N132HDBell OH-58A · 1972

During an aerial application flight while spraying a corn field, the helicopter’s tail section struck a powerline. The pilot did not see the powerline, which crossed over the middle of the cornfield perpendicular to the spray pass he was performing, but he knew what he had struck as soon as the helicopter came into contact with it. He had already begun to pull up out of the field when the helicopter struck the powerline and was still moving forward at approximately 50 mph. As the helicopter slowed and he reached about 200’ agl, the helicopter began a yaw to the right that developed into an uncontrollable spin in the same direction. As the helicopter began spinning faster and faster, the pilot rolled off throttle to minimize the torque induced rotations. During the touchdown, the helicopter impacted in an approximately level attitude, and then rolled over on its right side, and was substantially damaged. The pilot noted that there were no preimpact mechanical malfunctions or failures of the helicopter that would have precluded normal operation and that the accident could have been avoided if more “field recon” procedures were done to be certain that powerlines are avoided.

On September 24, 2010, about 1245 central daylight time, a Bell OH-58A helicopter, N132HD, operated by Cahaba Forestry Services, was substantially damaged during a forced landing into trees, following a total loss of engine power while surveying an area for spraying near Taylorsville, Mississippi. The certificated commercial pilot incurred serious injuries. The aerial application flight was conducted under the provisions of 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed and no flight plan was filed for the local flight, which had departed a nearby field.

The pilot reported that he was flying at 100 feet above ground level, at 57 knots, when the engine lost all power without warning. The pilot saw a hole in the trees at his 2 o'clock position and attempted to autorotate to that spot; however, the helicopter impacted trees. During the impact, the tailboom separated, a main rotor blade separated, and the fuselage was substantially damaged.

According to a Federal Aviation Administration (FAA) inspector, during a postaccident wreckage examination, impact signatures observed on the rotor blades and transmission were not consistent with high engine power or rotor rpm at impact. The inspector drained about 16 gallons of fuel from the wreckage, including fuel in the fuel line to the fuel nozzle. No visible contamination was observed in the drained fuel.

The pilot, age 46, held a commercial pilot certificate, with a rating for rotorcraft helicopter. He also held a private pilot certificate, with a rating for airplane single-engine land. The pilot reported a total flight experience of 10,000 hours; of which, 8,000 hours were in helicopters and 800 hours were in the same make and model as the accident helicopter. His most recent FAA second-class medical certificate was issued on June 14, 2010.

The helicopter was originally manufactured in 1973 by Bell Helicopter and delivered to the U.S. Army. The helicopter subsequently received a restricted type certificate from Garlick Helicopters in 1997. It was equipped with a Rolls Royce (Allison) T63-A-720, 420-shaft horsepower engine. At the time of the accident, it was registered with the FAA in the restricted category and used for aerial application. The helicopter's most recent 100-hour inspection was completed on May 17, 2010. At that time the helicopter had accrued about 8,911 total hours of operation and the engine had accumulated 329 hours since overhaul. The helicopter had flown 119.7 hours since the last inspection.

The helicopter was recovered to a hangar. The fuel boost pump was removed from the helicopter and examined under the supervision of an FAA inspector. In addition to providing added fuel pressure, all fuel passed through the fuel boost pump to reach the engine. The examination revealed that the fuel boost pump inlet shut-off valve arm was bent, and the bending was not consistent with impact forces. The fuel boost pump was then setup for a field test. When power was applied to the pump, it pumped fuel from a bucket; however, it did not appear to pump the fuel at maximum capacity. The fuel boost pump was then forwarded to Bell Helicopter for further examination under the supervision of an FAA inspector. The pump was subsequently tested with both the bent arm installed and a replacement stock arm. The test results were similar for both arms, which were both below the pump's flow requirements.

The bent inlet shut-off valve arm was re-installed and the fuel boost pump was then forwarded to the pump manufacturer's facility for a third examination under the supervision of an FAA inspector. That examination revealed that the pump was manufactured in 1983 and overhauled by a different company in 1989. The pump's ring tong terminals and pump cartridge were not the models that were originally installed in 1983. Rather, they were for a different model fuel boost pump; however, the pump passed flow tests as received. Additionally, flow improved when the inlet valve stem assembly and cartridge were replaced, respectively.

The engine was removed from the helicopter and placed in a test-stand for a test-run under the supervision of an NTSB investigator. During the set-up, leaks were detected at both ends of the Pc line connecting the Pc filter to the power turbine governor T-fitting; however, the engine was started and generated 368 shaft horsepower. Although the engine did not attain the rated 420 shaft horsepower, no anomalies were detected during the test-run that explained the total loss of engine power.

The annunciator panel and fuel pressure switch were examined at Bell Helicopter, under the supervision of an FAA inspector. The filaments of the "FUEL BOOST" caution bulbs of the annunciator panel were intact and did not exhibit any elongation. The fuel pressure switch passed a functional check, opening and closing within specifications.

Review of U.S. Army Technical Bulletin TB 1-1520-248-20-60 revealed:

"... During two accident investigations, the inlet shutoff valve arm of the cartridge type fuel pump was found bent. This condition may result in power loss or flameout due to restriction of fuel flow...WARNING...A bent inlet shutoff valve arm may prevent the shutoff valve from completely opening causing a restricted fuel flow..."

The recorded weather at an airport 20 miles southeast of the accident site, at 1255, included calm winds and visibility 10 miles.