Crash review: two on the same day, two for the same reason...
Read. Do not repeat...
NTSB Identification: CEN13FA121
14 CFR Part 91: General Aviation
Accident occurred Wednesday, January 02, 2013 in Seminole, OK
Probable Cause Approval Date: 05/08/2014
Aircraft: EUROCOPTER EC130 B4, registration: N334AM
Injuries: 4 Serious.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot reported hearing a sound like something had struck the helicopter shortly after departure while about 1,600 to 1,700 feet mean sea level. The engine lost power, and the pilot performed an autorotation to a field. While maneuvering to land, he saw a barbed wire fence obstructing the intended landing area, so he maneuvered the helicopter to clear the fence. The helicopter subsequently cleared the fence and landed hard in a field.
Engine examination revealed that the four axial compressor blades exhibited significant deformation on the outboard tips of their leading edges in the direction opposite of normal rotation consistent with the ingestion of soft body foreign object debris, such as ice. A subsequent engine run did not detect any preimpact anomalies that would have precluded normal operation. For 3 days before the accident flight, the helicopter was parked outside without its engine cover installed and was exposed to light drizzle, rain, mist, and fog. The engine inlet cover was installed the day before the accident at an unknown time. The helicopter remained outside and exposed to freezing temperatures throughout the night until 2 hours before the flight. Although the helicopter was maintained in a ready status on the helipad and maintenance personnel performed daily preflight/airworthiness checks, the inlet to the first-stage of the axial compressor was not inspected to ensure that it was free of ice in accordance with the Aircraft Maintenance Manual. Based on the weather conditions that the helicopter was exposed to during the 3 days before the accident, it is likely that ice formed in the engine air inlet before the flight and that, when the pilot increased the engine power during takeoff, the accumulated ice separated from the inlet and was ingested by the engine and damaged the compressor blades.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The loss of engine power due to ice ingestion. Contributing to the accident was maintenance personnel’s delayed decision to install the helicopter's engine inlet cover until 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.
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NTSB Identification: CEN13FA122
14 CFR Part 91: General Aviation
Accident occurred Wednesday, January 02, 2013 in Clear Lake, IA
Probable Cause Approval Date: 02/12/2015
Aircraft: BELL HELICOPTER 407, registration: N445MT
Injuries: 3 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
GPS tracking data revealed that, after departure, the helicopter proceeded westbound about 600 ft above ground level (agl), following a roadway. About 6 minutes after liftoff, when the helicopter was about 3/4 mile south of the accident site, it turned right and became established on a northerly course. The helicopter subsequently turned left and appeared to be on a southerly heading at the final data point. Shortly before beginning the left turn, the helicopter entered a climb, reached an altitude of about 1,800 ft agl, and then entered a descent that continued until impact. Weather observations from the nearest Automated Surface Observing System, located about 7 miles east of the accident site, indicated that the ceilings and visibility appeared to be adequate for nighttime helicopter operations and did not detect any freezing precipitation. Although an airmen’s meteorological information advisory for icing conditions was current for the route of flight, and several pilot reports of icing conditions had been filed, none of the reports were in the immediate vicinity of the intended route of flight. Witnesses and first responders reported mist, drizzle, and icy road conditions at the time of the accident. It is likely that the pilot inadvertently encountered localized icing conditions, which resulted in his subsequent in-flight loss of helicopter control. A postaccident examination of the helicopter revealed no preimpact failures or malfunctions. The engine control unit recorded engine torque, engine overspeed, and rotor overspeed events; however, due to their timing and nature, the events were likely a result of damage that occurred during the impact sequence. Evidence also indicated that the cyclic centering, engine overspeed, and hydraulic system warning lights illuminated; it is also likely that their illumination was associated with the impact sequence. Further, the engine anti-ice status light was illuminated, which was consistent with the activation of the anti-ice system at some point during the accident flight.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot’s inadvertent encounter with localized icing conditions and his subsequent in-flight loss of helicopter control.
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NTSB Identification: CEN13FA174
14 CFR Part 91: General Aviation
Accident occurred Friday, February 22, 2013 in Oklahoma City, OK
Probable Cause Approval Date: 01/14/2016
Aircraft: EUROCOPTER AS 350 B2, registration: N917EM
Injuries: 2 Fatal, 1 Serious.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
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.
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The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
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.
