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Service Bulletin 177B replaces Service Bulletin 177A dated August 28,1990.
This version clarifies general inspection procedures, particularly as
they pertain to blades versus other propeller components. **
indicates changes.)
This service bulletin details the necessary and required inspection
criteria for McCauley propellers following a suspected lightning strike.
Determination of Lightening Strike:
**If doubt exists as to the occurrence
of a lightning strike, the following criteria can be used to verify any
suspicion:
- Check for burns or signs of arcing on blades and hub.
- Using a magnetism detector, check all exposed steel areas of propeller
for magnetism.
- Look for any signs of localized melting or metal flow, particularly
on blades.
**(Please note that the above definition
is intended for use as example only. Determination as to whether or not
a "lightning strike" actually occurred is ultimately the responsibility
of the operator.)
If preliminary inspection suggests and actual strike, the following steps
are to be performed:
Procedure:
Complete propeller overhaul is to be accomplished as per the applicable
McCauley overhaul manual. During the overhaul inspection procedure, the
following additional investigations should be performed:
**Check propeller
components, other than blades, for indications of lightning entrance or
exit.
Determination:
Carefully inspect propeller components (other than blades) for the presence
of a small, dark, discolored area. Some erosion and/or localized metal
flow (melting) will possibly be present.
Correction:
Any non-blade components showing signs of damage as described above are
considered unairworthy and should be scrapped.
**Inspect
all non-damaged steel components for signs of magnetic charge.
Determination:
Check all suspected components using any standard magnetic detection device.
Correction:
All components showing any signs of magnetic charge should be completely
demagnetized using an GAA approved method.
**Inspect blades
for indication of lightning entrance or exit.
Determination:
This damage will be evident, in most cases, by the presence of a small,
dark, discolored area. Some erosion and/or localized metal flow (melting)
will possibly be present.
Correction:
All lightning damage indications must be removed from blade prior to return
to service as follows:
- All burn indications must be removed using mill file, sand paper and/or
crocus cloth.
- **Following damage indication
elimination, remove and additional .020" of material from the affected
area.
- Following material removal, perform a dye-penetrant inspection on
the affected areas per MIL-STD-6866.
- **If any indications of cracks
or other flaws are found, additional material must be removed until
all indications are gone.
- Inspect blade per the appropriate overhaul manual. If blade is found
within dimensional limits, it may be returned to service.
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