A320 / B739, en-route, northwest of Surabaya Indonesia, 2018

A320 / B739, en-route, northwest of Surabaya Indonesia, 2018

Summary

On 6 January 2018, a Boeing 737-900 and an Airbus A320 both inbound to Surabaya with similar estimated arrival times were cleared to hold at the same waypoint at FL100 and FL110 respectively but separation was lost when the A320 continued below FL110. Proximity was limited to 1.9nm laterally and 600 feet vertically following correct responses to coordinated TCAS RAs. The Investigation found that all clearances / readbacks had been correct but that the A320 crew had set FL100 instead of their FL110 clearance and attributed this to diminished performance due to the passive distraction of one of the pilots.

Description

On 6 January 2018, a Boeing 737-900 (PK-LPF) being operated by Lion Air on a scheduled domestic passenger flight from Sentani to Surabaya as LNI3795 and an Airbus A320 (PK-LUI) being operated by Batik Air on a scheduled domestic passenger flight from Makassar to Surabaya as BTK6137 lost separation in the TIRUS hold coming to within 1.9nm laterally when approximately 600 feet vertically apart. An ATC attempt to intervene after an STCA annunciation had occurred as the A320 descended onto the 737 was unsuccessful as both calls were ignored, but soon afterwards coordinated TCAS RAs were generated and followed and a closer conflict thereby averted. The two aircraft then completed their respective flights in sequence.   

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