There is a self-powered artificial horizon on all air transport certified aircraft.
Unfortunately, with some main instrument specs, it is an Acceptable Deferred Defect. A colleague, who insisted that his was replaced at base before departure, found himself invited for tea without biscuits.
-- The aircraft flew into an area of storms which other aircraft avoided by steering around them.
-- The pitot tubes (speed sensors on the front of the plane) suffered faults
-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots.
-- The pilots may not have had sufficient training to retain control of the malfunctioning aircraft.
-- The pilots may not have had sufficient training to retain control of the malfunctioning aircraft.
I find that very wrong and feel like complaining, but Ill get sued. That is one of the most upsetting statements Ive ever read, absolute bs, It just points the finger at two people who actually tried to save the lifes of all on board, very very wrong.
Actually, it points the finger AWAY from the two individuals, who, sadly would not, and should not be blamed as they are not here to defend themselves. The fact they were unable to successfully deal with the situation they found themselves in, would leave open the POSSIBILITY that they had not received adequate training from their company in limited panel flying, recovery from unusual attitudes, and operation in alternate and direct law. And that possibility would form one more hole in the " swiss cheese" , leading to an accident.
Beyond that, partial panel, unusual attitude recovery are 'recoverable' because they are trained in a setting where the pilot will know if his inputs have corrected the upset. Here, if it happened due to Unreliable airspeed, AP chasing crap IAS and trimming as if it was part of a fairy tale, there is no reason to think the pilots could have recovered from an unknown and uncued 'status'; when would they know they had succeeded? Without cues to rely on (demonstrably absent if UAS is the culprit), where is straight and level? what is our position? where is up? Unreliable airspeed recoveries as reported in other instances have proven resistant to a checklist; it is perhaps possible to train UAS in conditions similar to what we imagine existed for 447, but why? Who will determine what 'Recovery' looks like on the panel? Repetitive loss of airspeed is demonstrated in this type involving thousands of feet lost in altitude, and visual extra cockpit cues for reference.
More important to me would be an a/p that annunciates its actions, with visual cues on the glass, so the pilot can 'get' the a/c by panel when the pitots go astray, knowing that what he has is flying, and what is required is constant duplication by manual handling after disconnect, which itself would be announced prior to, not after its occurrence, and that by surprise.
Oh, and an Artificial Horizon.
Let me ask a quick question. If the pilot had been hand flying the a/c in Normal Law, what's the probability of losing it to Alt Law2 after loss of pitot probes? This flight went to AltLaw2 because the a/p quit. If the a/p isn't in the mix, would the outcome have been substantially different?
Last edited by Will Fraser; 24th Sep 2009 at 00:08.
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Indeed, Will. And despite lawyers and cultural norms, sometimes <censored> happens.
I suspect that describes the situation better than a lot of commentary here. The burr under my saddle is a desire to find the contributing causes, not a apportion any sort of blame. With the data I want engineers can work to prevent it happening again. And I am just techie enough that I would enjoy hearing outlines of ideas for improvement of equipment such as people have had.
One such idea is new pitots. An even better idea is being adopted, probably for the wrong reason, with two new probes and one old Thales probe on the same plane. Different probes give different failure mechanisms, even if only slightly different. That would give computers something to chew on.
One idea I've entertained is phase tracking GPS as a means of detecting attitude using three or better four antennas, wing-tips, aft, and optionally forward. The GPS pretty much has to be tracking carrier phase to derive meaningful attitude data. The nice thing about phase tracking GPS is that you don't need to know precisely where you are to determine relative differences in position of nearby locations to surprising degrees of precision. The breaking point for this is that this does not account for up or down drafts that are not perfectly up and down. At some altitudes flying over mountain ranges can give winds at rather odd angles, I've observed on the ground. I don't know if that holds at altitude.
What I don't know is whether floating such technical ideas in the group to see what actual pilots salute and what they kiss off is within this group's purview.
I'll allow for journalistic mis-quoting, but where is the evidence that
Quote:
-- The aircraft flew into an area of storms which other aircraft avoided by steering around them.
- I was not aware that the precise track of 447 was known?
Quote:
-- There was a malfunction in the ADIRU, the three air data computers which feed information to the flight system and the pilots?
I was under the impression that the ADIRUs were thought to have behaved exactly as designed, rejecting supposedly conflicting information - ie intially a detected IAS change of at least 30kts in one second?
It would be of significant interest to AB operators to know what particular 'malfunctions' were fed into the simulator in these tests, what sequence of warnings were generated (eg did you receive a cascading failure of ADIRUs?), and what instrumentation was then left available to the crew - eg did the standby attitude still function correctly?
