CEN13FA174

The loss of engine power due to engine ice ingestion during initial climb after takeoff in dark night light conditions. Contributing to the accident were 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.

The emergency medical services helicopter departed a hospital helipad in dark night visual flight rules conditions and proceeded on its mission. Satellite data showed that, after takeoff, the helicopter began a gradual climb toward its planned destination. The data stopped about 3 minutes and 30 seconds into the flight. No distress calls were heard from the pilot. Fixed video surveillance cameras located near the accident site showed the last few seconds of the helicopter descending toward the ground. The helicopter impacted a parking lot, and a postimpact fire occurred. Examination of the wreckage revealed that three of the engine's first-stage axial compressor blades exhibited deformation consistent with soft body foreign object damage. The remainder of the engine and airframe exhibited no evidence of malfunction that would have contributed to an in-flight loss of engine power. The helicopter's air intake design, which had been modified to accommodate a different engine than that originally supplied by the helicopter's manufacturer, incorporated a blanking plate attached to the top side of the engine cowling that covered a portion of the air inlet screen. A gap in the area where the blanking plate and the screen overlapped made it possible, in certain meteorological conditions, for water or snow to pass through the screen, accumulate on the blanking plate, and freeze into ice. Ice accumulation in this area, if left undetected, could result in the ice detaching from the blanking plate and entering the engine during operation, causing soft body foreign object damage and a loss of engine power. Precipitation and outside temperatures ranging from 35 to 19 degrees F occurred during the 12-hour period preceding the accident. The combination of these meteorological conditions was conducive to the formation and accumulation of ice in the area between the air inlet screen and the blanking plate. Although the helicopter's flight manual supplement for cold weather operations recommended installation of an air inlet cover after the last flight of the day, during the day and night before the flight, the helicopter was parked outside on the helipad without an air inlet cover installed. According to the helicopter's mechanic, he inspected the helicopter on the afternoon before the flight and noted that some snow had accumulated on it. It is likely that the lack of an engine air inlet cover allowed precipitation to accumulate in the vicinity of the engine air intake. The helicopter's flight manual cold weather operations supplement also contained instructions for the pilot to perform a visual and manual (tactile) inspection of the air intake duct up to the first-stage compressor for evidence of snow and ice. Furthermore, the manufacturer and the Federal Aviation Administration had previously released information notices regarding inflight loss of engine power due to snow or ice ingestion caused by inadequate inspection or removal of snow or ice from the engine air inlet. These notices recommended a thorough inspection in and around the engine inlet area in order to detect and remove any snow or ice accumulation before flight. The initial on-scene examination found no remnants of ice or snow on these components because exposure to the postcrash fire would have melted such evidence. Surveillance video of the helipad showed that most of the helipad lights were off at the time of the pilot's preflight inspection immediately before the flight, making it difficult for him to detect any ice or snow accumulation in the area of the engine air intake. Thus, the ice accumulation between the air inlet screen and the blanking plate remained undetected, and shortly after takeoff, the ice detached from the blanking plate, slid into the air inlet, and was subsequently ingested by the engine, resulting in an in-flight loss of engine power. .

