What happened
On 18 January 2014, an Etihad Airways Airbus A319, registration A6-EID, arrived at Abu Dhabi International Airport from Minsk, Belarus. Following passenger disembarkation, a maintenance team began scheduled daily and transit checks. During these procedures, an engineer identified that the flight crew oxygen system pressure was at 1450 psi, which fell below the required 15/00 psi threshold for dispatch.
While a technician was assisting with the in-situ oxygen servicing, the pressure regulator transmitter (PRT) exploded. The event produced a loud bang, a flash of light, and a rapid depressurization of the oxygen bottle. The sudden discharge caused minor facial irritation to the maintenance engineer. The technician immediately halted the oxygen supply, and the aircraft was subsequently de-powered. The engineer was treated at a hospital for minor skin and eye irritation.
The investigation
The GCAA AAIS investigation focused on the mechanical failure of the oxygen components and the procedures used during servicing. The aircraft was moved to a maintenance facility for quarantine, and the oxygen cylinder, regulator transmitter, and associated plumbing were sent to the manufacturer in France for analysis.
Investigators utilized CT scans of the cylinder valve, which revealed that the stem had partially melted and the outlet filter had been destroyed. The investigation examined two potential ignition scenarios: mechanical impact from component chatter or adiabatic compression. By analyzing the pressure readings and the sequence of events, investigators determined that the fire likely originated at the filling valve of the PRT.
Findings
- The primary cause of the fire was adiabatic compression within the filling line.
- This compression occurred because the quick-acting toggle (QA) valve was opened after the servicing trolley regulator had already been pressurized to 1600 psig.
- This sequence of operation deviated from the manufacturer's user instructions, which advise increasing pressure slowly to avoid rapid pressurization.
- The sudden pressure surge caused temperatures to spike to approximately 800°C at the PRT filling port, initiating a fire that spread through the PRT body and the cylinder valve.
- The fire created a kindling chain involving the O-ring, poppet, spring, and the aluminum body of the PRT.
Safety action
Following the incident, the operator implemented several safety measures:
- Issued a Quality Notice regarding the introduction of new oxygen servicing tool kits.
- Established new maintenance instructions to prioritize the replacement of crew oxygen bottles.
- Developed and approved a specialized oxygen servicing and maintenance training program for all maintenance personnel.
- Revised the operator's maintenance organization exposition (MOE) to incorporate the new training syllabus.