The ATSB on Wednesday concluded what it called “one of its most substantive and complex” investigations in recent years into a serious incident on a Malaysia Airlines A330.
It revealed an aircraft, bound for Kuala Lumpur and carrying 215 passengers, eventually had to turn around mid-air and return home after it was identified too late that the vital airspeed sensors were covered up.
Two similar incidents in 1996 involving 757s led to fatal crashes that killed more than 200 people. It concluded a catalogue of basic errors made by Malaysia Airlines staff, and other individuals and organisations, led to the situation occurring.
Here, we summarise the key findings from the full report:
What happened in brief
On 18 July 2018, a Malaysia Airlines Airbus A330, registered 9M-MTK, took off from Brisbane to Kuala Lumpur in Malaysia, with 14 crew and 215 passengers on board. However, covers had been left on the aircraft’s three pitot probes (airspeed sensors).
The instruments (onboard in the cockpit) showed a red speed flag in place of the airspeed indication from early in the take‑off, and unrealistically low airspeeds afterwards.
The flight crew did not respond to the speed flags until the aircraft’s speed was too high for a safe rejection of the take-off, and the take‑off was continued. The flight crew’s initial radio announcement of an urgency situation was not heard by the air traffic controller.
The flight crew climbed to 11,000 feet and circled while performing troubleshooting and other procedures, which led to the shutting down of the aircraft’s air data systems. Doing so activated the back up speed scale (BUSS), a safety function that displayed safe flight envelope information to the flight crew in lieu of airspeed. Using this system, airspeed management procedures and assistance from air traffic control, the flight crew conducted an approach and landing at Brisbane.
For technical reasons, the main landing gear doors did not retract and were slightly damaged on landing. Also, nose wheel steering was not available, and the aircraft remained on the runway for a short period before being towed to the gate.
‘Forgot about the covers’: Ground operations and pre-flight walk-arounds
A support engineer placed covers on the aircraft’s three pitot probes (airspeed sensors) to prevent these from becoming blocked by wasp nests (a particular hazard at Brisbane Airport). The operator’s (Malaysia Airlines) certifying engineer, who was primarily responsible for the aircraft’s airworthiness, did not initially know about the covers due to a miscommunication with the support engineer who had fitted them.
The flight crew, engineers and dispatch coordinator were required to conduct various pre‑departure checks, meant to identify aircraft damage or other unsafe conditions such as the fitment of pitot probe covers. However, these checks were omitted entirely or only partially completed, for a variety of reasons including inadequate communication and reduced diligence. On other turnarounds from the same operator, some flight crew, engineering and dispatch walk-around checks were also omitted or incomplete.
The certifying engineer saw the covers early in the turnaround but later forgot about them and there was ambiguity around the division of responsibilities with regard to the final walk-around portion of the transit check.
The support engineer who had fitted the pitot covers left to work on another aircraft and was unable to return before the occurrence aircraft was dispatched. There was no reliable method to ensure the return of tools and equipment before an aircraft departed.
The ATSB identified that the pitot probe covers used, which were different to those approved by the aircraft manufacturer, had streamers that were not prominent enough to be noticed by ground crews during incidental activities, including pushback, and so increased risk during turnarounds if other methods of ensuring their removal were not effective.
Surprise, uncertainty, time pressure and ineffective communication between the two pilots during the take-off probably led to stress and high cognitive workload. The captain, as pilot monitoring, did not assertively announce the presence of a problem or clearly specify its nature when it was detected, delaying the first officer’s response. Then, although the captain and first officer attempted to convey information about the airspeed issues, there was limited coordination between them which reduced their capacity to interpret the situation and make a decision early enough to safely reject the take-off.
Pilots are trained to monitor airspeed on take-off, and Airbus recommends that pilots reject a take‑off if unreliable airspeed is identified early enough for this to be a safe action. However, take‑offs have sometimes been continued, or rejected at high speed, even with multiple airspeed anomalies. This suggests that the flight crews involved were not detecting unreliable airspeed early enough in the take-off, or if they did, other factors prevented or delayed a decision to reject the take-off.
The ATSB found that aircraft alerts related to unreliable airspeed were either not available during take-off or were not prominent enough to gain both the flight crew’s attention in a manner that the presence and importance of the problem were both immediately apparent.
In addition, there was limited guidance provided to flight crews to aid in the detection and decision-making processes in response to unreliable airspeed indications. For example, there was no clear guidance to flight crews whether the failure of a single airspeed display should result in a rejected take-off when below a nominal speed, which can leave the flight crew in a difficult position when identifying such a problem when approaching the decision speed.
‘Someone else’s responsibility’
At first glance, an observer might be puzzled as to how multiple checks can fail to detect the fitment of pitot probe covers before flight, or how a flight crew can complete a take-off without any valid airspeed being displayed. This occurrence illustrates how a range of individually straightforward factors can combine to nullify multiple critical safety barriers.
For all individuals working in the aviation industry, the occurrence shows that coordination and diligence can make a difference. Several individuals on the night—as well as their counterparts on other occasions—all acted as though the conduct of various external aircraft inspections was someone else’s responsibility; in fact, all had separate, key roles in detecting problems with the aircraft before departure. Had all such inspections been conducted diligently it is very likely that the pitot probe covers would have been seen and subsequently removed.
Most of these problems could have been resolved with better communication. Nevertheless, the working environment allowed errors and miscommunications to occur and propagate because individual responsibilities and work processes were not well-defined.
For flight crew, the occurrence also highlights the importance of vigilance, communications and decision-making in adverse circumstances. Had the flight crew reacted more quickly, the take-off could have been rejected at low speed. Flight crews need to bear in mind the typical symptoms associated with unreliable airspeed on take-off in order to detect this situation as early as possible and reject the take-off if still safe. If uncertain of the aircraft’s proximity to the decision speed when an anomaly is detected, Airbus flight crews should immediately apply full take-off thrust and attain 15 degrees pitch attitude when they feel that the aircraft is close to the rotation speed to maximise aircraft performance.
However, the flight crew’s delayed response vividly illustrates the falsity of the assumption that flight crews will always act as expected. Accordingly, the contribution of aircraft warning and indication systems design, combined with flight crew training and guidance, must be considered. Flight crews need to have information presented in a way that the importance of an adverse event, and possibly the right decision, is immediately apparent.