Flight hour based requirements.
Inspections that are due after
an appointed number of flight hours.
For example, filter replacement,
Calendar based requirements.
Inspections that are due after the
expiration of days, months, or years.
For example, a fire
extinguisher weight check, or aircraft inventory inspection.
Combined calendar and flight hour requirements.
that have dual criteria flight hours and/or calendar time.
Inspections are due at the next flight hour or calendar time,
whichever comes first.
For example; the
requires a battery
check every 25-flight hours or every 30 days, whichever occurs first.
d. Rounds fired, cycles, starts, or HSF.
Inspections that are due
after an appointed number of rounds fired (weapons), cycles operated
(landing gear, fixed wing), engine starts or Hot Section Factor (HSF)
counts (OH-58D helicopter).
APU hours or APU starts.
Inspections that are due after an
appointed number of APU operating hours or APU starts.
Scheduling of Recurring Special Inspections.
inspections may be accomplished within a window of plus or minus 10
percent of the inspection interval, not to exceed five flight hours or
30 calendar days, unless otherwise stipulated in the individual
aircraft or system TM.
The importance of accomplishing and
documenting recurring special inspections and maintenance actions when
they are due is critical.
The tolerance window will not be used to adjust the due time
of any Phase/Periodic or any type of PMS inspection.
Tolerance window for flying hour based special inspections:
(1) The tolerance window for flying hour special inspections with
an interval of less than 50 hours is obtained by multiplying the hours
in the inspection interval by 10 per cent. For example, the tolerance
for an inspection with a 25 hour interval would be 2.5 hours (25 X 10%
Therefore, if the inspection is due at 1472.7 aircraft hours
the tolerance window starts at 1470.2 hours and ends at 1475.2 hours.
If the inspection is completed anywhere in that hour range (1470.2 --
1475.2) the next inspection due time will be 1497.7 (1472.7 + 25 =
1497.7) aircraft hours.