of pitch change available, and anticipating the change in attitude necessary to avoid exceeding aMax?

Possibly, but it could be any number of reasons, and with absolutely zero knowledge of the VFW laws I would rather not speculate.

I would add though that the time history as shown is not IMO a very good response to a step elevator command. It certainly shows an effective limitation to alphamax, but as a response to a demand for maximum lift NOW! it leaves a lot to be desired. Sure it gives alphamax fairly quickly (as it should at 180 kts) but it only stays there for a very short time and that is followed by a very large response reversal and a slow climb up to maximum lift. In fact it takes about 20 seconds to get to a sustained alphamax.

[Winnerhofer]

AF447

May we go back to AF447 instead of pantomiming?
Order of French tragedies:
1) Rio
2) Perpignan
3) Toulouse
4) St Odile
5) Habsheim

[DozyWannabe]

Originally Posted by Owain Glyndwr

Possibly, but it could be any number of reasons, and with absolutely zero knowledge of the VFW laws I would rather not speculate.

OK, so coming back to this after a brief absence I just have to check - we're talking about the VFW-Fokker 614 used in the ATTAS programme - *not* the A320 - right?

From DLR Portal - Research Aircraft - VFW 614 / ATTAS - out of operation :

ATTAS was primarily designed as a 'flying simulator', to simulate the flying behaviour of other - real (existing) or virtual - aircraft

Or in other words, a European version of NASA's "General Purpose Airborne Simulator" JetStar. So I think it is at least safe to assume that the specification of that EFCS would have had significantly different behaviour goals than that of the A320.

Originally Posted by Chris Scott

I agree with CONF_iture, however, that it would be good to see the DFDR for the whole flight.

Would you also say that while it may have been "good", it was nevertheless reasonable to truncate the published DFDR output to the time period relevant to the accident by the standards of the time?

Originally Posted by CONF iture

Thanks for such first hand information, I am satisfied with point (1) - It is the minimum the BEA should have mentioned.
Point (2) is more delicate - Your information seems accurate to me, but the correlation with the CVR data, and also the Asseline's account, would need that crucial missing piece of info that BEA kept out of our sight ...

The BEA are only charged with publishing material proven relevant to the accident. Neither of those issues on the face of it seem to be relevant to the accident itself. The A320 at the time had some technical issues to be ironed out - this was and is true of every new type one cares to mention (and the truism has been demonstrated recently with the A380 Trent issues highlighted by QF32 as well as the B787 battery issues demonstrated several times).

That the report didn't mention those particular issues is not a case of "hiding" anything, it's a case of those issues being irrelevant to the accident sequence in the first instance, and stating the bleedin' obvious in the second!