The pilot reported that, during the landing flare, the Schilling S-19, an experimental, amateur-built airplane, “ballooned.”
He then relaxed back pressure on the control stick to correct, however the plane then hit the runway hard and departed the left side at the airport in East Falmouth, Mass.
Examination of the wreckage revealed that the stabilator trim tab (antiservo tab) push-pull tube’s threaded end had separated from its connection, that the associated nut remained loose on the threads, and that the three end threads were stripped.
Further examination revealed that only three of the threads in the push-pull tube’s threaded end were engaged in the trim tab connection and that about 1 inch of the threaded portion of the push-pull tube was exposed and visible on the opposite side of the securing plain nut.
The kit manufacturer’s assembly manual cautioned that a minimum of 10 threads must be engaged to secure the stabilator trim tab push-pull connection.
The manual also stated that about 0.5″ of the threaded end of the push-pull tube should be exposed and visible on the opposite side of the securing plain nut.
The builder assembled the airplane from a kit, and it was issued a special airworthiness certificate about 20 months before the accident. The pilot purchased the airplane from the builder about five months before the accident.
At the time of the accident, the airplane had accumulated 94.5 total flight hours.
The pilot performed the last condition inspection about four months before the accident, which was 32.8 total flight hours before the accident.
The excessive thread exposure on the opposite side of the securing plain nut would have been detectable during the most recent condition inspection, however, the pilot/owner failed to detect the excessive thread exposure during the inspection.
Probable cause: The experimental airplane builder’s failure to properly secure the stabilator trim tab push-pull tube’s connection, which resulted in the tube’s separation and a subsequent hard landing. Contributing to the accident was the pilot/owner’s failure to detect the improperly secured connection during a recent condition inspection.
NTSB Identification: ERA15LA360
This September 2015 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.