Skwentna, AK, USA
N2814C
CESSNA 170B
The wheel/ski-equipped airplane was departing to the northwest from a remote, frozen and snow-covered lake toward rising terrain. A gusty northwesterly wind was blowing, and the frozen lake was covered with soft snow. Witnesses said that just after takeoff, the airplane began to climb slowly with a nose-high attitude. As the airplane approached the area of rising terrain, it began a left turn, and the airplane subsequently descended to the ground in a nose-down attitude, colliding with snow-covered terrain nearly vertically. The pilot reported that just after takeoff, the airplane encounter a downdraft and that it was not climbing sufficiently to avoid rising terrain ahead. As he started a left turn, he lowered the nose, applied full engine power, but the downdraft pushed the airplane into the snow-covered terrain. The pilot reported that there were no preaccident mechanical problems, and a subsequent postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. An estimated weight and balance calculation indicated that the airplane was at or near its maximum gross weight and within the center-of-gravity envelope at the time of the accident. Given the lack of mechanical deficiencies with the airplane and engine, along with the witness statements and the nature of the damage to the airplane, it is likely that the pilot did not maintain sufficient airspeed and inadvertently stalled the airplane when it reached the critical angle of attack during the turn, and the pilot was unable to recover because of the low altitude.
On February 17, 2013, about 1505 Alaska standard time, a wheel/ski-equipped Cessna 170B airplane, N2814C, sustained substantial damage when it collided with snow-covered terrain following a loss of control during takeoff initial climb from a remote, snow-covered lake, about 44 miles west of Skwentna, Alaska. The airplane was registered to and being operated by the pilot as a visual flight rules (VFR) cross-country personal flight under 14 Code of Federal Regulations Part 91. The private pilot and sole passenger both sustained serious injuries. Visual meteorological conditions prevailed at the time of the accident. The pilot was volunteering his time and use of his airplane, supporting a race team competing in the annual Iron Dog snow machine race. The flight was departing Puntilla Lake at the time of the accident, and was en route to McGrath, Alaska, with preplanned stops at various race checkpoints along the anticipated race route. No flight plan was filed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on February 18, the operator of a remote wilderness lodge located at Puntilla Lake, where the airplane crashed, said he and others watched (and photographed) the airplane's takeoff run and initial climb. He said that as the airplane departed to the northwest, it became airborne after using about two-thirds of the available takeoff area. He said that the airplane continued a shallow climb towards an area of rising mountainous terrain, commonly known as the "notch", which is known to have downdrafts when the wind is from the north. As the airplane approached the rising terrain, it began a steep left turn, away from the notch. During the turn, the airplane nosed down abruptly, entered a near vertical descent, and collided with the snow-covered terrain. He said numerous people rushed to the crash site and pulled the two occupants out of the airplane. He added that the passenger was unconscious, and he remained that way throughout the rescue. During a telephone interview with the NTSB IIC on February 19, an additional pilot-rated witness said that he observed the takeoff and the accident, and was one of the first to arrive at the accident site. He said the accident airplane was heavily loaded, and during its takeoff run, it used two-thirds of the available takeoff distance before becoming airborne. He also reported strong gusting wind conditions, and recalled seeing spindrifts coming off the surrounding, snow-covered peaks. He reported that after the airplane became airborne, it began a shallow, nose high attitude climb, but the engine sounded strong. The airplane appeared to descend as it approached rising terrain, and it subsequently rolled into a left turn. He said the airplane continued the turn, stalled, and descended steeply, impacting the ground. Arriving at the accident site, he said the cargo in the rear of the airplane had moved forward, pinning the pilot and passenger against the instrument panel. He and other responders had to remove the cargo, and then they began attending to the occupants. The pilot-rated witness added that the airplane was equipped with seatbelts and shoulder harnesses, and that the pilot's seat had been pushed forward during the accident, putting tension on the pilot's seatbelt. He noted that the passenger's seatbelt was found unbuckled, and laying to the side. Both occupants were wearing bulky, cold weather clothing. During an interview with the NTSB IIC on March 19, the pilot reported that the flight had been planned for several months, and the purpose of the trip was to provide logistical support of a race team entered in the Iron Dog snow machine race. The pilot said that on the first leg of the flight, he departed Merrill Field, Anchorage, Alaska, for the short flight to the Big Lake Airport, Big Lake, Alaska, which is located about 22 miles north. Prior to departing Merrill Field the airplane was fueled and the cargo loaded on board. The pilot departed Merrill Field by himself. After arriving at Big Lake, the pilot picked up his passenger, and departed for Shell Lake, where he maintains a remote cabin. The pilot added 5 gallons of fuel at Shell Lake. From Shell Lake the flight departed for Puntilla Lake, which is a check point along the Iron Dog race route. The pilot had not landed at Puntilla Lake previously, but said the landing was uneventful. They spent several hours at the lake and then planned to depart for the Rohn Roadhouse, the next checkpoint on the race route. The pilot explained that the takeoff run distance was longer than he expected, using about two-thirds of the available area, which he attributed to the soft snow conditions. He departed to the northwest, into gusting wind conditions, and toward rising terrain. He said the engine sounded fine, and was