A 737 aircraft landed at an airport near the Caspian Sea. 142 passengers had departed along with the 5 crew members. The crew reported that the cabin oxygen pressure was at 900 psi. The ground crew was attempting to trans fill the oxygen from an 1800 PSI oxygen source. It is reported that the ground crew tested the equipment to assure the supply gas was at 1800 psi. They disconnected the cabin oxygen regulator assembly and attached the equipment to transfer the oxygen to the depleted system.
During this operation, a spark occurred starting the combustion process. An explosion was then reported with fire destroying the fuselage. It is reported that the technicians jumped from the plane to turn off the supply oxygen, but it was too late. It took 5 minutes for firefighters to arrive and extinguish the fire. The aircraft was destroyed.
The investigation concluded that the aircraft was a total loss. They attributed the fire/explosion to a damaged oxygen line combined with hydrocarbons. The investigation also recommended that employees get proper training on checking oxygen systems and locating “peculiarities”.

Monday Morning Quarterback:
Reading the limited details of the incident, the crew reported low pressure in the oxygen system. There did not appear to be any report of the emergency oxygen being used. The first question a fill technician should ask is “why is the system losing pressure?” Taking time to locate the cause of the leak may disclose damaged or malfunctioning equipment.

Finding damaged lines on a high-pressure oxygen system would indicate a different approach than simply re-filling the leaking system. When dealing with any high-pressure gas system, operators require proper training. They must understand the components, proper operation, and associated risks. The technician should feel comfortable asking questions before continuing with a process. Providing a quick solution without understanding the underlying cause of a problem can be very risky.