Iliamna, AK, USA
N95RC
DE HAVILLAND BEAVER DHC-2
The airline transport pilot of the float-equipped airplane was attempting a takeoff with the load of passengers that he had flown to the lake earlier in the day. The pilot's calculated takeoff distances for the water run and over a 50-ft obstacle were 1,050 ft and 2,210 ft, respectively. The pilot did not add a safety margin to his takeoff distance calculations. The approximate shore-to-shore distance of the takeoff path was 1,800 ft. During taxi, the pilot retracted the wing flaps, where they remained for the takeoff. GPS data showed that the airplane attained a speed of about 49 knots before impacting terrain just beyond the shoreline. The airplane's stall speed with flaps retracted was about 52 knots. Postaccident examination revealed that the left wing flap was in the fully retracted position; the right wing flap assembly was damaged. The airplane flight manual takeoff checklist stated that flaps were to be selected to the "TAKE-OFF" position before takeoff. Additionally, the takeoff performance data contained in the flight manual was dependent upon the use of "TAKE-OFF" flaps and did not account for no-flaps takeoffs. Even if the pilot had used the correct flap setting for takeoff, the calculated takeoff distances were near the available takeoff distance, and it is likely that the airplane would still not have been able to avoid a collision with terrain. The pilot stated that there was no mechanical malfunction/failure with the airplane, and he should have "done the right thing," which was to conduct two flights, each with a half load of passengers.
HISTORY OF FLIGHTOn August 8, 2016, about 1651 Alaska Daylight Time, a float-equipped DeHavilland DHC-2 (Beaver) airplane, N95RC, sustained substantial damage during takeoff when the floats collided with the banks of Crosswind Lake, about 30 miles south of Iliamna, Alaska. The commercial pilot and three passengers sustained serious injuries, and three passengers sustained minor injuries. The airplane was registered to and operated by Rapids Camp Lodge Inc under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident. The flight was originating at the time of the accident and was destined to King Salmon, Alaska. The airplane sustained substantial damage to the wings and fuselage. The pilot said that this was the first season that he flew into Crosswind Lake and last year he had flown into Crosswind Lake five times and has never had to perform "shuttle" flights of people from the lake. The pilot stated that he, two fishing guides, and four guests departed Rapids Camp Lodge, from the Naknek River, located about 4 miles east of King Salmon Airport, King Salmon, Alaska, a little after 0800. After a flight of less than an hour, the flight landed at Crosswind Lake. They planned on returning to the airplane about 1630 for a return flight to Rapids Camp Lodge that was to depart before 1700. The pilot stated that he discussed with the head fishing guide about performing shuttle flights, with a half load per flight, to a nearby location with an "unrestricted runway." The head guide stated that he had done that numerous times and would show him the best location. The pilot said that he watched other airplanes taking off from the lake toward the west, and he thought "it was no problem" to attempt the takeoff. The pilot's calculated takeoff water run distance and takeoff distance over a 50-foot obstacle for the flight was 1,050 feet and 2,210 feet, respectively. The approximate shore-to-shore distance along the takeoff path was 1,800 feet. The pilot did not state that he added a safety margin to his takeoff distance calculations. The pilot stated that during takeoff, the wind was gusting and either it died down or there was a change of wind direction [during the takeoff]. He said that if he "cut back" the takeoff power, the impact would have been greater. He said that "his decision should have been to shuttle half of the people," and he "made the wrong decision." The passenger seated in the right front pilot seat stated that during the takeoff, the airplane was "heading into a strong wind." He watched the GPS display of ground speed during the takeoff and saw an indication of 28 mph and then saw the lake bank getting closer. He said it was apparent that the airplane was getting "very close" without lifting off. When the airplane lifted off, it hit the bank with one of the floats and