What happened
On 28 February 2020, a Sigma Airlines Airbus A300B4-203F, registration UP-A3003, arrived at Sharjah International Airport from Juba, South Sudan. During the descent phase of the flight, the aircraft encountered moderate turbulence, which triggered a fracture in a high-pressure filter head within the yellow hydraulic system. This failure caused a rapid drop in fluid levels, illuminating the HYDRAU warning light and disconnecting the autopilot.
Despite the hydraulic issue, the flight crew completed the landing and taxiing to the cargo apron without further incident. Upon reaching the parking bay, the commander brought the aircraft to a stop and began the parking checklist. While the crew prepared to shut down the engines, the aircraft unexpectedly began moving forward, propelled by engine idle thrust. The commander attempted to use manual brakes and set the parking brake, but the aircraft failed to stop. In an effort to avoid a nearby cargo hangar, the commander steered the aircraft to the left, resulting in a collision with a parked tug.
There were zero fatalities among the five crew members on board, though the aircraft's left engine, pylon, and wing attachment sustained substantial damage, and the tug was also damaged.
The investigation
The GCAA AAIS investigation focused on why the aircraft became uncontrollable during the parking sequence. Investigators examined the hydraulic system and discovered that a fracture in the high-pressure filter head, combined with an undetermined failure in the system accumulators, had effectively disabled the parking brake.
Technical analysis also looked into the aircraft's maintenance history and the design of the filter head. The investigation found that while previous service bulletins had addressed bolt issues, the underlying design flaw regarding the flange radius remained a factor. Furthermore, the investigators reviewed the ground operations at the cargo bay, noting that the marshaller was not prepared with wheel chocks and that the lighting at the bay did not meet required intensity standards.