Prop Strike and Engine tear down requirements.

[Schllc]

My understanding was that both lycoming and continental have an AD that any prop strike requires an engine tear down. 
I was looking at a plane for a friend today, the broker said there was a partial nose gear collapse on taxi eleven years ago.  He told me continental “reviewed the incident, and decided no inspection was required”.
But they changed the prop due to damage from sudden stoppage.  
This does not sound right at all…

Has anyone ever heard of this?  Did I misunderstand the AD?

[Rick Junkin]

A quick google search yielded this from Lycoming:

https://www.lycoming.com/content/propeller-ground-strike-or-sudden-stoppage-can-be-dangerous and https://www.lycoming.com/content/service-bulletin-no-475c

And this from Continental:

https://www.airmarkoverhaul.com/wp-content/uploads/2019/02/Prop-Strike-Continental-Engine-SB96-11B.x43733.pdf

Reader's Digest Version - service bulletins from both manufactures recommend/direct(?) an engine teardown in the event of a prop strike.

EDIT: Thinking more about this I recall discussion of a crank run-out check being deemed sufficient in some cases with Continental engines, I think. Guidance from both manufactures is contained in a service bulletin and as such is not mandatory for non-commercial Part 91 ops.

If engineering at Continental was consulted there will be a record of their analysis that may be available to you if you ask Continental for it. That would provide evidence and insight into the decision to recommend against a tear down.
 

Cheers,
Rick

[toto]

Compliance with the Lycoming SB requires about 15 hours of shop time, but it’s not the same as taking the engine off the plane. If no damage is found, they reassemble and you proceed as usual. 
 

 

SB533C-Recommended-Action-for-sudden-Engine-Stoppage-Propeller.pdf

[Schllc]

29 minutes ago, Rick Junkin said:

And this from Continental:

This seems ambiguous in a SB….

”Following any propeller strike, complete disassembly and inspection of all rotating engine components is mandatory and must be accomplished prior to further flight. Inspect all engine driven accessories in accordance with the manufacturer’s maintenance instructions.”

Is it mandatory or not?

[Hank]

4 minutes ago, Schllc said:

This seems ambiguous in a SB….

. . . .

Is it mandatory or not?

SBs are not mandatory in Part 91, only ADs are mandatory. For commercial service, the rules all change . . . . But all of my commercial flights are in the back of multiengine turbo-fan-jet cattle cars, so you'll have to ask someone else.

[N201MKTurbo]

I think if the engine was going to fail from the prop strike, it would have done it by now. Time cures all. 
 

But still good for a bargaining chip.

[Rick Junkin]

1 minute ago, Schllc said:

This seems ambiguous in a SB….

”Following any propeller strike, complete disassembly and inspection of all rotating engine components is mandatory and must be accomplished prior to further flight. Inspect all engine driven accessories in accordance with the manufacturer’s maintenance instructions.”

Is it mandatory or not?

I’m going to legalese you a bit. Yes, it’s mandatory to execute these steps to comply with the service bulletin.

However, compliance with a service bulletin is voluntary for aircraft operated for private non-commercial use under Part 91.

So, I don’t have to comply with a service bulletin as an operator of my aircraft for personal use under Part 91, but if I choose to comply then I must execute the requirements of the service bulletin as written. And if I’m using the aircraft in a commercial capacity, like as a rental aircraft, then I AM required to comply with service bulletins, get 100 hour inspections, etc.

So in this instance, the service bulletin is regarded as advisory and it’s up to the aircraft owner to decide if he wants to comply.

I’m just another pilot with an understanding of how I believe this works, happy to be corrected by someone better informed or experienced.

Cheers,
Rick

[Schllc]

5 minutes ago, N201MKTurbo said:

I think if the engine was going to fail from the prop strike, it would have done it by now. Time cures all. 
 

But still good for a bargaining chip.

I tend to agree, I think I’m very dubious of continental saying it isn’t necessary. 

[Rick Junkin]

8 minutes ago, Schllc said:

I tend to agree, I think I’m very dubious of continental saying it isn’t necessary. 

I think that’s smart. Call Continental/TCM and see if they have an engineering record of the consultation on this engine. Or better yet, ask the broker to get that info for you.

