Malaysia A333 at Brisbane on Jul 18th 2018, unreliable airspeed, hydraulic leak

Last Update: March 16, 2022 / 09:30:15 GMT/Zulu time

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Incident Facts

Date of incident
Jul 18, 2018


Flight number

Aircraft Registration

Aircraft Type
Airbus A330-300

ICAO Type Designator

A Malaysia Airlines Airbus A330-300, registration 9M-MTK performing flight MH-134 from Brisbane,QL (Australia) to Kuala Lumpur (Malaysia), was in the initial climb out of Brisbane's runway 01 when upon contacting departure the crew declared PAN PAN PAN reporting their airspeed was unreliable. The crew requested to continue on runway track and climb to FL100, later requested to climb to FL150 but aborted the climb at about FL110, received an altitude block clearance from FL100 to FL120 and turned back towards Brisbane to remain closer to the airport. While the crew was still working on troubleshooting their issue, a runway inspection found traces of oil on the taxiway at the holding point, where the aircraft had been holding prior to enter the runway for departure. The crew requested to hold while working on the issues. While holding the crew reported they will need to be towed off the runway due to a hydraulic leak on the yellow hydraulic system and the loss of nose wheel steering. The aircraft landed safely on Brisbane's runway 01 about 65 minutes after departure.

On Jul 19th 2018 Australia's ATSB reported 9M-MTK suffered an airspeed indication failure on takeoff. The occurrence was rated an incident and is being investigated.

The occurrence aircraft returned to service on Jul 26th 2018.

On Aug 30th 2018 Australia's ATSB reported that soon after the arrival of the aircraft in Brisbane, while performing the inbound flight, pitot covers were placed on all three pitot probes of the aircraft, that was o remain at Brisbane airport for about 3 hours. The aircraft was prepared for departure, a surveillance camera showed the aircraft was pushed back from the gate with pitot covers still on, and taxied to runway 01.

Standard operating procedures require the crew to perform a cross check of airspeeds at 100 KIAS, at the same time a rejected takeoff at or above 100 knots is considered a serious matter and the captain should act go-minded according to the procedures. V1 was computed at 153 KIAS, Vr at 160 KIAS. The aircraft commenced takeoff with the first officer being pilot flying, the captain called out 100 knots, according to the FDR the ground speed of the aircraft was 100 knots at that time, the first officer subsequently initiated rotation for takeoff, at that time the recorded speed over ground was 165 knots. Both flight crew stated they recalled observing airspeed anomalies including red flags for the speeds on both primary flight displays.

After takeoff the crew performed the checklist for unreliable airspeed indications and declared PAN PAN. The aircraft climbed to 10,000 feet, the crew worked several checklists and prepared for a return to runway 01. In accordance with the procedures the crew turned off all three Air Data Reference systems (ADR), which activated the aircraft's backup speed scale (BUSS), which provides a colour coded speed scale based on angle of attack and other information and altitude derived from GPS data. In addition the crew received ground speed information from ATC and used the aircraft's "radar altimeter".

With all three ADRs off the landing gear could not be lowered normally, an alternate gear extension was carried out before the aircraft returned to runway 01 for an overweight landing. The aircraft stopped on the runway as nose wheel steering was not available as result of the alternate gear extension. The landing gear doors, which had remained open following the gravity extension, received minor damage due to contact with the runway surface. A post landing inspection revealed all three pitot covers were still fitted to the aircraft's three pitot probes.

The ATSB reported that during rotation for takeoff ADR1 (supplying captain's airspeed) had reached 38 KIAS, while ADR2 and ADR3 had not yet reached 30 knots. During the entire flight the maximum recorded airspeed was 66 knots. Analysis of the speed data over ground and angle of attack data showed the aircraft was flown within operational limits at all times.

The ATSB wrote: "Further investigation is required to determine the airspeed indications and related warnings and cautions being displayed to the flight crew during the take-off roll."

The ATSB reported there had been multiple reports of insect activity at Brisbane airport (between 2008 and 2018 there were 15 such cases reported to high capacity public transport aircraft with partial pitot blockages due to insect nests) including insect nests being built inside pitot probes.

The ATSB then wrote with respect to the use of pitot covers:

The pitot probe covers were fitted on the aircraft’s three pitot probes by one of the engineering support personnel, as it was his understanding this was normal practice. He later reported that he advised the operator’s maintenance engineer that pitot probe covers were fitted during a brief exchange discussing turnaround tasks, but that the maintenance engineer did not directly respond. The maintenance engineer later reported that he did not recall hearing the advice, and he did not make an entry in the aircraft’s technical log to record that the covers had been fitted.

