Pilot fatigue and distraction have been identified as the primary factors in a 6 January 2018 air proximity incident between two aircraft operated by Indonesia’s Lion Air Group.
In its final report on the incident, Indonesia’s National Transport Safety Commitee (NTSC) says the incident involved a Batik Air Airbus A320 (PK-LUI) and a Lion Air Boeing 737-900ER (PK-LPF) that were asked to hold before landing at Surabaya’s Juanda International Airport.
At 10:16 local time, air traffic control (ATC) instructed the Lion 737, operating flight LNI3795 from Sentani, to enter a holding pattern at 10,000ft over waypoint TIRUS.
One minute later the Batik A320 crew, operating flight BTK6137 from Makassar, was also instructed to enter a holding pattern over TIRUS. Cognizant of a potential conflict, ATC instructed the A320 to hold at 11,000ft, ensuring separation.
“At 10:20:15, the [Batik A320] passed altitude of 11,000 feet while the [Lion 737] was maintaining on altitude 10,000 feet, and then the Short-Term Conflict Alert of the controller radar system for the [Lion 737] and [Batik A320] activated with aural and visual alert,” says the NTSB.
The crews of both aircraft received traffic collision alert system (TCAS) warnings, and reacted to reestablish separation. The closest separation was 1.9nm laterally and 600ft vertically.
Analysis of the Batik A320’s flight data recorder showed that immediately before the incident the Flight Control Unit was set to 11,000ft, the correct altitude, but one second later changed to the incorrect altitude, 10,000ft.
Interviews with the Batik crew revealed that they had operated an overnight service the evening of 4 January. Despite a day of rest on the following day, this overnight service could have contributed to fatigue when the crew reported for BTK6137 early the morning of 6 January.
The first officer, who was the pilot flying during the incident, reported feeling sleepy during the flight. The captain, who was the pilot monitoring, meanwhile said that his mind was on an illness in the family. The mental state of both was dulled by a period of low workload in the cockpit.
Following the incident, Batik Air reminded its pilots maintain situational awareness, and if the crew has any doubts as to ATC clearances, they need to check with ATC.
The NTSC issued safety recommendations to Batik and the Directorate General of Civil Aviation. It suggested that Batik establish fatigue risk management based on ICAO fatigue guidelines, and that the DGCA issue more detailed guidelines about fatigue management.