Accident Overview
On January 24, 2018, about 1656 eastern standard time, a Schweizer 269C-1, N3947C, operated by Pelican Flight Training LLC, was substantially damaged during a 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 conducted under Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed. The intended destination was North Perry Airport (HWO), Hollywood, Florida.
Flight Details
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, while the flight instructor kept the engine running at 2,500 rpm. Once the student re-entered, 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 and started traveling forward. As the helicopter approached the edge of the rooftop, the low rotor rpm light and horn activated simultaneously. The helicopter began sinking. The instructor immediately lowered the collective and attempted to add throttle, which did not stop the descent. He repeated the procedure a second time and realized 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.
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.
Aircraft and Engine Information
According to FAA airworthiness records, the two-seat, skid-equipped helicopter was manufactured in 2008 and 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.
Weather
Weather conditions reported about the time of the accident at Fort Lauderdale/Hollywood International Airport (FLL), about 3 miles south of the accident site, included wind from 030° at 8 knots, visibility 10 statute miles, scattered clouds at 2,700 ft, broken ceiling at 6,000 ft above ground level, temperature 23°C, and dew point 21°C.
Examination Findings
During a postaccident examination conducted by an FAA inspector, engine cylinder compression was checked with the engine at ambient temperature. Each cylinder produced a normal result, except the No. 4 cylinder, which produced 20/80. As the pressure gauge was being evaluated, a "metallic snap or click" was heard, 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 rpm drop 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 buildup 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 buildup. A subsequent wobble test on the No. 4 cylinder intake and exhaust valve showed the exhaust valve had normal side play, but the intake valve had no side play, which was abnormal.
Maintenance History
According to engine overhaul records, four factory new cylinders were installed on the engine in April 2015. According to the mechanic who 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.
The flight instructor, who routinely flew the accident helicopter on training flights, reported that about 3 months prior to the accident, he experienced a "knocking" sensation that could be felt through the flight controls. He did not believe it was anything serious but verbally reported the event to the flight school's mechanic. The mechanic reportedly said he should report it if it happened again. During a postaccident interview, the flight instructor further reported that 3 days before the accident, while flying straight and level, he would occasionally feel a "tiny bump."
The Textron Lycoming Service Instruction No. 1425A, dated January 19, 1988, titled "Suggested Maintenance Procedures to Reduce the Possibility of Valve Sticking," stated that field experience has shown engine oil contamination increases the possibility of sticking and/or stuck valves. The instruction noted that contaminants in engine lubrication oil can become deposited on valve stems, restricting valve movement and resulting in intermittent engine hesitation or miss. If corrective action is not taken, a valve could become stuck, causing engine damage. The instruction also stated that operating in high ambient temperatures, slow flight with reduced cooling, or high lead content of fuel can promote deposit buildup and result in valve sticking. It recommended inspection and cleaning of valves if any of these conditions are present or if hesitation is observed.
No maintenance record was found indicating that this service instruction or a cleaning of the valves had been performed.