Fort Lauderdale, FL, USA
N3947C
SCHWEIZER 269C
The helicopter was departing from a rooftop helipad, and the flight instructor noticed that, during the initial climb, as the helicopter crossed over the rooftop edge, the low rotor rpm horn and light activated. The helicopter then began to descend. The flight instructor lowered the collective and attempted twice to increase the throttle, but his actions did not stop the descent. Subsequently, he performed an autorotation to a street below the helipad and landed hard, resulting in substantial damage to the tail rotor and tailboom. During a postaccident examination and test run of the engine, the engine produced idle power, but the No. 4 cylinder's compression checks were not normal. The No. 4 cylinder intake and exhaust valves were examined, and both displayed a significant amount of carbon deposit buildup on the valve stem. The intake valve was found stuck in its valve guide and was scratched and scarred. The source of the scarring to the intake valve was not determined. Given the signatures observed on the No. 4 cylinder intake valve, it is likely that, during the initial climb, the intake valve became stuck, which resulted in a partial loss of engine power.
On January 24, 2018, about 1656 eastern standard time, a Schweizer 269C-1, N3947C, operated by Pelican Flight Training LLC., was substantially damaged during an forced landing after takeoff from the Downtown Fort Lauderdale Heliport (DT1), Fort Lauderdale, Florida. The flight instructor and student pilot were not injured. The flight was operated in accordance with Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed for the flight that was destined for North Perry Airport (HWO), Hollywood, Florida.According to the flight instructor, the purpose of the flight was to demonstrate radio communication procedures to the student pilot, who was enrolled in an air traffic control training program. The flight departed HWO and after about 35 minutes of flight time, the helicopter landed uneventfully at the DT1 rooftop helipad. The student pilot exited the helicopter for a few minutes to take photographs, the flight instructor kept the engine running at 2,500 rpm, and once the student re-entered the helicopter, the instructor entered a hover to depart the helipad. The flight instructor reported that he demonstrated a maximum performance takeoff procedure; the helicopter gained altitude, started traveling forward, and as the helicopter approached the edge of the rooftop, simultaneously, the low rotor rpm light and horn activated. The helicopter started sinking and he immediately lowered the collective and attempted to add throttle, which did not stop the descent, so he repeated the procedure a second time, and realized that he already had full throttle applied. The sink continued, and he performed an autorotation landing to a street below and ahead of the helicopter's flight path. According to Federal Aviation Administration (FAA) airman records, the flight instructor held commercial pilot and flight instructor certificates with ratings for rotorcraft-helicopter and instrument-helicopter. His most recent second-class medical certificate was issued in May 2017. According to FAA airworthiness records, the two-seat, skid-equipped, helicopter, was manufactured in 2008, and was equipped with a Lycoming HIO-360-G1A, 180-horsepower engine. The most recent annual and 100-hour inspection was performed in September 2017. The engine had accumulated 297.1 hours since the last major overhaul in April 2015. The weather conditions reported about the time of the accident at Fort Lauderdale/Hollywood International Airport (FLL), Fort Lauderdale, Florida, which was located about 3 miles south of the accident site, included wind at 030° at 8 knots, visibility 10 statute miles, sky conditions scattered at 2,700 ft and broken at 6,000 ft above ground level, temperature 23°C, and dew point 21°C. The helicopter landed hard on a street about 700 ft east, and about 110 ft below the rooftop helipad. During the landing, the helicopter's tail rotor and tail boom sustained substantial damage. During a postaccident examination conducted by an FAA inspector, the engine cylinder compression was checked with the engine at ambient temperature. Each cylinder produced a normal result, except for the No. 4 cylinder, which produced 20/80. As the pressure gauge was being evaluated during the test, a "metallic snap or click" was heard by the inspector, and the pressure jumped to 40/80. The engine was then cranked with the electric starter for about 15 seconds, and the No. 4 cylinder compression rose to 78/80. The engine was started with its existing fluids and accessories and produced idle power. Both magnetos produced an acceptable drop in rpm during the test. Further examination of the No. 4 cylinder by the FAA inspector revealed that the exhaust valve stem had a thick coating of lead and carbon deposit build up but moved freely out of its valve guide. The intake valve was found sticking in its valve guide and had to be removed with a drift punch hammer. The intake valve stem displayed scarring and scratches and had significant carbon deposit build up. A subsequent wobble test was performed on the No. 4 cylinder intake and exhaust valve; the exhaust valve displayed normal side play, but the intake valve had no side play, which was abnormal. According to engine overhaul records, four factory new cylinders were installed on the engine in April 2015. According to the mechanic who had performed the past three annual and 100-hour inspections on the helicopter, none of the cylinders were removed during the inspections, nor would it be routine for him to do so. According to the flight instructor, who routinely flew the accident helicopter on training flights, about 3 months prior to the accident, he experienced a "knocking" sensation that could be felt through the flight controls. The flight instructor reported that he did not believe it was anything serious, but he verbally reported the event to the flight school's mechanic. According to the flight instructor, the mechanic said that he should report it if it happens again. During a postaccident interview, the flight instructor further reported to an FAA inspector that 3 days prior to the accident, while flying in the accident helicopter straight and level, he would occasionally feel a "tiny bump." The Textron Lycoming Service Instruction, No. 1425A, dated January 19th, 1988, Suggested Maintenance Procedures to Reduce the Possibility of Valve Sticking, stated in part: Field experience has shown that engine oil contamination increases the possibility of sticking and/or stuck valves. This situation occurs when the contaminants in the engine lubrication oil become deposited on the valve stems, restricting the valve movement, and resulting in intermittent engine hesitation or miss. If corrective action is not taken to remove the deposits, a valve could become stuck causing engine damage. The service instruction further stated in part that, operating in high ambient temperatures, slow flight with reduced cooling, or high lead content of fuel, can promote deposit build-up reducing valve guide clearance and result in valve sticking. If any of the conditions are present or hesitation is observed, the service instruction recommended inspection and cleaning of the valves. There was no maintenance record found that this service instruction, or that a cleaning of the valves, had been performed.
The partial loss of engine power during the initial climb due to a stuck intake valve on the No. 4 cylinder.
Source: NTSB Aviation Accident Database
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