Aviation From My Rocking Chair: Electrical Bonding (What?)

Greetings, Chapter 430. As some of you know, I have been relying on articles I wrote originally in the 20th Century! Thank Heaven some things don’t change much. It seems that I have been stuck on electrical problems and troubleshooting lately. Bear with me one more time, and maybe next month will be different.

In a prior life I was an inspector for American Airlines and was asked one night to check a couple bonding jumpers attached to a 757 elevator. Aha! Electrical Bonding, that looks like an easy subject. Man, when I’m wrong, I’m really wrong! However, having already committed to this subject, let’s see if it’s possible to simplify a little.

An Electrical Bond is defined as any fixed union existing between two metallic objects that results in electrical conductivity between them. This can be either physical contact or from an electrical connection, i.e. bonding straps, clamps, jumpers, etc. O.K., why is electrical bonding so important to our aircraft? As anyone who has witnessed lightning can see, clouds can become highly charged with electrical energy. An aircraft (especially rotorcraft) in flight can also become very highly charged, primarily due to static electricity caused by atmospheric and slipstream effects. If an aircraft is improperly bonded, all metal parts will not have the same amount of charge. This causes a difference in electrical potential between various metal components.

When these charges neutralize along paths of variable resistance (such as intermittent contact caused by vibration or control surface movement) they produce electrical disturbance or noise in radio receivers. If the resistance between isolated metal parts is great enough, charges can accumulate until the potential difference becomes high enough to cause a spark. This could be very detrimental to the airframe, especially sensitive avionics or fuel tanks.

To my dismay, it would take more pages than I have available to cover this subject in our newsletter. However, I can list some of the reasons for electrical bonding in aircraft.

They are:

(1) To minimize radio and radar interference by equalizing accumulated static charges.

(2) Eliminate a fire hazard by preventing static charges from building up between two isolated members and creating a spark.

(3) To minimize lightning damage to aircraft or occupants.

(4) Provides a ground for proper function of radios.

(5) Provides a low resistance return path for single wire electrical circuits.

(6) Aids the effectiveness of ignition or radio shielding.

(7) Provides a means of bringing the entire aircraft to ground potential and keeping it there when not in flight.

Well, did that water your eyes as much as mine? To find out how to bond an aircraft, check out AC43.13-1c. With that troopers, class dismissed and Rick has left the building!

Rick Vaux TC 4130