Accident investigators said that engine modifications made to an air ambulance helicopter may have left it more susceptible to icing and contributed to its fatal crash in 2013.
The Airbus Helicopters AS350 B2, operated by EagleMed, had taken off early on Feb. 22, 2013, from Integris Baptist Hospital in Oklahoma City to commence an inter-hospital patient transport flight. It appeared to suffer loss of engine power during its initial climb, crashed into a nearby parking lot and erupted in a post-crash fire. Both the pilot and flight nurse were killed, while the paramedic sustained severe injuries.
The NTSB, in its Jan. 14 Probable Cause Report, blamed loss of engine power due to engine ice ingestion for the crash, citing as contributing factors, “the lack of an installed engine air inlet cover while the helicopter was parked outside, exposed to precipitation and freezing temperatures before the accident, and the pilot’s inadequate preflight inspection that failed to detect ice accumulation in the area of the air inlet.”
Details concerning an engine modification stand out in the report. Instead of the Turbomeca Arriel 1D1 turboshaft engine that comes standard on the AS350 B2, the helicopter had been given a Honeywell LTS101-700D-2 turboshaft engine under an STC from Soloy Aviation Solutions—a process that involved modification of the engine air intake system. The NTSB said that as a result of this modification, the air inlet screen was “angled slightly upward,” leaving an unprotected opening at the aft end of the air inlet screen as well as “a gap in the area where the air inlet screen and blanking plate overlap” in which moisture or debris could feasibly collect.
Soloy said the STC offered the option of installing an inlet air filter kit by Aerospace Filtration Systems during the engine conversion, while another STC offered its installation after engine conversion. The accident helicopter was not equipped with the kit.
On the night before the accident, the helicopter was left out overnight without an engine intake cover installed. On the morning of the accident, camera footage showed that the pilot, Mark Montgomery, performed his morning preflight check in low lighting conditions, leading the NTSB to believe that he may have not seen the accumulation of ice in the intake.
But according to Seattlepi.com, Timothy A. Loranger, an attorney for the pilot’s family, criticized that implication—saying that the “design issue” impeded the pilot’s ability to inspect the aircraft. The pilot's wife, EagleMed and an insurance company have sued the helicopter and engine manufacturers, as well as the engine modification package designer. The case is currently with the Oklahoma Court of Civil Appeals.
The NTSB investigation has resulted in a number of changes from the involved parties. EagleMed has painted the blanking plate adjacent to the air intake screen matte black to aid in future preflight inspections and modified its engine air intake inspection procedure. It also has begun carrying engine air intake covers at all times. Also, Honeywell, Airbus and the FAA Rotorcraft Directorate each have released safety documents pertaining to flight operations in icing and snowing conditions.