Robinson Helicopter Company R44 II N233WT accident near Basin, Montana

Probable cause

The pilot’s decision to continue performing a high-performance takeoff in a full throttle and low-rotor-rpm condition, which resulted in a loss of control and subsequent impact with terrain.

NTSB analysis

The pilot was departing from a high-altitude, confined, off-airport site with 2 passengers. The pilot stated that the helicopter was under its maximum gross weight, and he calculated that the helicopter would be able to hover and take off up to about 7,700 ft mean sea level (msl), about 600 ft above the field elevation.

During multiple attempts to climb from a hover, the full throttle light on the annunciator panel illuminated; the light would then extinguish when the helicopter altitude was closer to the ground. After some discussion between the pilot and his passengers about the best way to depart the site, the pilot decided to initiate a maximum performance turning takeoff from a hover. Shortly after liftoff, while in a hover, the pilot initiated a climb and the full throttle light illuminated again. The helicopter yawed slightly to the right and continued a slow climbing right turn.

The engine and rotor rpms decreased to 95% during the climbing turn. About 2 seconds later, the engine and rotor rpms dropped to about 90%. After turning 270° from its original takeoff heading, the helicopter shallowed its right turn and, after another 2 seconds, the rpms dropped to about 85%. About 4 seconds later, the altimeter showed that the helicopter climbed to about 100 ft above ground level (agl) and increased its right turn rate. The helicopter impacted terrain about 18 seconds later, with the engine and rotor rpms indicating approximately 60%.

The pilot thought there might have been issues regarding the fuel that was used during the accident flight. However, the investigation was unable to determine whether the fuel was contaminated or of substandard quality.

The manufacturer’s performance charts revealed that the helicopter had in-ground effect hover capability under the conditions of the accident takeoff; however, the helicopter did not have out-of-ground effect hover capability. Furthermore, the pilot knew from multiple attempts to climb from a hover that the helicopter was reaching full throttle and could not continue climbing. Instead of following through with alternative options to safely depart the mountain site, the pilot decided to perform a maximum-power takeoff with limited engine performance. As a result, the helicopter could not maintain the engine and rotor rpms, which resulted in the helicopter settling and subsequently impacting terrain.

Text from the NTSB. Open the NTSB docket for WPR24LA307 for the full record.