Documentation of the Integris Hospital Helipad (OK19) A search of the helipad at OK19 did not reveal any evidence of debris. A fixed surveillance video of the helipad immediately prior to the helicopter's departure for the accident flight revealed most of the helipad lights were off. In comparison, the surveillance video from the two evenings prior showed all helipad lights were on, completely illuminating the helipad. According to the helicopter mechanic, the day prior to the accident, the helicopter was forced to park outside and overnight on the helipad due to adverse weather conditions. Typically, the helicopter would be parked inside a hanger at a different location. According to the helicopter mechanic, the helicopter did not have the engine air inlet cover and exhaust blank installed while the helicopter was parked on the helipad and exposed to precipitation. The helicopter remained exposed to low temperatures overnight. The helicopter mechanic stated he had last examined the helicopter at about 1430 the day before the accident and that during his last examination, he discovered residual snow and slush had accumulated on the top surfaces of the helicopter and the horizontal stabilizer. A broom was used to brush off the accumulated snow and slush. The on-scene examination found no remnants of ice or snow on these components because exposure to the post-crash fire would have melted such evidence. The operator stated the pilot performed a preflight inspection immediately prior to the accident flight. Engine Examination and Teardown The engine was removed from the wreckage and transported to Honeywell facilities in Phoenix, Arizona. On March 7, 2013, members of the Powerplants Group convened at Honeywell to perform an engine examination and teardown. General The external condition of the engine was visually examined. The insulation had melted from the majority of the electrical wiring. There was soot on the engine, particularly on the right side of the accessory gearbox and on both sides of the combustor plenum at about the 3 o'clock and 9 o'clock positions. The airframe-supplied front and rear drive shafts remained installed. The forward driveshaft was not deformed. The cover over the forward driveshaft was partially burned and melted down onto the driveshaft. The rear driveshaft was fractured about 13 inches aft of the forward coupling. The forward coupling of the rear driveshaft did not exhibit evidence of deformation. The PT rotor could be rotated by hand with light finger pressure. When the forward driveshaft stub shaft was rotated in the clockwise direction, the rear driveshaft and PT rotor turned concurrently confirming continuity and engagement of the freewheeling clutch7. When the forward driveshaft stub shaft was rotated in the counterclockwise direction, the rear driveshaft rotated concurrently, but the PT rotor did not turn, consistent with disengagement of the freewheeling clutch. Air Inlet Section The upper air inlet scroll duct was in place on the lower air inlet scroll duct. However, the upper and lower air inlet scroll ducts were separated on the left side and the strap was separated from the clamp. The upper air inlet scroll duct was partially broken away on the left side, about halfway down the duct. The upper rear frame of the upper air inlet scroll duct was displaced forward. The right side of the upper air inlet scroll duct had several splits and areas burned through. The right side of the interior of the upper air inlet scroll duct was sooted. The optional anti-ice system, Honeywell kit No. 4-201-080-01, was not installed. The lower air inlet scroll duct was in place. The lower air inlet scroll duct exhibited delamination in several locations. Debris, including several pieces of re-solidified molten metal, was found lying in the bottom of the lower air inlet scroll duct. The left side drain on the lower air inlet scroll duct was open, but the right side drain was blocked with debris from the wreckage. The compressor inlet housing was intact. The exterior of the compressor inlet housing was sooted. The 12 bolts attaching the compressor inlet housing to the air diffuser housing flange were tight. The air diffuser housing was intact and did not exhibit evidence of damage. No evidence of bird remains was found in the air inlet scroll ducts. Compressor Section The No. 1 bearing was intact, wet with oil, and free to rotate. The bearing balls were in good condition. The disk portion of the axial compressor rotor was intact. The disk bore and rim were coated with soot. All of the axial compressor blades remained in place. Two axial compressor blades exhibited leading edge tip curling deformation in the direction opposite of rotation consistent with soft body object impact damage. One of the deformations was observed to be about 0.344 inches chordwise and the other deformation was observed to be about 0.406 inches chordwise. A dent about 0.031 inches chordwise was observed on the leading edge of a third axial compressor blade. After the axial compressor blades were cleaned, no evidence of hard body impact damage was observed in the damaged areas of the three aforementioned blades. Nine additional axial compressor blades exhibited leading edge tip curling deformation in the direction opposite of rotation; the curling deformation was about .031 inches wide for all nine blades. Several of the blades exhibiting tip curls exhibited a slightly torn leading edge at the location of the deformation. Eight blades exhibited a bend at the tip end directly aft of the leading edge. One of the blades exhibited a circumferential rub mark on the tip end. The axial compressor stator vane halves remained intact. All of the axial compressor stator vanes were in place and did not exhibit damage. The upper axial compressor stator vane half aft shroud rail had a 0.188 inch long section that was pushed rearward at about 1:30 o'clock. The lower axial stator vane half forward shroud rail had a 0.25 inch long section that was pushed rearward to the center rail at about 6:30 o'clock. The axial compressor stator vane halves did not have any apparent circumferential rub marks on the blade shroud. The centrifugal compressor was intact. All of the centrifugal compressor blades had a 0.094 inch wide rub mark on the edges of the blades about 0.156 inches from the exducer end of the impeller. The centrifugal compressor impeller had a light coating of soot. The centrifugal impeller shroud was intact. The inner surface of the impeller shroud was sooted. The centrifugal impeller shroud did not have any visible circumferential rub marks. Combustion Section The combustion chamber liner was intact. The combustion chamber liner aft louver exhibited a white residue at about the 9 o'clock position. The combustion chamber liner did not exhibit evidence of sooting. The fuel manifold hoses between the fuel nozzles were all in place and their red insulation were partially burned away. There were no indications of leakage or thermal distress around the fuel manifold hoses as well as around the flow divider. The fuel nozzles were all in place. There was no sooting on the fuel nozzles or on the combustor dome around each of the nozzles. The first stage nozzle assembly and curl were intact and did not exhibit evidence of thermal distress. All of the first stage nozzle airfoils were in place and did not exhibit evidence of damage. The outer transition liner was intact and did not exhibit evidence of thermal distress. Turbine Section The rear bearing (Nos. 2 and 3) support housing outer case was intact but exhibited evidence of sooting. The rear bearing support housing outer case did not reveal signatures consistent with thermal distress or ruptures. The inner diameter forward edge of the de-swirl vanes contained two notches of broken away material, 0.375 and 0.438 inches long, at the 5 o'clock and 12 o'clock posi