Bell Helicopter Textron Canada 407 N600CE accident near Decatur, Texas

Probable cause

The pilot's inadequate preflight inspection and the momentary loss of engine power due to snow or ice ingestion.

NTSB analysis

The pilot, flight medic, and flight nurse were departing from a hospital helipad for the purpose of a cross-country positioning flight. As the helicopter ascended about 50 to 60 feet above ground level (agl), the pilot heard two warning horns sound, followed by the helicopter yawing 90 degrees to the left. The pilot lowered the collective in an effort to preserve rotor rpm and maneuvered the helicopter back over the helipad. Around 5 to 8 feet agl the pilot increased collective pitch, but the helicopter continued a quick descent until it experienced a hard landing back on the helipad.

A review of hospital video surveillance footage for the 24 hours prior to the accident revealed that the helicopter remained parked outside for approximately 5 hours in blowing snow conditions; during this time, it was not equipped with plugs or covers over the engine inlets or the exhaust. The plugs and covers were installed later and the helicopter remained outside in temperatures ranging from 16 degrees Fahrenheit (F) to 34 degrees F for the next 19 hours. The video also revealed that at no time did anybody look at the exhaust stack, right side engine intake, or open any access panels prior to the operation of the helicopter.

An examination of the recorded Engine Control Unit (ECU) data revealed that during the flight, the helicopter’s engine experienced a momentary flameout followed by a successful relight. Although the engine power was increasing, due to the helicopter’s close proximity to the ground, the pilot was unable to recover main rotor rpm before ground impact. As part of the postaccident examination, the engine was removed from the airframe and an engine run was performed. There were no anomalies found with the airframe or engine that would have contributed to the loss of engine power. The operator’s procedure manual stated that the pilot must ensure that all ice, snow, and frost is removed from the engine inlet area. The helicopter manufacture’s flight manual stated that as part of the preflight inspection, the pilot must check that the engine inlet area is cleaned of all debris, accumulated snow and ice. The engine manufacturer’s Operation and Maintenance Manual gave a precaution that the accumulation of snow or ice may result in the engine experiencing a flameout.

Text from the NTSB. Open the NTSB docket for CEN10LA078 for the full record.