MT Prop overhaul

[carym]

This discussion started on the Travel forum, and has been carried over to a PM discussion I am having with CFIDave, but we thought it worthwhile to discuss here because it may be of interest to others. Here is the essence of the discussion to date:
I have a 2007 DA42 with original propellers. My mechanic just informed me that I am required to overhaul the props to maintain airworthiness of the plane. This took me (and him) by surprise but I think he may be correct and here is the logic:
1) Section 4 of the AMM (Airworthiness limitations) states that for the MT propeller refer to MT Manual ATA 61-01-24 for Mandatory Maintenance Actions
2) ATA 61-01-24 under airworthiness limitations says there are no airworthiness limitations.
3) But the Type Certificate Data Sheet (P19NE) under which the propeller is shipped to the US and applied to a US registered plane says:
"provided they are installed, operated, and maintained as prescribed by the approved manufacturer's manuals" (this is ATA 61-01-24) and NOTE 10(b) of this TCDS says that they "are to be operated within the limits of the MT-Propeller Operation ... Manual No. E-124 ... and adhere to the TBO-limits shown in MT-Propeller Service Bulletin No 1"

So the Manual says there are no airworthiness limitations, but the TCDS says that in addition to the manual one must adhere to the TBO-limits which gives a TBO of 2400 hours or 72 months. The question then is: Is a part 91 operator required to adhere to the limits set forth in the TCDS or only to the limits set forth in the operating manual?

As expected the MT propeller shop says that to remain airworthy I have to overhaul at 72 months. My mechanic has nothing to gain either way, and he says that I have to overhaul at 72 months. I understand that if I was operating under Part 135 I have to abide by the SB's that state I have to overhaul at 72 months, and EASA mandates that all SB's be followed to maintain airworthiness. But, in the US under part 91 do I have to follow the TCDS?

[ihfanjv]

I think you have answered your own question. The FAR says as follows:

***
§43.16. Airworthiness Limitations.
Each person performing an inspection or other maintenance specified in an Airworthiness Limitations section of a manufacturer's maintenance manual or Instructions for Continued Airworthiness shall perform the inspection or other maintenance in accordance with that section...
***

It looks like you go to your step (1), then step (2), then you stop. It does not appear that you have to go beyond ATA 61-01-24 to hunt for an airworthiness limitation. This issue is discussed here:

http://www.askbob.aero/node/156

Good luck!

[CFIDave]

As we discussed via private messages:

The Diamond AMM "Limitations" section 4 says to follow the manufacturer/supplier guidance on airworthiness limitations and in section 5 refers to the MT Propeller E-124 manual for guidance.

If you then read E-124 it very explicitly says "No Airworthiness Limitations!" (with the exclamation point added by MT to show how certain they are about this).

Since there are no Airworthiness Limitations associated with your MT props, you as a Part 91 operator can still have an airworthy aircraft without overhauling the props at 72 months.

See you at Oshkosh.

[GLDAS]

Dave,
6.12 Overhaul reads:
The time between overhauls is expressed in hour flown and calendar months since manufacture or overhaul. The figures are also presented in Service Bulletin.......[snip] In any case, a calendar time inspection must be performed after a maximum of 72 months from installation, if no more than 24 months have passed since manufacturing overhaul when properly stored. This means that calendar time TBO can be max 96 months....

http://www.mt-propeller.com/pdf/manuals/e-124.pdf

This is how we have been treating our aircraft.

I believes this is the authoritative text.

-dan
dan@greatlakesdiamond.com

[carym]

Dave,
6.12 Overhaul reads:
The time between overhauls is expressed in hour flown and calendar months since manufacture or overhaul. The figures are also presented in Service Bulletin.......[snip] In any case, a calendar time inspection must be performed after a maximum of 72 months from installation, if no more than 24 months have passed since manufacturing overhaul when properly stored. This means that calendar time TBO can be max 96 months....

http://www.mt-propeller.com/pdf/manuals/e-124.pdf

This is how we have been treating our aircraft.

I believes this is the authoritative text.

