Background
On 26 April 2000, a Robinson R-44 helicopter, registration LY-HBH, owned by AB "Baltijas Helikopteri" and operated by UAB "Klaipėdos avialinijos", was involved in an accident near Lake Ungurs in the Cesis district of Latvia. The helicopter, serial number 0445, was manufactured on 16 March 1998 by the Robinson Helicopter Company in the United States. It had accumulated 118.2 hours of total flight time and had never undergone repairs. The airworthiness certificate (No. 00824) was valid until 3 May 2000. The engine, a Textron-Lycoming O-540-F1B5 (serial L-25198-40A), had also logged 118.2 hours. The last 100-hour periodic maintenance was performed on 3 September 1999 by a technician licensed by the Latvian CAA, and the helicopter had not flown for four months prior to the accident (since 23 December 1999).
Flight Sequence
The flight originated from Tallinn aerodrome at 11:55 local time, landing at Riga (Skulte) aerodrome at 13:40. After refueling with 98 liters of AVGAS LL-100, the helicopter departed Skulte at 15:23 and landed at Riga (Rumbula) aerodrome at 15:35. Following a post-flight check, it departed for Cesis aeroclub at 16:50 and landed there at 17:20. At 17:30, the helicopter took off with three passengers for a sightseeing flight. According to the pilot, the flight was conducted at an altitude of 500 feet, with occasional descents to 250 feet. A passenger seated in the left front seat was taking photographs.
Accident
While flying along the shore of Lake Ungurs over trees at an altitude of 250 feet and a speed of 40 knots, in a left bank of 10–15 degrees, at approximately 18:00, the pilot heard an audible warning and observed the "LOW RPM" warning light on the instrument panel. The helicopter began to descend and turn left. The pilot reduced collective pitch and entered autorotation. To avoid trees, he turned left toward a clearing. At a height of 8 feet, the pilot increased collective pitch to maximum. The landing was hard, with a high vertical descent rate. During the landing, the helicopter broke the landing gear skids and cross tubes, and a main rotor blade struck the tail boom twice. The helicopter then rolled onto its left side. One main rotor blade broke in half, and another bent. The aircraft sustained substantial damage, with debris scattered up to 130 meters.
Injuries and Damage
No injuries were sustained by the pilot or the three passengers. The helicopter was heavily damaged. No third-party property damage occurred. The pilot, a Lithuanian citizen, held a valid license (expiring 9 August 2000) and a Class I medical certificate (also expiring 9 August 2000). He had obtained his R-44 type rating on 17 June 1999. His total flight time was 5,568 hours, with 18 hours and 4 minutes in the previous 90 days. Total time on the R-44 was 17 hours, with 5 hours and 24 minutes in the previous 90 days. His R-44 qualification was last checked on 7 April 2000. An alcohol test on the pilot was negative.
Post-Accident Examination
Examination of the helicopter revealed: deformed fuselage; broken main landing gear supports and skids; one main rotor blade broken and another deformed; tail boom cut and broken; tail rotor blades broken; tail rotor driveshaft broken into three pieces; deformed instrument panel; damaged air filter housing; deformed air filter; first transmission belt fallen off, second and third jumped one pulley groove, fourth in place; broken front cockpit windows; deformed left front seat; and deformed main rotor hub synthetic vertical dampers. The left front seat's cyclic and pedals were not removed; the Robinson R-44 flight operations guide recommends removal if the occupant is not a qualified pilot.
Engine examinations found no obvious malfunctions. Fuel (90 liters remaining) and oil quantities were adequate. Fuel and oil filters were clean. Valve train components were normal. The engine rotated freely. Magneto timing marks were correct. All 12 spark plugs had gaps within limits (0.019 inches). High-tension lead resistances were normal. Fuel supply lines were intact. No fuel leaks were found. The carburetor was clean. Fuel and oil samples tested by the Vilnius International Airport Fuel Service laboratory met specifications. Transmission belt tension mechanism was normal. Compression readings (in PSI) for cylinders 1–6 were: 80/70, 80/70, 80/75, 80/75, 80/75, 80/67. Governor operation was normal.