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Loss of Engine Power (Total): Mooney M20K 231, N5756W; accident occurred December 09, 2018 near Lincoln Park Airport (N07), Morris County, New Jersey


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This happened after a 36K Overhaul. 

Analysis

During cruise flight, the pilot noticed an  increase in cylinder head temperature on two cylinders and unsuccessfully attempted to reduce the temperature. He  reported that he  soon heard "an explosion" and noted a  hole in the engine cowling. He performed a forced landing  to a golf course, during which  the landing  gear collapsed, which resulted in substantial damage  to the right  wing. Postaccident examination of the engine revealed that the Nos. 1 and 2 connecting rods exhibited thermal discoloration consistent with a  loss of lubrication. Additionally, the breakaway torques measured at 8 of the 12 through-bolts showed  that they were  below the manufacturer's specifications. The No. 2 main bearing  saddles exhibited  impingement  damage, and  the No. 2 bearing was partially rotated clockwise, which blocked the oil passages leading to the  connecting rod bearings. The mating surfaces of the main bearing  saddles had remnants of silk thread around the  through-bolt holes, which was contrary to manufacturer guidance  that prohibited placing silk thread in these  areas. Given this information, it is likely that maintenance personnel applied silk thread to a prohibited area  during an engine overhaul that occurred about 255.8 flight hours before the accident. This resulted in a  loss  of torque on the crankcase through-bolts, which  allowed the No. 2 main bearings to shift, resulting in restriction of lubrication to that  area and subsequent engine failure. Probable Cause and  Findings The National  Transportation  Safety  Board  determines  the  probable  cause(s)  of  this  accident  to  be: Maintenance personnel's improper assembly of the engine  during overhaul, which resulted in lubrication restriction due to a bearing shift and the subsequent  engine failure.

 

http://www.kathrynsreport.com/2020/06/loss-of-engine-power-total-mooney-m20k.html?m=1

 

Edited by Jonás
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Good on the NTSB.  I get almost numb to reading one accident report after another where the pilot made some series of mistakes that led to a preventable accident.  Here's an honest-to-goodness maintenance issue that resulted in an off-field landing, and four people walked away.  But the NTSB clearly took it very seriously and put a lot of effort into a root cause determination.

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6 minutes ago, Jonás said:

Yes, unfortunately there was a ditch on the fairway. The plane was total. If you see the pictures of the engine, you will find a 2in hole. 

Yuck. So the gear collapsed when you rolled through the ditch?

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This was a thread from the time the accident occurred....

I believe they are related...

Great to see you stop in to MS, Jonás!

I reread the thread... to see what the thoughts were at the time...

1) Great airmanship!

2) I don’t think anyone could even guess your mechanical issues would be the challenge...

Best regards,

-a-

 

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Thanks for sharing the link to the early postings regarding the accident. 

 The incident attracted a lot of attention because of the AOPA and PBS report that was released just 5 days before the accident and because of the 5.2 M I got for my HS school to start an aviation program in the heart of NYC. 

Indee landing was challenging. Primarily because of the the low altitude we were flying at, under class B at only about 1500 to 1600 ft. However, all pilot are trained to deal with emergencies like this one. In my case, I was lucky enough to spot a golf course a few miles away. I feel that Luck is a deterning factor. 

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What I don't understand is who would put anything, anything at all near main bearing journals that were to be mated and think that was a good idea. I've seen silk thread used around the periphery of the case halves for the sealant, but the main journals?  Why would you do that? What is going to leak and why would you care if it leaked, it is supposed to be in oil and lots of it.

 

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53 minutes ago, GeeBee said:

What I don't understand is who would put anything, anything at all near main bearing journals that were to be mated and think that was a good idea. I've seen silk thread used around the periphery of the case halves for the sealant, but the main journals?  Why would you do that? What is going to leak and why would you care if it leaked, it is supposed to be in oil and lots of it.

 

I just read the Lycoming service instruction regarding case sealing. It says which sealants to use and where to put the silk thread. There is a whole paragraph in red that talks about the prohibition of putting sealant or silk thread around the through bolts. Apparently it has been a problem for a long time. Some mechanics think it will keep the engine from leaking oil. They say doing this will lead to loss of clamping force and engine failure. You would think the engine shops would be required to be trained on this stuff. 

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