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ASN Wikibase Occurrence # 213820
Last updated: 14 July 2021
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Date:26-DEC-2014
Time:c. 13:45 UTC
Type:Silhouette image of generic A332 model; specific model in this crash may look slightly different
Airbus A330-243
Owner/operator:XL Airways France
Registration: F-GRSQ
MSN: 501
Fatalities:Fatalities: 0 / Occupants: 317
Other fatalities:0
Aircraft damage: None
Location:FIR Cairo/Athens -
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Saint-Denis-Roland Garros Airport, Réunion (RUN/FMEE)
Destination airport:Marseille-Marignane Airport (MRS/LFML)
Investigating agency: BEA
Narrative:
The aircraft operated a flight from the island of Réunion to Marseille, France.
During the preparation of the aircraft, the crew became aware that an Inertial Reference System (IRS) 2 drift had been reported by the previous crew. The captain on the flight was Pilot Monitoring. One of the first officers was Pilot Flying and performed a complete alignment of the three IRS's in accordance with planned procedures. For departure, the three crew members are present in the cockpit. The plane departed at 05:38 UTC.
As soon as the flight began, the crew saw the message "Check IR 2 / FM position" on the Multi-Function Control and Display Unit (MCDU) and noticed a drift of the IRS 2. Throughout the remainder of the flight, the crew regularly monitored the drift of the IRS 2. It indicated reading values between about 6 and 15 NM. The primary GPS mode was active throughout the start of the flight.
The captain took the first rest, about one hour after takeoff and was replaced by the third crew member. On returning from the rest, at about 09:40, one of the other pilots left the cockpit to rest.
At 10:34, the IRS 3 changed from NAV mode to ATT mode. In this mode, the IRS provides attitude data but no more other data such as position and ground speed. The flight automation rejected IRS 3 and used only IRS 1 and IRS 2 data during the remainder of the flight. This loss of redundancy had no impact on the displayed navigation data and did not require any crew action in the short or medium term. In accordance with the philosophy of the manufacturer, the crew was therefore not immediately warned.
At approximately 13:00, the last pilot was relieved from the cockpit to rest. Shortly thereafter, while attempting to monitor the drift of the IRS 2 on the MCDU, he noticed that the IRS 3 was in ATT mode. There was no alarm displayed on the ADIRU panel.
The three mode switches are on NAV. He explained that he had seen boxes inviting him to enter a course for IRS 3 on the MCDU IRS MONITOR page.
The crew consulted the IR FAULT paper procedure, which lead them to perform the IR ALIGNMENT IN ATT MODE procedure for IRS 3. This procedure required the mode dial to be set to ATT and the heading to the MCDU. The captain remembered seeing an ECAM message requesting that this IRS be switched to ATT mode. The crew commands the IRS 3 to go into ATT mode. The three crew members indicated that no action on the IRS mode selectors had been made during the flight before that time.
At 13:36, the Flight Director (FD), Autopilot (AP) and AutoThrust (A/THR) automatically disengaged. The position and flight plan information on the Navigation Displays (ND) disappeared.
The flight crew activate the NAV BACK-UP mode on their respective MCDUs and retrieved position and flight plan data.
The captain indicated that he was unsuccessfully trying to verify the IRS information in BACK-UP NAV mode.
At 13:44, the internal data of each IRS recorded the message "IN FLIGHT ALIGNMENT". The flight control law became direct law. Attitude information disappeared from the PFDs until the end of the flight. Position information and flight plan were no longer available on the ND. The crew must use electromechanical emergency instruments for the remainder of the flight, without autopilot or auto thrust.
A few minutes later, the captain chose to become Pilot Flying because the reading of the emergency instruments is easier from the left seat.
The first officer informed Greek air traffic control that they had lost their RVSM capacity and declared an emergency situation. The crew examined the possibilities of diversion to Heraklion and Athens. They retained Athens because of the favourable weather conditions and the support they could expect from air traffic control. The crew was radar-guided to the runway 21L final. During the descent, the crew declared a distress situation.
The plane landed at 14:37.

The incident consisted of the unavailability of the three IRS leading to a degradation of the flight control laws and the degradation of the aircraft's autonomous navigation capabilities. This unavailability occurred in four main stages:
- at 10:34, the change from IRS 3 from NAV mode to ATT mode, likely the result of manual action by a crew member;
- at 13:36:
- the disconnection of the AP and A/THR, probably due to a navigational discrepancy between the IRS 2, which had been drifting since take-off, and the IRS 1,
- the loss of position and navigation information on the NDs, a consequence of the previous event according to the logic of the FMS Honeywell P3 and lower standards. This information was recovered two minutes later when the crew activated the BACK-UP NAV mode.
- shortly before 13:44, the loss of left-side position information following the exit of the left-side BACK-UP NAV mode (Captain);
- at 13:44, the in-flight alignments of the three IRS, probably as a result of improvised and possibly uncoordinated actions by the crew during attempts to retrieve position information on the captain's ND.
The loss of positions was a major concern for the crew.
The new FMS standards would have prevented this loss of information.
Improved robustness in maintaining autonomous navigation capabilities is of interest when flying over oceans or desert areas, or near conflict zones.
The IRS drift problem, previously identified, has not been resolved due to incorrect chassis labelling. However, the drift of a single IRS in flight is not a major abnormal situation.
The following factors were considered in an attempt to understand the reasons for the probable non-standard crew actions on the IRS rotactors, without it being possible to specify their degree of contribution:
- ADIRU control panel ergonomics that do not visually recall the irreversible nature of IRS mode changes;
- the presentation of the IRS information on the MCDU MONITOR POSITION page in numerical order (1,2,3) different from the layout of the rotators (1,3,2), which is representative of the aircraft's architecture;
- a logic for presenting ECAM information to the crew that does not allow them to understand the reason for the disconnection of the AP and the loss of positions that occurred at 1336;
- low crew exposure to IRS failure situations.

Sources:

https://www.bea.aero/en/investigation-reports/notified-events/detail/article/incident-grave-de-lairbus-a330-immatricule-f-grsq-exploite-par-xl-airways-survenu-le-26-decembre-20/
http://aerossurance.com/safety-management/improvised-a330-avionics-hf/

Accident investigation:
cover
  
Investigating agency: BEA
Status: Investigation completed
Duration: 3 years and 7 months
Download report: Final report


Images:

Photo of F-GRSQ courtesy AirHistory.net


Paris - Charles de Gaulle (LFPG / CDG)
23 June 2011; (c) Mick Bajcar

Revision history:

Date/timeContributorUpdates
30-Jul-2018 11:03 harro Added
30-Jul-2018 19:54 harro Updated [Time, Total occupants, Narrative]
26-Dec-2018 10:27 Aerossurance Updated [Country, Source]

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