11/19/08 05:41 PM

The Australian Transport Safety Bureau (ATSB) has issued a preliminary report indicating that the accident involving a Quantas airbus flying from Singapore to Perth was likely caused by spurious information being sent to the flight control computer. The Australian safety “watchdog” is investigating whether transmissions from the Harold E. Holt Naval Communications Station interfered with the aircraft’s onboard systems. The possibility that passenger electronic devices caused the problem is also under investigation. The ATSB considers both possibilities unlikely, but neither can be ruled out at this stage of the inquiry.

Readers of the eNews will recall that the airbus was cruising at 37,000 feet when it suddenly descended up to 650 feet causing serious injury to forty-four of the 313 people onboard. The ATSB is focusing on a flight computer system dubbed an ADIRU (air data inertial reference unit). Examination of flight data recorder information indicated that this system was producing erroneous information, possibly from a hardware or software glitch. Authorities have not yet determined whether the communications station, which transmits very low-frequency signals at high power, was on-air at the time. The ADIRU has been transferred to its manufacturer US firm for Northrop Grumman for extensive testing. The entire 43-page ATSB report can be viewed online.

Failures and directives

May 3, 2000 - FAA Airworthiness directive 2000-07-27 was issued, addressing dual critical failures during flight, attributed to power supply issues affecting early Honeywell HG2030 and HG2050 ADIRU ring laser gyros used on several Boeing 737, 757, Airbus A319, A320, A321, A330, and A340 models.[2][9]

January 27, 2004 - FAA Airworthiness directive 2003-26-03 (later superseded by AD 2008-17-12) called for modification to the mounting of ADIRU3 to prevent failure and loss of critical attitude and airspeed data.[2] [10]

25 June 2005 - An Alitalia Airbus A320-200 registered as I-BIKE departed Milan with a defective ADIRU as permitted by the Minimum Equipment List. While approaching London Heathrow Airport during deteriorating weather another ADIRU failed, leaving only one operable. In the subsequent confusion the third was inadvertently reset, losing its reference heading and disabling several automatic functions. The crew was able to effect a safe landing after declaring a Pan-pan.[11]

1 August 2005 - Malaysia Airlines Flight 124, a Boeing 777-2H6ER departed Perth, Western Australia for Kuala Lumpur. Climbing through 38,000 feet a faulty accelerometer caused the aircraft's ADIRU and autopilot to command changes of altitude. The flight crew overrode the system and manually returned to land the aircraft at Perth. The subsequent ATSB investigation led the US FAA to issue emergency airworthiness directive 2005-18-51 on the fly-by-wire software.[12]

6 August 2008 - The FAA issued airworthiness directive 2008-17-12 expanding on the requirements of the earlier AD 2003-26-03 which had been determined to be an insufficient remedy. In some cases it called for replacement of ADIRUs with newer models, but allowed 46 months from October 2008 to implement the directive.[13]

7 October 2008 - Qantas Airlines Flight 72, an Airbus A330 departed Singapore for Perth. Some time into the flight, while cruising at 37,000ft, a failure in the No.1 ADIRU led to the autopilot automatically disengaging followed by two sudden uncommanded pitch down manoeuvres, according to the Australian Transport Safety Bureau (ATSB). The accident injured up to 74 passengers and crew, ranging from minor to serious injuries. The aircraft was able to make an emergency landing without further injuries. The aircraft was equipped with a Northrop Grumman made ADIRS, which investigators sent to the manufacturer for further testing.[14][15]