LAMOILLE, NV, USA
N27736
BELL 206B3
THE HELICOPTER (HEL) WAS LANDED AT A REMOTE SITE DUE TO POOR WEATHER. AFTER LANDING, SNOW FELL & ACCUMULATED ON THE AIRFRAME. NO EXTERNAL ENGINE SNOW COVERS WERE AVAILABLE. THE AIR INDUCTION SYSTEM HAD SNOW BAFFLES & PARTICLE SEPARATORS, BUT THE ENGINE WAS NOT EQUIPPED WITH AN (OPTIONAL) AUTO RE-LIGHT IGNITION SYSTEM. THE PLENUM AT THE ENGINE INTAKE WAS INACCESSIBLE TO THE PILOT FOR REMOVAL OF ANY SNOW THAT MAY HAVE ACCUMULATED. ABOUT 1 HR AFTER LANDING, HE RESTARTED THE ENGINE & RAN IT ABOUT 15 TO 20 MIN. AFTER ABOUT ANOTHER HOUR, HE RESTARTED THE ENGINE AGAIN & RAN IT ABOUT 5 MIN. AFTER DISCUSSING SITUATION WITH DIR OF OPS BY RADIO, HE THEN TOOK OFF WITH A GROSS WEIGHT & DENSITY ALTITUDE OF ABOUT 2940 LBS & 7000', RESPECTIVELY. SHORTLY AFTER LIFT-OFF, THE ENGINE LOST POWER. DURING AN AUTOROTATION, THE HEL IMPACTED ON A 30 DEG SLOPE & ROLLED OVER. THE FLIGHT MANUAL (F/M) SHOWED THAT AT 2940 LBS, THE MAXIMUM DENSITY ALTITUDE FOR A SAFE AUTOROTATIVE LANDING WAS 2500'. THE F/M LIMITED HOVER FLIGHT IN FALLING AND/OR BLOWING SNOW TO A DURATION OF 20 MIN, AFTER WHICH THE HEL MUST BE LANDED & CHECKED FOR SNOW AND/OR ICE ACCUMULATION. HOWEVER, GROUND OPERATION IN THESE CONDITIONS WAS NOT ADDRESSED. TESTS OF SNOW/ICE INGESTION IN AN EARLIER MODEL OF THE SAME ENGINE (ALLISON 250-C18) RESULTED IN FLAMEOUTS WITH SLUGS OF SNOW THAT WERE AS LITTLE AS 30 GRAMS.
HISTORY OF FLIGHT On April 3, 1994, approximately 1636 hours Pacific daylight time (PDT), a Bell 206B3 helicopter, N27736, registered to/operated by El Aero Services, Inc., was destroyed during collision with terrain, following a loss of power shortly after takeoff from an intermediate landing site located approximately five nautical miles east of Lamoille, Nevada. The commercial pilot, seated in the right-front seat, was fatally injured, as were the two passengers seated in the center-rear and left-rear seats. The left-front seat passenger, a ski guide, sustained serious injuries, and later expired on April 12, 1994. The passenger seated in the right-rear seat sustained serious injuries. Variable meteorological conditions existed at the time of the accident, and no flight plan had been filed, although company flight following was in effect. The flight, which was engaged in heli-ski operations, was to have been conducted in accordance with 14CFR135. The aircraft, and a sister Bell 206L3, N3185A, being flown by the Director of Operations for El Aero, had been carrying skiers into the Ruby Mountains during the day. At 1402, N3185A (85A) departed for the Hoonie pickup landing zone to retrieve skiers due to a "fast moving storm." N27736 (736) was to also proceed to Hoonie for the same purpose (refer to Ruby Mountain Heli-ski dispatch log transcription, ATTACHMENT CT-I). At 1410, 85A radioed lifting off from Hoonie with three skiers. At 1414, 736 (having picked up the guide and remaining three skiers) radioed lifting off from Hoonie, that contact with the valley had been lost, and that 736 would proceed to/land near the Cherry Pie pickup point (refer to CHARTS I and II and photograph 01). At 1440, 736 (having landed at the site across from the Cherry Pie pickup point) radioed 85A and inquired about the visibility. At 1545, 736 radioed that he had run the aircraft to keep warm. The aircraft remained parked on a knoll near the Cherry Pie pick- up point (photograph 01) until approximately 1634. At 1634, 736 radioed good visibility and his departure from the landing site. Approximately one minute later, 736 radioed that he had the valley in sight (refer to photographs 02/03 and note the similarity between photograph P5 [pre accident] and photograph 03 [post accident]). At 1636, 736 radioed twice that he had engine failure. Mr. Michael Hoover, a professional photographer seated in the right-rear seat of the helicopter, and the only survivor, took photographs P1 through P6 in that order. He reported that he had "been filming from helicopters since the early 1970's" and that he had flown frequently in Bell Jetranger aircraft (refer to attached interview transcriptions). Mr. Hoover was initially interviewed by an FAA inspector, then by his brother using a questionnaire generated by the investigative team, and finally by the investigator in charge, and reported the following: After the pilot landed near the Cherry Pie pickup point and shut down, he queried the pilot about putting covers over the engine intakes. The pilot said that it would