seconds later the airplane impacted the ground. A second passenger, who had over 3,000 hours of flight time, said that he suggested to the pilot to "hug" the lake shore and accelerate turning out into the lake in a running takeoff. The passenger said that the pilot then pulled 50 yards from the shoreline and reduced the engine throttles to idle, letting the airplane floats sink into the water. The passenger then yelled at him asking what he was doing and the pilot then started adding full engine power. The passenger stated that he did not see the pilot select the wing flaps, which should have been "at least" 15 degrees. The passenger stated that the next thing he heard was a loud bang and saw limbs of shrubs and leaves coming over the plane and then woke up between the copilot's seat and his door. The passenger said his seat belt must not have worked; it was pulled out of the "floor or something." The only way out was through the pilot's door and which everybody crawled out of. The plane had come to rest about 400 yards from where it impacted the bank. The passenger stated that the wind was "not a problem" and "it could not have been more than 10 knots." A witness, who was a pilot with about 6,000 hours of flight time and had flight experience in float airplanes, recorded an image/video of the airplane. He "believed" that the airplane wing flaps were in the down position at "some point," and then the flaps were in the up position. He stated that the flaps were not extended during the takeoff. He said that the airplane was "motoring around," and it "motored" over to the beginning of the takeoff point about 3-4 times and would "motor away" before starting the takeoff. He said that it was not a "normal" amount of time to warm up the engine oil. He said at the end of the video, the right aileron was deflected down to "break" the right float out of the water. Figure 1: The left and right images were taken by the witness. The left image shows the airplane with flaps extended during the taxi prior to takeoff and right image shows the airplane with its flaps retracted during its takeoff run. The pilot reported that there was no mechanical malfunction/failure with the airplane and that he should have "done the right thing," which was "to do two takeoffs with half load each!!!" PERSONNEL INFORMATIONThe pilot began employment as a pilot for Rapids Camp Lodge Inc in 2015. The pilot's resume showed two periods in which he was pilot flying DHC-2 float equipped airplanes in Alaska. The most recent was his employment as a Part 135 pilot from June to September 2014 flying DHC-2 and Cessna 185 float equipped airplanes, and wheel-equipped Cessna 206 airplanes. From June to September 2012 he was employed as a pilot for Part 135 pilot operator flying DHC-2 float equipped airplanes. The operator had no training records that were available and/or provided to the National Transportation Safety Board (NTSB) Investigator-In-Charge (IIC). The operator did not hold a Part 135 certificate and its operations conducted under Part 91 did not require an FAA approved training program and records of that training. AIRCRAFT INFORMATIONThe airplane was manufactured in 1956 and according to the airplane type certificate data information it was certified under civil air regulations (CAR) 3 and CAR 10. The airplane registration certificate was issued to the operator on June 22, 2000. The airplane had a supplemental type certificate (STC) installation for Aerocet 5850 floats (SA 01722SE), which was dated September 9, 2011, and a STC installation for a Kenmore Air Harbor gross weight increase (SA 4025NM), which was dated June 28, 2000. The Aerocet float STC had a flight manual supplement correction factor for takeoff distances. The Kenmore Air Harbor gross weight increase STC had no flight manual supplement correction factor for takeoff distances. The airplane was not required nor was it equipped with shoulder harnesses under CAR 3 and 10 certification standards. FAA airworthiness records, dated May 9, 2001, show that shoulder harnesses were installed for the airplane pilot and copilot seats. There were no shoulder harnesses installed for the passenger seats. Airplane Flight Manual and Takeoff Performance Charts The DHC-2 Beaver Flight Manual states that the cockpit wing flaps indicator is situated on the instrument panel and is marked: FULL FLAP, LANDING, TAKE-OFF, CLIMB, and CRUISE. Section 2.8 (f) of the flight