Compression check dangers/questions...


New Member
I'm an AMT student here in Corpus Christi, Texas. Yesterday, while doing a compression check, I got a little bump on the noggin courtesy of a Piper Pawnee, Lycomng engines and Sensenich Propellers. Six staples. When dad (who's had his A&P since 1989) heard we were hand-turning props for the check, he was a little more than upset and completely astounded that we were hand-turning props for this compression check. He said "When I was in school, we were told repeatedly 'Props kill.' We never hand-turned any propeller 'cause they have machines that turn the props for you!"

I was lead to believe you had to turn a propeller by hand to do a compression check, because we weren't told otherwise. Then I hear there's equipment designed to avoid catastrophies like this. When I returned one of my instructors' phone calls (he was checking up on me to see how I was doing), he tells me they don't have a machine which turns the prop, contrary to what I was told by my A&P licensed father. I can't help buy wonder if my school's trying to cover their arse. So apart from being upset, right now, I'm currently looking into it.

That being said, are there machines that turn propellers for compression checks to avoid mishaps like mine? If there are such machines available and I'm being told there aren't... woooohhhh mamma.

"IRON MAN" not feeling or looking so "Iron" right now. :D


Well-Known Member
I've always done it by hand. I'm not saying that such a machine doesn't exist, but I've never heard of one before now. Proper technique eliminates most of the risk.


New Member
I think what I did is I moved it slightly past the point where it was gonna stay put. Only thing it wanted to do was turn over and I just-so-happened to be in the way. It's no big deal if such a machine doesn't exist. If not, I think a machine like that SHOULD. If one does exist, why aren't they in every hangar and in every school?

I can't believe hand-turning props is still an acceptable method of performing compression checks. That just seems so incredibly dangerous. I just don't understand why a safer method hasn't been developed. Even if it is standard procedure to turn it by hand, it's still dangerous and a safer method should be at least researched.


New Member

I've never heard of nor been informed of a machine that turns the prop for you in order to do compression checks--I've always done it by hand whether it was a C-172 or a DC-6 with a radial engine and 18 cylinders. You just have to be aware of the inherent dangers of putting a volume of air on top of a piston--it will try to force the piston down; therefore, the prop will move if you don't have the piston set at the sweet spot (TDC). It really sucks that you had to learn that lesson the hard way and hope the recovery goes okay. I hope the school makes it policy to inform ya'll of the dangers for the tasks ya'll set out to do. I know this doesn't help you out now, but you can help ensure it doesn't happen to someone else in your class and when you get out into the field.

Pac Man


Tre Kronor
hmmm.... since they didn't inform you of the dangers.... I'll bet you could make some good money if you found the right lawyer.:bandit:

Roger, Roger

Yeah, all the ones I've done we rotated them by hand. Were you doing it alone?


New Member
Looks like you took a hard knock. I've been doing compression checks for 29 years and always did it by hand. Never heard of such a machine and never have any of my co workers. When dealing with piston engines a prop arc is the place to NEVER be! You've learned the hard way. Too bad the school didn't pound this into your head before the prop did. Always been this way and always will as best as I can tell.
Your instructors need to take a hard look at their syllabus. Definitely lacking.


New Member
I ahve always done it by hand as well. I have never heard of a machine that does it for you..... Sorry to hear of your misfortune. Hope you get feeleing better.


Well-Known Member
I have never heard of anything that can turn the prop. Just hold the prop, get a good grip and try to make sure that your head or other parts of your body are not in the way. That way, if it does happen then the only thing it can hit are your arms or hands. I always grab the tip or near it, hold on tight, and just watch out for the other person who is reading the gauges and working the valve to make sure that person is not in the way.