Reports into separate accidents involving Eurocopter helicopters published by the US National Transportation Safety Board (NTSB) and the Transportation Safety Board of Canada (TSB) have both blamed the ingestion of ice into the engine for the loss of power in flight. The reports, both published in May, deal with a hard landing made by an EC130 B4 operated by Air Methods in Oklahoma, US, on 2 January 2013, and an AS350 B3 flying for the Royal Canadian Mounted Police (RCMP) that crashed on 17 January 2012 in British Columbia, Canada.
Air Methods, EC130
In the Oklahoma incident, the NTSB ruled that a contributing factor was the delayed decision by maintenance personnel to install the helicopter’s engine inlet cover after the engine had been exposed to moisture and freezing temperatures, and their ‘inadequate’ daily preflight/airworthiness checks, which did not detect the ice formation. The aircraft had been parked outdoors for three days before the accident flight without its engine cover installed, said the NTSB, during which time it was exposed to light drizzle, rain, mist and fog. The cover was installed the day before the flight, but the helicopter remained outside and exposed to freezing temperatures throughout the night until two hours before the flight took place.
The accident occurred at around 12:45 hrs while the AS350 was being flown at around 1,650 ft (500 m) above mean sea level in a positioning flight to a hospital in Okemah with a pilot and three crew members onboard, all of whom were injured when the engine lost power and the pilot performed an autorotation that concluded with a hard landing in a field. The NTSB’s examination of the engine, a Turbomeca Arriel 2B1 turbine, revealed that four axial compressor blades showed damage consistent with ingestion of soft foreign object debris such as ice. According to a statement provided by the pilot, in preparation for the flight, the pilot removed the inlet cover and performed a walk around inspection of the helicopter before starting a normal start-up. During the flight, the pilot heard a sound like something had struck the helicopter and the engine stopped producing power.
Given the weather conditions that the helicopter was exposed during the three days before the accident, it is likely, said the NTSB, that ice had formed in the engine air inlet and was ingested by the engine when the pilot increased power during take-off. The Board noted that the inlet to the first stage of the axial compressor was not inspected before the flight to ensure that it was free of ice in accordance with the manufacturer’s aircraft maintenance manual. The manual contains instructions on procedures to take before flight in cold or extreme cold weather conditions that include a step to ‘manually and visually check for snow and ice inside the air intake duct up to the first stage of the compressor’, said the NTSB.
The RCMP AS350 was taking part in human external transportation system (HETS) training at a Department of National Defence property on 17 January 2013. After flying during the morning in occasional light snow, the aircraft was shut down at the start of the lunch break. At that time, it was not snowing, and the engine air inlet covers carried onboard the helicopter were not installed. Heavy snow then fell for around 20 minutes. At 13:15 hrs, the pilot decided to cancel the training and return to Vancouver International Airport. At that time, there was a ‘significant accumulation of snow’ on the helicopter, although little or no snow was then falling. As the pilot entered the cockpit, ground crew members removed snow from the front windscreens. When the helicopter was started, snow was flung from the blades, but a significant covering remained on the upper fuselage and tailboom.
Witnesses reported that shortly into the flight, when the helicopter was at a height of around 80 ft (25 m) above ground level, there was a ‘muffled bang and a puff of grey/white vapour from the exhaust area’. The TSB noted that this height was insufficient to allow the pilot to perform an autorotation procedure. The rotor revolutions per minute decayed immediately, and the familiar sounds from the engine, a Turbomeca Arriel 2B, and rotor blades faded away. The helicopter descended almost vertically, colliding with the terrain in a nose-down, right-side-down attitude. Although ground crew members extracted the pilot from the cockpit and performed first aid, the pilot did not regain consciousness and died as a result of severe injuries, said the TSB.
The TSB noted that there have been several accidents involving Eurocopter AS350 helicopters with Arriel engines (including accidents in Chile, Sweden and Canada) in which the circumstances and the damage to the axial compressor blades were similar to the above incident. Some of these helicopters were not equipped with filters and were not covered during snowfall while parked, and all were parked outdoors. The risks associated with soft ice ingestion were well understood by Eurocopter and Turbomeca, said the TSB, and they had provided procedures and instructions to reduce these risks. However, the Board also stated that the procedures to remove snow, ice, and water from the intake system are impractical for field operations.
The report reads: “Transport Canada advises that it is imperative that the engine inlet (plenum) of the AS 350/EC130-type helicopter be free of all snow, ice, and liquid water before starting up in cold weather operations and/or snowy conditions. However, compliance with these instructions for the inspection and cleaning of the engine inlet (plenum) of the AS350/EC130-type helicopter cannot be done without elevating and supporting the engine cowling or, where installed, removing and reinstalling the grill that covers the filter. These tasks cannot easily be accomplished in field operations, which significantly limits operators’ ability to operate in some weather conditions.” The TSB concluded by stating its concern that in certain cold weather conditions, when the manufacturer’s instructions are not fully followed, AS350 and EC130 helicopters are at increased risk for engine flame-out shortly after take-off.
Read the reports in full: