Factual Information
On 24 November 2018, a Pakistan International Airlines Corporation (PIAC) ATR 72-212A, registration AP-BKW, was conducting engine performance ground run-up checks at Jinnah International Airport (JIAP) in Karachi. The aircraft had recently undergone both engine replacements and a scheduled Check-A inspection. During the run-up, while at maximum reverse setting, the aircraft initially rolled rearward approximately 10 feet before moving forward due to incorrect selection of engine controls. The parking brakes were engaged and pedal brakes were applied, but the aircraft did not stop. The wheel chocks used were smaller than the recommended size. The maintenance engineer was unable to regain control, and the aircraft traveled forward about 450 feet.
During its forward movement, the left wing tip first struck a dormant Shaheen Air International (SAI) B737-400 (AP-BJT) between the captain and first officer windshields. The aircraft then hit the nose radome of another dormant SAI B737-400 (AP-BJU). The rotating No. 1 engine propeller became embedded in the fuselage of the second parked aircraft, at which point the ATR came to a stop. The collision caused substantial structural damage to all three aircraft.
A senior technician seated on the observer seat sustained a minor injury to his left leg due to the sudden stop. Post-accident X-ray revealed no abnormalities. The aircraft had been grounded since 31 August 2018 (84 days prior) for Check-A maintenance, during which major components including brake assemblies, engines, and propellers were cannibalized for other aircraft. These components were reinstalled during recovery.
Analysis
Following the Check-A maintenance and component reinstallation, hydraulic brake system high-pressure line bleeding was required per maintenance procedure JIC 32-42-00-BLD-10010. The aircraft technical logbook documented tasks related to brake bleeding and operational checks, but the investigation determined that the bleeding or purging was either not performed or performed inadequately. This resulted in brake failure during the ground run-up checks. Flight data recorder data showed brake pressure remained between 39 and 45 psi throughout the run-up, far below the required 3,000 psi. Additionally, the aircraft moved forward due to wrong selection of engine controls, which, combined with ineffective brakes, led to the uncontrolled forward movement.
Cause
The Safety Investigation Board concluded that the accident resulted from inadequate brake system bleeding/purging after maintenance, leading to brake failure, and wrong selection of engine controls during the ground run-up.
Safety Recommendations
The report includes safety recommendations directed at PIAC engineering management, line maintenance, and quality assurance to prevent recurrence of similar events.