JOINT BASE LEWIS-MCCHORD If an engine fire breaks out aboard a C-17 Globemaster III, aircrews have a system that allows them to extinguish the flames.
But that system would be useless without properly functioning engine fan duct fire seals; seals that, until recently, C-17 maintainers did not realize were critical for fire suppression. In January, a team of jet engine mechanics from the 62nd Maintenance Squadron here discovered a rubber seal protruding into the airflow of a C-17 engine. It was something they had not seen before. After being unable to identify the seal using a technical order, the group contacted Tech. Sgt. Joseph Bilger, 62nd Maintenance Squadron product improvement manager.
Together, they worked with engineers from The Boeing Company to identify the torn piece of rubber as a engine fan duct fire seal, which had not been properly identified as critical to fire suppression in the technical order. The seals are required to maintain the integrity of nacelle fire zones and were not specifically listed in current technical orders.
This is a big ordeal because a bad fire seal in an aircraft engine is a no-fly condition for the affected C-17, Bilger said. If one of these seals is bad, we have to ground the jet and fix it immediately.
The seals play a crucial role if the fire occurs mid-flight, specifically preventing air an accelerant to the flames from entering the engine. Once pilots become aware of an engine fire, they can deploy an extinguishing agent inside the engine to put out the fire. If the engine fan duct fire seals are torn, however, the agent would blow out of the back of the engine causing aircrews to lose their fire suppression capabilities.
The seals are important for two reasons, said Tech. Sgt. Joshua Taylor, 62nd Maintenance Squadron engineering and logistics liaison. They keep the air from blowing across a fire and they hold the extinguishing agent inside the engine to fully smother the fire.
When McChords product improvement section discovered that these seals had been improperly classified, Bilger initiated an urgent technical order change to correctly identify the seals fire suppression properties in the manual. This gained the attention of leadership at the Air Mobility Command who initiated a Crisis Management Team telephone conference with McChord Fields MXS leadership, Boeings engineers and members of the product improvement section.
During the teleconference, we agreed to add the fire seal inspection to the home station check work cards, Bilger said. Until we have a final fix or a solution in the TOs, we use engineering dispositions as guidance.
Since the discovery in January, McChord has had 120 engineering dispositions for repair. 62nd MXS maintainers conduct a home station check inspection on different C-17s every three days and have found anywhere from five to 15 bad seals on each plane. There are 19 seals inside of each engine and four engines on each aircraft. That means the maintainers are checking on almost 4,000 seals, one by one.
While it sounds bad, we have not lost a single mission since the finding, said Master Sgt. Dennis Kauffman, 62nd MXS engineering and logistics liaison.
The Air Force is now waiting for repair procedures and fly-back limitations to be added to the technical orders.
The Boeing Company currently has technical writers working on an updated technical order to explain why the seals are fire critical and how to fix them.