What happened
On 3 August 2017, a collision occurred on runway 23 at Kualanamu International Airport in Medan, Indonesia, involving two commercial aircraft. The first aircraft, a Boeing 737-900ER operated by Lion Air (registration PK-LJZ), was on final approach for landing with 151 people on board. Simultaneously, an ATR 72-500 operated by Wings Air (registration PK-WFF) was taxiing via intersection taxiway D to depart.
As the Boeing 73 and 900ER was on its landing approach, the air traffic controller issued a conditional clearance to the ATR 72-500 crew, instructing them to enter the runway only after the landing aircraft had passed. However, the crew of the ATR 72-500 entered the runway while the landing aircraft was still active. Shortly after touching down, the Boeing 737-900ER impacted the ATR 72-500. While there were no fatalities, both aircraft sustained substantial damage, and debris was scattered across the runway.
The investigation
The KNKT investigation utilized CCTV footage from the tower, flight data recorders (FDR), cockpit voice recorders (CVR), and interviews with personnel to reconstruct the sequence of events. The inquiry examined the movement of both aircraft, the effectiveness of air traffic control attention, the clarity of the conditional clearance provided, and the identification of hazards on the runway.
Findings
- The primary cause of the accident was a communication misunderstanding regarding the conditional clearance. The pilots of the ATR 72-500 were not aware that the Boeing 737-900ER had been cleared to land.
- The air traffic controller's movement of the ATR 72-500 was unobserved, which allowed the aircraft to enter the runway into the path of the arriving flight.
- There was a lack of specific procedures for air traffic controllers to provide extra precautions when departure aircraft use rapid exit taxiways (RET) under conditional clearances.
- The existing standard operating procedures (SOP) for air traffic services were found to be insufficiently detailed regarding the execution of conditional clearances.
Safety action
Following the incident, AirNav Indonesia updated its air traffic services SOP to better align with ICAO standards and include more specific requirements for conditional clearances. The airline operators, Lion Air and Wings Air, issued various notices to pilots emphasizing the importance of situational awareness, sterile cockpit procedures, and the necessity of verifying all ATC instructions before proceeding.