Factual Information
The incident occurred on 23 January 2021 involving SriLankan Airlines flight UL1430, an Airbus A330-300 registered as 4R-ALP, parked at Bay C21 at Bandaranaike International Airport, Katunayake, Sri Lanka. The flight was scheduled as a cargo operation from Colombo to Singapore. The aircraft had two flight crew and a cabin supervisor (acting as purser) on board. The cabin supervisor completed safety and security checks, then closed and armed the L1 door at 1113 hours local time, after obtaining permission from the pilot-in-command. The cabin supervisor then went to the flight deck. Shortly after, she heard a noise from the forward area and found the L1 door open with the slide pack resting on the passenger step. A junior aircraft mechanic was standing near the door. There was no damage to the aircraft and no injuries reported. The aircraft departed after a 41-minute delay under Minimum Equipment List provisions.
Analysis
The cabin supervisor had conducted her security check from the rear forward, not physically verifying the area near R1 door before arming the L1 door. She made a public address announcement for ground personnel to disembark, but the first officer reported hearing it only faintly. A junior aircraft mechanic, who had been repairing life vest covers in business class, did not hear the announcement. The approval holder on the apron called the mechanic to disembark, prompting him to rush to the L1 door and open it without checking its armed status.
Conclusion
The investigation concluded that the L1 door was opened while it was armed, causing the slide to deploy. The mechanic was unaware that the door had been armed and failed to verify its condition before opening.
Probable Cause
The probable cause of the incident is that the L1 door was opened while it was armed (slide girt bar connected to the floor) without first disarming the door as per the procedure, while a mechanic was still on board after a security check had been completed and the door had been armed.