Aircraft Alternator
Maintenance Manual
24-30-01
ES1031
Page: 6-16 Rev.
B: 20 Apr. 2022
© 2022 - Hartzell Engine Technologies - All rights reserved
(2) If “sudden stoppage” as defined by the engine manufacturer has occurred or if a sudden stoppage has
caused the belt to twist or come off, the alternator must be inspected. Refer to the appropriate engine
or airframe manuals to remove the alternator. Check the following:
(a) Belt - remove belt - check for flat spots, cuts, or broken fabric.
(b) Pulley - check for damage such as bending or scarring. Check for pulley grove for damage. Make
a run out check on the face of the pulley to check for alteration of the pulley due to bending.
Refer
to section 5.3(G) for checking pulley run out.
Check appropriate engine or airframe manuals
for run out spec’s as many pulleys ARE NOT supplied by HET.
(c) Alternator Fan - with belt removed, spin the pulley to check for alternator external fan or back plate
wobble. Refer to section 6.4(B) for inspection of the external fan.
(d) Alternator - with belt removed, snap spin the pulley to check for interference between the rotor and
stator and to check for bearing noise. Refer to section 5.2(B) for checking the bearings.
(e) Pulley Nut - check for fractures and assure proper torque at the completion of these procedures.
(f) Brushes - remove brush holder and brushes to check for broken or chipped brush, and other
damage. Refer to section 5.2(F) for brush holder and brush checks.
(g) If you find damage in step (2), b through e, repair, overhaul, or replace the alternator. In addition, all
supporting bracketry or mounts associated with the alternator should be inspected in accordance
with the appropriate engine or airframe manuals. Assure all steps are taken to properly return
the aircraft to service.
C.
Lightning Strike
NOTE:
For engine OEM’s Special Condition “Lightning Strike”, refer to the latest revision of
Lycoming Engines, Inc. SB 401 or Continental Motors, Inc. SB 88-9.
(1) Lightning strike is a very unpredictable event both in occurrence and in resultant damage. A
lightning bolt entry point may have many exit points or only one. On a well bonded aluminum
aircraft, the lightning bolt will stay on the outer surface throughout the aircraft with little damage to
components. The path of the electrical current cannot easily be determined in most cases because
while the current may surge through well bonded areas without damage, a gap in any metal contact
point will result in an arc or flash burn. This is especially true of rotating parts such as gears or
shaft.
(2) If a report of a potential or actual lightning strike is made the first thing to do is to inspect the aircraft
for entry and exit points for the lightning bolt. The purpose is to assure that there was indeed a strike.
The points of entry or exit are generally on the aircraft extremities such as the wing tip, propeller tips,
spinner tip or the tips of tail surfaces. Commonly, the entry point is a single burn mark and the exit
several burn marks or burnt static wicks. This discussion is important because if there was a strike it
may have coursed through the engine. Cowlings, especially fiberglass or other non-metallic types may
not have as good a bond. Many cowlings will not be well bonded due to frequent removal. This many
times will force the electric charge to take a route through the engine components. Lightning will arc at
any gap where the path of resistance is less that the surrounding air.