The presence of the pitot covers was not detected by the operator’s maintenance engineer or captain during separate external aircraft inspections. The operator’s maintenance engineer boarded the aircraft during turnaround, and the engineering support personnel left the bay to attend to other aircraft. The pitot covers were not detected by ground handlers during pushback.

The flight crew and operator’s maintenance engineer later reported that they would not routinely use pitot probe covers on a turnaround. They advised that the operator did not normally fly to airports where the use of pitot probe covers was standard. Security video recordings of the operator’s three previous turnarounds at Brisbane Airport showed that pitot probe covers were not used.

The ATSB released an immediate safety recommendation.

On Mar 16th 2022 the ATSB released their final report concluding the probable causes of the serious incident were (emphasis added by ATSB):

Contributing factors

- In the absence of clear instruction or guidance, the Aircraft Maintenance Services Australia support engineer fitted pitot probe covers to the aircraft shortly after its arrival, as was done for some other airlines to mitigate the threat of wasp infestation. Later, the engineer left to perform tasks on another aircraft and did not return to the aircraft prior to its departure as intended.

- Due to miscommunication or error, a technical log entry was not made following the fitment of pitot probe covers. As a result, when the technical log was reviewed prior to flight, the presence of pitot probe covers was not detected.

- The Malaysia Airlines engineer saw the pitot probe covers fitted to the probes during the transit check, about 2 hours before departure, and intended to ask the support engineer to remove them. However, associated with the limitations of prospective memory, the operator’s engineer subsequently did not remember to do so.

- The captain did not expect, or detect, the presence of the pitot probe covers during their preflight exterior inspection (walk-around). The captain did not include a number of the required check items, including the right side pitot probe, and looked at the left side pitot probe area briefly.

- The Malaysia Airlines engineer did not perform a final walk-around inspection of the aircraft, including a check for pitot probe covers, as required by the transit check that the engineer had certified as complete. The engineer assumed that the walk-around would be completed by the support engineer and/or ground handlers.

- The Menzies Aviation person assigned as dispatch coordinator for the aircraft handed over that duty to another person immediately before pushback, and neither person conducted the required dispatch walk-around. This was the last procedural opportunity to identify the presence of pitot probe covers before the flight.

- The aircraft was released for flight with covers fitted to all three pitot probes, preventing the air data systems from measuring airspeed.

- There was limited and ineffective communication between the captain and first officer in response to the speed flag on each of the primary flight displays (which appeared at about 50 kt groundspeed during the take-off). This significantly reduced their coordination and capacity to interpret the situation with the limited time available.

- While independently trying to diagnose a rare and unfamiliar problem during take-off, the flight crew experienced high cognitive workload, time pressure, and stress. This reduced their capacity to effectively interpret the situation and make a decision early enough to safely reject the take-off.

- The Airbus guidance provided in the flight crew techniques manual and other manuals for assisting A330 flight crews to decide whether to continue or reject a take-off did not discuss unreliable airspeed indication scenarios. (Safety issue)

- In the Airbus A330, there was no auditory alert associated with nil or unreliable airspeed from two or more sources during take-off (a high workload, critical phase of flight). Comparatively, other critical failures provide both visual and auditory indications. (Safety issue)

- Although suitable for use in most situations, the streamers attached to the pitot probe covers supplied and used for A330 operations by Aircraft Maintenance Services Australia provided limited conspicuity due to their overall length, position above eye height, and limited movement in wind. This reduced the likelihood of incidental detection of the covers, which is important during turnarounds. (Safety issue)

- Some Aircraft Maintenance Services Australia (AMSA) engineers extended the use of pitot probe covers (to mitigate the threat of wasp infestation) to operators that did not explicitly require it, including Malaysia Airlines. This increased the likelihood of error associated with the use of pitot probe covers because AMSA engineers were not controlling the engineering activities and were not permitted to make technical log entries. (Safety issue)

- Aircraft Maintenance Services Australia did not have a reliable method to account for tooling and equipment (such as pitot probe covers) prior to aircraft dispatch when providing non-certifying engineering support. (Safety issue)

- Menzies Aviation staff did not consistently carry out the required arrival and pre-departure aircraft checks of Malaysia Airlines aircraft, and Menzies Aviation audit processes were not effective at evaluating compliance with these requirements. (Safety issue)

