Factual Information
On 6 April 2016 at 11:16 UTC, a Robinson R44 Raven I helicopter, registration OK-SCI, was conducting an engine run-up test on the apron of Roudnice Airport (LKRO) in the Czech Republic. The aircraft was owned and operated by Letecké práce a služby, s.r.o. The pilot, a 50-year-old male holding a valid Private Pilot License (Helicopter) with type ratings for the R44 and R22, was preparing for his first solo flight on the type after a period of inactivity.
Sequence of Events
According to the pilot's statement, he arrived at the airport around midday, refueled the helicopter, and performed a preflight inspection. After climbing into the right seat, he started the engine and carried out pre-takeoff checks. During the test of the low rotor RPM warning system (sound and light), the helicopter suddenly began to rotate to the left. The pilot reported that he held the collective down and attempted to counteract with right pedal input, but was unsuccessful. He then turned off the governor, reduced throttle, and pulled the mixture control. The helicopter completed several 360-degree turns, moving approximately 21 meters backward and to the left from its original position. The tail boom struck a wooden fence on the northeast edge of the apron, and the tail rotor and main rotor blades contacted the trunk and branches of a tree behind the fence. The helicopter came to rest at the impact location.
Aircraft and Pilot Information
The helicopter, a Robinson R44 Raven I (serial number 1649, year of manufacture 2006), had accumulated 1365 hours total time. It was powered by a Lycoming O-540-F1B5 piston engine. The fuel tanks contained about 36 liters (20% capacity) of AVGAS 100LL at the time of the accident. The pilot's total flight experience was 64 hours and 36 minutes on all helicopter types, with 8 hours and 18 minutes on the R44. His last flight prior to the accident was on 4 April 2016, and he had decided to perform a refresher flight with an instructor due to the break, but on the accident day he was conducting an engine test.
Meteorological Conditions
According to the Czech Hydrometeorological Institute, the weather was influenced by a ridge of high pressure behind a cold front. Surface wind at the time was from 230-240 degrees at 10-14 knots, with occasional gusts up to 24-30 knots. Visibility was greater than 10 km, with scattered to broken clouds at 4000-5000 feet above mean sea level.
Damage
The helicopter sustained serious damage. The tail boom was deformed at its attachment to the fuselage and had a dent approximately 780 mm from the attachment point. The tail rotor gearbox was torn out, along with the mounting bracket for the horizontal and vertical stabilizers. Both tail rotor blades were damaged; one blade separated completely, and the other was severely deformed. The main rotor blades were also damaged by contact with tree branches. The fuselage had a small dent on the left door frame from a tail rotor fragment. No fire occurred.
Probable Cause
The accident investigation determined that the pilot did not pay sufficient attention to the position of the foot control pedals during the engine test and, contrary to the flight manual, did not press the governor release button when needed.