Avionics Technology: What to Do When . . .

The fire alarm does not go off!


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.

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