100 hours checks "same work as an annual" (UK)

I just checked the inspection checklist for our TB10, and there isn’t a lot of overlap between the 100hr items and the annual. And where there is overlap, you don’t have to repeat the 100hr items on the annual if they’ve already been done within the last 3 months. So it would seem to me (based on the TB schedule anyway) that for most of the items we’re paying for only a small amount of duplicate work if we don’t colocate the two inspections. However it does seem to mean that we have more frequent inspections of a subset of the list if the aircraft is flown much over 100 hrs in a year.

This strikes me as completely silly. Thousands and thousands of C172s in their native land get an Annual inspection by government regulation, and that’s all (in relation to condition inspections). Those in commercial service (which it seems the subject plane is not) get an inspection every 100 hrs instead because they are flown so much that inspecting them only once a year isn’t often enough. A 100 hr is the same as an Annual except the A&P mechanic isn’t required to have an IA (inspection authorization) as he is for an Annual. So once a year the inspection sign off has to be done by an A&P IA. Often the same A&P will sign off the Annual as a 100 hr, then get an IA to add an additional log book entry to make it officially an Annual. But only once a year and any 100 hr at any time during the year can be signed off as an Annual, restarting that clock.

That’s the expectation of the manufacturer in terms of regulated inspection process. If this is real, it’s nuts.

The 100 hour inspection is only required on an N registration aircraft if passengers are carried for hire or flight instruction is provided for hire in an aircraft provided by that person. Repetitive AD’s may have a 100 hour requirement, but this is independent of whether or not a 100 hour inspection is provided, and unlike the 10 hour grace period for a flight returning to the inspection location for the 100 hour, there is no grace period for AD compliance. There were times when I operated a flight school that an instructional aircraft that was dual use, that is both rental and instruction. When we could not get the aircraft into the shop for a 100 hour, we would sometimes designate it as rental only, no instructional use, until the 100 hour was completed.

91.409(b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection and been approved for return to service in accordance with part 43 of this chapter or has received an inspection for the issuance of an airworthiness certificate in accordance with part 21 of this chapter. The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done. The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service.

Indeed. I saw that in Arizona too when doing the IR there.

For European-reg owners, this is yet another example of why the heavily advertised and heavily praised SDMP route is actually a total PITA for a lot of people – basically anybody whose MM is as long as their arm (Socata are a favourite there – a very “European way, heavily prescriptive” company).

And the cases where SDMP is an advantage are hated by the maintenance business, due to loss of revenue

FWIW, when I was G-reg, I was on the then called “LAMP” (light aircraft maint something) which had no 100hr. It was not based on the Socata MM at all. All G-regs had the 150hr though, and this was so onerous that most people either grounded the plane at 150hrs, until the Annual, or did the Annual at 150hrs (which in effect makes the Annual more expensive, plus it moves it earlier and earlier until eventually you are doing it in the middle of the summer). I used to do the latter. The other obvious solution is to stop logging flights…

LAMP was no better than anything else, but N-reg beats the lot by a big margin.

The other obvious solution is to stop logging flights

Which in relation to aircraft logs went away anyway under reasonable regulation when Hobbs meters (or recording tachs) were invented. Maybe 70 years ago for most planes.

I used to log flights on my non-electrical, OEM tach Luscombe, and most people had no idea what I was doing, or why. It’s still required by FAA if you don’t have an hours recording device, a little known fact. Previous owners kept track of hours on a loose piece of paper, transferred hours into the airframe and engine logs at every annual inspection and then threw away the piece of paper. I bought a logbook for the purpose, the first for that plane since 1946 when the original combined airframe/engine/flight log was used for a few months and 500 hrs (that summer alone).

I never referenced a Hobbs or any other counter, since I got the plane. I just log airborne time (for maintenance) and moving time (for pilot logbook).

Schools and syndicates prefer installed counters/timers because they can’t be cheated (that’s a real problem as I found out).

I am surprised a C172 has this issue. I wonder how others in the UK or elsewhere (the UK regs have not changed recently) deal with this?

I never referenced a Hobbs or any other counter, since I got the plane. I just log airborne time (for maintenance) and moving time (for pilot logbook).

Really? I have no idea of the difference between airborne time and moving time in my flying and simply record tach time in the aircraft logs when maintenance or Annual is recorded. It’s close enough for me and legal for the purpose.

After flying I generally use Flightaware ADS-B data on my phone to get time for my pilot logbook, adding a few tenths for taxi. That eliminates clerical error, and whether I like it or not almost every flight is recorded by others. I might as well use their ‘work’ to my advantage.

All the below is for EASA NCO/Pt.-ML, and accurate for UK only if the pre-BREXIT regs are still in place unaltered.

but it’s clear to me that I should check our AMP and MIP

You can either base your AMP on

- MIP
or
- DAH AMM

The MIP+Airworth. Limitations*+AD compliance is the absolute minimum possible to stay airworthy.

*none for C172

There’s an AMC containing a MIP for Pt.-ML, however one could draft a custom MIP as well.

The Pt.-ML AMC MIP stipulates:
„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.“

So, the advantage of the MIP is it’s „lean“, the disadvantage is the 100hr/annual interval if one flies more than 100 hours between annuals.
Then again, taking a look at Pilot Owner maintenance, most MIP tasks can be done yourself.

For an AMP based on the DAH AMM, for C172 it says:

„Inspection Requirements
A. As required by U.S. Federal Aviation Regulations, all civil aircraft of U.S. registry must undergo a complete inspection (annual) each twelve calendar months. In addition to the required annual inspection, aircraft operated commercially (for hire) must have a complete inspection every 100
hours of operation.
B. Compliance with the regulations is accomplished using one of three methods:
(1) Traditional (Annual/1OU Hour) inspection program which utilizes 14 CFR 43, Appendix D (scope and detail) to inspect the airplane. In addition, Cessna recommends certain components
or items be inspected at 50 hour intervals.“

So, perhaps you could get away with doing „only“ an annual based on the DAH (ICA) AMM for an aircraft operated under NCO.

LAMP was no better than anything else, but N-reg beats the lot by a big margin.

If you fly less than 100 hours a year, what difference is there between N-reg and EASA reg?
If you fly more, and maintain according DAH AMM, what difference is there?

I understand your motivation many years ago to go N-reg, but things have changed and improved dramatically to the point where N-reg isn’t better as a „no brainer“ like it is communicated again and again on this forum.