It Gets Curiouser: Computer error behind Qantas midair drama

[Ellipse]

http://www.sott.net/articles/show/167548-It-Gets-Curiouser-Computer-error-behind-Qantas-midair-drama

The plane was cruising at 37,000 feet when a fault in the air data inertial reference system caused the autopilot to disconnect.

I was wondering if the system at the root of the air data inertial reference system of such plane is always mechanical (gyroscope) and, in this case, what can make it fail. But I realise that, even if it's the case, there's a lot of electronic involve between the gyro and the autopilot. So it's impossible to guess.

Moderator: I changed "code" for "quote" in your post.

 

[Vulcan59]

There was another very similar incident with a Malaysian B777 some time back. That incident was also a result of the inertia reference unit fault.

Added later:- Oh and notice that this latest incident happen close to the location of the Malaysian airlines incident.

 

[Ellipse]

Thx for the link.

This event is 3 years old and due to a 'faulty accelerometer' if we believe the report. It can happen, hard to see a direct link between the two events and then, find the last one 'curious'.

 

[nicklebleu]

Just a quick aside re gyroscopes.

Nowadays most gyroscopes are not mechanical anymore, the are electronic (solid-state, ring laser), but or course they may fail just as well - or even more so? Mechanical gyros used to be precision tools, extremely expensive, while today's solid-state gyros are cheap mass produts - fwiw.

 

[rrraven]

from free patent online:

Integrated fault-tolerant air data inertial reference system
Document Type and Number:
United States Patent 5297052

Abstract:
A fault-tolerant air data and inertial navigation reference system utilizes skewed axis inertial sensors and fault-tolerant redundant electronics to provide higher redundancy with fewer parts. Parallelly operating processor circuits each receive the individual outputs of six skewed-axis gyros and six skewed-axis accelerometers. Each processor independently processes parity equations using the outputs to identify malfunctioning sensors. Further, the output of each processor is transmitted to three parallelly operating voter circuits. The voters are operable to discard a processor if its output does not agree with the majority. The voter outputs are similarly fed back to the processor circuits, which compare these outputs, and discard any voter whose output disagrees with the majority, thus providing a completely integrated system.

from wikipedia
Air data computer
From Wikipedia, the free encyclopedia
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An air data computer is an essential avionics component found in modern glass cockpits. This computer, rather than individual instruments, can determine the calibrated airspeed, Mach number, altitude, and altitude trend data from an aircraft's pitot-static system. In some very high speed aircraft such as the Space Shuttle, equivalent airspeed is calculated instead of calibrated airspeed.

Air data computers usually also have an input of total air temperature. This enables computation of static air temperature and true airspeed.

In Airbus aircraft the air data computer is combined with attitude, heading and navigation sources in a single unit known as the Air Data Inertial Reference Unit (ADIRU). This has now been replaced by Global Navigation Air Data Inertial Reference System (GNADIRS).
hmmm
RRR

 

[Devar]

New article from AAP;

Naval base may have caused plane to dive: ATSB
14th November 2008, 8:45 WST

An investigation into a mishap involving a Qantas flight last month is centring on an electronic black box which produced spurious message signals causing the aircraft to dive suddenly.

There was also a possibility the incident was caused externally by signals from a naval communications base near Exmouth in Western Australia, the Australian Transport Safety Bureau said today.

Forty-four of the 313 people on board required hospital treatment after the Qantas Airbus A330, flying from Singapore to Perth on October 7, suddenly plunged, hurling passengers around the cabin.

The aircraft was cruising at 37,000 feet when the fault occurred, causing it to descend up to 650 feet in seconds. The pilot made an emergency landing at Learmonth in north-western WA.

An initial investigation pointed to a fault in the plane's air data inertial reference system which sent erroneous information to the flight control computer, causing the autopilot to shut down.

The bureau today released a preliminary report of its inquiry, saying the electronic black box - known as ADIRU (Air Data Inertial Reference Unit) - was normally highly reliable.

It was extremely rare for such failures to have an effect on an aircraft's flight control, inquiry official Kerryn Macaulay told reporters in Canberra.

“The three ADIRUs will be subject to comprehensive testing at the manufacturer's facility in the US,” she said.

Testing is planned to start on Monday.

The bureau's investigation is also considering the possibility the incident was caused by external interference, possibly by signals from the Navy's Harold E Holt submarine's communications base.

AAP