"During evaluation of specific engine failure cases at take-off on Airbus flight Simulators, it has been evidenced that with FCPC1 inoperative, in the worst case, when FCPC2 and FCPC3 resets occur during rotation at take off, a transient loss of elevator control associated with a temporary incorrect flight control law reconfiguration could occur. It leads to a movement of the elevators to the zero position, which induces a pitch down movement instead of a pitch up movement needed to lift off. In addition, it leads to a limitation of the pilot authority in pitch axis and limits the capacity to counter the pitch down movement during this flight
one auto pilot engaged at altitude, all that triple redundancy is for approach and auto land.one a/p one adiru feeding it.
Interesting.... Boeing 747-400 autopilots use a single ADC as a source of (autopilot) data, but use all 3 IRU's as a source of information at almost all times (not just for landing). If all three IRU's are giving different data, then a "mid value" is chosen (not "average", as a wildly erroneous value would affect the data too much).
On an Airbus, even if one ADIRU is plugged into the A/P, wouldn't there be data sharing via databusses to that ADIRU? (if not for "ADC" data such as AOA, then, say, IRU data, such as attitude?)
I'm also wondering how aircraft computers process "spiking". Obviously the spiking on this particular aircraft was not large or rapid enough to be considered ridiculous and the value rejected.
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nseu
as I understand it nseu the bus uses similar philosophy for position at least.
as for air data/aoa, not certain, its been a while since I delved.
I am quite sure a fault in one should flag a failure in another if not by the box itself.
Flying along fat dumb and happy, a/p engaged (one) its onside adiru is the source.alternate adiru is selectable manually.IR or air data can be turned off also.
Even so,it just seems odd such a flt profile can be allowed given its in crz phase at speed regardless of the monitoring and available redundancies.
If there are not software changes to limit the authority of systems in such an event I'd be amazed not to mention more authoritative monitoring of aoa and air data to further limit flt ctl movement at speed.
my redundancy comment was meant as fully independent systems operating in parallel ie on coupled approach.
This is interesting. As others have pointed out, there are 3 ADIRUs. Are there really no cross-checks to detect a failure in one?
Quote:
Originally Posted by NSEU
I'm also wondering how aircraft computers process "spiking". Obviously the spiking on this particular aircraft was not large or rapid enough to be considered ridiculous and the value rejected
The way it works, the system does not automatically discard a faulty unit but it identifies that faulty unit and advises the crew to first select a reliable source of information and then turn the faulty unit off.
As you know that’s the crew responsibility to perform the requested ECAM action(s)
According to the ATSB an Inertial Reference System 1 Fault ECAM Message has been triggered which would mean the crew has been advised but it is not clear if the requested ECAM action(s) were properly completed ?
In order to "minimize risk in the unlikely event of a similar occurrence" … an Operational Engineering Bulletin is on its way … Is it simply to emphasize the already published procedure or is it something new the QF72 crew could not have known before ?
Sorry, folks, I don't know why it's apparently posted twice
It headlines today's Slashdot page and there are some interesting comments from the people who actually work at the coalface ,where these magic boxes are concerned...........
In regard to my ealier question to VLF, the trasmission station at Exmouth puts out VLF at 1000 KiloWatts is the highest transmittor in the Southern Hemisphere with Aerials up to 1200' high.
Ironically the station is operated by Boeing and it is still functional
Can someone put some technical explanation on here how high powered VLF will not interfere with computers.
It looks like Malaysian had a similar incident in a 777 down near Geraldton which also happens to be next to a fairly serious restricted area.
Location: not the @r$& end of the earth but can see it from here.
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I think I said it'd do jack to an aircraft without any tech reason my apologies, just opinion , however my opinion is based on the extraordinary wavelengths of the actual radio signal at vlf freq's.A full wave at 19.8 kilohertz is over 15,000 metres in length if my maths is correct.
Antennae will function at any length for receiving just the efficiency suffers (tx'ing is another issue) but a resonant antenna is best.1/4 wave is widely used and still works well.Even at 1/4 wavelength an antenna is nearly 4 kilometres in length.One can shorten an antenna hugely but I think you get the point I'm making.
I understand some video /pc monitors produce a lot of vlf "noise" so I would hazard a guess that the shielding and filtering to prevent or at least minimise the opportunity for stray RF to interfere with computer ops would be very low as its a known issue.I would say that filtering and shielding would be the best arguments against vlf interference as the source of trouble.
