Qantas QF 72

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Qantas QF 72

Unread post by spokes » Sat Sep 14, 2019 6:38 pm

During this flight the computers were fed duff gen. The flight computers pitched the nose down by 10degs with full down elevator. The captain saved the day by by passing the correct computer and going to manual trim. In normal law the pilot asks the computers to do something and if they Agree they will command the control surfaces. If they dissagree? bugger the pilot.
Why did the computers on AF 447 not override the 3d pilots full up elevator command when they were obviously stalled? Were they in Alternate law?
Im reading ; No mans Land by Kevin Sullivan the captain on QF 72. Very informative on the spate of automation accidents we saw since Airbus started.
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Re: Quantas QF 72

Unread post by Aquila » Sat Sep 14, 2019 6:53 pm

spokes wrote:
Sat Sep 14, 2019 6:38 pm
During this flight the computers were fed duff gen. The flight computers pitched the nose down by 10degs with full down elevator. The captain saved the day by by passing the correct computer and going to manual trim. In normal law the pilot asks the computers to do something and if they Agree they will command the control surfaces. If they dissagree? bugger the pilot.
Why did the computers on AF 447 not override the 3d pilots full up elevator command when they were obviously stalled? Were they in Alternate law?
Im reading ; No mans Land by Kevin Sullivan the captain on QF 72. Very informative on the spate of automation accidents we saw since Airbus started.
Curious to what the actual point/question is? :-?
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Re: Quantas QF 72

Unread post by spokes » Sat Sep 14, 2019 7:05 pm

On QF72 the flight computer commanded a very rapid down elevator, as it was designed to do, when it was told the AOA was 54 degs! It would not allow the pilots to correct it.
Yet AF447 was allowed to be held in a stall by the pilots and the computer did not do as it was designed to do by overiding the pilots and correcting the stall.
Why not?
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Re: Quantas QF 72

Unread post by Aquila » Sat Sep 14, 2019 7:19 pm

spokes wrote:
Sat Sep 14, 2019 7:05 pm
On QF72 the flight computer commanded a very rapid down elevator, as it was designed to do, when it was told the AOA was 54 degs! It would not allow the pilots to correct it.
Yet AF447 was allowed to be held in a stall by the pilots and the computer did not do as it was designed to do by overiding the pilots and correcting the stall.
Why not?
Its two very different scenarios...

AF772 was basically an unreliable airspeed event initially caused by a very short sensor failure due to environmental conditions. The aircraft reverted to alternate law so some of the protections was lost.

QF72 was a very complex situation and here is the ATSB Summary:
On 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA and operated as Qantas flight 72, departed Singapore on a scheduled passenger transport service to Perth, Western Australia. While the aircraft was in cruise at 37,000 ft, one of the aircraft's three air data inertial reference units (ADIRUs) started outputting intermittent, incorrect values (spikes) on all flight parameters to other aircraft systems. Two minutes later, in response to spikes in angle of attack (AOA) data, the aircraft's flight control primary computers (FCPCs) commanded the aircraft to pitch down. At least 110 of the 303 passengers and nine of the 12 crew members were injured; 12 of the occupants were seriously injured and another 39 received hospital medical treatment.

Although the FCPC algorithm for processing AOA data was generally very effective, it could not manage a scenario where there were multiple spikes in AOA from one ADIRU that were 1.2 seconds apart. The occurrence was the only known example where this design limitation led to a pitch-down command in over 28 million flight hours on A330/A340 aircraft, and the aircraft manufacturer subsequently redesigned the AOA algorithm to prevent the same type of accident from occurring again.

Each of the intermittent data spikes was probably generated when the LTN-101 ADIRU's central processor unit (CPU) module combined the data value from one parameter with the label for another parameter. The failure mode was probably initiated by a single, rare type of internal or external trigger event combined with a marginal susceptibility to that type of event within a hardware component. There were only three known occasions of the failure mode in over 128 million hours of unit operation. At the aircraft manufacturer's request, the ADIRU manufacturer has modified the LTN-101 ADIRU to improve its ability to detect data transmission failures.

