View Full Version : Another Qantas ADIRU mishap

3rd Jan 2009, 03:43
"Australia's air safety watchdog is now investigating two in-flight system malfunctions on Qantas jets.

In the latest incident, on December 27, a Qantas Airbus A330-300 destined for Singapore was forced to return to Perth after the autopilot disconnected.

The malfunction occurred while the jet was cruising at 36,000 feet about 500km north-west of Perth.

'The crew elected to return to Perth and an uneventful overweight landing was conducted,' the Australian Transport Safety Bureau (ATSB) said in a statement.

It says the incident is 'similar' to one that occurred in October last year and will be investigated as part of the inquiry into that emergency.

. . .

The air safety watchdog is focusing on a flight computer system component called an ADIRU - air data inertial reference unit.

When the autopilot disconnected on December 27, the crew received a message indicating a problem with the plane's number 1 ADIRU.

They then followed revised guidelines from Airbus issued after the October emergency." - aap

3rd Jan 2009, 05:32
Some more details in ATSB press release:

MEDIA RELEASE : 02 January 2009 - Qantas Airbus A330 incident, 480km North West of Perth on 27 December 2008 (http://www.atsb.gov.au/newsroom/2009/release/2009_01.aspx)

3rd Jan 2009, 09:12
Qantas plane hit by computer problems

9:58AM Saturday Jan 03, 2009

Qantas has had computer problems on another of its Airbus planes.
Sky News reports that the plane's autopilot system shut itself off during a flight from Perth to Singapore.
It happened as the jet approached a large US naval communications base in northwestern Australia. The base was identified as a possible source of interference with systems on another Qantas flight in October.
Seventy passengers were injured on that flight when the same model of Airbus jet plunged suddenly and violently.
- Newstalk ZB

3rd Jan 2009, 10:08
If it WAS in the same area, this is beginning to look bad for those who provided 300 word posts explaining why it couldn't happen :=

Electronics ( & IMHO Airbusses ) Black Magic . . . :eek:

3rd Jan 2009, 10:36
It happened as the jet approached a large US naval communications base in northwestern Australia.

ATSB report says it occurred about 350NM from learmonth airport. (350NM= about 402 statute miles/648 Km)
I would not describe that as "approaching the US NavComSta".
The problem is more likely to have been caused by Global Warming. :ugh:


3rd Jan 2009, 16:38
The IRU portion is self-contained navigation: simply said, integrating accelerations from a known starting point.

The Air Data portion senses air.

These are the last systems to suspect of being affected by USN activities.

Now if a nav system were to get lost crossing the equator, or the International Date Line, that has been too common. The $350 Million per copy F-22 got lost on their first trip to Guam.


3rd Jan 2009, 16:54
It happened as the jet approached a large US naval communications base in northwestern Australia. The base was identified as a possible source of interference with systems on another Qantas flight in October.
Seventy passengers were injured on that flight when the same model of Airbus jet plunged suddenly and violently.
- Newstalk ZBAh.....
You now see the consequences of 'loose' talk on PPRuNe :ok:

We should have insisted more on the UFO that was following the A330.


Capt Kremin
3rd Jan 2009, 18:51
While I don't believe the North-West Cape VLF station is responsible, the only three known failures of this type have now occurred on aircraft flying the Perth-Singapore route. Two of them in the last three months.
Can anyone of a mathematical orientation give us the probability of that?

3rd Jan 2009, 18:55
You'd have to know where the aircraft were maintained and what other routes the same group of aircraft fly. If it's a maintenance issue or an environmental issue then that could be why it's only that group of aircraft suffering the problem. Then perhaps you'd be in a position to give an accurate probability.

3rd Jan 2009, 19:05
The only sensible pull together of the facts I've read so far was an item on Plane Talking which makes you wonder why the media falls for the naval base theory.

Then I nearly wet myself when someone on a spotter forum pointed out that Boeing operates the communications contract at the base, which reverted to being an Australian naval facility some years back after the US found better ways of communicating with ships and subs.

My step son who works for Virgin Blue said there were lots of A330s, 777s, some 717s and other assorted jets plus at least two Singapore A380s flying as close or not closer than the 630 kilometres that were between the Qantas jet and the base in the 24 hours during which the ADIRU No 1 in this Airbus went AWOL. He also said the quality of work done on the Qantas A330s is supposed to have been really **** house in general and that the rumors are that big red is pretty pissed off.

