Introduction
On September 14, 2013, at approximately 1224 mountain standard time, a Cessna 182A (registration N6324B) sustained substantial damage during a forced landing while on approach to Casa Grande Municipal Airport in Casa Grande, Arizona. The aircraft was registered to Aivcon Inc. and operated by Phoenix Aerial Skydiving under 14 CFR Part 91. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local skydiving flight, which had originated from the same airport about 24 minutes prior.
Sequence of Events
The pilot reported having completed six earlier skydiving flights that day. After the sixth flight, he had the airplane refueled by a fixed base operator, requesting 10 gallons added to each wing tank. The lineman indicated that the right tank took only a couple of gallons before becoming full. The pilot visually confirmed the right tank was full and then asked for seven gallons in the left tank. He believed the total fuel onboard after refueling was 40 gallons. He then performed three more skydiving flights.
During the final approach for landing, the pilot reported that engine oil temperature and pressure were within normal ranges. He performed the GUMPS checklist, which included checking that carburetor heat was on. About 100 feet above ground level, he added throttle, but the engine did not respond. He verified that the engine controls were fully forward. Despite attempts, he could not restart the engine and initiated a forced landing to an open area adjacent to the airport. During the landing roll, the airplane struck a ditch and nosed over.
Post-Accident Examination
An FAA inspector examined the wreckage and noted the left wing was buckled, and the vertical stabilizer and rudder were damaged. The smell of fuel was present, and fuel was leaking from the wings. The wreckage was recovered to a secure facility; recovery personnel removed 7 gallons from the right fuel tank and 11 gallons from the left fuel tank.
The engine and airframe were examined by FAA and NTSB representatives. The Continental O-470-R engine was prepared for a test run using an external fuel source attached at the wing roots. The carburetor inlet screen was partially blocked (about one-third) with light fibrous debris. The engine started and ran smoothly at various power settings. No evidence of mechanical malfunctions or failures that would have precluded normal operation was found.
Fuel System Findings
The cabin fuel gauges were inoperative. The airframe fuel system from the wing roots to the engine showed no anomalies. Both wing fuel tank bladders were examined. The left bladder was loose from one of its upper attach points. The right bladder had a large fold (about 2.5 inches high) on the lower surface directly below the filler neck, running diagonally from the aft wing root to the leading edge, about 2 feet outboard. The fuel sending unit was undamaged. Interior surfaces of the bladder showed multiple folds on the lower surface and a drooping upper surface outboard and aft of the filler neck. Several hanger clips were not attached to their wing structure attach points; the forward outboard and two forward inboard clips remained attached. The upper aft outboard and two lower aft outboard hanger clips were missing.
Weather and Maintenance
Weather recorded at the airport at 1235 included wind 130° at 4 knots, visibility 10 statute miles, clear skies, temperature 35°C, dew point 16°C, and altimeter 29.71 inHg. According to an FAA Special Airworthiness Information Bulletin on carburetor icing prevention, these conditions were conducive to icing at glide power.
A review of maintenance logbooks showed the most recent annual inspection was completed on August 30, 2013. That inspection included replacement of seven upper fuel bladder hanger clips on the left tank and replacement of the right bladder. An airworthiness directive aimed at preventing power loss due to water contamination, requiring detailed inspection of wing fuel bladder assemblies, was reportedly complied with at that annual inspection, 15 days before the accident.