CHI93DCD02

The airplane was on a swath run, when the right wing buckled, and the airplane rolled into a descent and crashed. A post-accident examination of the airplane revealed that the forward spar fuselage attachment assembly for the right wing had failed from fatigue at the clevis ears. On 9/21/91, there was a similar failure of a Piper PA-25. On 5/13/92, the NTSB made an urgent recommendation to the FAA that an airworthiness directive (AD) be issued for Piper PA-25 airplanes to be inspected immediately for corrosion and cracking of the clevis ears; that if such corrosion or cracking was found, repairs be made; and that periodic inspection requirements be established to detect cracks before they become critical. On 7/16/92, the FAA agreed with the intent of the recommendation, but as of the date of the accident, no inspection procedure was in effect.

History of flight

On May 21, 1993 at approximately 1045, Piper PA-25, N6453Z crashed and burned while conducting aerial application of a weed herbicide spray (2-4-D). A witness observed the right wing "buckle" upward and the aircraft struck the ground inverted and came to rest in an upright position approximately 100 feet from the primary impact point. The 14 CFR Part 137 flight was operating in day VFR meteorological conditions. No flight plan was on file. The aerial application flights originated at the Shenandoah Municipal Airport, (SDA) Shenandoah, Iowa, which was the operator's normal base of operations. The exact time of the departure of this flight was unknown. The pilot had conducted several aerial application flight that day, however, the exact count of flights is not known.

Personal information

The pilot held a commercial pilot certificate with a multi-engine rating. He held a flight instructor certificate with single- engine land, multi-engine land and instrument ratings. The pilot had a second class medical dated December 6, 1992, with the limitation to wear corrective lenses.

Aircraft information

Piper PA-25, S/N 25-640, N6453Z Estimated total airframe time in service: 5375 Last inspection: 11/09/92 @ 2668 hrs Tach., 5341 hrs Total Time

Wreckage and impact information

The ground marks indicate that the aircraft struck the ground in an inverted, nose down, wing level attitude. The wreckage path was approximately 150 feet from, and nearly parallel to a power transmission line. There was no evidence of any contact with the power lines.

Pieces of white colored paint flakes with fabric imprint on the blue colored back side were found along the witness observed flight path. The first pieces were found approximately 40 yards prior to the first impact point. The paint flakes matched the finish on unburned bits and pieces of fabric covering found on the aircraft.

The first impact mark contained pieces of green (right) wing tip position light lens and a piece of the lens retaining cover which matched the portion of the cover still attached to a piece of the right wing tip. This impact mark was roughly centered along the centerline of the wreckage path. The primary impact crater was located approximately 15 yards further along the wreckage path. It contained a crater in which the fixed pitch propeller and a portion of the engine cowling were found. Approximately 5 yards further along the wreckage path was a slightly visible impact mark line to the right of the wreckage path. This line was approximately 20 feet long, had regularly spaced indentations along its outer portions and was at a right angle to the wreckage path centerline. Pieces of the red (left) wing tip position light lens and wing tip were located in a small crater at the outermost end of that impact line. Examination of the relatively intact left wing disclosed flattening of the upper portion of the leading edge along its outer length beyond the wing strut attachment. The spacing of the leading edge nose ribs matched the regular spacing of the indentations observed in the impact line described above.

There was no physical evidence nor any witness observations of the aircraft contacting any "electrical wires".

Medical and pathological information

According to the autopsy report, no medical or pathological causative factors were noted.

Fire

The aircraft was destroyed by impact and post impact fire. All of the fabric covering of the wings, fuselage and empennage was consumed. The fire in the area of the cockpit was of sufficient intensity to consume the aluminum components of the instrument panel and instruments. Only ferrous and copper/brass alloy parts and wiring remained.

Tests and research

Both front spar fuselage fittings and associated wing spar attachment parts from the left and right wings were removed for laboratory analysis of the fractured surfaces. See NTSB Metallurgist's Factual Report No. 93-138 / Sept. 21, 1993.

Additional data / information

The wreckage has been released to the operator's insurance company representative.