manual, Takeoff Check, states in part: "Flaps – TAKE-OFF position." Section 2.9 (f), Takeoff, states in part: "Allow aircraft to fly itself off at 55 to 65 mph in a tail down attitude and climb at 65 mph. Flight Manual Takeoff Distance Chart The Operating Data Charts section of the flight manual provides takeoff distance charts for land and seaplane configurations. All the takeoff distance charts are based upon a wing flap configuration that is in the takeoff configuration. There are no distance charts within the manual that provide takeoff distances with retracted wing flaps. STC Flight Manual Supplements for Takeoff Performance The STC flight manual supplement for Aerocet floats states the correction factors to be applied to the seaplane takeoff and landing performance. At a gross weight of 5,090 lbs or less: water run – none, takeoff to 50 feet – add 50 percent. At a gross weight between 5,090 lbs and 5,370 lbs: water run – 15 percent, takeoff to 50 feet – add 70 percent. Approximate Flight Manual/STC Takeoff Distances The pilot reported that the airplane maximum gross weight was 5,370 lbs, and the airplane weight at the time of the accident as 5,150 lbs. The pilot reported that the winds were 240 degrees at 13 knots, gusts were 8 knots, and the outside air temperature was 15 degrees Celsius. Recorded GPS data shows that the altitude of the airplane at takeoff was about 950 feet. According to Aerocet, the approximate water run was 914 feet. The approximate total distance to clear a 50-foot obstacle was 1,989 feet. Airplane Stall Speeds Section 4.6.1, Load Factors, of the flight manual, states that the Section 4.10.1, General, of the flight manual states that the stalling speed with flaps up is 60 mph indicated airspeed (IAS) and with flaps "Landing" is 45 mph IAS. A stall speed of 60 mph is equivalent to about 52 knots. AIRPORT INFORMATIONThe airplane was manufactured in 1956 and according to the airplane type certificate data information it was certified under civil air regulations (CAR) 3 and CAR 10. The airplane registration certificate was issued to the operator on June 22, 2000. The airplane had a supplemental type certificate (STC) installation for Aerocet 5850 floats (SA 01722SE), which was dated September 9, 2011, and a STC installation for a Kenmore Air Harbor gross weight increase (SA 4025NM), which was dated June 28, 2000. The Aerocet float STC had a flight manual supplement correction factor for takeoff distances. The Kenmore Air Harbor gross weight increase STC had no flight manual supplement correction factor for takeoff distances. The airplane was not required nor was it equipped with shoulder harnesses under CAR 3 and 10 certification standards. FAA airworthiness records, dated May 9, 2001, show that shoulder harnesses were installed for the airplane pilot and copilot seats. There were no shoulder harnesses installed for the passenger seats. Airplane Flight Manual and Takeoff Performance Charts The DHC-2 Beaver Flight Manual states that the cockpit wing flaps indicator is situated on the instrument panel and is marked: FULL FLAP, LANDING, TAKE-OFF, CLIMB, and CRUISE. Section 2.8 (f) of the flight manual, Takeoff Check, states in part: "Flaps – TAKE-OFF position." Section 2.9 (f), Takeoff, states in part: "Allow aircraft to fly itself off at 55 to 65 mph in a tail down attitude and climb at 65 mph. Flight Manual Takeoff Distance Chart The Operating Data Charts section of the flight manual provides takeoff distance charts for land and seaplane configurations. All the takeoff distance charts are based upon a wing flap configuration that is in the takeoff configuration. There are no distance charts within the manual that provide takeoff distances with retracted wing flaps. STC Flight Manual Supplements for Takeoff Performance The STC flight manual supplement for Aerocet floats states the correction factors to be applied to the seaplane takeoff and landing performance. At a gross weight of 5,090 lbs or less: water run – none, takeoff to 50 feet – add 50 percent. At a gross weight between 5,090 lbs and 5,370 lbs: water run – 15 percent, takeoff to 50 feet – add 70 percent. Approximate Flight Manual/STC Takeoff Distances The pilot reported that the airplane maximum gross weight was 5,370 lbs, and the airplane weight at the time of the accident as 5,150 lbs. The pilot reported that the winds were 240 degrees at 13 knots, gusts were 8 knots, and the outside