What happened
On August 24, 1999, at 12:36 local time, UNI AIR Flight 873, an MD-90-30 registered as B-17912, was completing its landing roll on Runway 21 at Hualien Airport, Taiwan. During the landing sequence, an explosion occurred in the forward section of the passenger cabin, immediately followed by the appearance of smoke and fire. The pilot responded by applying brakes to bring the aircraft to a halt on the runway and initiated an emergency evacuation via the passenger slides.
Emergency responders from both Hualien Airport and the local Air Force Wing arrived at the scene to combat the blaze, which was eventually extinguished by 13:45. While the upper portion of the fuselage sustained extensive damage, the crew of 6 and 90 passengers were successfully evacuated. The incident resulted in 28 injuries, consisting of 14 serious injuries and 14 minor injuries, with most victims suffering from burns. One passenger was struck by fragments ejected during the explosion.
The investigation
The investigation, led by the Taiwan Aviation Safety Council with support from the NTSB, FAA, and Boeing, examined the structural damage and the chemical nature of the items on board. Parallel criminal investigations by local prosecutors provided critical evidence, including a ruptured bleach bottle.
To understand the mechanics of the blast, the Chung Shan Institute of Science and Technology (CSIST) conducted simulation experiments. These tests focused on the interaction between leaking flammable liquids and electrical components. The experiments confirmed that gasoline vapors leaking from a plastic bottle could reach explosive concentrations within a stowage bin. Furthermore, the testing established that a short circuit from a 12V motorcycle battery could provide sufficient energy to ignite these accumulated vapors.
Findings
- The primary cause of the explosion was the presence of flammable gasoline inside bottles (disguised as bleach and softener) that had been sealed with silicone.
- A leak in one of these bottles allowed gasoline fumes to accumulate in the stowage bin.
- The physical impact of the aircraft landing caused a short circuit in a 12V motorcycle battery, which acted as the ignition source for the gasoline vapor.
- Security screening failures allowed both the prohibited corrosive substances and the prohibited motorcycle battery to pass through airport checkpoints.
- There was a lack of clear regulatory responsibility for hazardous materials management within the Civil Aeronautical Administration's organic regulations.