not be necessary, as "they weren't going to be there that long." Mr. Hoover stated that the helicopter was on the ground for approximately one hour, after which the engine was started and run for fifteen to twenty minutes. He further stated that "No snow was removed from the exterior of the helicopter prior to the first engine (ground warmup) run." According to Mr. Hoover, prior to taking off, the pilot (assisted by the guide) removed snow from the helicopter's exterior. The pilot, using the steps on the left side of the helicopter's fuselage, climbed up and "worked around up there. I think cleaning stuff off up there." Mr. Hoover didn't think the pilot had a flashlight during the exterior inspection and "didn't see him look into the plenum viewports." The engine was run for about five minutes between the second start and liftoff from the site. Mr. Hoover recalled that, after liftoff, the helicopter "headed down the canyon. Then beared kind of over to the left to get over a ridge" (refer to CHART II). He also commented on the altitude and airspeed of the helicopter, stating that "it seemed to me we were pretty low. I'm guessing between seventy to on(e) hundred feet. We weren't very high at all. I could be wrong. It could have been at two hundred feet" and "going forward, we were going pretty slow, I thought. I would guess between twenty-five miles per hour and maybe fifty, but it didn't even seem that fast" (refer to photographs P5 and P6). Mr. Hoover recalled that shortly after takeoff (thirty seconds to two minutes) he leaned forward and saw several red lights "flashing and beeping" (refer to attached statements). PERSONNEL INFORMATION The pilot's logbook showed that he had flown for two consecutive years with the operator. The first year (1992) showed flights between January 23 and March 29 (168.2 hours total/PIC). The second year (1993) showed flights commencing on January 28 and concluding on March 28 (153.8 total hours/PIC). A personal flight ledger for 1994 showed a third year of entries commencing on January 28, with the last entry on April 2 but not including the day of the accident (April 3). A total of 161.3 hours (including the accident day's flight time) of PIC/total flight time was accrued during this time. All flights were conducted in the Bell 206B. The pilot's most recent recurrent FAR Part 135 check ride was documented on FAA Form 8410-3 and completed on October 10, 1993. The flight was conducted in a Bell 206 over a duration of 0.7 hours and included a satisfactory rating for autorotations. Training records maintained by the operator indicated that pilot Walton had completed initial/recurrent ground training with the operator on January 23, 1994, and that an oral check in accordance with FAR Parts 135.293 and 135.299 was completed on the same date. AIRCRAFT INFORMATION The aircraft was equipped with snow baffles and particle separators, but was not equipped with an auto-ignition system, nor was such a system required. The rotorcraft flight manual (RFM) contained supplements for both the "deflector kit - engine air induction system" and "particle separator - engine air induction system" which were installed on the aircraft. Both sections state that the engine air intake areas should be checked clear of accumulated snow, slush and ice before each flight. A small, plexiglass inspection port is provided on either side of the plenum chamber to allow the pilot to inspect the interior of the chamber. Additionally, both sections state that the plenum chamber should likewise be checked and "clean(ed) thoroughly before each flight (see ATTACHMENTS FMS-10 and FMS-12) although, the plenum chamber cannot be accessed by the pilot (refer to photograph 17). Both supplements state that the snow baffles and particle separators must be installed in conjunction with one another when "conducting flight operations in falling and/or blowing snow and the following limits apply:" "Hover flight in falling and/or blowing snow is limited to 20 minute duration after which the helicopter must be landed and checked for snow and/or ice accumulation." "Flight operations are prohibited when visibility in falling or blowing snow is less than one-half (1/2) statute mile." The RFM supplements do not address operating the engine in non-flight conditions (e.g., ground idle) in "falling and/or blowing snow." The aircraft's estimated takeoff weight at the last departure was calculated to be 2940 lbs based upon the following