Question about 100-hour inspections and the 10-hour buffer

[RussR]

If you have an airplane you are renting out as a trainer, and you are providing the flight instruction, then you need to have 100-hour inspections. That's simple.

If you aren't doing flight instruction, then you don't need 100-hours. Got it.

Once you get to 99.9 hours, you have up to 10 additional hours if needed to get it somewhere to do the 100-hour inspection. This is part of what I don't understand. After 99.9 hours, you cannot provide flight instruction, so as a result, for the flying to get to the mechanic, you don't even have to have a 100-hour inspection. So, what if at 99.9 hours you decide "you know, I'm tired of teaching in this airplane, I'm just going to fly it around some". Then, at 120 hours you decide "okay, that's enough fun, I need to start teaching again", and you get a 100-hour.

Have you violated anything? I don't think so.
When is the next 100-hour due? I assume at 220 hours.
If so, then what's the point of the "10-hour" buffer, since that flight to the mechanic is (to me), no different than taking it off the line for a while, which I presume would reset the 100-hour clock.

I'm sure some people try to game the system like this. But is it even really "gaming the system"? As long as you don't provide instruction past 99.9 hours, there's no violation, is there?

(This is academic. Although I am using an airplane for flight instruction that does get 100-hours, I have no need or interest in reverting it to "non-instructional use". Just trying to understand the rules.)

 

[Ravioli]

When is the next 100-hour due? I assume at 220 hours.

I assume it's 200 hours. Wouldn't make sense to have a loophole like that, and if you're renter/learners are using your plane for check rides your logs are getting looked at by official type people pretty frequently. 100 hrs at 100, 240, 370 are gonna become obvious.

 

[RyanB]

So, what if at 99.9 hours you decide "you know, I'm tired of teaching in this airplane, I'm just going to fly it around some". Then, at 120 hours you decide "okay, that's enough fun, I need to start teaching again", and you get a 100-hour.

That’s perfectly legal, you just couldn’t give flight instruction in the airplane until the 100hr clock is reset.

As long as you don't provide instruction past 99.9 hours, there's no violation, is there?

Nope. As long as the instruction is given during the 100hr window it’s perfectly legal. The 10hrs is just time allotted to get said airplane to the place of inspection, nothing more. Keep in mind that the airplane can still be rented out even if the 100hr is expired.

 

[RyanB]

I assume it's 200 hours.

No, the additional time you take to get the inspection done has to be accounted for when calculating the next 100hrs.

Ex. If 100hr is done at 2500.0 and it takes you 5.0 additional hours after the 100hr window (2605.0) to get the airplane to the shop, than the next 100hr would begin at 2605.0 not 2600.0

 

[Bell206]

Have you violated anything?

FYI: the key thing to remember is how the aircraft is operated that triggers the 100hr. No instruction, no 100hr requirement regardless the situation. The 10 hour grace period would only come into effect if you needed to fly past the 100 hour during an instruction flight. While you can not purposely fly into that 10 hr period, if your flight diverted around weather or for other reasons put you over the 100hr limit, then the 10 hr grace gives you a legal way to get back without violating Part 91. There is an LOI that gives specific examples of your questions.

100 hrs at 100, 240, 370 are gonna become obvious.

Obvious to what? Where the 100 hr inspection cycle falls for a Part 91 aircraft is immaterial provided the 100hr is valid during the instruction flights. However, there are some inspection programs were the use of the mx grace period reduces the next inspection cycle by the same amount of time used in the grace period.

 

[midlifeflyer]

@Ryanb pretty much nailed it. There is no "every 100 hours" rule. The rule is that, if the airplane is being used for one of the two applicable operations (passengers for hire and provided by the trainer for flight instruction for hire), it must have received the inspection "within the preceding 100 hours of time in service."

The grace period is subject to a lot of misunderstanding. Lets try this:

• For a covered operation, it must have the inspection within the 100 hours before the covered operation.
• The grace period applies to unintentionally overflying the 100 hours during an operation which requires a 100 hour inspection.

Unless that flight to get the inspection done is being done during an instructional flight or with a paying passenger on board, the 100 hour rule doesn't even apply. No grace period to worry about.

The simplest examples I can think of are, do a planned 2 hour instructional flight with 2.5 left before the inspection is due and encounter an unexpected delay, and you are in the grace period. Do that same flight with 1.5 left and you do not have grace period protection.

So in your example, you get to 99.9 hours and stop teaching in the airplane. 20.1 hours you decide to start teaching again and you get a 100-hour inspection.

No, you have not violated anything.
The next 100 hour is due at 220 hours.

Here, the two Greenwood interpretation letters should help. They discuss a number of 10 hour inspection scenarios.
Greenwood 2014
Greenwood 2015

 

[Tom-D]

Seemly it is better to do the inspection early.
and remember you can do a annual anytime.

 

[midlifeflyer]

Seemly it is better to do the inspection early.
and remember you can do a annual anytime.

True. And if you also have 100-hour ADs, you can't overfly those anyway.

But some flight schools try to defer, like deferring an annual to the beginning of the following month. I've even heard of schools with enough airplanes to take the ones which are close off the training line (rental only) until they do the 10 hour.

 

[dmspilot]

No, the additional time you take to get the inspection done has to be accounted for when calculating the next 100hrs.

Ex. If 100hr is done at 2500.0 and it takes you 5.0 additional hours after the 100hr window (2605.0) to get the airplane to the shop, than the next 100hr would begin at 2605.0 not 2600.0

What? You just contradicted yourself. The inspection would be due at 2600.0, there are even questions about it in the private pilot test bank.

 

[RyanB]

What? You just contradicted yourself. The inspection would be due at 2600.0, there are even questions about it in the private pilot test bank.

Not in the case I outlined above. If an unforeseen event causes the operator to fall into that 10hr buffer window after the 100hr expired, then the new 100hr clock resets at the time of inspection, not at the time the prior one expired - otherwise the operator wouldn’t get a whole 100hrs before the next is due.

 

[dmspilot]

Not in the case I outlined above. If an unforeseen event causes the operator to fall into that 10hr buffer window after the 100hr expired, then the new 100hr clock resets at the time of inspection, not at the time the prior one expired.

The grace period counts against the next 100 hour inspection.

The clock is only reset if the aircraft was discontinued being used for operations requiring a 100-hour inspection, like in the OP's question.

 

[RyanB]

The grace period counts against the next 100 hour inspection.

The clock is only reset if the aircraft was discontinued being used for operations requiring a 100-hour inspection, like in the OP's question.

I see what you’re saying, my apologies - misinterpretation of that part on my end. You are correct.

 

[Marshall Alexander]

OTOH....if you do a 100 hr at 90 hrs. the next 100 hr is due within the 100 hrs. you don't get 110.