What happened
On 11 May 2018, two commercial aircraft experienced a significant loss of separation near Tambolaka Airport, Indonesia. The first aircraft, a Garuda Indonesia Bombardier CRJ1000 (registration PK-GRJ), was preparing for departure on flight GIA460. Simultaneously, a Wings Air ATR 72-500 (registration PK-WFW) was operating flight WON1921, arriving from Kupang and preparing to join the circuit for runway 10.
During the takeoff roll of the PK-GRJ, the crew of the PK-WFW reported they were joining the left downwind for runway 10. However, the crew of the PK-GRJ believed the incoming traffic would join the right downwind. Shortly after the PK-GRJ climbed to approximately 600 feet and executed a standard left turn, the Traffic Collision Avoidance System (TCAS) on both aircraft triggered a Resolution Advisory (RA). The pilots of both aircraft successfully executed the prescribed maneuvers, and no injuries or aircraft damage occurred.
The investigation
The KNKT investigation focused on the communication between the pilots and the Aeronautical Communication Officer (ACO) at Tambolaka, as well as the internal cockpit coordination of the departing aircraft. The investigation examined the flight data and cockpit voice recordings to determine why the aircraft paths converged.
Investigators found that the service provided at Tambolaka was Flight Information Service within Class G airspace, which does not include separation responsibility. However, the use of certain phraseology by the ACO led to confusion regarding the nature of the service. Furthermore, the investigation looked into the health of the PK-GRJ pilot, noting that the pilot had been hospitalized with typhoid shortly after the incident, which may have impacted performance.
Findings
- The primary cause was the pilot justification based on unverified information, where the PK-GRJ crew acted on an incorrect assumption regarding the PK-WFW flight path without proper verification.
- A lack of effective Crew Resource Management (CRM) on the PK-GRJ meant that the Pilot Monitoring (PM) failed to challenge the Pilot Flying's (PF) incorrect assumption that the traffic would be on the right downwind.
- Ambiguous communications from the ACO, which occasionally used instructional phraseology, created a risk that pilots might mistakenly assume separation services were being provided.
- The pilot of the PK-GJR may have experienced degraded performance due to an underlying medical condition (typhoid) present on the day of the flight.
Safety action
Following the incident, the Directorate General of Civil Aviation conducted surveillance of Aerodrome Flight Information Services to ensure standard compliance. The KNKT issued several recommendations, including the need for AirNav Indonesia to standardize phraseology to clearly distinguish between flight information and air traffic control services, and for aircraft operators to strengthen CRM and pilot self-assessment reporting for medical fitness.