air temperature was 15 degrees Celsius. Recorded GPS data shows that the altitude of the airplane at takeoff was about 950 feet. According to Aerocet, the approximate water run was 914 feet. The approximate total distance to clear a 50-foot obstacle was 1,989 feet. Airplane Stall Speeds Section 4.6.1, Load Factors, of the flight manual, states that the Section 4.10.1, General, of the flight manual states that the stalling speed with flaps up is 60 mph indicated airspeed (IAS) and with flaps "Landing" is 45 mph IAS. A stall speed of 60 mph is equivalent to about 52 knots. WRECKAGE AND IMPACT INFORMATIONOn-scene examination of the accident site by an FAA Aviation Safety Inspector revealed that the southwest side of the lake, at the shoreline, had an indentation from the impact of the floats. Approximately 100 yards to the southwest from the lakeshore was a small hill, just south of a small pond. The wreckage of the airplane was on the hill, angled down towards the pond, with the right wing of the airplane partially in the water. A trail of small pieces of fiberglass from the floats was in a direct line from the initial lakeshore impact area to the scene of the crash. An impact area on the edge of the hill showed where one float and then the engine had impacted, with the airplane coming to rest about 30 feet further, facing to the southwest. No fuel was present on the ground, nor was any fuel line broken open/separated. The fuselage was fully intact, and the wings were intact. The left wing appeared to be largely undamaged, except for the left float, which had broken in half and the rear half was bent up and had cut several inches into the trailing edge of the flap, about 12 inches outboard from the fuselage. The left-wing flap was in the fully retracted position. The right-wing flap was extended and was undamaged. The right-wing flap extension/retraction mechanism was broken off from the flap. The propeller exhibited damage consistent with engine power. TESTS AND RESEARCHGPS Download of Recorded Data A Garmin Aera 500, which was a portable GPS unit, was removed from the airplane by the operator and later sent, upon request, to the NTSB IIC. The GPS unit was then sent to the NTSB Vehicle Recorders Division for the download of recorder data. The GPS unit can store a detailed tracklog including latitude, longitude, date, time, GPS altitude, and groundspeed information – within the unit whenever the receiver has a lock on the GPS navigation signal. All recorded data was stored in non-volatile memory. The first track point was recorded at 16:29:57 as the aircraft was shown in the water on the east side of the lake. By 16:40:44, the aircraft had turned toward a southwest track and began a takeoff run over the water. By 16:41:09, the aircraft had reached the midpoint of the lake and the groundspeed was 40 knots. By 16:41:18, the aircraft had crossed the lake's western shore and was near terrain at a recorded of 49 knots. At 16:41:51, the groundspeed was 0 knots. At 16:48:11, the last track point was recorded associated with the event flight. Figure 2: The figure is a Google Earth overlay of GPS data points showing a path toward the southwest. Presented data points located about in the middle of the path and lake show a speed of 40 knots and a data point over terrain near the southwest lakeshore of 49 knots. Effect of Flaps on Maximum Lift Coefficient Aerodynamics for Naval Aviators (January 1965) states: "In many aircraft the effect of intermediate flap deflection is of primary importance in certain critical operating conditions. Small initial deflections of the flap cause noticeable changes in [maximum lift coefficient] CLmax, without large changes in drag coefficient. This feature is especially true of the airplane equipped with slotted or Fowler flaps (refer to fig. 1.17). Large flap deflections past 30 to 35 degrees do not create the same rate of change of CLmax but do cause greater changes in [drag coefficient] CD. A fact true of most airplanes is that the first 50 percent of flap deflection causes more than half of the total change in CLmax and the last 50 percent of flap deflection causes more than half of the total change in CD.
The pilot's decision to perform the takeoff despite calculations showing that the distance available was inadequate, which resulted in impact with terrain.
Source: NTSB Aviation Accident Database
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