Spun Aluminum Spinner Failures

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PIREP Submitted by: Carlos Emmons

My pucker story starts at 2000 feet AGL on a beautiful Sunday afternoon. I was returning from our local EAA Chapter's open house at Gwinnett County airport. Dekalb-Peachtree tower had just cleared me to a left base to 20L when quite unexpectedly, the aircraft started to vibrate badly and the engine sound changed appreciably. I pulled the power back to idle as I reduced my speed to best L/D and found that the vibration still continued but to a lesser extent. I concluded that something was very wrong with the engine so I shut it down. When the windmilling prop stopped the cause of my problem was readily apparent, I had a splintered propeller in front of me.

The question now was finding a place to land. I contacted the tower and requested a straight-in into 27 which was promptly denied (there was heavy traffic on the parallel runways) until I declared an emergency. Once I had declared my emergency I got the reassuring words of "cleared to land anywhere" or something to that effect. Thank goodness for high L/D's (those of you considering short wing Moni's take note). Once I knew I had the airport made I was breathing a little easier as there are few landable areas in northeast Atlanta, other than overcrowded freeways. I went ahead and landed on 20L and pulled off onto one of the taxiways. As I was unstrapping myself from the airplane and was getting out I found myself greeted by one of the biggest fire trucks I'd ever seen; water cannons aimed right at me. The little Moni looked like a model airplane next to it. After convincing the fire crew that all was well an inspection of the airplane revealed the cause of the problem. The spinner had flung off and on the way out hit one of the prop blades.

So why did my spinner decide to leave? Well, there's where I come into the picture. This was the second spinner I had put on my airplane. The first started to crack after about 20 hours at the corner of the prop blade cutout (see diagram).

Concerned about that, I removed it and ordered another one. This time I made doubly sure that I had a LARGE SMOOTH radius around the cutouts. To my disappointment, cracks started to appear again after about another 20 hours. Something was stressing and fatiguing the spinner in a hurry but I could not figure out what it was. I decided to stop drill the cracks and made sure before and after every flight to keep a close eye on the spinner. It looked like the cracks had gone as far as they had wanted to and did not progress any further. That is, until they "progressed" all at once. There was only about 20% of the spinner left with the airplane.

The lesson to be learned here is that if you are flying with the original Moni spinner (not the solid one) be VERY careful about any cracks. Closely inspect the spinner, particularly around the cutouts, prior to every flight. If you find even the smallest of cracks discard that spinner. It doesn't take long at 6000 rpm for something to self-destruct. Cosmetically the spinner really dresses up the airplane, but it's not worth it if it has the chance to come off. I was lucky in that I had enough altitude to evaluate the problem and make a successful landing. What is really scary is to think of all the hours I flew with that cracked spinner just waiting to come off.

Carlos Emmons

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