The project

Over pressure protectors (OPPs) are safety devices installed in aircraft fuel tanks to protect the aircraft structure from overpressure if other primary means of system protection fail.  Some OPPs utilise frangible carbon discs that are designed to rupture at a specific pressure to provide immediate pressure relief.

• A particular aircraft had suffered a number of unexplained in-service failures of this device type and a root cause analysis was requested by the client.
• The investigation was complicated owing to the absence of direct evidence pointing to the cause of failures; a fish bone analysis was used to explore possible failure causes.
• The fishbone analysis resulted in a wide-ranging investigation considering many factors associated with the equipment design and manufacture, aircraft systems operation, aircraft in-service operation, including airport refuelling procedures.
• The investigation required a managed collaborative approach involving the operator, the equipment supplier, client customer service and systems engineering resource. The team worked closely together to manage both the implications of the failures and determine the most probable root cause.
• A design and performance comparison with other types of frangible OPP devices was undertaken, and this led to the failing equipment being replaced with a different type of OPP that had both equivalent performance and improved reliability.