Accident Overview
On February 19, 2022, at 1310 eastern standard time, a Robinson Helicopter R44, registration N544SB, was substantially damaged when it impacted water near Miami Beach, Florida. The pilot and two passengers sustained serious injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
Flight and Sequence of Events
The pilot reported departing a helipad in Marathon, Florida, about an hour before the accident, and was returning along the coastline to North Perry Airport (HWO) in Hollywood, Florida. While flying overwater parallel to the South Miami Beach area, the helicopter experienced a sudden and violent left-to-right shaking and vibration, followed by a loss of engine power and activation of a low rotor rpm warning light and horn. The pilot attempted to increase engine power but realized the engine had lost power and initiated an autorotation. He maneuvered the helicopter toward an area of shallow water between two groups of people. The helicopter impacted water about 10 seconds after the vibration began. The pilot assisted his passengers in evacuating, and beachgoers provided additional assistance to reach the shore. The pilot recalled flying at 420–450 ft above ground level at an airspeed of 85–95 knots when the loss of engine power occurred. Before the loss of power, the helicopter had been functioning normally without issue.
Post-Accident Examination
A Federal Aviation Administration inspector examined the helicopter at the accident site and recovery facility. The fuselage, tail boom, and tail rotor sustained substantial damage. One main rotor blade remained intact with little damage, while the other had fractured about mid-span. The National Transportation Safety Board examined the helicopter at the recovery facility. Examination of the flight controls found no anomalies that would have prevented normal control or contributed to the vibration. The engine and its accessories displayed significant saltwater corrosion consistent with submersion post-accident. Examination of the engine revealed no evidence of a catastrophic failure of the engine core or its accessories. All cylinders were removed from the engine case and disassembled to examine individual exhaust and intake valves, springs, and pistons. No anomalies were found within the cylinders except varying amounts of corrosion to valves, cylinder walls, and pistons, consistent with saltwater submersion.
Maintenance History
According to maintenance records, four cylinders were replaced in the year preceding the accident. From March 1, 2021, through December 11, 2021, the Nos. 2, 4, and 6 cylinders (and a second time, the No. 2 cylinder) were removed, overhauled, and reinstalled. According to maintenance endorsements and interviews with the mechanic who performed the work, the cylinder replacements were due to low compression and stuck piston valve issues. The pilot reported experiencing a similar engine malfunction and vibration sensation while in hover flight months before the accident, around the time of one of the cylinder replacements. During that event, he performed an autorotation from a hover and landed without incident. After the event, a burnt intake valve was discovered. He recalled that a total of four intake valves were discovered burnt over the year before the accident. The most recent 100-hour inspection occurred on August 1, 2021, at hour meter time 1,509.5; the most recent annual inspection was completed on March 1, 2021. The hour meter at the time of the accident was 1,646.6. The Robinson Helicopter R44 maintenance manual specifies inspection intervals at 100 hours’ time in service or 12 calendar months, whichever occurs first. The Textron Lycoming Service Instruction No. 1425A (January 19, 1988) noted 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; it recommended inspection and cleaning of valves if these conditions are present or hesitation is observed, and noted that exposing the engine to sudden cool down (as in a rapid descent with reduced power or shutting down before sufficient cool-down) can also induce valve sticking.