producing normal power, but the airplane was not climbing as he had expected. He said he elected to takeoff favoring airspeed over altitude, and did not attempt to climb immediately. The pilot said that with the airplane not climbing as he expected, and approaching rising terrain, he elected to make a left turn, away from terrain. He said the airplane then started to descend in the turn, and he was unable to arrest the descent, the airplane consequently impacted the ground. The pilot stated that there were no preaccident mechanical problems with the airplane. On April 29, 2013, the pilot submitted a written statement to the NTSB, stating that just after takeoff the airplane encounter a downdraft and it was not climbing sufficiently to avoid rising terrain ahead. He said that as he started a left turn to avoid the terrain ahead, he lowered the nose, applied full engine power, but a downdraft pushed the airplane into the snow-covered terrain. INJURIES TO PERSONS Both the pilot and passenger received serious, life threatening injuries, and were transported by helicopter to a hospital in Anchorage. The passenger was unconscious when rescuers arrived at the accident, and he did not regain consciousness prior to being transported. DAMAGE TO AIRCRAFT Witnesses provided the NTSB IIC with numerous photographs of the airplane, which were taken as the airplane was taking off, and just after the accident. The on-scene photographs revealed that the airplane impacted the snow-covered terrain in a near vertical attitude. On February 22, an NTSB postaccident examination of the airplane's wreckage was accomplished in a hangar facility at the Big Lake Airport. In attendance with the IIC was a representative of Cessna Aircraft, and two FAA air safety inspectors assigned to the Anchorage Flight Standards District Office (FSDO). Crush lines appear to be consistent with the airplane impacting the ground in a left wing down, nose low, and steep descent. All of the airplane's major components and flight controls were present, and control continuity was established. The engine was intact, and showed signs of power during the impact. The propeller was manufactured by MT Propellers, and was made of wood/composite construction. Both propeller blades sheered at the propeller's hub. The manually actuated wing flaps are operated with a bar/lever mechanism that rests horizontally on the floor between the two front seats when the flaps are retracted. Rescue personnel at the accident site indicated that the handle was in the up (flaps down) position. During the exam, the handle appeared to be in the flaps 20 degrees, down position. The on-scene photographs that were provided to the NTSB showed that the right flap was extended. The elevator trim actuator was not measured. However, when the elevator was placed in the streamlined position the trim tab was observed in the neutral position. The fuel gascolator assembly was made of glass, and it had broken during the impact sequence. What appeared to be aviation fuel was found in both tanks, both tanks had been leaking, and witnesses at the accident site reported fuel leaks. The postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. PERSONNEL INFORMATION The pilot, age 44, held a private pilot certificate with airplane single-engine land, and single-engine sea ratings. According to the Pilot/Operator Aircraft Accident Report, (NTSB Form 6120.1) submitted by the pilot, dated April 29, 2013, his total aeronautical experience ranged between 1,500 to 2,000 flight hours, of which about 1,300 to 1,800 were in same make and model as the accident airplane. He completed a biennial flight review on June 25, 2012. The pilot's most recent third-class medical certificate was issued to the pilot on March 1, 2011, which contained no limitations. AIRCRAFT INFORMATION The four-seat, high-wing, tailwheel-equipped airplane, serial number, S/N 26357, was manufactured in 1954, and originally equipped with a 145 horsepower, Continental O-300 engine. At the time of the accident the airplane had since been modified with a 180 horsepower, Lycoming O-360-A1A engine. The propeller had been modified with a two-bladed, MT-Propeller, wood/composite propeller assembly. The airplane was outfitted with hydraulic wheel/skis, and a tailwheel mounted ski. Weight and Balance Rescuers recovered baggage, personal items, equipment, and spare parts from the wreckage, which weighed about 309 pounds. Weight and balance calculations based on estimated fuel and weight distribution showed that the airplane was at or near gross weight (2,200 pounds), and the center-of-gravity was 40-42 inches aft of the datum, as reported by the pilot. The calculations were within the normal category operating range of the airplane. Stall Airspeed Aerodynamic stall airspeed varies with aircraft weight, power setting, wing flap setting, and angle of bank. The power-on stall speed for the Cessna 170 series airplane at gross weight varies from 49 mph with flaps down, and zero degrees angle of bank (wings level), to 69 mph at 60 degrees angle of bank (steep turn). METEOROLOGICAL INFORMATION The lodge operator and his wife were certified weather observers. The latest weather observation had been recorded about 20 minutes prior to the accident, and was in part: wind, 310 degrees at 10 knots, gusting to 18 knots; visibility, 25 statute miles; clouds and sky condition, 6,000 broken. The elevation at the lodge is about 1,875 feet above sea level. COMMUNICATIONS There were no reported or known communications with the pilot of the accident airplane. The pilot was not using any air traffic control (ATC) services. OTHER INFORMATION Restraint Examination Due to the extent of the injuries to the pilot and passenger, the accident airplane's Am-Safe, Inc., restraint systems were removed from the wreckage, and subsequently sent to the NTSB's Washington D.C. materials laboratory for examination and documentation. The examination was done at the direction of an NTSB senior metallurgist. A complete copy of the NTSB's materials laboratory factual report is included in the public docket for this accident.
The pilot’s failure to maintain airspeed during a departure turn, resulting in an aerodynamic stall and collision with terrain.
Source: NTSB Aviation Accident Database
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