PACOIMA, CA, USA
N112WM
Miller ROTORWAY EXEC 162F
The experimental helicopter experienced a loss of engine power in the takeoff initial climb, about 450 feet agl, and the pilot autorotated to a hard landing on a city street. A witness who saw the helicopter hovering before takeoff said that the engine 'missed' twice before the helicopter took off. After the helicopter took off and was about 80 to 90 feet agl, he heard the engine make a 'sputtering' or 'popping' noise. This flight was the first test flight after building the helicopter and the pilot had completed 4.3 hours of engine run-ups and hover time. Examination of the engine found that the No. 3 cylinder intake valve stem cap was damaged and the rocker arm was loose. The valve lash clearances on the other three cylinders were found to be from 0.006 to 0.022 inches greater than the manufacturer's specifications. No other damage was noted to the engine or valve train. The No. 3 cylinder intake valve stem cap was replaced and the other valve clearances set to the proper 0.004-inch specification. The engine was then installed in a test cell and performed normally during all operational tests. The RotorWay Engine Manual instructs owners to measure and adjust the valve lash, and states, 'if any adjustment is necessary at one hour, valve adjustment should be repeated hourly until the lash stabilizes.' The pilot reported that he had made a total of four adjustments during the first inspection, but after that, all measurements had been within the manufacturer's specifications.
On June 25, 1999, at 1543 hours Pacific daylight time, a amateur-built Miller Rotorway Exec 162F helicopter, N112WM, experienced a loss of engine power and force landed on a city street after takeoff from the Whiteman Airport, Pacoima, California. The experimental helicopter, owned and operated by the pilot, sustained substantial damage. The pilot, who held an airline transport pilot certificate for multiengine aircraft and had private privileges for helicopters, suffered serious injuries. The local area test flight was conducted under the provisions of 14 CFR Part 91 and originated at the Whiteman Airport about 1536. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that the accident flight was his first planned test flight after building the helicopter. Prior to that, he had completed 4.3 hours of engine run-ups and hover time. The pilot stated that after receiving a clearance from the air traffic control tower, he took off from the taxiway parallel to runway 12 for a left crosswind departure. He turned left about 450 feet agl and immediately felt a vibration and observed the rotor rpm decreasing to the lower portion of the green arc (approximately 96 to 104 percent). He added power to increase the rpm and the engine failed. He lowered the collective, applied slight left pedal, and established a glide speed of 65 knots. He engaged the starter to re-establish power but received no response. He turned left toward a park, but decided to alter his course to land on a city street to minimize injury to people on the ground. The helicopter impacted the ground in a hard landing. The pilot closed the fuel shutoff valve, turned all electrical switches off, and exited the helicopter without assistance. The fire department reported that they drained fuel from the tanks following the accident. The pilot said that he had taken off with 17 gallons of fuel on board. A witness at the airport reported that he was watching the helicopter as it was running up. He was about 40 feet away from the helicopter at the time. When the helicopter started to liftoff the ground, he heard the engine "miss." He stated that a few minutes later as more power was applied, he heard the engine "miss" again. Two more witnesses approached as the pilot began hover taxiing. The witnesses stated that the helicopter took off, and about 80 to 90 feet agl, the engine made a "sputtering" or "popping" noises. He assumed that the helicopter was returning to land on the helipad and was surprised when it continued away from the airport. A postcrash examination of the helicopter was conducted. Continuity of the flight controls was established. No external damage was noted to the engine. When the rocker covers were removed from the engine, the No. 3 cylinder intake valve stem cap was found damaged and the rocker arm was loose. No other damage was observed to the valve train. The engine was removed from the helicopter and shipped to RotorWay's facilities in Chandler, Arizona. The engine was examined and run on a test cell under the supervision of the Federal Aviation Administration (FAA). While preparing the engine for the test run, the valve covers were removed and all valve clearances were measured with the following results. The No. 1 cylinder exhaust valve was loose; the intake valve clearance measured 0.012 inches. The No. 2 cylinder exhaust valve clearance measured 0.010 inches; the intake measured 0.008 inches. The No. 3 cylinder exhaust valve clearance measured 0.024 inches; the intake valve stem cap was damaged. The No. 4 cylinder exhaust valve clearance measured 0.019 inches and the intake measured 0.028 inches. According to the RotorWay International RI-162F Engine Manual, the valve lash specification is 0.004 to 0.006 inches. A copy of the relevant portions of the manual is appended to this file. The No. 3 cylinder intake valve stem cap was replaced. All other valve lash clearances were then set to the specified 0.004 inches. The engine was rotated by the crankshaft with no unusual noises or binding observed, then installed onto the test stand. The engine started without difficulty and was warmed up at an idle speed of 1,900 rpm. When the oil temperature reached 160 degrees Fahrenheit, the engine was then accelerated to full power, 4,250 rpm and 28.2 inches of manifold pressure. No discrepancies were noted. Rapid accelerations/decelerations were performed smoothly and responsively with no abnormalities. The engine performed normally during all operational tests. The RotorWay International Engine Manual lists specific maintenance requirements to measure and adjust the valve lash and inspect the valve train. In pertinent part, the manual states, "If any adjustment is necessary at one hour, valve adjustment should be repeated hourly until the lash stabilizes . . . (Initial 'break in' of the valve train may require several hourly adjustments . . . It is extremely important to make these inspections and adjustments.)" The pilot held a FAA repairman certificate for this RotorWay Exec 162F. Further, he reported that an FAA certified airframe and powerplant mechanic assisted him with the work performed on the helicopter. The pilot/repairman supplied the Safety Board investigator with the notes he had taken during the four hourly valve inspections. On one side he noted what measurement he had actually read, and on the other side he noted what measurement he adjusted the valve to. The notes reflected that on the second, third, and fourth inspections, all measurements were within the manufacturer's specifications and no adjustments were performed. During the first valve inspection, the pilot/repairman made a total of four adjustments. When asked what he used to measure the valve lashes, the pilot/repairman reported that he used the feeler gauge specified by RotorWay. Further, he stated that he had modified the feeler gauge, in accordance with the RotorWay manual, which instructed owners to narrow the gauge to 0.375 inches.
The pilot's improper valve adjustments and failure to follow the manufacturer's instructions, which resulted in a loose number 3 cylinder rocker arm and a loss of engine power.
Source: NTSB Aviation Accident Database
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