Check your Prop Bolts!

Yesterday 2 friends landed back home after a 5 hours flight with an RF5 with a fixed pitch wooden Prop.
The engine made a very unusual noise during taxi. The crew did not notice any thing in the cockpit.

A bit later, another pilot takes off with the RF 5 for a sightseeing flight. Nothing special with the engine!
Only the people on the ground wonder about the abnormal noise, like an old diesel tractor!

Again, after landing everybody looks at and listens to the engine like a doctor: everything seems OK but the drumming noise is frightening! Probably a rod bearing damage or maybe a main crankshaft bearing damage!
Very unusual, but it can happen!
The engine was taken down for an emergency delivery to the clinic!

After removing the prop, what a surprise! 3 propeller bolts out of 6 were broken and the other 3 were loose in spite of the safety wiring!
The mechanic couldn’t believe his eyes! He re-installed the 18 months old prop last April, using a torque wrench (with 18 N/m torque) and secured the bolts as requested by the maintenance manual.
In spite of that, 3 bolts sheared within a very short time. Look at the picture, we are now at the end of August 2002! There is only one explanation: during the past 8 weeks with very hot weather, the prop wood shrunk and the bolts got lose until 3 out of 6 of them broke within a few flight hours!

It was a lucky chance that this RF5 did not lose its prop in flight!
It is not a bad idea to check the torque of the wooden prop screws regularly, especially in hot summers!

Germany 23. Aug. 2002