Accident Overview
On 19 April 2017, at 13:30 local time, Thai Smile Airways flight WE291, an Airbus A320-200 registered HS-TXB, was parked at stand B-2 at Suvarnabhumi Airport preparing for departure to Narathiwat Airport. A mobile belt conveyor operated by ground staff from Thai Airways International Public Company Limited was being used to load luggage. The conveyor scraped the aircraft's lower fuselage, causing a long scratch. No injuries were reported.
Sequence of Events
According to the investigation, the mobile belt conveyor was initially positioned at the forward compartment to load luggage. After adjusting the belt to normal level, the driver moved the conveyor to the aft compartment. He slowed down and applied the brake about 3 meters before reaching the aircraft, stopping one meter away. He set the equipment to cargo area level, placed the transmission shift lever in neutral, pulled the handbrake, and positioned chocks in front and behind the wheel. He then left to attend other flights.
Approximately 15 minutes later, a ground staff member from another unit noticed the conveyor was parked on the opposite side of the aircraft. He asked the loader, who was working in the aft compartment area. The loader, who was not responsible for driving or adjusting the conveyor, was sitting on it and reached to lower the belt level. However, he inadvertently shifted the transmission shift lever to the forward (D) position instead. This caused the conveyor to move forward, and its beacon light scraped against the aircraft's lower fuselage.
Damage and Repairs
The aircraft sustained a scratch 10 millimeters wide and 1,040 millimeters long at frame FR55 between stringers STGR39R and STGR40L. The mobile belt conveyor's beacon light was bent approximately 30 degrees rearward. The conveyor was otherwise in good condition. The damaged aircraft parts were repaired in accordance with Repair Design Approval Data Sheet RDAS Ref. 80297228/003/2017, a major repair procedure that involved polishing and installing Hi-Lok fasteners.
Personnel and Equipment
The loader held a loader permit issued by Suvarnabhumi Airport. The mobile belt conveyor's transmission shift lever was marked with D, N, and R. A test conducted after the accident showed that when chocks were placed normally (close to wheels), shifting to D did not move the conveyor. However, if chocks were placed slightly away, the conveyor could move forward slightly. The chock used on the day was reported to be worn and smaller.
Probable Cause
The investigation determined that the loader inadvertently shifted the Transmission Shift Lever to the forward position while attempting to lower the belt level, causing the mobile belt conveyor to move forward and scrape the aircraft lower fuselage.