Accident Summary
On July 28, 2017, at 1532 central daylight time, a Guimbal Cabri G2 helicopter, registration N722TX, sustained substantial damage when it impacted terrain while maneuvering at Beaumont Municipal Airport (BMT) in Beaumont, Texas. The flight instructor and student pilot sustained minor injuries. The helicopter was registered to American Helicopter Leasing Corp and operated by Texas Rotorwing LLC under 14 Code of Federal Regulations Part 91 as an instructional flight. Day visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from BMT approximately 1500.
Flight Sequence
The flight instructor reported that after completing three normal approaches, the helicopter practiced basic hover skills at the north ramp area. During the hover, a high engine oil temperature condition occurred due to the ambient air temperature and reduced airflow for engine cooling. To increase airflow and reduce temperature, the instructor performed a low altitude circuit at 60 knots, about 100 feet above ground level (agl), around the airport perimeter. Approximately halfway around, the oil temperature returned to normal, with all other engine indications normal. However, during a turn at the southwest corner of the airport, the helicopter began to lose altitude and did not respond to control inputs. Efforts to regain control were unsuccessful, and the helicopter impacted an open grass area southwest of the runway.
Aircraft and Operational Information
The instructor noted that the helicopter was within gross weight and center-of-gravity limits, and that turns did not exceed 45 degrees of bank. No pre-impact anomalies were reported with the helicopter. The instructor stated that high temperatures, low wind, and high density altitude likely resulted in the accident.
Post-Accident Examination
A Federal Aviation Administration inspector conducted an examination of the helicopter at the accident site. The flight instructor stated that during the turn, the helicopter was unable to maintain altitude. The helicopter came to rest on its right side. The main rotor blades were fragmented, and the tail boom was partially separated. Impact marks indicated that the main rotor struck the ground before a landing skid. Examination of the flight control system revealed no pre-impact anomalies.
Weather Conditions
Weather at BMT reported by the Automated Weather Observing System (AWOS) did not include wind information. The most recent observation recorded a temperature of 35 degrees Celsius and a dew point of 21 degrees Celsius, with a calculated density altitude of about 2,650 feet. Wind at Jack Brooks Regional Airport (BPT), located about 12 miles southeast of BMT, was variable at 4 knots at 1453 and variable at 3 knots at 1553.
Engine Performance Considerations
The maximum engine power was derated to 145 hp for takeoff and continuous operation in the Cabri G2, but under accident conditions the engine was capable of approximately 160 hp. Full throttle would provide 160 hp. Engine performance was referenced to the 145 hp continuous limit, with 100% power corresponding to 145 hp and 111% power corresponding to 160 hp. Helicopter geometry indicated that a bank angle exceeding 40 degrees would result in main rotor ground impact before the landing skids. The manufacturer stated that at an operating weight of 1,440 lbs (650 kg), about 90% engine power would be required to maintain an in-ground-effect (IGE) hover at 32 ft agl and 32 degrees Celsius. Full throttle (111% power) would provide a 21% power margin for an IGE hover under accident conditions, but maintaining altitude in a 45-degree bank turn would require a 1.4 load factor, exceeding the available margin.