information: AIRCRAFT EMPTY WEIGHT: 1815 LBS PILOT: 160 LBS GUIDE: 145 LBS PASSENGER 1: 210 LBS PASSENGER 2: 200 LBS PASSENGER 3: 140 LBS PERSONAL GEAR/SKIS: 60 LBS MISC ACFT EQUIPMENT: 40 LBS FUEL: 170 LBS TOTAL WEIGHT: 2940 LBS MAX GROSS TAKEOFF WEIGHT: 3200 LBS Refer to DIAGRAM AGW-I, "Altitude vs. Gross Weight Limit for Height - Velocity Diagram," and DIAGRAM HV-I, "Height Velocity Diagram." The aircraft's center of gravity was estimated to be within limits at the time of takeoff. The Operator reported that the engine inlet protective covers were not carried on board the aircraft (see ATTACHMENT RFM-2-13). METEOROLOGICAL INFORMATION Meteorological conditions relative to the landing site near the Cherry Pie pickup area during the helicopter's stopover, and as observed and reported by passenger Hoover, are noted as follows: Mr. Hoover stated that photograph P1 was taken approximately five minutes after landing at the remote site. Note the reduced visibility and lack of snow accretion on the helicopter. Mr. Hoover stated that while outside the helicopter "it was coming down pretty good at that point." Note the snowfall, reduced visibility, and snow buildup on the helicopter's exterior surfaces (refer to photograph P4). Mr. Hoover responded to the question of wind direction at the landing site by stating that "as we sat there over the next couple of hours, the snow was pretty much coming from, I would say, the ten o'clock position on the helicopter. Because that's how it was piling up on that side of the helicopter." Mr. Hoover estimated an "inch or an inch and a half" of snow accumulation and indicated "there might have been four inches on the windward side" (the left side of the helicopter). Mr. Hoover described the snow as "mostly in spurts (short showers) consistent with brief snowstorms. The winds were estimated at 10-15 mph, gusty and non stable." The density altitude at the time/location of the accident site was estimated to be 7000 feet (based upon the estimated outside air temperature and pressure altitude). WRECKAGE AND IMPACT INFORMATION The aircraft was observed aerially by helicopter to be lying on a 30 degree sloped mountainside at an elevation of approximately 7100 feet above mean sea level (MSL). The site was located approximately 700 feet northwest and upslope from a drainage. The base of the drainage was filled with numerous multi-layered, sharp rock outcroppings. The latitude and longitude of the site, established by GPS on site, was 40 degrees 43.47 minutes North and 115 degrees 22.69 minutes West, and the terrain was characterized by snow-covered soil and loose rock, with occasional scrub trees (refer to CHARTS I & II and photograph 04). The airframe and all control surfaces/rotors and flight controls were observed at the ground impact site. The investigative team, upon arriving on site, noted the odor of jet fuel. The helicopter was observed lying on the ground and rolled slightly on its left side. The longitudinal axis was oriented along an approximate 273 degree magnetic bearing (tail pointed east) and the nose oriented upslope. The forward portion of the airframe (cockpit area) was observed impacted into the base trunk of a large scrub tree. The tail rotor remained attached to the tailboom and the main rotor-hub assembly was observed to be separated from its drive shaft. The hub assembly remained attached to both rotor blades, however, a substantial section of the red blade had separated and was observed lying nearby (refer to photographs 05 through 08). A ground impact characterized by a broad area of disrupted fresh soil was observed a short distance southwest of the cockpit area. The west edge of the churned soil area was packed smoothly into a near vertical soil dam or wall, the vertical dimension of which were consistent with the chord dimension of the main rotor blade (refer to photograph 09). A second similar ground impact site was noted slightly northwest of the cockpit area. This impact, however, did not display the same "vertical soil dam" effect. Additionally, the outboard portion of the red main-rotor blade was observed lying on the ground nearby, with the blade tip situated over the disrupted soil impact area (refer to photograph 10). This same rotor blade section displayed soil adhering to its outboard leading edge. The blade was observed to have a permanent upwards bending set towards the separation point near the attachment to the main rotor-hub assembly (refer to