COMANCHE TECH TALK
A SMALL PIN MAY CAUSE A MAJOR TROUBLE
by Ben Ayalon
Our Comanche 260C had its annual check in March this year, as usual, my mechanics were presented with a list of extra work that I required doing. This year's list included a repair to the flap 'up position' stop, alternator inspection, replacement of the gear bungees and my pet maintenance job, re-packing the 'Dukes' gear screw with its fresh unique and strange looking grease/thick oil as it tends to consume it during gear operation and more. I was sure that there would be no surprises during the year to come.
One of the design advantages of the Single Comanche is the minimal effort that is required to open the cowling and inspect the engine, however, this feature is also a weakness point. Think about it. How many times have you opened and closed the cowling during pre-flight? How many times did your mechanics do the same when they were working on your aircraft? Have you ever spent a second thought regarding the cowling latches and the hinges? I am quite certain many of you did not, neither did my mechanic or myself. It was in April, a month after the annual, when I have pre-flight checked the aircraft before taking off for a short local flight. As you have guessed, one of the cowling latches fell off and remained in my hand, a closer look revealed that the hinge (a clevis pin) was corroded and worn around the contact points with the latch. I thought to myself "If one is so bad what about the others? It would be sensible to replace them all".
Two days later a new set of clevis pins arrived, not thinking too much I walked to the grinding machine as the pin heads need grinding to allow them to go into position. In my haste I did not pay attention to a 'small' point, the heads should be ground in one way only. Of course, I did not think about it so some pins have lost the wrong part of their head. Pay attention, when you grind the heads you must grind it in parallel to the split pin that goes in the other end.
In the attached pictures you can see one of the pins that were removed, all were in the same condition. Replace or at least inspect these pins before you lose your latches or your cowling become loose during flight.
The New and the Old Pin
The Old Pin.
Ben Ayalon, born in Israel in 1955, studied aircraft engineering at Holtz Technical College in Tel Aviv. He served for 6 1/2 years in the Israel Air Force and later joined Israeli Aircraft Industries where he took part in the development of the "Lavi" fighter. In 1987, Ben moved to the UK to study and obtain a degree in Business Administration. There, he started his own computer business, and now owns a Comanche 260-C, based at Elstree, England (EGTR).