At least 60 of the aircraft's passengers were seated without their seat belts fastened at the time of the first pitch-down. The injury rate and injury severity was substantially greater for those who were not seated or seated without their seat belts fastened.

The investigation identified several lessons or reminders for the manufacturers of complex, safety‑critical systems.
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Re: Quantas QF 72

Unread post by spokes » Sat Sep 14, 2019 7:31 pm

Tx Aquilla. It is to complicated for a novice to understand. Suffice it to say the incident severly damaged the pilots
pchyque? and trust of automation
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Re: Quantas QF 72

Unread post by Dragon » Sat Sep 14, 2019 8:43 pm

I’m speaking very generally here so don’t take this as referring specifically and exclusively to this accident, but this is as good a place as any to point out something that not enough people grasp: that is, the interpretation of statistics. Manufacturers are always quick to point out that there is only a 1 in a million chance of this or a 1 in 40 million chance of that. And as lay people in the public we get a warm fuzzy comfortable feeling that it will never happen. This is misleading.

For the individual case the odds are indeed very rare. So lucky are those who only fly once in their lives. However fly multiple times and the odds change rapidly. For a business traveller who is traveling all the time the odds are astoundingly different and if you are crew and you look at these odds over a lifetime suddenly they take on a whole new significance, with events that you previously dismissed as exceptionally rare, now not so unlikely anymore.

The same goes for fleets. If an event only occurs once in 140 million hours we dismiss it instantly, yet do you realize how quickly a fleet of aircraft will fly that. A fleet of ten thousand aircraft will fly that in 3 yrs or less. Worldwide it will be achieved very quickly. A single occurance might be rare but when you spin the dice over and over again eventually you get a hit. Or if you spin a thousand dice once.

And also realize that the odds don’t have to rise to 1 to make alarm bells ring. If I told you there was a 1 in 3 million chance each flight your wings would fall off, you wouldn’t bat an eyelid. But if you were a career pilot and worked out you might fly 30 thousand flights over a lifetime, suddenly the odds over the whole time period are 1 in 100 and that might stop you to think. From harmless to significant.

So when quoted stats that you are at first tempted to dismiss, stop and ask yourself what these figures mean to you, to your aircraft, to your company and to your passengers.
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Re: Quantas QF 72

Unread post by Keith Quixley » Sun Sep 15, 2019 10:06 pm

Dragon wrote:
Sat Sep 14, 2019 8:43 pm
I’m speaking very generally here so don’t take this as referring specifically and exclusively to this accident, but this is as good a place as any to point out something that not enough people grasp: that is, the interpretation of statistics. Manufacturers are always quick to point out that there is only a 1 in a million chance of this or a 1 in 40 million chance of that. And as lay people in the public we get a warm fuzzy comfortable feeling that it will never happen. This is misleading.

For the individual case the odds are indeed very rare. So lucky are those who only fly once in their lives. However fly multiple times and the odds change rapidly. For a business traveller who is traveling all the time the odds are astoundingly different and if you are crew and you look at these odds over a lifetime suddenly they take on a whole new significance, with events that you previously dismissed as exceptionally rare, now not so unlikely anymore.

The same goes for fleets. If an event only occurs once in 140 million hours we dismiss it instantly, yet do you realize how quickly a fleet of aircraft will fly that. A fleet of ten thousand aircraft will fly that in 3 yrs or less. Worldwide it will be achieved very quickly. A single occurance might be rare but when you spin the dice over and over again eventually you get a hit. Or if you spin a thousand dice once.

And also realize that the odds don’t have to rise to 1 to make alarm bells ring. If I told you there was a 1 in 3 million chance each flight your wings would fall off, you wouldn’t bat an eyelid. But if you were a career pilot and worked out you might fly 30 thousand flights over a lifetime, suddenly the odds over the whole time period are 1 in 100 and that might stop you to think. From harmless to significant.

So when quoted stats that you are at first tempted to dismiss, stop and ask yourself what these figures mean to you, to your aircraft, to your company and to your passengers.
Terry Pratchet said it best: "Scientists have calculated that the chances of something so patently absurd actually existing are millions to one.
But magicians have calculated that million-to-one chances crop up nine times out of ten.”
Keith Windsor WcRostie Quixley (in case you were wondering)

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