LONDON, TX, USA
N7404F
HUGHES 269C
DURING A COYOTE ERADICATION FLIGHT, THE AIRCRAFT EXPERIENCED A PARTIAL POWER LOSS. THE PILOT STATED THAT WHILE HE WAS MANEUVERING AT LOW ALTITUDE AND AIRSPEED, HE FELT A VIBRATION THROUGH THE AIRFRAME, THE ENGINE AND MAIN ROTOR RPM BEGAN TO DECREASE, AND THE NEEDLES SPLIT. HE APPLIED FULL POWER, BUT THE ENGINE WOULD ONLY DEVELOP 2,000 RPM. WHILE THE PILOT WAS MANEUVERING TO A CLEAR AREA, THE MAIN ROTOR BLADES STRUCK TREES AND THE AIRCRAFT ROLLED TO THE RIGHT AND IMPACTED THE GROUND. FOLLOWING THE ACCIDENT, THE ENGINE WAS TEST RUN IN THE AIRFRAME AND FOUND TO BE RUNNING ROUGH. INVESTIGATION REVEALED THAT THE ENGINE CAMSHAFT LOBES WERE WORN BEYOND LIMITS AND THE #4 EXHAUST VALVE WAS HEAT DISCOLORED AND SHOWED SIGNS OF STICKING.
On June 20, 1994, approximately 1830 central daylight time, a Hughes 269C, N7404F, was destroyed when it collided with trees and the ground near London, Texas. The helicopter, leased to and operated by the U. S. Department of Agriculture and flown by a commercial pilot, was on a local animal damage control flight. Company flight following was being utilized and visual meteorological conditions prevailed. The pilot and the one observer/gunner received minor injuries. According to the operator, the flight was part of a coyote eradication program. The flight had departed the Junction, Texas, Kimble County Airport at 1730, and flown to a local ranch, where the pilot and observer met with the ground search team. Shortly thereafter, the flight departed to the search area. The pilot stated that, due to the nature of the mission and the terrain cover, he was flying the search pattern at a height of 35 to 40 feet at about 30 knots. After searching the area for several minutes, the observed informed the pilot that he had spotted a target. Shortly after the gunner had spotted and opened fire on a coyote, the pilot felt what he described as a "short but violent" vibration in the anti- torque pedals. He said he initiated a right turn and began looking for a place to land. He then noticed that the engine RPM was dropping rapidly, the engine/rotor RPM needles were split, and the rotor RPM was bleeding off with the engine RPM. The pilot said he immediately applied full throttle, but the engine would only produce 2,000 RPM. At that point, he attempted to maneuver around some 10 foot high trees to a clear area. During the maneuver, the main rotor blades struck the trees and the aircraft rolled onto its right side and impacted the ground. Following recovery of the wreckage, the engine was run in the accident airframe with the main rotor and tail rotor drives disconnected. The engine started on the second attempt and was run at idle power and 2,000 RPM for a period of 25 minutes. The engine ran rough and there was a vibration through the airframe. Following the test run, the engine was removed from the airframe and disassembled. During the disassembly, wear was noted on all of the camshaft lobes, except the #2 cylinder exhaust valve lobe and the lobe for the #3 and #4 intake valves. It was also noted that the #4 exhaust valve was scored and had heat discoloration two thirds of the way down the valve stem. The #4 exhaust discharge ran cooler than the rest of the cylinders during the engine test run.
THE PARTIAL POWER LOSS DUE TO A STICKING VALVE. FACTORS WERE THE REMAINING WORN LOBES ON THE CAMSHAFT AND THE LACK OF SUITABLE TERRAIN ONTO WHICH A SUCCESSFUL FORCED LANDING COULD BE EXECUTED.
Source: NTSB Aviation Accident Database
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