photograph 11). The remainder of the red blade, the entire white blade, and the main rotor hub assembly connecting the two, was observed lying alongside the right side of the helicopter. The same permanent upwards bending set towards the main-rotor hub assembly was observed (refer to photograph 12). The tail-rotor assembly (blades and hub) remained attached to the 90 degree gearbox and tailboom. One blade displayed minor bending deformation just outboard of the hub assembly, while the opposing blade was observed to be folded back 180 degrees. The leading edges of both blades displayed minimal impact damage (refer to photograph 13). The vertical stabilizer remained attached to the tailboom and displayed minor damage (refer to photograph 14). The horizontal stabilizer remained attached to the tailboom. The right stabilizer was undamaged. The left stabilizer displayed upwards bending deformation (refer to photograph 15). During on-site examination, no snow was observed on any of the external surfaces of the wreckage. However, a small amount of snow conforming to the interior shape of the inside forward portion of the left engine-intake snow baffle was observed. The snow was partially melted with bits of debris lying on its exposed surfaces (refer to photograph 16). During on-site and post-crash wreckage examination, mechanical continuity of both fixed and rotating controls, the main transmission, and the tail-rotor drive system, was established, as well as integrity of the main input-driveshaft. The fuel shutoff valve was found to be in the "open" position. The tail rotor and main transmission chip-detector plugs were found to be clean. Additionally, the airframe fuel filter was removed and examined. The filter element was found to be clean. The engine deicing switch was found in the "ON" position and the engine bleed valve was found in the open position. No protective covers (pillows) for plugging the aircraft's engine intakes were found within the wreckage or at the accident site. MEDICAL AND PATHOLOGICAL INFORMATION Post mortem examination of the pilot was conducted by Dennis A. Mackey, M.D., at the facilities of the Washoe County Coroner's Office, Reno, Nevada, on April 5, 1994. The cause of death was reported as "multiple traumatic injuries due to blunt force trauma." Toxicological evaluation of samples from the pilot was conducted by the FAA's Toxicology and Accident Research Laboratory, Oklahoma City, Oklahoma. All test results were negative (refer to attached report). TESTS AND RESEARCH The Caution Panel light bulbs were individually examined. Both type 327 bulb filaments (two per light casing) were found to be stretched for the three following caution lights: "ENG OUT", "ROTOR LOW RPM", and "FUEL PUMP." Additionally, both filaments for the "TRANS OIL PRESS" caution light were lightly stretched. All other filaments were observed to be either broken, distorted, or in most cases in good condition. The aft boost-pump was examined and found to operate satisfactorily with the application of 24-volt battery power. The forward boost-pump was examined and found to have sustained impact damage. Although the pump could not be tested, a satisfactory electrical continuity test was accomplished. The Allison Model 250-C20B engine (serial number 832045), including its associated fuel-control unit and governor, was shipped to the Allison Engine Company, Indianapolis, Indiana. The engine was subsequently subjected to a "cursory inspection" on April 26, 1994, and after replacement of a damaged No. 8 bearing scavenge line was run in a test cell. Engine performance during the test run "exceeded new engine limits" and acceleration/deceleration tests were within limits as well. The report provided by Allison stated that "No operational difficulties were noted during the test" (refer to ATTACHMENT E- I, which contains extract
THE INGESTION OF FOREIGN MATERIAL (SNOW) IN THE ENGINE, WHICH RESULTED IN A FLAMEOUT (LOSS OF ENGINE POWER). FACTORS RELATED TO THE ACCIDENT WERE: THE ADVERSE WEATHER CONDITIONS (SNOW FALLING & HIGH DENSITY ALTITUDE), THE LACK OF SNOW COVERS TO PROTECT THE ENGINE INTAKES WHILE PARKED AND AWAITING FOR THE WEATHER CONDITIONS TO IMPROVE, IMPROPER PLANNING/DECISION BY THE PILOT AND THE COMPANY/OPERATOR MANAGEMENT, INADEQUATE INFORMATION IN THE FLIGHT MANUAL, AND THE LACK OF SUITABLE TERRAIN FOR AN EMERGENCY LANDING.
Source: NTSB Aviation Accident Database
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