-dan
dan@greatlakesdiamond.com

Yes, Dan. But this begs the question of whether an aircraft flown under part 91 is no longer airworthy after 72 months (or 96 months if stored and not flown) without an overhaul. Are you requiring all your DA42s to undergo a prop overhaul after 72 months?

[GLDAS]

Yes, Dan. But this begs the question of whether an aircraft flown under part 91 is no longer airworthy after 72 months (or 96 months if stored and not flown) without an overhaul. Are you requiring all your DA42s to undergo a prop overhaul after 72 months?

I am doing the overhauls on everything I buy, and I've been advised that it is a requirement. I wish it were otherwise....

-dan
dan@greatlakesdiamond.com

[ihfanjv]

I am doing the overhauls on everything I buy, and I've been advised that it is a requirement. I wish it were otherwise....

-dan
dan@greatlakesdiamond.com

If you are a Part 91 operator, then it looks like you are doing the prop overhauls voluntarily. The AMM and MT ATA 61-01-24, when read together and applying the applicable FAR (§43.16), clearly state that there is no time-related airworthiness limitation on the propellers. Section 6.12 of ATA 61-01-24 has nothing to do with limitations as set forth in FAR §43.16.

[CFIDave]

Read MT's manual ATA 61-01-24, E-124 that applies to DA42 propellers:

http://www.mt-propeller.com/pdf/manuals/e-124.pdf

Take a look at page 42-1, section "10.0 Airworthiness Limitations Sections", where the first sentence is:

"No Airworthiness Limitations!"

It then goes on to state that this is approved by the FAA as well as EASA, and the page is dated March 5, 2014.

Why would MT publish this explicit statement in its manual if props exceeding a 72 month TBO would make a plane un-airworthy?

US Part 91 operators have always been able to run engines and props beyond manufacturer recommended TBOs, maintaining these aircraft components "on condition."

[GLDAS]

Dave,
The TCDS reads differently. This is from our service center:


"Refer to the TCDS on MT-Propellers:
And I quote (b) :

Note 10: Special Notices
(a) ---------------------------
(b) All MTV-6 propellers are to be operated within the limits of MT-Propeller Operations and Installation Manual No. E-124 for non reversible and E-504 for reversible propeller, and adhere to the TBO-limits shown in MT-Propeller Bulletin No. 1 ( ).
(c) -----------------

This is found in the Type Certificate Data Sheet for the MT-Propeller. I do not have access to the overhaul manual, but I would bet it says the same thing.

I looked at section 10.0, but the TCDS trumps all."



-de
dan@greatlakesdiamond.com

[carym]

I appreciate the discussion and understand the arguments. Despite that ?understanding, I remain confused. In order to remove any confusion from my feeble mind, I talked with an Airworthiness Director at our Indianapolis FSDO this AM. I explained, and went over, all the details discussed in this forum in order to get a definitive answer to this issue. Guess what - he was also confused and could not give me a definitive answer He also stated that with older engines and props there was a direct link between the POH, the OMM, and TCDS and that is why under part 91 you could exceed the manufacturer's "recommendation" but you couldn't under part 135. With the newer engines/props this direct link is not always there and may need to be handled on a case by case basis. He gave me a couple of options. I could leave it up to the IA to sign off on the airworthiness, or I could ask for an opinion by the FAA chief counsel (yeah, like I am going to do that!!!). Interestingly, the TCDS for the Thielert/Centurion/Technify engine says that "engine are Life-Limited. Whole engine must be removed from service in accordance with the Airworthiness Limitations Section, Chapter 5 of the Maintenance manual" and Chapter 5 is not regulatory under part 91, so that is why the engine can be run past TBO under part 91. Referral to chapter 4 or 5 is not given in the TCDS for the propeller.

The bottom line seems to be that it will be up to your IA to decide if you need to overhaul or not. Because I am more concerned with safety (and the props are not thoroughly examined at annual) I have elected to take the conservative approach and have them overhauled. If anyone writes to the Chief Counsel to get a definitive answer to this question please let me know what that answer is.