MIA96LA028

The pilot stated he was making an approach for landing at a field site when the helicopter experienced a partial loss of engine power. He lowered the collective and rolled the throttle to the full on position. The helicopter collided with power lines and the ground. Review of the aircraft log books revealed that the last annual inspection was completed 3 months before the accident. The carburetor was not approved for use by the franklin engine company. Examination of the carburetor heat control valve revealed an incorrect spring installed, and the carburetor heat could not be activated from the cockpit. The carburetor icing probability chart shows the possibility of carburetor icing conditions based on the weather at the time of the accident. Prior to the approach, the pilot had completed the before-landing check without the aid of a checklist, and the carburetor heat was not turned on.

On November 15, 1995, about 1100 eastern standard time, a Bell 47D1, N4702S, registered to a private owner, operating as a 14 CFR Part 137 aerial application flight, without having been issued an FAA Part 137 certificate or operating specifications, experienced a partial loss of engine power on landing, and crashed in the vicinity of Jasper, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The helicopter sustained substantial damage. The commercial pilot reported no injuries. The flight originated about 15 minutes before the accident.

The pilot stated he was returning to a field site to pick up chemicals. The before landing check was completed without the aide of a checklist, and he did not turn the carburetor heat on. He planned his approach to an open field bordered by houses on both sides, and a power line that crossed the final approach path. He started his descent at about 100 feet agl and 50 knots, when the engine experienced a partial loss of engine power. He felt he had sufficient altitude to clear the power lines. The engine sputtered, rotor rpm decayed, and manifold pressure decreased. He lowered the collective pitch and rolled the throttle to the full on position. The skids of the helicopter collided with the power line and separated. He lowered the collective pitch to full down position. No forward application of cyclic was applied. The helicopter descended vertically. Full up collective pitch was applied at about 3 feet, and the helicopter collided with the ground.

Review of the aircraft log books revealed the last annual inspection was conducted on August 6, 1995. Examination of the engine assembly and accessories by Gulf Coast Helicopters Inc., Panama City, Florida, revealed no evidence of a precrash failure. Compression was found on all cylinders using a pressure differential check. The helicopter was equipped with a Marvel Schebler carburetor, part number 10-4025-12. The carburetor was not approved for use by the Franklin Engine Company. An incorrect spring was installed on the carburetor heat control valve and the carburetor heat could not be activated from the cockpit. (See Gulf Coast Helicopters. Inc., statement.)

Review of the probability icing chart revealed that the engine would encounter icing at glide and cruise power based on the weather observation at the time of the accident.