Avionics Technology: What to Do When . . .

The fire alarm does not go off!


It started out as a typical day in the world of corporate aircraft maintenance. The sun was shining, the grass was green, and the clouds all looked to be at peace. It was shortly after the midmorning break that the Blackberry came to life announcing my attention was needed.

The note came from the flight coordinator stating we just received notice one of the aircraft out on the road and assumed to be quietly at rest in a storage hangar had just been exposed to some fire retardant.

The FBO representative said this was a courtesy call and there was nothing to worry about as the aircraft had been splashed with some soapy water. How bad could that possibly be?

It was then the desk telephone rang, on the other end was one of the technicians from the breakroom. It seems that CNN was airing aerial video of a hangar (that looked a lot like one we use) full from floor to ceiling of a white foamy substance. After a few moments, movement was detectable at the marshmallowy fringe and distinguishable shapes began to appear. First, the back end of a tug, then the driver and eventually a long pointy thing vaguely resembling the front of an aircraft. It was about then that the clinging foam dissipated in the breeze and a very recognizable paint scheme appeared on the object being pulled from the abyss.

Know what you’re dealing with

We were able to get the FBO to send us the Manufacturer Safety Data Sheet (MSDS) for the suppressant foam and the initial review confirmed the presence of various salts along with glycol. It appeared that the safety risk to humans was relatively low but the agent was reactive in certain situations and possibly corrosive.

So, where do we go to find decontamination methods? There is some data available for dealing with biohazard events and decontaminating aircraft cabins but information pertaining to cleanup of residual fire suppressants is not within easy grasp. After perusing the MSDS further, we concluded the airframe and engine manufacturers should be consulted.

The MSDS did recommend the use of water for agent cleanup. We did authorize a thorough flushing of the entire machine with the stipulation that only a low pressure clean water rinse be used. I learned in a previous professional life that clearly defining expectation is an important thing. In certain coastal areas, ocean or sea water is very available and usually at a lower cost than fresh water. Of course washing an aircraft with saltwater is never a good idea.

In our case the incident had relatively minor impact. The aircraft was closed and none of the interior or avionic equipment was exposed to the fire retardant. We did have some infiltration into the engines but it was minor and by following the engine manufacturer’s inspection and cleaning recommendations we were able to return the aircraft to service within a relatively short time span. Another plus in our case is that the aircraft had been recently painted and many of the exterior access panels were still sealed preventing migration of the foam.

First, evaluate

So, what is the correct approach to an event involving aircraft exposure to fire retardant materials? First and foremost in my judgment is a thorough evaluation of the incident prior to taking action.

Take into account the type of fire suppressant used and the method of delivery. This may impact the ability of the aircraft to be extricated especially if the suppressant possesses any biohazard characteristics. There is also a risk of moving an aircraft to a location where rinsing is to occur and runoff could enter public waterways.

The foam we recently encountered is normally delivered from above using a deluge system and the main component is water. This foam didn’t have much of a tendency to migrate. That is, when discharged, the foam would not move into engine inlets or pitot and static ports.

Some hangars employ a cannon system for deploying fire suppression foam. These devices often pivot enabling delivery in a large arc with the discharge agent under pressure.

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