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Bonding jumper across avionics shock mounts

Aviation Mechanic Airframe (AMA) practice question 8 of 26 on Communications, Light Signals, and Runway Lighting Systems. ACS element AM.II.I.R5 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONWhy must an electronic unit installed on shock mounts be connected to aircraft structure with a bonding jumper?

  1. AThe jumper carries cooling air past the mount.
  2. BThe shock mount material is an insulator.
  3. CThe jumper holds the unit during landing shock.
Show the answer and explanation

Correct answer: B. The shock mount material is an insulator.

  • A — incorrect Cooling is handled by conditioned air, a blower or ducted ram air over the equipment, not by a bonding conductor.
  • B — correct Shock-absorbing materials used in shock mounts are usually electrical insulators, so the unit must be bonded to structure to provide a current path to ground.
  • C — incorrect Mechanical retention comes from the mounting bolts and locking devices; the shock mount itself absorbs landing shock and vibration.

BACKGROUND

Avionics equipment is sensitive to mechanical shock and vibration and is normally shock mounted for protection against in-flight vibration and landing shock. The shock-absorbing materials commonly used in those mounts are usually electrical insulators, so each electronic unit mounted on shock mounts must be electrically bonded to a structural member of the aircraft to provide a current path to ground. This is accomplished by securely attaching a tinned copper wire braid from the component, across the mount, to the aircraft structure; solid aluminum or copper is used occasionally where a short flexible strap is not possible. Bonding provides a low-impedance ground return and prevents the build-up of electrical potential, and it also serves as the low resistance return path for single-wire electrical systems. Bonding jumpers should be as short as possible, with finishes removed in the contact area so metal-to-metal contact exists.

STUDY TIP

Whenever you see a non-conductive mount in an electrical installation, expect a bonding jumper bridging it, and check that the contact surfaces are bare metal.

KEY POINTS

  • Shock mount material is an electrical insulator, so it breaks the ground path.
  • A tinned copper wire braid bonds the unit across the mount to structure.
  • Bonding gives a low-impedance ground return and prevents electrical potential build-up.

SOURCES

  • ama-airframe/ch11.txt "Vibration Isolation"
  • ama-airframe/ch11.txt "Bonding"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.