Ely, NV, USA
N612CK
Croman Corporation SH-3H
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.
1.1 HISTORY OF FLIGHT On January 18, 2006, at 1330 Pacific standard time, a Croman Corporation SH-3H helicopter (modified version of a military Sikorsky SH-3H), N612CK, lost power in both engines and rolled over during a hard forced autorotative touchdown on a road 28 miles northwest of Ely, Nevada. Croman Corporation was operating the helicopter under the provisions of 14 CFR Part 91 of the Federal Aviation Regulations on a positioning flight. The helicopter sustained substantial damage. The two commercial pilots and two additional crew members were not injured. Visual meteorological conditions prevailed and a company flight plan was filed. The flight departed Winnemucca, Nevada, at 1130, en route to Page, Arizona. According to Federal Aviation Administration (FAA) records, an individual who identified himself as the pilot of N612CK called on the telephone and obtained three preflight weather briefings on January 18 at the times of 0628, 0730, and 0850. The first two calls were handled by the McMinnville, Oregon, Automated Flight Service Station (AFSS), and the last one by the Boise, Idaho, Automated Flight Service Station. Complete transcripts of these briefings were reviewed by National Transportation Safety Board investigators, and are contained in the Public Docket for this accident. In the 0628 call, the pilot requested a visual flight rules (VFR) weather briefing from the Medford, Oregon, area to Bakersfield, California, with an ultimate destination of Abilene, Texas. During this call, the pilot also requested weather information for the Truckee and Reno, Nevada, areas. According to the transcript, the AFSS specialist described the general conditions as being influenced by a low pressure system off the Oregon coast and a trough in western Oregon and Northern California with associated atmospheric instability. The specialist stated that instrument flight rules (IFR) conditions, due to reduced visibilities, clouds, rain, and fog, existed from southern Oregon down through the central portions of California to just above Bakersfield. Mountain obscurement was also forecast along with AIRMET's for moderate turbulence and moderate rime or mixed icing below 18,000 feet. Cloud tops were generally described as at 25,000 feet. Isolated thunderstorms scattered throughout the area were also predicted. The specialist concluded with a statement that the route down through California to the Bakersfield area "does not look like a good way even for a helicopter to go today, at least until after noon." The pilot then inquired about the Truckee/Reno area and the general conditions east of the Sierra Nevada Mountains. The specialist provided the information, which included multiple cloud layers, reduced visibilities below 3 miles, and snow showers. At 0730, the pilot telephoned again and requested another briefing for the same initial routing through Oregon and California to Bakersfield, with an ultimate destination of Albuquerque, New Mexico. The specialist said that he had a suggestion for the pilot to consider; if the pilot did not have to go through California for some reason that they should consider going through northern Nevada. The pilot replied that he thought northern Nevada's weather was "stinko" and that getting across the Sierra Nevada Mountains would be a big problem. The specialist then stated that two stations east of the Cascade Mountain range, Klamath Falls and Lakeview, Oregon, had high scattered clouds with good visibility, and Winnemucca had current conditions of 8,500 broken. The pilot responded, "Oh, really." The specialist then said that he had overheard the other specialist in the facility talking to the pilot earlier that morning and that he had looked at conditions east of Winnemucca and "it was...like clear below 12,000" all the way to Cedar City, Utah. The pilot then asked about the conditions south of Cedar City toward the Farmington/Albuquerque areas and the specialist told him the conditions were clear below 12,000 feet 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." In the 0850 telephone call (which was routed to another AFSS facility), the pilot asked for weather information for a flight eastbound from Klamath Falls, Oregon, to Cedar City, Utah, with stops in Winnemucca and Ely. The specialist told the pilot that presently there were AIRMETS in effect over the route for moderate 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. The pilot then inquired about various alternative routings, including through southern Idaho. The specialist provided reports for the stations requested; the reports delineated varying conditions from visibilities less than a mile in snow to areas of multiple cloud layers with visibilities between 3 and 5 miles. The specialist said 