Etihad A332 at Brisbane on Nov 21st 2013, &quot;we lost our airspeed&quot;

Last Update: May 6, 2016 / 14:16:03 GMT/Zulu time

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Photo of Etihad Airways A6-EYJ, Airbus A330-200 — Etihad Airways A6-EYJ, Airbus A330-200 (Photo credit: D464-Darren Hall / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Oct 21, 2013

Classification
Incident

Airline
Etihad Airways

Flight number
EY-473

Departure
Brisbane, Australia

Destination
Singapore, Singapore

Aircraft Registration
A6-EYJ

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

An Etihad Airbus A330-200, registration A6-EYJ performing flight EY-473 from Brisbane,QL (Australia) to Singapore (Singapore) with 164 passengers and 11 crew, was in the initial climb out of Brisbane's runway 01 when the crew declared "Mayday, Mayday, Mayday, ... we lost our airspeed". The crew subsequently announced they would reduce their speed to 240 knots. The crew levelled off at 5000 feet and entered a hold informing tower they needed some time to prepare for the approach. After about 40 minutes in the hold the crew advised they would be doing an overweight landing, requested emergency services on standby in case of brakes or tyre problems and they were ready for the approach. The crew requested a long final (14nm) to runway 01. The aircraft landed safely on runway 01 at a normal speed over ground about one hour after departure.

The airline confirmed a flight deck instrument failure. The flight was cancelled, the passengers were rebooked onto flights of other carriers.

Radar data show the aircraft had accelerated to about 300 knots over ground while climbing through FL017. The speed reduced shortly afterwards and remained consistently within 210 to 230 knots over ground until final approach, radar showed 148 knots over ground on touch down.

On Nov 25th 2013 the ATSB reported the occurrence was rated a serious incident and an investigation has been opened. The ATSB reported that the crew shortly after takeoff detected the loss of an airspeed indicating system and possible other system failures. The crew declared Mayday and returned to Brisbane. The investigation will read out flight data and cockpit voice recorders as well as interview the crew and examine ATC recordings and technical documentation of the aircraft.

On Feb 27th 2014 the ATSB provided an interim update stating, that the aircraft had arrived normally at Brisbane. About 2:03 hours later the aircraft was pushed back for the incident flight and initiated takeoff, the takeoff was rejected however due to an airspeed disagree at the 80 knots call with the captain's airspeed having failed. Maintenance subsequently swapped ADIRU1 and ADIRU2, switched the first officer's instruments to ADIRU3 with the captain's instruments connected to ADIRU1, and dispatched the aircraft under minimum equipment list requirements with ADIRU2 set to inoperative. The aircraft taxied out again and initiated the takeoff roll, after the aircraft had accelerated beyond V1 the crew again noticed an airspeed disagree, continued takeoff, declared emergency and returned to Brisbane for a safe landing. Subsequent engineering inspection detected that the captain's pitot probe was obstructed, the probe was removed from the aircraft and sent for further analysis. The manufacturer found that the probe had been almost completely blocked by a wasp nest composed of sand and mud consistent with nests of "mud-dauber wasps". The investigation continues.

On May 6th 2016 the ATSB released their final report concluding the probable causes of the serious incident were:

- Pitot probe covers were not installed by maintenance staff during the period that the aircraft was at the gate.

- The captain’s pitot probe was almost totally obstructed by an insect nest, consistent with mudwasp residue, during the 2 hour and 3 minute period while the aircraft was in transit on the ground at Brisbane.

- The blocked captain’s pitot probe was not detected by engineering staff after the initial rejected take-off. The relevant tasks in the trouble shooting manual did not specifically identify the pitot probe as a potential source of airspeed indication failure. [Safety issue]

- During the second take-off roll, the faulty airspeed indication (displayed on the captain’s PFD) was not detected and acted upon by the crew before V1 and the take-off was continued.

The ATSB analysed with respect to flight crew actions:

The SOPs require the PM to scan airspeed throughout the take-off and for the PF to cross-check airspeed at 100 kt. A red flag is displayed on the captain’s PFD when no valid airspeed data was available from ADR 1 at the same time as ground speed data was valid and greater than 50 kt.

The crew reported that during the RTO, a red airspeed flag was displayed on the captain’s PFD. This is consistent with the flight data, which showed that the captain’s CAS remained fixed at zero. During the RTO the maximum recorded CAS was 88 kt, so the take-off was able to be rejected below V1 (151 kt).

During the second take-off roll, the crew reported that the red airspeed flag was not apparent until after V1. However, the recorded flight data again indicated that it was likely that a red airspeed flag would have been displayed on the captain’s PFD, after the groundspeed had reached 50 kt.

As a result, the aircraft became airborne with only a single valid source of airspeed information, with consequential serious degradation of other aircraft systems.

With respect to maintenance actions following the rejected takeoff the ATSB analysed:

By following the TSM procedures for an ‘ADIRU1 (1FP1) BUS ADR’ fault message, the aircraft maintenance engineer performed a BITE test of the EFCS 1 and 2. The units tested with normal indications and no faults were identified. The TSM procedure did not specifically identify the pitot probe as a possible cause.

Although no ‘hard’ (permanent) faults had been identified, the engineer, in consultation with the operator’s Maintenance Control Centre, considered that the best resolution would have been to make ADR 1 inoperative. However, this was not permitted under the MEL requirements for ETOPS dispatch. Therefore the engineer transposed ADIRU 1 and 2 and performed a BITE test of both units. The aircraft was dispatched with the ADR part of ADIRU 2 inoperative (switched off) in accordance with the MEL. The FO’s air data source was switched to ADIRU 3 and the captain’s air data source remained switched to the normal (ADIRU 1) position. As a result, the blocked captain’s pitot probe remained undetected and the aircraft was dispatched with only one of the three airspeed sources able to provide valid data.

With respect to mud wasp activities at Brisbane the ATSB wrote: "Mud-dauber wasp activity at Brisbane Airport has been investigated previously by the ATSB and continuing reports and incidents indicate that it is an ongoing hazard. As the wasps cannot be completely eradicated, it is necessary to have control measures in place to minimise the chance of a pitot probe becoming obstructed." The ATSB further analysed that despite the short period of time of 2 hours and 3 minutes on the ground analysis of the material recovered from the pitot probe make it highly likely "that the obstruction was due to mud-dauber wasp activity after the aircraft had landed." The ATSB concluded analysis with respect to the mud dauber wasp: "Pitot probe covers were not installed by maintenance staff during the period the aircraft was at the gate. The maintenance staff advised that the use of pitot covers was dependent on customer requirements and was not a standard practice. Operators can minimise the risk of pitot probe obstruction by consistently using pitot covers, even during short transit periods."