With powerful transmissions the front end of a radio or electronic equipment can be open to brute force but given my above theorising and the fact fbw aircraft have been flying around these for years without apparent problems leads me to that conclusion.But like I said elsewhere I've never seen an oxy cyl explode in situ let alone go thru the cabin floor and exit the hole in the floor and out of the aircraft either.
I'm a mug punter with quite a few years in the industry but not for one moment would I suggest am 100% correct or even 10% , just offering an opinion to a very good question.
Neville , your theory in my opinion would only be valid in the event of no faults being found with the hardware. The MAS incident found a hard fault and resulted in ADIRU mods to eliminate the potential for this. I think these incidents highlight the fact that you cant test for every potential failure, especially in the FBW area. So you can potentially have something waiting for years before the right set of circumstances that no one thought of . Not just FBW but also electrical power , i.e 747-400 water leak and various relay failures on 737/320 over the last few years. Just hope we all learn from these incidents and it improves our system knowledge , so that the guys at the pointy end in the hot seat are able to deal with whatever happens when it doesnt conform to the book .
"then a "mid value" is chosen (not "average", as a wildly erroneous value would affect the data too much"
Well, if the stats have been properly configured the sampled range should be examined, remove the highest and the lowest values to remove extremes, and the total remainder divided by the remaining number of values... sounds a bit geeky, admittedly, but potentially significantly differences can be gained from "mean" values as opposed to more representative properly configured actual "averages".
EVERY time our industry changes technologies, we undergo a long period of teething...figuring out new problems that didn't show up before.
For example: High powered turboprop engines and a confluence of engine mount, and wing harmonic frequency and we get WHIRL MODE and the crash of L188 electras.
New structures, new demands and environment and BAM... metal fatigue in the comet.
So, now the computer runs the flight controls by wire. BAM, plane goes nuts.
Fly by wire...weight savings, computer precision.
WELL, I say, take the most reliable, bullet proof methods and stick with them.
Flight controls, by cable, with redundant pathways. Information from computers, but used by human pilots (who are well trained, rested and paid).
IF the Airbus 330 had conventional, cable based flight controls, a simple autopilot easily disengaged by the crew, and easily understood computer information indicating angle of attack AND WE WOULDN'T have had this post/thread at all.
CAN you imagine if this happened during air to air refueling? (proposed airbus330 tanker for USAF)
I think I said it'd do jack to an aircraft without any tech reason my apologies, just opinion , however my opinion is based on the extraordinary wavelengths of the actual radio signal at vlf freq's.A full wave at 19.8 kilohertz is over 15,000 metres in length if my maths is correct.
Your maths are pretty much on the mark, but there are a couple of other factors that are more relevant.
Firstly, because the VLF stations transmit intelligence they emit sidebands and the resultant harmonics at the power levels we're talking about can still be quite significant.
Secondly, though the electronics are often well shielded along with L/C filters in all the power supplies etc, it is still possible that the enormous power from the VLF transmitters *can* modulate the airframe and any poorly bonded panels *can* behave in a non-linear fashion thus injecting a detected signal into the electronics via the shields or ground returns.
As I've said elsewhere, it's a long shot, (hence the *can*) and hard to buy, but I have seen stranger pheomena with aircraft electrics/electronics.
That makes it pretty hard to rule out.
(If you're not an ex-fighter pilot, you'd be clueless..)
Bloody hell....
Ex-fighter pilot saved plunging flight
By ARJUN RAMACHANDRAN - SMH
As unfortunate as the 74 passengers injured last week in dramatically plunging Qantas jet were, perhaps they can be thankful for one thing - a former top fighter pilot was in charge.
The pilot at the controls as QF72 dived to the earth has not spoken publicly about how he handled the drastic scenario, but a colleague says he would have been "calm and methodical".
"I know the captain quite well," said Captain Michael Glynn, a fellow A330 pilot and acting president of the Australian and International Pilots Association.
"He came to Australia as an exchange pilot ... and flew the Mirage in the Australian airforce. So he's a highly trained pilot."
Despite his experience, the situation the pilot faced - in which QF72 made two plunges of 20 and 16 seconds that sent passengers slamming into the cabin's ceiling and walls - was one never seen before, Captain Glynn said.
