Avionics Technology: What to Do When . . .

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.

These type devices can often wreak havoc on open aircraft. Having witnessed an aircraft with the nose avionic compartment, main cabin door, and the avionics rack under the entry way floor all opened while being pummeled by fire suppressant cannons I learned the devastation that can ensue. One observation was how the agent was propelled into any and all openings including cooling ports and non-sealed covers. Once inside an avionics box the only real alternative is to remove the component and send it out for evaluation.

Clean what you can

In some cases, electronic components may be cleanable. Strangely enough clean water and mild soap will often serve as a good means of eliminating dirt and grime on circuit boards and I have been in more than one avionics shop where an automatic dishwasher is employed for doing more than cleaning the dirty lunch dishes.

This is by no means a recommendation to take any sort of aircraft computer down to the local restaurant and place them in the hands of a professional dishwasher. It should also be noted that anytime maintenance is performed on any component going in an aircraft; performance testing needs to be accomplished to ensure the component is capable of achieving the desired results.

Check seals and test airworthiness

Electrical connectors are another area of concern. Some are well sealed while others may allow moisture ingress to either the mating area or the back shell. A good rule here: if there is a sign of exposure to contaminants on the outside of the plug it is probably justified to look on the inside. The same rules apply with removed components, if the circuit is broken, there is a chance of introducing a problem and testing for proper operation should follow.

Regardless of the type of exposure all external probes should be checked. In the case of pitot static systems a comprehensive visual inspection may reveal the extent of contaminants and in some cases a pipe cleaner or other nondamaging device can be inserted beyond normal visual range to check for traces of contaminants. It may be necessary to purge the plumbing of air data systems to ensure trapped moisture along with other foreign objects are evacuated and should of course be followed by testing in accordance with appropriate airworthiness requirements.

Air data probes such as temperature sensors may contain hidden chambers requiring a more comprehensive evaluation and cleaning. Also, angle of attack vanes often have pivot mechanisms supported on very fine bearings; if there was a chance of fire retardant ingestion then the component manufacturer should be contacted for an approved method of component validation.

Antenna bases are another area of concern. In the event of an imperfect seal with the aircraft skin the chemical agent may travel under the antenna and start some type of electrolysis process. If a seal around an antenna base is questionable it is usually justifiable to remove the antenna, inspect the area, restore appropriate protection, and test the system.

Static dischargers must also be considered. Even though they may have appeared to weather the fire suppression storm, there may be contamination in the mounting area either between the probe and base or the base and aircraft skin. A comprehensive external bonding check is usually a viable procedure to accomplish when an aircraft is exposed to certain extinguishing agents.

Positive note

Our recent event ended on a positive note and although it did disrupt a weekend we did not find any significant issues plus our aircraft received a nice wash job along with an unscheduled lubrication.

I have learned from this and other previous events that it is always best to leave the aircraft with as many protective covers installed as practical and anytime avionic sensitive access panels are exposed it is worth covering them with some form of protection even when the main compartment can not be secured. This is one way to help ensure the outcome may be an inconvenience versus a disaster. AMT

Jim Sparks has been in aviation for 30 years and is a licensed A&P. He is the manager of aviation maintenance for a private company with a fleet including light single engine aircraft, helicopters, and several types of business jets. He can be reached at sparks-jim@sbcglobal.net.