[EricJ]

There is an AD for Lycomings after a prop strike (AD 2004-10-14) but it does not require engine removal or tear down, just inspection of the crankshaft gear and replacement of its fastener and lockplate.   Some have done this (even on Mooneys) without removing the engine.   It requires removing the accessory case, which isn't trivial, but is definitely doable.

I'm not aware of an AD for Continentals, and if there isn't one then the only guidance is the SB96-11B, which isn't mandatory for Part 91.

I think the usual practice of automatic full tear down after a prop strike is because the insurance companies typically support it and often want it done (maybe require it? I dunno.)   The FAA doesn't require it, neither do the manufacturers. 

At a minimum, careful checks should be made and the engine closely monitored afterward for metal in the oil, etc.   Crank flange runout can be spot checked by turning the blades and checking each against a stationary object on the ground (a bucket or something placed against a prop blade face, then checked against the other blades).

But +1 that if it has some hours on it and isn't making metal or doing bad things, it may be okay.   A bad case is if the crank obtained a latent crack which grows over time, and the only way to be sure of that is to take it out and get it magnafluxed or something.   That has happened but seems to be rare, and seems to be limited to the cases of hard strikes with significant prop damage.

[1980Mooney]

I am curious to  know if you had a chance to review the entries in the engine and airframe logs.  Rather than relying on broker hearsay what did the A&P and IA actually enter? And is there any written documentation from Continental attached to the logs or in the maintenance file?

[Schllc]

2 hours ago, 1980Mooney said:

I am curious to  know if you had a chance to review the entries in the engine and airframe logs.  Rather than relying on broker hearsay what did the A&P and IA actually enter? And is there any written documentation from Continental attached to the logs or in the maintenance file?

Requested but not received yet

[philiplane]

4 hours ago, Rick Junkin said:

 And if I’m using the aircraft in a commercial capacity, like as a rental aircraft, then I AM required to comply with service bulletins, get 100 hour inspections, etc.

Commercial Part 91 operations still do not require compliance with SB's. Part 135 operations might, but only if the ops specifications required it. It depends on how the maintenance program was written.

[philiplane]

7 hours ago, Schllc said:

My understanding was that both lycoming and continental have an AD that any prop strike requires an engine tear down. 
I was looking at a plane for a friend today, the broker said there was a partial nose gear collapse on taxi eleven years ago.  He told me continental “reviewed the incident, and decided no inspection was required”.
But they changed the prop due to damage from sudden stoppage.  
This does not sound right at all…

Has anyone ever heard of this?  Did I misunderstand the AD?

There is no AD to compel an engine teardown on a Continental engine. Only a Service Bulletin with a recommendation for inspection of the crankshaft flange area, and a few other items in the engine. It is perfectly legal to take a bent prop off of a Continental engine, check for flange run-out, bolt a new prop on, and fly away. 

Even the Lycoming AD does not compel a tear-down. It calls for removal of the accessory drive cover, inspection of the crank drive gear, and replacement of the gear retaining bolt and lockplate. That's it.

FWIW, I've been involved in dozens of engine tear downs over 25 years, and we have never found any internal damage related to the prop strike. Corrosion pits on cylinders, camshafts, and cranks from sitting, yes, but no damage from the strike itself. These engines are very robust, and the props take the hit and dissipate the energy enough that real damage is extremely rare. 

FWIW, the famous Aerostar gear up landing and fly away that happened in Fort Pierce FL a few years ago- that plane's engines were on their second prop strike tear down when the owner landed gear up, powered up and flew back to Fort Lauderdale. The props were curled back six inches. The subsequent owners had the Lycoming crank gear AD done (does not require a tear-down), bolted new props on it, and it flew for some time before being sold again. If any engines should have been impacted by a prop strike, this would be the poster child. 

 

 

 

 

All that said, the insurance companies are always happy to pay for a tear down out of an abundance of caution. There's no way to know if anything else inside is damaged, without disassembly.

Edited October 8, 2023 by philiplane

[GeeBee]

I have seen two cracked cranks from prop strikes. Both Lycoming, one a O-320 another an IO-540