I think we are all pretty much on the same track generally, John, but to state categorically 4 primary individual causes of the accident is indeed a bold step.
If I recall correctly, this has been used for a long time as part of fighter jet stabilization technology, and I wonder why it hasn't been brought into commercial aviation. Gee, it first came over my horizon in the early 1990s... Hardly rocket science by today's standards.... ?? / CP
To my memory, the ship had deviated left, the buzz about 'lightning', company 'pirep' for 'fortes turbulence' and Msr. Gourgeon's claim that 447's aircrew had been 'unlucky' in reading the Radar were red herrings.
Been awhile, but is GPS to Mil standard nowadays? Used to be purposely degraded to prevent folks like google earth to have the capability of Uncle's satellites.
GPS in hyper accurate mode x4 would very nearly provide sufficient data to turn a wide body into a 'drone'. Oh-Oh, incoming.
Mil sets work on a different frequency and use a highly encrypted PN (Pseudo Noise) code, which, if not known by the receiver, prevents use of the inherently higher accuracy mil signals. The consumer grade PN code is, I think, 1023 bits long, while the mil one is "months" long, and is changed at shorter intervals than that, so there are never any repeated binary streams that would give a clue to decrypting it.
On the Civilian (consumer) side, there was something called "selective availability (SA) which caused the satellites to "lie" about what time it was, on a purely random basis, thus increasing the amount of error introduced at a receiver. One of the recent Presidents had that removed from service, primarily to allow aviation to have the best possible (non-mil) GPS accuracy for nav purposes.
SA was turned off, by the way, during the Desert Storm operation, to allow Civilian sets to be used by tanks, as there was a shortage of mil GPS receivers for deployment. And there are other stories and anecdotes, of course.
The phase-tracking used in attitude detection is a different animal. The wavelength at GPS frequencies is roughly (very) 25cm, so the theory predicts that one receiver moving vertically (e.g.) relative to a second one, toward or away from the satellite(s), would experience a detectable phase difference in the order of centimeters. Needs superfast processor and GPS chips, but it works....
Just a thought, I don't know if this has been raised previously as I don't have the time to read the last 200 pages of posts. Given the speculation on a departure from controlled flight due to either stalling or mach tuck, and the idea that this was due to the discrepancy between indicated airspeed and actual airspeed. Couldn't one consider upgrading the flight computer system to challenge the Air Data based on the aircrafts angle of attack and power settings.
For example, ice blocks the pitots slowly, CAS remains the same but the A/P slowly decreases AoA and increases power. Surely if a certain number of parameters are known ie. performance based on CAS AoA and power settings C of G, Trim etc. The aircraft would be able to tell if performance is not meeting what is expected and alerts the pilots.
Just a thought, I am no expert at all but it seems with so much automation and cross checking by the automation systems it could be wise to have this.
The ADMs, Air Data Modules, used in the A330 can be pretty dumb sensors, equivalent to the blind encoders that came out 25 years ago: just an absolute pressure transducer and a digital output. I'm not intimate with the A330, but here's a logical way to build a pitot/static system with modern devices:
Each ADM for static pressure puts out a 429 word labeled, ALT, which is fed to its companion ADR with minimal monitoring. The ADR passes the ALT on to the using devices, such as pilot displays, AP and transponder. The using devices receive ALT from two or three ADR for redundancy and/or voting.
No airspeed input is needed or used in the altitude calculation.
For airspeed measurement, we use an identical ADM, but connected to a pitot probe, and its output word coded for impact pressure. The ADR merely subtracts ALT from impact pressure to calculate IAS, which is then forwarded on. There is no reason for the ADR to report ALT Fail if it can't compute IAS. Each output from an ADIRU stands on its own.
So, I come back to my original premise: blocked pitot tubes do not cause TCAS Fail to be reported. There must be another cause of the TCAS Fail that was reported by the ACARS.
Beyond that, if there were ALT Fail out of the ADR it would have caused the transponder to revert to Mode A, thereby causing the TCAS to report TCAS OFF to the ACARS, and not TCAS Fail. There is no direct connection between the ADR and the TCAS processor.
TCAS Fail is reported in case of: TCAS processor computation fail TCAS directional antenna fail Loss of valid data from transponder
The first ACARS reports mentioned a TCAS Antenna Fail, which should have been coded in the report.
Again, I agree with the BEA report: the TCAS Fail is unexplained. It may be a symptom of an event that was otherwise unreported.
The TCAS antennas are roughly overhead and beneath the forward fuselage just aft of where the nose transitions to constant diameter. A diagram of antenna locations on the A330 was posted in this thread, back about 9 June.
GB