- Malaysia Airlines flight crew and engineers did not fully complete the required aircraft inspections. (Safety issue)

- Malaysia Airlines did not clearly specify the division of engineering responsibilities between Malaysia Airlines and Aircraft Maintenance Services Australia engineers at Brisbane, leading to ambiguity with regard to who should conduct the final walk-around portion of the transit check. This risk was increased by the operator commencing and continuing flights to Brisbane with interim ground handling and engineering arrangements that varied from usual industry practice. (Safety issue)

- Malaysia Airlines did not develop and disseminate guidance and procedures about the use of pitot probe covers to flight crews and engineers, and there was limited awareness among those groups of the need for pitot probe covers at Brisbane Airport. (Safety issue)

- The Malaysia Airlines risk assessment for the recommencement of operations into Brisbane had numerous errors and omissions that potentially reduced its effectiveness.

- Although Malaysia Airlines identified the potential risk of pitot probe obstruction by wasps at Brisbane, and decided to address the risk with the use of pitot probe covers, it did not effectively communicate risks and required actions between departments and follow them through to completion.

- Malaysia Airlines’ processes for the management of change did not follow recommended industry practices, and its risk and change management processes were not detailed and clear enough to assure:
+ the appropriate level of involvement of subject matter expertise and safety groups­
+ that risk controls were implemented and monitored. (Safety issue)

Other factors that increased risk

- The flight crew briefly attempted to conduct troubleshooting during a critical stage of flight without calling for and adhering to the pitch attitude and thrust setting memory items of the Unreliable speed indication procedure, and also omitted the After Take-off/Climb procedure.

- For reasons that could not be determined, the tower controller did not respond to the initial PAN PAN call made by the flight crew after take-off.

- The Lido airport operational information did not include the Australian Aeronautical Information Publication (AIP) advice to fit pitot probe covers at Brisbane Airport (related to significant mud wasp activity), as well as other safety related AIP information. (Safety issue)

Other findings

- Once activated, the aircraft's back up speed scale (BUSS) was highly effective in reducing the flight crew's workload during approach and landing and provided critical flight information that would have otherwise been unavailable. The BUSS is available as an option on the Airbus A330 and other Airbus types.

- After the initial climb, the flight crew managed the unreliable airspeed issue with effective communication and coordination.

- The departures controller provided effective support to the flight crew from soon after take-off, including taking the initiative to provide groundspeed information.

The ATSB annotated:

After further discussion and revision of the required actions the flight crew determined that all ADRs should be selected off, which is a procedurally irreversible action in-flight (that is, there is no procedure to enable the crew to turn them back on until after landing - This action does not actually turn the ADRs off, but prevents the data from being used for display and control purposes). As a way of crosschecking the correct action before taking it, they decided to exchange duties so that the captain would fly and the FO would perform the procedural actions. The FO announced the current pitch and thrust settings to maintain level flight, and the assigned heading before handing control of the aircraft to the captain. The FO revised the required actions for the Unreliable speed indication procedure and reconfirmed the required action with the captain before switching all ADRs off. Once completed, the flight crew confirmed the amount of fuel remaining and requested a block level altitude between 10,000 ft and FL 120 which was approved by ATC.

The FO pre-read the All ADR off procedure in preparation for the next step, which was to turn all ADRs off. At 2343, with the aircraft at about 11,000 ft, the flight crew turned all three ADRs off. This activated the back up speed scale (BUSS), an alternate display mode which permits pilots to keep the aircraft in a safe performance envelope when airspeed data is unreliable or unavailable. Further information on the BUSS is provided in Back up speed scale. The airspeed tape on the ISIS is retained, and in this case would have stayed at the bottom of the speed scale (30 kt).

In addition to activating the BUSS, turning off all ADRs resulted in the following notable effects:

- the ECAM warning message NAV ADR 1 + 2 + 3 FAULT (fault with all 3 ADRs)
- pressure altitude was replaced with GPS altitude
- spoilers and speed brake are not to be used
- normal hydraulic extension of the landing gear was not possible, and the main landing gear doors could not be retracted after a gravity extension
- cabin pressure needed to be manually controlled by the flight crew
- nose wheel steering was not available on landing.

ATSB analysis of flight data indicated that the aircraft did not approach an aerodynamic stall condition at any point during the flight.
Incident Facts

Date of incident
Jul 18, 2018


Flight number

Aircraft Registration

Aircraft Type
Airbus A330-300

ICAO Type Designator

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