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Updated: 27 February 2014

On 21 November 2013, after a flight from Singapore, A330 A6-EYJ landed at Brisbane airport and was taxied to the terminal. It came to a stop at 0949 EST1. At 1152 EST, the aircraft was pushed-back for the return flight to Singapore. At 1204 EST, the captain discontinued (rejected) the takeoff after observing an airspeed indication failure on his display. The maximum airspeed recorded by the flight data recorder during the rejected takeoff was 88 kt.

The aircraft taxied back to the terminal where trouble-shooting was carried out. As part of this work, ADIRU2 1 and ADIRU 2 were transposed and the aircraft was dispatched with the air data reference part of ADIRU 2 inoperative in accordance with the MEL3. The first officer’s air data source was switched from ADIRU 2 to ADIRU 3. The captain’s air data source remained switched to the normal (ADIRU 1) position.

At 1345 EST, during the second takeoff, the crew became aware of an airspeed discrepancy after V1 and the takeoff was continued. Once airborne, the crew declared a MAYDAY and decided to return to Brisbane where an overweight landing4 was carried out at 1439 EST.

Subsequently, the pitot probes (which measure airspeed information that is sent to the ADIRUs) were visually inspected. The inspection found that there was an internal obstruction of the captain’s probe, while the first officer’s and standby probes were clear. The captain’s probe was removed from the aircraft and sent to the probe manufacturer in the USA. Examination showed that it had been almost completely blocked by an insect nest, composed of sand and mud, that was consistent with the nest of a ‘mud-dauber’ wasp.

A previous incident at Brisbane in 2006 also involved an obstructed pitot probe due to insect activity.

Airspeed measurement on the A330

The A330 has three independent systems for calculating and displaying airspeed information: (1) captain, (2) first officer, and (3) standby. Each system uses its own pitot probe, static ports, air data modules (ADMs), ADIRU, and airspeed indicator.

Each ADIRU comprises two parts; an air data reference (ADR) part and an inertial reference (IR) part which are integrated into a single unit. One part can be switched off while the other part can still operate.

Airspeed is measured by comparing total air pressure (Pt)5 and static air pressure (Ps). On the A330, Pt was measured using a pitot probe, and Ps was measured using two static ports. A separate ADM was connected to each pitot probe and each static port, converting the air pressure from the probe or port into digital electronic signals.

Each pitot probe consisted of a tube that projected several centimetres out from the fuselage, with the opening of the tube pointed forward into the airflow. The tube had drain holes to remove moisture and was electrically heated to prevent ice accumulation during flight.

Figure 1 shows the locations of the aircraft’s pitot probes.

Figure 1: Locations of pitot probes

 Fig 1_Locations of pitot probes

Source: ATSB

Normally, the airspeed displayed to the captain uses the captain’s pitot probe and ADIRU 1, but the crew can manually switch the source to the standby system (standby pitot probe and ADIRU 3) if required. Similarly, the airspeed displayed to the first officer normally uses the first officer’s pitot probe and ADIRU 2, but the source can be manually switched to the standby system if required.

Further investigation

The investigation is continuing and will include analysis of:

  • recorded data from the aircraft
  • aircraft systems
  • flight operations aspects
  • maintenance/trouble-shooting aspects.

It is anticipated that the investigation report will be released to the public by June 2014.

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The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the incident as outlined in this web update. As such, no analysis or findings are included in this update.



[1] Eastern Standard Time (EST) was Coordinated Universal Time (UTC) + 10 hours.

[2] Air data and inertial reference unit, which supplies air data and inertial reference information to the pilots’ flight instrument displays and other aircraft systems.

[3] A minimum equipment list (MEL) is a list of aircraft equipment and systems that may be inoperative for flight, subject to specified conditions.

[4] The actual landing weight was 199.7 tonnes while the maximum landing weight was 182 tonnes. After an overweight landing, depending on the vertical speed and acceleration at touchdown, an aircraft inspection may be required.

[5] Pt is the sum of static (or outside) air pressure and pressure due to relative airspeed. 

 

General details

Date: 21 Nov 2013 Investigation status: Active 
Time: 13:50 EST Investigation type: Occurrence Investigation 
Location   (show map):near Brisbane Airport Occurrence type:Avionics/flight instruments 
State: QLD Occurrence class: Technical 
Release date: 27 Feb 2014 Occurrence category: Serious Incident 
Report status: Pending Highest injury level: None 
Expected completion: May 2014  
 

Aircraft details

Aircraft manufacturer: Airbus 
Aircraft model: A330 
Aircraft registration: A6-EYJ 
Serial number: 737 
Operator: Etihad Airways 
Type of operation: Air Transport High Capacity 
Sector: Jet 
Damage to aircraft: Nil 
Departure point:Brisbane, Qld
Destination:Singapore
 
 
 
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Last update 06 June 2014