The flight instructor and private pilot were conducting an instructional flight when the private pilot made a hard landing at the airport in Longmont, Colorado, and the airplane bounced.
The flight instructor heard a “snapping” sound during the landing and took over the flight controls.
He increased engine power to compensate for the bounced landing, then landed the American Champion 7GCAA on the runway.
Upon touchdown, the left landing gear collapsed up and aft. The airplane continued forward on its nose and left wing, then left the left side of the runway.
The left landing gear through bolt was found fractured. A metallurgical examination of the landing gear through bolt fracture revealed two opposing regions of fatigue comprising 80-90% of the cross-sectional area of the bolt.
These were separated by a narrow region of overstress, consistent with reverse bending fatigue crack propagation, which likely grew under low stress as evidenced by the length of the fatigue cracks.
The airplane was subject to a manufacturer service letter for inspection of the landing gear through bolts due to previous instances of cracking and failure. The service letter recommended that the inspections be performed on or before the next 100-hour inspection and at 100-hour intervals thereafter, and at more frequent intervals if the aircraft is used in soft or rough runway operations.
The owner of the airplane was unaware of the service letter and stated that the airplane had not received the recommended inspection.
Although not required, it is likely that had the service letter been complied with and the through bolt been regularly inspected, the fatigued bolt would have been replaced and the accident would have been prevented.
Probable cause: The failure of the landing gear through bolt primarily due to fatigue during a hard landing, which resulted in a landing gear collapse and runway excursion. Contributing to the accident was noncompliance with the manufacturer service letter.
NTSB Identification: CEN18LA059
This December 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Here’s a prime example of why manufacturer’s service letters, service bulletins and service instructions should be complied with, even if they don’t later become AD notes. Manufacturers don’t issue these things for their health! It’s another reason to keep comprehensive maintenance records, also!
And, this service letter has been in place for over 40 years.! The A&P IA who is doing the annuals should have know about all ADs, SB and SLs….no excuses.
So, more stupid pilot tricks by the instructor/ owner….