Angoon, AK, USA
N50159
CESSNA 206
The commercial pilot was conducting a commercial on-demand flight between two villages over open water in an amphibious float-equipped airplane before navigating through mountainous terrain. As the airplane approached the usual route company pilots took through the mountains, the accident pilot relayed to the operator's director of operations via airborne communications that he was unable to make it through the pass due to low clouds and reduced visibility and that he was going to try an alternate route over lower terrain. After the director of operations determined that the airplane did not arrive at its destination, search and rescue efforts ensued. The airplane was subsequently found in an area of rising steep mountainous, snow-covered terrain at an elevation of about 2,240 ft mean sea level in a near-vertical attitude. A postaccident examination of the airframe and engine revealed no mechanical malfunctions or anomalies that would have precluded normal operation. GPS data for the accident flight showed the airplane making a total of five 360° turns in various locations in cloud-obscured, mountainous terrain while attempting to make it to the destination; the last turn was made shortly before impact. Based on the conversation the pilot had with the director of operations and the location of the wreckage, it is likely that the pilot thought he had taken a path over lower terrain but that he actually flew into a different valley which had higher-than-anticipated terrain, and then executed a 360° turn to gain altitude before continuing the flight. However, the airplane did not gain sufficient altitude to clear terrain, and it is likely that the pilot attempted another climb, which reduced the airspeed and led to the exceedance of the airplane's critical angle of attack. The disposition of the airplane at the accident site was consistent with an aerodynamic stall and a right spin.
HISTORY OF FLIGHTOn April 8, 2016, about 0914 Alaska daylight time, an amphibious float-equipped Cessna 206 airplane, N50159, sustained substantial damage after impacting snow-covered, rising terrain about 17 miles southeast of Angoon Airport, Angoon, Alaska. The airplane was being operated by Sunrise Aviation, Inc., Wrangell, Alaska, as a visual flight rules 14 Code of Federal Regulations (CFR) Part 135 commercial on-demand flight. The commercial pilot and two passengers sustained fatal injuries, and one passenger sustained serious injuries. Visual meteorological conditions existed at the airport at the time of departure, and company flight-following procedures were in effect. The flight departed from Wrangell Airport, Wrangell, Alaska, about 0810, destined for Angoon. The area between Wrangell and Angoon consists of remote inland fjords, coastal waterways, and steep mountainous terrain. During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) 4 days after the accident, Sunrise Aviation's Director of Operations stated that, while flying another company airplane, he spoke with the accident pilot over the company radio frequency. The accident pilot commented to the director of operations that, while en route to Angoon, he was unable to make it through Pybus Bay due to low clouds and reduced visibility and that he was going to try an alternate route over lower terrain. The director of operations added that, about 15 to 20 minutes after speaking with the accident pilot, he landed in Wrangell and noticed that the Spidertracks signal for the accident airplane was stationary in an area of mountainous terrain. (As part of their company flight-following procedures, Sunrise Aviation incorporated Spidertracks, which provided company management personnel with a real-time, moving map display of an airplane's progress.) He then called personnel at the Angoon Airport and was told that the flight had not arrived. Shortly after attempting to reach the pilot on his cell phone and over the company radio frequency, he received a phone call from the Alaska Rescue Coordination Center notifying him that the 406-Mhz emergency locator transmitter (ELT) assigned to the accident airplane was transmitting a signal. The Alaska Rescue Coordination Center notified the US Coast Guard (USCG) Air Station Sitka about the overdue airplane and the ELT signal transmitting along the accident pilot's anticipated flight route. About 1025, the USCG launched an MH-60 helicopter to search for the airplane. About 1054, the airplane's wreckage was located by a helicopter operated by Temsco Helicopters who then relayed the location to the USCG. About 1117, the USCG crew located the airplane's wreckage in an area of steep mountainous, snow-covered terrain. However, due to hazardous weather and terrain conditions, the helicopter crew was unable to lower a rescue swimmer to the site, and the crew returned to Sitka to pick up rescue personnel from