NTSB Identification: LAX06LA092.
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Accident occurred Wednesday, January 18, 2006 in Ely, NV
Probable Cause Approval Date: 02/26/2007
Aircraft: Croman Corporation SH-3H, registration: N612CK
Injuries: 4 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
While en route on a positioning flight, the restricted category helicopter lost power in both engines and then landed hard and rolled over during an autorotative forced landing on a road. Both pilots said that as they neared the area of the accident site the flight had to maneuver around areas of bad weather. The helicopter was at 80 knots and 200 feet above ground level (agl) following a road while maneuvering around weather when a loud bang was heard and both engines suddenly lost power. The flying pilot entered an autorotation and managed to get the helicopter onto the road. The landing was hard and the main rotor blades flexed downward and damaged the empennage, then the helicopter rolled to the right. The pilot said that just prior to the loud noise and the dual engine failure, the engine instrument indications were normal and the fuel gauges were reading around 1,500 pounds in each tank. The fuel system was configured for normal operation; the number 1 engine feeding from the forward tank and the number 2 engine feeding from the aft tank, with boost pumps on and the crossfeed valve closed. The engine and airframe deice/anti-ice systems were on and functioning, and no annunciator lights were illuminated concerning any of the systems elements. The helicopter's Federal Aviation Administration approved and issued Type Certificate Data Sheet states that flight into known icing conditions is prohibited and notes that "the helicopters approved under this type certificate are done so under the concept of limited exposure associated with escape from inadvertent ice encounters." The anti-ice/deice systems on the helicopter consist of a combination of electrically and bleed air heated elements protecting the windshield, the oil tank mounting ring, engine air intake ducts, engine inlet guide vanes, starter cover, and the front frame of each engine. In addition to the anti-ice systems, an engine inlet ice deflector shield can be installed in front of the engine inlets to prevent any accumulation of ice and snow that forms around the upper deck and mast area ahead of the engines from entering the engine inlets. According to company Director of Maintenance and the subsequent examination of the wreckage, the optional engine inlet ice/snow deflector shields were not installed. The pilot received three preflight weather briefings from two separate Automated Flight Service Stations (AFSS), with the first two from the same station and the third from a different one. In the first briefing, the pilot was told that a routing from Oregon down to southern California could expect widespread IFR conditions due to mountain obscurement, clouds, precipitation, icing, and turbulence. An hour later the pilot called the same AFSS, but spoke to a different briefer, who told the pilot he had overheard the earlier briefing and then suggested the pilot consider a routing through northern Nevada to Utah, then south to Arizona. The specialist then stated that two stations east of the Cascade Mountain range had high scattered clouds with good visibility, and Winnemucca, Nevada, had current conditions of 8,500 broken. The pilot responded, "Oh, really." The specialist then said "it was...like clear below 12,000" all the way to Cedar City, Utah, and concluded with, "I think once you get by like Winnemucca or Elko (Nevada) things improve drastically." The pilot responded, "We may just try that." An hour and a half later the pilot called and reached a different AFSS facility and asked about the conditions on the northern Nevada routing. The specialist said that presently there were AIRMETS in effect over the route for moderate rime and mixed icing, moderate turbulence, mountain obscurement and general IFR conditions over the entire area. The specialist said that VFR flight was not recommended over that route and another two alternate routings the pilot inquired about, and he cautioned the pilot that icing conditions would be moderate rime and mixed icing in clouds and precipitation from the surface to 21,000 feet, especially in the Ely, Nevada, area. Analysis of the actual weather conditions disclosed that en route to the accident site, the helicopter probably encountered occasional snow showers with low ceilings and visibilities. The freezing level was at or near the surface and that in-flight icing was likely from the surface to 18,000 feet. The formation of airframe ice due to the freezing of melted snow was also possible. The airframe fuel and anti-icing systems were functionally tested and operated normally. The number 1 engine had inlet guide vane trailing edge and first stage compressor blade leading edge damage that was consistent with the ingestion of ice chunks. Detailed disassembly of the number 1 engine revealed no other damage, condition, or abnormality that would have precluded normal operation. The number 2 engine was not damaged and was installed in a test cell where it ran normally. The fuel system components from the number 1 engine where then installed on the number 2 and the test cell run repeated with identical results to the first test.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the loss of power in both engines due to the ingestion of ice and snow. Also causal was the pilot's preflight and in-flight decisions to fly into areas of known and forecast moderate icing conditions in contravention to the prohibitions contained in the helicopter's Federal Aviation Administration approved Type Certificate Data sheet. A factor in the accident was the failure of the company maintenance organization to install the optional ice/snow deflector shields in front of the engine inlets that are designed to prevent the ingestion of ice and snow. An additional factor was the inaccurate and inappropriate weather briefing provided by the second AFSS specialist. Full narrative available
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