Pilots underwent simulator training four times a year in which they faced emergency situations, such as planes plunging in altitude.
But on QF72, the plane seemingly acted of its own accord even after the pilot had taken manual control of the aircraft, he said.
"I believe the situations he was faced with have not be seen before.
"But that's one of the things we are trained to prepare for - when things crop up that you've not seen or thought up before and you have to ... get the aircraft to ground safely."
The pilot would not be available to describe how he handled the emergency as Qantas was still conducting its own investigation into the incident, a Qantas spokesman said.
But Captain Glynn said the first sign he would have realised something was wrong was when the autopilot system disconnected at about 37,000 feet, he said.
"They would have been in cruise, they would have been watching what was going on with the aircraft and having a chat ...
"They would have got a message from ECAM - that's the thing that tells us that something is maybe going wrong with the system - and given a checklist response to try to fix it."
The checklist would likely have advised the pilot to reset some of the computer systems, he said.
At that point, the pilot would have also taken manual control of the aircraft, but minutes later, the plane made two downward plunges.
"The thing to remember about Airbus is the flight control computer is always flying the plane - even when you're controlling it by hand, you're controlling it through the flight control computer.
"[After the initial problem that led to the autopilot disconnecting] they were hand-flying the plane and then the aircraft pitched down by itself.
"They would have been trying to correct that. Then it happened again ... it pitched down a second time.
"What he would have been trying to do is use the control stick to stop the pitch, using all his background knowledge to understand what's going on.
"It would have been very frightening. It would be very disconcerting."
Captain Glynn did not know what was done to eventually regain control of the plane, or whether control returned to the pilots as sporadically as it had left.
But even in the moment the plane was plunging towards the earth, the captain would have been calm, having faced "very realistic" simulations of the same scenario, he said.
"Sometimes the best thing to do as a pilot in that situation is to sit back and get a sense of what's going on, instead of leaping in and trying to fix it without understanding what's going on.
"It would have been tense, no two ways about it. But I know the captain - he would have been very calm."
Flight controls, by cable, with redundant pathways. Information from computers.....
Two score years ago, we already had fly-by-wire. Nobody quite trusted it, so cables were added as a final mechanical back-up to a dual monitored system . Regularly reverted to in training... but never in service as far as the records show.
Oct. 15 — Airbus SAS issued an alert to airlines worldwide after Australian investigators said a computer fault on a Qantas Airways Ltd. flight
switched off the autopilot and generated false data, causing the jet to nosedive.....
Toulouse, France-based Airbus, the world’s largest maker of commercial aircraft, issued a telex late yesterday to airlines that fly A330s and A340s fitted with the same air-data computer. The advisory is “aimed at minimizing the risk in the unlikely event of a similar occurrence.”
.......The flight control system was supplied by Litton Industries, a subsidiary of Los Angeles-based Northrop Grumman Corp., according to the telex issued to airlines. Carriers can choose data computers made by Litton or Honeywell International Inc. forthe model. The fault hasn’t occurred with Honeywell equipment.
Bloomberg - 22:28Z
A bit more on the technical end:
A “preliminary analysis” of the Qantas plunge showed the error occurred in one of the jet’s three air data inertial reference units, which caused the autopilot to disconnect, the ATSB said in a statement on its Web site.
The unit continued to send false stall and speed warnings to the aircraft’s primary computer and about 2 minutes after the initial fault “generated very high, random and incorrect values for the aircraft’s angle of attack.”
The flight control computer then commanded a “nose-down aircraft movement, which resulted in the aircraft pitching down to a maximum of about 8.5 degrees,” it said.
Last edited by pattern_is_full : 15th October 2008 at 23:57.
Reason: addition
Posted 43 minutes ago
Updated 28 minutes ago
Air safety investigators say they will look into claims signals from a naval communications base near Exmouth in Western Australia's north may have caused last week's Qantas mid-air emergency.
Early last week a Qantas Airbus travelling from Singapore to Perth was forced to land near the town after nosediving hundreds of feet in seconds, injuring about 70 people.
A preliminary investigation by the Australian Transport Safety Bureau (ATSB) found a computer fault caused the aircraft to nosedive twice.
The ATSB says it will examine whether signals from the communications base could have sparked the glitch.
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