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 area. The pilot then concluded the telephone call. According to a verbal and written statements from the crew, the flight was to position the helicopter to Texas for a firefighting contract. The flight departed Winnemucca about 1130 with the intention of going all the way to Page, but with the understanding that they might have to stop somewhere en route due to weather conditions. Aboard was the second pilot, who was the flying pilot and acting as pilot-in-command for this leg, and two other company employees, a mechanic, and a third pilot. While en route the flight had to maneuver around areas of bad weather. Near the location of the accident there was a low ceiling and 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. A portion of the vertical stabilizer and the tail rotor gearbox were knocked off and the tail wheel separated. The helicopter then 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. He believes that 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 1.2 PERSONNEL INFORMATION According to information supplied by Croman Corporation, both pilots were qualified to act as pilot-in-command in the SH-3/S61 helicopters operated by the company. The information contained in this section of the report was obtained from the company, the pilots, and from the FAA Airman and Medical Records databases. The left seat is the normal command pilot station in the Sikorsky S-61/SH-3 helicopter. 1.2.1 First Pilot The pilot occupying the left seat held a commercial pilot certificate with a rotorcraft-helicopter rating that was last issued on June 21, 1993. The commercial certificate also contained type ratings for the MBB BV-107 and Sikorsky S-61 helicopters, both limited to VFR conditions only. The certificate was also endorsed for private privileges for single engine land airplanes. A second-class medical certificate was issued on July 21, 2005, without limitations. The pilot's total flight time was 20,000 hours, of which 19,800 were accumulated in helicopters. The pilot had accrued 8,000 hours in the Sikorsky S-61/SH-3. In the preceding 90 and 30 days prior to the accident the pilot had flown 60 and 10 hours, respectively. His most recent competency flight check in the S-61 was completed on June 30, 2005. 1.2.2 Second Pilot The pilot occupying the right seat held a commercial pilot certificate with ratings for rotorcraft-helicopters, single and multiengine land airplanes, and instrument ratings for airplanes and helicopters, the most recent issuance of which was dated April 1, 2004. His certificate contained type ratings for the Sikorsky S-58, S-61, and S-64 helicopters, all limited to VFR conditions. He also held a Certified Flight Instructor certificate for helicopters. His most recent second-class medical certificate was issued on March 3, 2005, with the limitation that correcting lenses be worn. The pilot's total flight time was 20,000 hours, of which 19,500 were accumulated in helicopters. The pilot had accrued 15,000 hours in the Sikorsky S-61/SH-3. In the preceding 90 and 30 days prior to the accident the pilot had flown 35 and 10 hours, respectively. His most recent competency flight check in the S-61 was completed on June 28, 2005. 1.3 AIRCRAFT INFORMATION 1.3.1 General The SH-3H and predecessor versions of this helicopter were originally manufactured by Sikorsky for the US Navy. A civilian version with a lengthened fuselage and other differences was manufactured by Sikorsky under the model designation S-61. The SH-3H is a 21,000-pound gross weight helicopter powered by two General Electric T58-GE-402 turbine engines. On June 2, 2004, the FAA issued Croman Corporation a Type Certificate Data Sheet (R00004SE) that authorizes Croman to convert surplus military SH-3H helicopters to a specific airworthiness configuration standard and obtain an FAA issued restricted category airworthiness certificate expressly for external load operations under 14 CFR 21.25 (b)(7). Flight operations limitations and maintenance requirements are those specified in the pertinent US Navy NAVAIR publications for the SH-3H. 1.3.2 Maintenance History The helicopter airframe was serial number 149713, and had accumulated a total time in service of 14,305 hours. Review of the maintenance records disclosed that the last continuous airworthiness inspection event was completed on January 16, 2006, about 43 hours prior to the accident. Engine serial number 281-323 was installed on the number one position and had accumulated a total time in service of 8,339 hours, with 606 hours accrued since the last major overhaul. Engine serial number 281-447 was installed on the number two position and had accumulated a total time in service of 5,869 hours, with 504 hours accrued since the last major overhaul. According to the statements of both pilots and the company maintenance information, there were no unresolved maintenance discrepancies at the time of departure from Winnemucca. 