3rd Jan 2009, 19:21
What baffles me slightly is that ADIRUs are LRUs, so they'd be unlikely to be maintained directly by Qantas or their 'general' maintenance subcontractor, no?

They would be maintained by a "service station" for ... Northrop-Grumman, IIRC? or the manufacturer itself.

Oh sorry, realised while typing that I did forget a moment about level 1, level 2, level 3, etc.

But rather than UFOs and ELF transmitters at naval bases and mystery software bugs, I'm sticking my neck out... who's maintaining these things for Qantas?


Capt Kremin
3rd Jan 2009, 20:36
I doubt it is the maintenance. From reading another thread, these ADIRU's are supposed to remain in situ for long periods of time. They are designed with multiple redundant systems so they can have failures and not need to be removed.
The MAS B777 had some parts of the ADIRU fail a couple of years beforehand, as did the first QF one. Neither meant the unit required replacement.
Why was it the No 1 ADIRU again? Another coincidence?
My money is on a software fault deep in the bowels of the system somewhere.

Robert Campbell
3rd Jan 2009, 22:37
My money is on a software fault deep in the bowels of the system somewhere.

Bummer. Windows 7 isn't due to be released until the end of the year.

Seriously, if the ADIRUs are designed with redundant systems or levels, why the autopilot disconnect?

3rd Jan 2009, 22:39
It could be an obscure software bug. I don't know the exact locations of the three failures, but it could be some sort of hiccup to do with a particular latitude and longitude combination associated with certain other control inputs. If the FMC programming is nominally the same as all the other flights where there was no trouble, it could be a particular wind strength at a critical point in the flight. The whole problem is that for any software above the trivial, the number of potential test cases rapidly rises to a level where it is impossible to test all possible scenarios.

4th Jan 2009, 02:51
This link (http://www.iasa.com.au/folders/Safety_Issues/FAA_Inaction/another_Automation_incident.htm) bears examination (recently released near-accident interim report)

4th Jan 2009, 03:32
From the link at Belgique's post above
The air data sensor heating system operated electrically to prevent the formation of ice on each of the eleven air data system sensors. Ice protection for the pitot probes (including the captain's, first officer's, auxiliary, and rudder limiter), static plates, static ports, Ram Air Temperature (RAT), and angle of attack transducers was provided by electrical heating elements.
Heating elements may stop ice forming on external sensors - but what's to stop pre-existing water in static lines from freezing and obstructing ADIRU sensor inputs at low points in the lines? How often are static lines checked for water?
Quest: How can water get into static lines?
Answer: It gets sucked in during pressure changes when parked in rain.
Quest: What effect will ice-obstructed (i.e. closed) static lines have on systems linked to ADIRU's?
Answer: A mite unpredictable with an ADIRU, but in a non-automated jet:
a. The airspeed rapidly winds back on climb i.e. to zero over a surprisingly short vertical displacement (and rapidly increases during any descent)
b. VSI locks at zero
c. Altimeter will (at the very least) be inaccurate - and atworst willsimply freeze
d. Machmeter?
e. Autopilot? Most autopilots will auto-disengage because of the conflicting inputs

Quest: Will both ADIRU's be affected in the same way?
Answer: Should be, but different pneumatic tubing hook-ups and lengths may make that "not necessarily so"

The standard solution would be to depressurize and break the VSI/RCDI glass or select an alternate static source (thus providing a cockpit source of static pressure) - BUT what would work in an A330/B717's ADIRU??

What residual DFDR evidence will there be that any incident is "frozen ice in the lines" related? Not a lot. Most investigators wil stop short at evidence that all heating elements were powered.

4th Jan 2009, 12:23
within, say a CEP of one hour flight time geograpically, all three events...

about ~1.0E-23, or in that order of magnitude, which is kind of funny, as the approximate time since the big bang is about ~4.32E+17 seconds (lots of +/-).... ie, about 1 in 50 chance of happening in the age of the universe to date. Lies, damned lies etc...

This assumes a uniform distribution of A330 (+B777) operations around the world (doesn't happen) and estimates of fleet size and utilization. reduce this p by the % of the types using the Honeywell ADIRU if you only want to look at the types of systems rather than the aircraft types.

It is a fairly rare event if there isn't a common factor. It has been an interesting year.