Accident Summary
During the departure takeoff roll at approximately 700 feet of ground travel, the pilot observed that the left engine "seemed to lose a little manifold pressure" and initiated an aborted takeoff. While reducing power, the outboard section of the right wing "exploded." The airplane was brought to a stop on the runway, and all occupants were evacuated without further incident.
Examination Findings
Post-accident examination of the airplane revealed that the upper and lower portions of the right outboard wing skin had separated from the wing structure. The inboard fuel cell vent line nipple was found broken off from the fuel cell. Inspection of the area where the nipple had separated showed that the rubber was brittle and deteriorated.
Further investigation of the wing structure identified a 28-volt power wire associated with a wingtip recognition light modification. This wire was routed from the wing root area to the wingtip, following an aft stringer and passing through ribs via stringer cutouts without any chafing protection. The wire was found to be shorted, with evidence of arcing to the wing structure.
Maintenance Background
The airplane was equipped with four flexible rubber fuel cells, two in each wing panel. The fuel cell involved in the accident was produced in 1977 and installed during the airplane's completion in 1978. The wingtip recognition light modification was completed in 1987. According to the PA-31-350 Service Manual Inspection Report Checklist, maintenance requirements included inspecting fuel cells and lines for leaks, checking the condition of the fuel cell material every two years, and inspecting and replacing fuel cell vent lines as required or every five years, whichever came first.