I thought I saw this particular incident mentioned here, and in this thread, perhaps it was another thread, anyway I'll try and get into the spirit of this thread consolidation thing, its not strictly a case of electrical power loss on landing but anyway.
Apparantly there was an incident with a Qantas airbus, on October 7 2008 flight qf 72. A severe dive causing injury. There has been some speculation that the flight suffered interference from NW cape.
The
ATSB released an interim reportsaying they don't know much the other day.
Some Australian bloggers are suggesting
interference, others are suggesting component failure:
[url]On October 7th last year, several passengers and crew were seriously injured when Qantas Flight 72 decided to enter a severe dive - one dramatic enough to throw them around the cabin. The initlal culprit was identified as a faulty ADIRU unit - a gadget that provides information from the plane’s sensors to both the pilots and, crucially, the flight control system. Courtesy of the interim report of the Australian Transport Safety Bureau, it’s now a bit clearer what happened. What follows is a somewhat technical examination of the issue.
Extensive testing has still not explained the ADIRU failure. The theory that it was the low-frequency, high-power radio transmissions from the Learmonth Naval Communication station hasn’t been completely ruled out, but it was always pretty dubious: the units were certified to operate correctly in the presence of much stronger radio signals than result from the Learmonth transmissions, planes have been operating for many years in Learmonth’s vicinity without incidents, and similar emissions from other high-power low frequency transmissions haven’t been reported to cause issues. The faulty ADIRU unit was also tested to see whether radio interference could reproduce the effects seen in-flight, with no success.
But as I noted at the time, the specific reason the ADIRU failed was far less important than why why a single faulty component was able to cause a plane to misbehave to such an extent. The interim report explains the problem in some detail.
The Airbus A330, like all Airbus airliners and more recent Boeing models, is fly-by-wire - the pilot’s stick movements, and the sensor data, are fed into flight control computers that determine what the bits of the aircraft that move - ailerons, flaps, rudder, and tail - actually do. Some of that sensor data comes through the ADIRU units; each ADIRU processes the data from a different set of sensors, and the three ADIRUs feed their data to the flight control computer (which in itself has redundant backups, but they don’t come into play here).
But what if one of the ADIRU units starts malfunctioning, and providing “rubbish” information to the flight computer?
For most pieces of information, if an ADIRU or the attached sensor breaks, the system will notice that the value is radically different to the other redundant sensors and ignores the rubbish value. But for angle of attack, this approach isn’t ideal, because there are situations where you’d expect, in normal operation, for different sensors to report different readings. So a different method was used for the angle of attack data.
In a nutshell, if an ADIRU generates an obviously incorrect angle of attack data for an instant, the flight control computer uses the last known good value it had, over a period of 1.2 seconds. If the ADIRU misbehaves continuously for a second or more, the flight computer concludes “Hang on, you’re faulty”, and will ignore anything it says for the rest of the flight.
But there’s another, rather diabolical possibility. What if the ADIRU (or angle of attack sensor) goes haywire for, say, half a second, starts working again for half a second, then misbehaves for another half-second or so? The ADIRU doesn’t misbehave long enough for the flight computer to disconnect it. But it can’t keep using the old value. So it calculates a new value based on the misbehaving ADIRU.
The end result, unfortunately, was a plane that thought it was pointing its nose somewhere towards the Moon when it was actually flying straight and level. The dive was its attempt to correct itself.
Nasty as it was, A330s are not in danger of crashing due to this design flaw, if I understand the report correctly. The automatic system that pushed the nose down only operates at cruising speeds and at high altitudes. Nevertheless, it is a serious flaw, and the report indicates that Airbus will be modifying the flight control software so as to avoid this situation repeating itself.
From my professional perspective (as an academic who specializes in testing computer software), the real question is why this problem wasn’t picked up before an A330 ever flew. Aircraft manufacturers take design checking and testing more seriously than just about anyone. The report doesn’t go into this question. To be fair, the A330 flight control software was written nearly 20 years ago, so the software quality assurance procedures used then were probably considerably less advanced than those used today. But Airbus (and Boeing) will undoubtedly be thinking hard about their review and testing procedures, to figure out if the same design flaw would be picked up today - before it made it into an aircraft carrying paying passengers.[/url]
http://larvatusprodeo.net/2009/03/09/why-qf72-developed-a-mind-of-its-own/#more-8025
