Sunday 19 February marks the anniversary of a crash that serves as a grim lesson in the importance of clear communication in aviation.
On 19 February 1989, a Boeing 747 operated by Flying Tiger Line (a cargo airline not affiliated with Tigerair), was approaching Kuala Lumpur, Malaysia, on a short flight from Singapore. The crew were cleared to route direct to the Kayell (KL) beacon for a runway 33 approach.
The Aviation Safety Network’s record of the crash says, ‘While on the NDB approach, the crew were cleared to “… descend two four zero zero …” which was interpreted by the crew as “… to 400 …”. The aircraft descended below minimum altitude and crashed into a hillside at 600 ft (180 m) just before reaching the Kayell NDB, where minimum descent height was 2400 feet. The aircraft hit treetops and started to break up until bursting into flames.’ The crew of four were killed.
The cockpit voice recorder CVR transcript shows the North American crew having trouble understanding the accented English of the Malaysian air traffic controller (‘What did he say?’, ‘I don’t know’), and having to ask for instructions and questions to be repeated.
The CVR also reveals non-standard and inconsistent phraseology with altitudes sometimes described in the form ‘number-zero-zero’ (e.g. three five zero zero), sometimes ‘number-thousand, number-hundred’ (e.g. three thousand five hundred), and sometimes as ‘number-number hundred‘ (e.g. thirty-five hundred).
‘Descend and maintain two thousand four hundred feet’, was the correct phrase that might have saved flight 66.
There was also potential for confusion between the Kayell navaid and the abbreviation for Kuala Lumpur, which is KL. The crew, having inadvertently accepted a false mental model of their position, did not react to several ‘whoop-whoop, pull up!’ warnings from the ground-proximity warning system.
Flight Safety Australia looked in depth at aviation English in September–October 2012.