Aviation safety issues and actions

Air data inertial reference unit (ADIRU) failure

Issue number: AO-2008-070-SI-01
Who it affects: All operators of aircraft fitted with LTN-101 ADIRUs
Issue owner: Northrop Grumman Corporation
Transport function: Aviation: Air transport
Background: Investigation Report AO-2008-070
Issue release date: 19 December 2011
Current issue status: Partially addressed
Issue status justification:

The ADIRU manufacturer has reviewed the potential mechanisms that may have led to the data-spike failure mode and was examining options to improve the robustness of some of the CPU modules processing activities. In addition, some aspects of the ADIRU's BITE have been enhanced to aid in the detection and management of the failure mode (see other related safety issue).

Safety issue description

One of the aircraft’s three air data inertial reference units (ADIRU 1) exhibited a data-spike failure mode, during which it transmitted a significant amount of incorrect data on air data parameters to other aircraft systems, without flagging that this data was invalid. The invalid data included frequent spikes in angle of attack data. Including the 7 October 2008 occurrence, there have been three occurrences of the same failure mode on LTN-101 ADIRUs, all on A330 aircraft.

Proactive Action

Action number: AO-2008-070-NSA-127
Action organisation: Northrop Grumman Corporation
Date: 19 December 2011
Action status: Closed

The ADIRU manufacturer advised in November 2010 that it had examined a wide range of possible mechanisms within the LTN-101’s central processing unit (CPU) module that may have produced the air data reference data spikes. Although the exact mechanism could not be identified, it was considering options to improve the robustness of some of the CPU module’s processing activities.

Last update 11 February 2014