Hello
I’d like some help to determine the kind of tolerance that can be expected on maintenance operations for a Part-ML aircraft.
From what I read, but my document is applicable to (more restrictive) PartM
I’d like to know what is applicable and what can be done with the tolerance. Is it only to fly to the workshop, or can it be used as “normal” potential ?
My second question is related to anniversary date of maintenance.
Let’s imagine you decide to trigger a 50h after only 35h flown, or an annual two months in advance. What the next deadline will be calculated on ? What rule applies ?
@Snoopy and @mh may help, as they did brilliantly in a previous post.
Tolerance can be used for normal ops.
When using MIP AMP according
AMC.ML.A.302(d)
MIP for aeroplanes of 2 730 kg MTOM and below
To be performed at every annual/100-h interval, whichever comes first.
A tolerance of 1 month or 10 h may be applied. The next interval shall be calculated from the time the inspection takes place.
When using DAH AMP it’s what’s written there, but I assume not less restrictive than the MIP.
My understanding is:
PetitCessnaVoyageur wrote:
Let’s imagine you decide to trigger a 50h after only 35h flown, or an annual two months in advance. What the next deadline will be calculated on ? What rule applies ?
Under Part-ML, always from when the inspection is made. So make it early, “loose” it. But if you make it late (use the extension), you get extra time free! Under Part-M, the extension would be removed from the next extension interval, but under Part-ML you get a fresh new whole inspection interval.
Thank you Snoopy.
In the DAH MM (Cessna), you can find two different procedures:
The intervals shown are recommended intervals at which items are to be inspected based on normal usage under average environmental conditions. Airplanes operated in extremely humid areas (tropics), or in exceptionally cold, damp climates, etc., may need more frequent inspections for wear, corrosion, and lubrication. Under these adverse conditions, perform periodic inspections in compliance with this chart at more frequent intervals until the operator can set his own inspection periods based on field experience.
(1) The 14 CFR Part 91 operator’s inspection intervals shall not deviate from the inspection time limits shown in this manual except as provided below: (Refer to 14 CFR 91.409)
(a) The aircraft can only exceed its inspection point up to ten hours if the aircraft is enroute to
a facility to have the inspection completed.
(b) In the event of late compliance of any operation scheduled, the next operation in sequence
retains a due point from the time the late operation was originally scheduled (reschedule if
late).
(c) In the event of early compliance of any operation scheduled, that occurs 10 hours or less
ahead of schedule, the next phase due point may remain where originally set.
(d) In the event of early compliance on any operation scheduled, that occurs more than 10 hours ahead of schedule, the next phase due point must be rescheduled to establish a
new due point from the time of early accomplishment
(2) Each inspection interval can be extended by 10 hours (if time-controlled), or by 30 days (if date-
controlled) or can be performed early at any time prior to the regular interval as provided below:
(a) In the event of late compliance of any operation scheduled, the next operation in sequence
keeps a due point from the time the late operation was originally scheduled.
(b) In the event of early compliance of any operation scheduled, that occurs 10 hours or less
ahead of schedule, the next phase due point can stay where originally set.
(c) In the event of early compliance of any operation scheduled, that occurs more than 10 hours ahead of schedule, the next operation due point must be rescheduled to establish a
new due point from the time of early compliance
So let’s take the example of the 500h internal inspection of magnetos. Do you have:
- 10h tolerance ?
- 25h tolerance ?
- 10h tolerance only to fly back to the workshop ?
@lionel wrote:
If your AMP is based on “the instructions for continuing airworthiness (‘ICA’) issued by the design approval holder (‘DAH’)”, then you start with what is on the ICAs, and can decide to deviate from it, e.g. increase inspection interval or increase tolerance, never to more than ML.A.302(d) (1) (see the end of GM1 ML.A.302(c) (3) ).
Yes I get it, you can do what you want, but you must declare it in advance in the AMP. That’s rhetoric exercice.
How often can you modify your self declared AMP ?
I agree with the posters above. But I would also add that the DAH can be more liberal than the MIP. I don’t know of any light GA that has a longer interval than 100 hrs between periodic inspections but it would in theory be possible.
The PC-12 has 300 hrs between inspections which is kind of cool.
PetitCessnaVoyageur wrote:
So let’s take the example of the 500h internal inspection of magnetos. Do you have:
- 10h tolerance ?
Yes, 10h tolerance. The DHA ICA and Part-ML give the same number, so no doubt you keep that. However:
PetitCessnaVoyageur wrote:
(c) In the event of early compliance of any operation scheduled, that occurs 10 hours or less
ahead of schedule, the next phase due point may remain where originally set.
Is a cool clause, which I’d like to keep in a Part-ML AMP. I’m not 100% sure it matches the letter of the Part-ML regulation, but in spirit…
PetitCessnaVoyageur wrote:
How often can you modify your self declared AMP ?
Every day if you want. If it is self declared you are in control.
Subject to factors already done to death 
Like, finding a maintenance company willing to sign off on it…
The PC-12 has 300 hrs between inspections which is kind of cool.
Indeed, but the 12 is a Part M aircraft.
But I would also add that the DAH can be more liberal than the MIP.
Good point.
Using DAH AMP as basis for declared AMP one can deviate from DAH ICAs, as long as the deviations are not less restrictive than the MIP.
If one uses the DAH without deviations than MIP limits should be possible to exceed, right?
