ATA 24

Electrical Performance Deterioration
Electrical gremlins have been teasing us since Benjamin Franklin hung that key on his kite string so long ago. With that in mind, I thought a quick refresher on the importance of proper grounding was in order. How many times has troubleshooting led us down the wrong path because of either a poor or non-existent grounding point? It is easy to forget the simple things when we are looking for power supply or component integrity, a blown fuse, or a popped circuit breaker. A simple ground connection overlooked can be a missed opportunity to look like a troubleshooting genius. Our venerable fleet of Westwind Aircraft has been in service now for quite sometime with the newest aircraft having more than 20 years of duty. With time, corrosion, dirt, vibration, and/or combinations thereof can play havoc on the overall performance of an electrical system. Anything that will increase the ground path resistance is a gremlin’s paint brush slowly eliminating the required bonding. It is important that electrical bonds are properly maintained in order to minimize radio interference due to precipitation of static electricity and to provide effective electrical grounding of the aircraft. Static discharge build-up, St. Elmo’s fire, and lightning strike damage potential are all affected by poor electrical bonding. Good electrical continuity is required between all wing panels, fuselage panels, doors, stabilizers, and flight controls. When inspecting the aircraft for continuity, the use of stainless steel test probes is recommended to ensure penetration of protective metal coatings and accurate resistance readings. It is also important to use calibrated testing equipment that is in good repair. Resistance of test leads and jumper cables must be subtracted from readings obtained to get the actual bonding resistances. For surfaces fitted with bonding straps, measure resistance across structures adjacent to the bond strap attachment points. Do not measure at either end of the strap at fasteners or terminal lugs. Visually check bonding jumpers to assure that they are not broken, frayed, or missing. If you’re new to the aircraft, you may not catch a missing jumper, but if the area looks to you like it should probably have one, check the manuals. The Aircraft Maintenance Manual (AMM) has the specific details for the correct resistance between each measurement point and the zero reference point; it will vary between bonded and un-bonded components and surfaces. Never leave it to memory. Always use the latest revision of the appropriate manual when working on an aircraft, as we continue to update and improve the manuals on a regular basis.