What happened
On 5 August 2021, an Agusta AB139 helicopter, registration A6-AWA, operated by Abu Dhabi Aviation, was preparing for a visual flight rules (VFR) mission to the NASR offshore oil complex. During the departure sequence at Abu Dhabi International Airport, a military fixed-wing aircraft was cleared for takeoff from runway 13R. Shortly after, the A6-AWA crew initiated their takeoff from the helicopter pad (FATO 13).
As the helicopter climbed and began a left turn, it intersected the flight path of the military aircraft. Radar data indicated that the two aircraft reached a vertical separation of only 100 feet at their closest point of approach, with a horizontal distance of approximately 1.07 nautical miles. The military pilot subsequently reported the close proximity to radar control.
The investigation
The GCAA AAIS investigation focused on the sequence of events leading to the unauthorized departure. Investigators examined ATC communications, radar screenshots, and flight records. The investigation established that the helicopter crew had not yet switched to the Tower South Control frequency when the controller issued takeoff clearances to other aircraft. Consequently, the crew missed critical instructions regarding the military aircraft's departure.
Findings
- The A6-AWA crew mistakenly believed they had received takeoff clearance, having misidentified a clearance issued to a different helicopter as their own.
- Expectation bias played a significant role, as the crew perceived the instruction intended for another aircraft to be directed at them.
- The similarity in callsigns within the Abu Dhabi Aviation fleet, which often differ by only a single character, contributed to the confusion.
- The Tower South controller was managing multiple tasks, including ground vehicle communications, which reduced situational awareness and prevented the timely interception of the unauthorized takeoff.
- The primary cause of the incident was the unauthorized takeoff of the helicopter, which directly interfered with the climb path of the military aircraft.