an aircraft is subjected to a depot level overhaul, before the end of
a cycle, the sequence number will be reset to number one.
sequence number will not be reset when only depot level repairs are
Depot level repairs must not be confused with depot overhaul.
A PM inspection is complete when all maintenance and inspection
requirements have been completed.
Progressive Phase Maintenance (PPM) Method.
a. This inspection method resembles the PM method; however, it is a
separate inspection method that must not be confused with the PM
This inspection method currently applies only to the OH-58D
The PPM inspection method consists of two
Part I is a series of separate progressive
inspection checklists that become due after a designated number of
Part II consists of a PMS type inspection that is
required after a designated number of flying hours, or expiration of a
number of calendar days (whichever comes first).
The PMS requirements
also included as a part of each PPM element.
The unique nature of
this inspection method provides the greatest mission flexibility;
however, the requirements stated in the PPM checklist must be followed
Part I of the PPM inspection method is a series of progressive
inspection checklists that are sequentially numbered and must be
performed in sequence.
Inspections are due after an appointed number
of flying hours.
Each progressive inspection due time is figured from
the start of the progressive inspection cycle, not from the completion
of the last PPM.
If an inspection is completed early or late it does
not effect the scheduling of the remaining inspections in the cycle.
For example, if there are 15 inspections per cycle, and the interval
between inspections is 40 flying hours, and the current cycle started
when the aircraft had 1380 hours, the first progressive inspection is
due at 1420 hours, the second at 1460 hours, the third at 1500 hours,
and so forth.
If the second progressive inspection was completed at
1455 hours, the third progressive inspection is still due at 1500
This method is unusual in that when a progressive inspection
comes due the aircraft is not taken out of service, instead it is
allowed to continue in use with the checklist requirements being
performed when the aircraft is available.
The checklist requirements
may be performed all at one time, or spread out over a period time
until the next progressive inspection is due.
For example, if the
progressive inspection interval is 40 hours, with the next progressive
inspection being due at 1320 hours, and the PPM checklist authorizes
the PPM element to be started up to 4 hours early (as early as 1316
aircraft hours), all tasks listed in the PPM element and the PMS
checklist must be completed no later then 1360 aircraft hours (a
If the PPM inspection element is not completed
window of 44 hours).