This is an excerpt from a report made to the Aviation Safety Reporting System. The narrative is written by the pilot, rather than FAA or NTSB officials. To maintain anonymity, many details, such as aircraft model or airport, are often scrubbed from the reports
I hired Company at ZZZ1 to conduct a top overhaul on my aircraft. The company is a FAA Part 145 Repair Station.
When I picked up the aircraft after the top overhaul was completed, I was met by a young man, who was not a certified A&P mechanic, who claimed that he had conducted the top overhaul of my engine by himself. Further questioning of this individual caused me some concern because when I spoke with him briefly he did not seem to be a very knowledgeable mechanic.
I then immediately spoke with the owner of the company about the repair work done to my aircraft. He assured me that he had personally conducted the top overhaul on my aircraft engine, that all work was completed properly, and that the young man was just bragging.
I had the word of an experienced IA and a signed endorsement stating that the work had been completed in accordance with the FARs and that the Repair Station Manual requirements were complied with, so I paid the invoice for the work and left.
Subsequently, I was flying over a densely populated area. I heard a bang from the engine compartment and observed a drop of about 300 rpm on the engine. There were no abnormal vibrations, and all the engine gauges were in the green. A visual check of the airframe showed no abnormal conditions.
I thought that I had a broken magneto, so I started to fly directly to my home base. By the time I was about five miles from my home base, all of the engine gauges were in the red except for oil pressure, and the engine RPM was dropping.
I landed and shut off the engine once I cleared the runway and taxiways.
The next two days of troubleshooting the engine revealed no visible signs of damage, and the cause of the power loss could not be determined.
The engine was taken to another company, which is also an FAA Part 145 Repair Station. Upon tear down of the engine it was discovered that the main bearing was crushed, which caused the crankshaft to break into two pieces. The metal debris from the broken crankshaft had gone throughout the engine, making most of the engine parts unairworthy.
The owner/operator of this repair station stated to me that the cause of this failure was the overtorquing of the cylinders during the top overhaul at the first company.
He called the first company on my behalf in my presence by telephone. The telephone call was very brief, with him telling the owner of the first company that the top overhaul was improperly done, and what would be his course of action for correcting this situation with me. When he hung up the phone, he told me that the owner of the first company was not going to do anything about the damage to my aircraft.
For that reason I then proceeded to have the new company order parts and have him rebuild the engine.
Fortunately my incident caused by the improper repair of my engine was not fatal. No one was injured when we landed with loss of forward thrust. However, the next pilot may not have the good fortune that we had.
Primary Problem: Procedure
ACN: 1900502
Insufficient information in the report for us to figure out the causes of what actually happened. From what is here, we start with an incompetent mechanic (“I did the top overhaul myself”) and a dishonest shop manager (“I did the top overhaul myself”) so we have two people claiming to have done the same job themselves – and that’s just the start.
Overtorqued through bolt pinching a main bearing and causing a failure – maybe, aircraft crankcases tend to be a bit fragile if mistreated. It would help to know what engine this was. Engine ran despite broken crank – I have seen engines still running with a broken crank. They aren’t happy about it and won’t run long or hard, but they’ll still run – for a while – until they puke. Old air-cooled VWs are especially good for this.
Years ago, I ran the warranty department for a well-known importer of fancy European cars, and what is here isn’t enough to make a decision or pay a claim. I’d start with engine type, TT SMOH, parts list, invoices, work orders, basically all the paperwork, then we would have a good chance of determining where the screw-up was (and it WAS a screw-up). I’d also be questioning the shop’s certification status and thinking about asking the FAA to review it very, very carefully.
Additionally, this looks like a lawsuit. The first engine shop should count their blessings and lucky stars at only having to write a check to replace the engine. If there had been a crash and someone got hurt or (God forbid) killed, they’d be looking at seven or eight figures in damages – I *personally* know of a case where nobody was seriously hurt and the verdict was $50,000,000!
Spend the money on quality maintenance, not on lawyers after the fact. My wife is a lawyer (doesn’t just play one on TV) and she advises me to do the same. Yes, dear, no problem!
None of the narrative makes mechanical sense. Over torque is an assumption since to move a torqued bolt requires somewhat more pressure in either direction to overcome the the applied torque. However, under torqued can be fairly obvious.
And a great many aircraft mechanics are actually apprentices.
And in the automotive field the best mechanics don’t work for hourly wages because they will not make more than the worst mechanics….like in unions.
Would like to know engine model. Was 2nd 145 repair station an engine shop? How would they differentiate between over torqued cylinders from under torqued cylinders. Either one could have produced a spun bearing. Usually that would result in a broken connecting rod due to oil starvation. Odd that crank broke before connecting rod, but? Still had oil pressure? I have seen oil pressure erroneously high due to a partially spun bearing. You would think that with a broken crank, cause by a “crushed” bearing would not have good oil pressure. Weird that only lost 300 RPM, broken crank and no vibration? I would want a factory rep to look at it.
Sorry, no detail in the ASRS report, so it’s useless to us.
The only way to check the torque on the thru bolts to to put a torque wrench on each and see if the nut rotates with a few lb-ft more than spec. If it doesn’t, loosen it and retorque it…..but the damage may have already been done.!
Under torqued base nuts can cause the cylinder to work loose and break off from the crankcase. Then all the oil is pumped overboard from the open pushrod tubes.
If you’re really unlucky, the cylinder puts a big hole in the side the cowl as it ‘departs the airplane’.
Report the offending shop to the FAA while filing a lawsuit to recoup your dollars spent with the shop.
There is not enough information in the report to know where the crank broke and how the engine could continue running ?
A ‘crushed main bearing’ ? Which one, and did it close the oil hole causing the bearing to seize ?
Most of the ASRS reports lack enough detail to be useful in understanding the situation and how we might avoid doing the same.
That experience has lawsuit written all over if were it my airplane engine and near-death experience. That shop has no business allegedly fixing airplanes.
What other gauges were in the red. You would think oil pressure would have had to drop with a main bearing failure. just askin.
Never underestimate the importance of a good, calibrated torque wrench!! Unfortunately, there may be more inherent issues with this story.
I am sorry for your unfortunate experience. Sounds like you handled the loss of power calmly and professionally with the outcome ending safely. But might this have been avoided if you had done your homework? Choosing a reputable engine shop or mechanic to perform the top overhaul is critical to having the job done right. The fact that shop xxx did not stand behind their work tells you something about their reputation. For those needing engine work, it is vitally important to seek out a shop that has established a reputation for doing quality work, who will stand behind their work.
I agree with Kelly,
“91.403 General. (a) The owner or operator of an aircraft is primarily responsible for maintaining that aircraft in an airworthy condition, including compliance with part 39 of this chapter.”
Owner/Operators should all be familiar with the FAA FARs especially Part 91:
https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-91
Even when an Owner/Operator ‘Delegates Responsibility’ they’re still responsible. Ownership requires a lot of knowledge and money. It’s best to spend your money on quality aircraft maintenance instead of lawyers. You may live longer.
Then there is 91.407[b]… a required flight. The pilot made this required flight when the engine failed.
91.407 Operation after maintenance, preventive maintenance, rebuilding, or alteration.
(a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless –
(1) It has been approved for return to service by a person authorized under § 43.7 of this chapter; and
(2) The maintenance record entry required by § 43.9 or § 43.11, as applicable, of this chapter has been made.
(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.