In article ,
"Dudley Henriques" wrote:

"Doug Palmer" wrote in message
ink.net...
Several pilots found themselves in a debate at our field yesterday. The
issue is weather it is safer to move the propeller on a (parked) aircraft
in the direction of usual engine rotation, or opposite usual rotation.
This is assuming that the propeller needs to move for some reason.

The reasonings ranged from "you should not turn an engine backwards" to
"turning the engine backwards disarms the impulse coupling", to several
issues in between.

Any thoughts from the groups collective wisdom?

This is one issue where you don't want to get bogged down in the
technicalities involving vacuum pumps and impulse couplings.
The bottom line on this issue is that you should NEVER.....EVER...... trust
a propeller not to kill you if you turn it by hand IN EITHER DIRECTION while
it's attached to the airplane.
Dudley Henriques

Some engines (I'm thinking Rotax in particular) are highly allergic to
turning the prop backwards. On a Rotax, it introduces air into the oil
galleys, which can result in premature engine failure.

I subscribe to the following precautions:

1. Check mag grounding prior to shutdown.

2. shut down with idle cutoff and throttle at idle.

3. If you turn the prop, do so in a way that it will not strike either
you or anything (or anyone else) if it kicks off.

I actually had a prop hit me from residual compression (no ignition) one
time.