1.3.3 Fueling According to records from Winnemucca Air Service, 346 gallons of Jet A fuel was loaded into the helicopter's fuel tanks just prior to the flight's departure, which was recorded by the facility at 1155. The technician who performed the fueling stated that the 346 gallons added topped the fuel tanks. The pilot's stated that a total of 700 gallons was onboard at takeoff. According to the FAA Type Certificate Data Sheet for the helicopter, the maximum fuel system capacity is 848 gallons. 1.3.4 Anti-Ice/Deice Systems 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. The systems are pilot controlled and automatically regulated to prevent ice from forming. The system includes cockpit control switches for the systems and advisory and caution lights to alert pilots to the operational status of each component. A complete systems description is included in the public docket material for this accident report. In addition to the above described 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 Croman Corporation Director of Maintenance and the subsequent examination of the wreckage, the engine inlet ice deflector shields were not installed. The FAA 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." 1.3.5 Prior Accident History, SH-3/S-61 1.3.5.1 Fuel System Misconfiguration According to information supplied by technical representatives from GE Aviation, Sikorsky, and the US Navy, a specific fuel system configuration can be detrimental to continued operation of the other engine following a failure or shutdown of one engine. This configuration would be for ALL aircraft fuel boost pumps to be OFF and the crossfeed valve to be OPEN. On the SH-3H, the forward tank system supplies fuel to the No 1 engine and the aft tank system supplies fuel to the No 2 engine. Each tank has two boost pumps. With the crossfeed valve open, fuel from both the forward and aft tanks can be directed to one engine during single engine operation, or fuel from one tank can be directed to supply both engines. The crossfeed system does not transfer fuel between tanks. During normal twin-engine cruise operation, the crossfeed valve would be CLOSED and fuel boost pumps will be ON as required. The Navy NATOPS Flight Manual states that, during normal operations, at least one boost pump shall be on in the forward and aft tanks. It also states that use of all fuel boost pumps is mandatory when flying at pressure altitudes of 4,000 feet and above ( also at >43°C OAT and <600 lbs of fuel in either tank). The flight manual goes on to state that fuel crossfeed may be utilized during normal operations to assist in fuel management, but with the crossfeed valve OPEN, both boost pumps must be ON in the crossfeeding tank and one boost pump must be ON in the non-crossfeeding tank. This is also true for single engine operation, when boost pumps must be ON. During twin-engine operation with ALL boost pumps OFF and crossfeed OPEN, if one engine should shutdown, the operating engine would immediately try to suck fuel not only from the fuel tanks, but also from the "shutting down" engine - its fuel lines, fuel control, fuel pump, fuel filter, etc. Because the engines are roof mounted and above the fuel tanks, the other engine offers a greater pressure head than the tanks (with boost pumps off) and therefore, the "path of least resistance" for fuel being demanded by the running engine. Once all the fuel in these lines and engine fuel system has been consumed, the running engine may now start to suck air past the various seals in the shutdown engine fuel system components, causing it to also shutdown. Both pilots provided oral and written statements at various times during the investigation, including submitting to oral interviews within hours of the accident. In all their statements, both pilots have consistently reported the fuel system configuration as normal for cruise with boost pumps on in each tank and the crossfeed valve closed. 1.3.5.2 Ice/Snow Ingestion Events According to information provided by Sikorsky and GE, there are prior instances where an uncommanded engine shutdown has been attributed to snow and/or ice build-ups on the fuselage upper deck ahead of the engine inlets entering the engines. GE was asked for information on the amount of snow and/or ice ingestion the T58 engine can tolerate and continue to run; however, the company had no reliable data on the amount. 1.3.5.3 Input Freewheel Unit Slippage The Canadian Transportation Safety Board (TSB) reported that there have been several accidents involving Sikorsky S61's where a one engine power loss and the slippage of the running engine's input freewheel uni
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.
Source: NTSB Aviation Accident Database
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