Sitka Mountain Rescue. About 1355, the USCG helicopter crew returned to the accident site and landed the helicopter on an adjacent ridgeline. Members of Sitka Mountain Rescue and the USCG hiked to the accident site. Once on scene, they discovered that three of the airplane's occupants had died at the scene and that one occupant had survived the crash. The sole survivor was hoisted aboard the USCG helicopter and then transported to Juneau. PERSONNEL INFORMATIONThe pilot, age 60, held a commercial pilot certificate with airplane single-engine land and sea and instrument ratings. His most recent second-class medical certificate was issued on October 21, 2015, and contained the limitation that he must "possess glasses for near/intermediate vision." No personal logbooks were located for the pilot. A review of company records revealed that the pilot had reported on his annual résumé, dated April 3, 2015, that his total flight experience was about 19,981 hours, 556 hours of which were in the previous 12 months. AIRCRAFT INFORMATIONThe airplane was a Cessna 206 manufactured in 1972, and it was equipped with a Continental Motors IO-550 series engine. At the time of its last annual inspection, completed on February 17, 2016, the airplane had 14,028 hours in service. METEOROLOGICAL INFORMATIONAt 0410, the National Weather Service Alaska Aviation Weather Unit issued an area forecast for central Southeast Alaska, including the accident site, which forecast scattered clouds at 800 ft mean sea level (msl) with a broken-to-overcast ceiling at 2,000 ft msl. Layered clouds were forecast from 2,000 ft msl through flight level 250. Occasional broken ceiling to 2,000 ft msl and light rain were forecast with isolated ceilings below 1,000 ft msl and visibility to 4 miles in light rain and mist. An AIRMET for mountain obscuration due to clouds and precipitation had also been issued and was valid at the accident site at the accident time. The closest weather reporting facility was Angoon Airport, about 17 miles northwest of the accident site. At 0856, Angoon Airport issued a METAR that reported, in part, calm wind; sky condition, broken clouds at 500 ft, overcast at 1,800 ft; visibility 7 statute miles; temperature 45° F, dew point 45° F; and altimeter setting 29.71 inches of Mercury. (Refer to the Meteorology Group Chairman's Factual Report in the public docket for further weather information and weather camera images). AIRPORT INFORMATIONThe airplane was a Cessna 206 manufactured in 1972, and it was equipped with a Continental Motors IO-550 series engine. At the time of its last annual inspection, completed on February 17, 2016, the airplane had 14,028 hours in service. WRECKAGE AND IMPACT INFORMATIONThe wreckage was located in an open area of snow-covered rising terrain at an elevation of about 2,240 ft msl. The impact area was sloped about 27°. The airplane impacted terrain in a near-vertical, nose down attitude and sustained substantial damage to the fuselage and wings. The right wing remained attached to the fuselage, and the leading edge exhibited extensive spanwise leading edge aft crushing. The right wing was displaced about 20° aft of the airplane's lateral axis. The left wing remained attached to the fuselage at the forward attachment point and exhibited minor impact damage. The left wing was displaced about 40° forward of the airplane's lateral axis. The horizontal stabilizer, elevators, vertical stabilizer, and rudder remained relatively free of impact damage. The elevator trim actuator was measured to be about 1.5 inches, consistent with a neutral setting. The rudder and elevator primary flight control cables were continuous from the cockpit controls to their respective flight control surfaces. The aileron primary flight control cable continuities were confirmed from the cockpit controls to their respective flight control surfaces with cable separations at the wing root area. All cable separations exhibited signatures consistent with tensile overload and recovery cuts. The fuselage exhibited crushing damage under the rudder pedals from the floor upward. The top of the fuselage was severed laterally the width of the cabin at the wing forward spar attachment points. The aft fuselage exhibited signatures consistent with stretching on the left side with the location corresponding to compression damage on the right side. ADDITIONAL INFORMATIONGPS Information A Garmin 396 handheld GPS was found mounted on the instrument panel, and all cables were still attached. The unit was removed and sent to the NTSB Vehicle Recorders Laboratory, Washington, DC, for examination. Extracted GPS data for the accident flight included, in part, time, latitude, longitude, and GPS altitude. Groundspeed and course information were derived from the extracted parameters. The GPS data indicated that the airplane departed Wrangell Airport at 1208:33 heading toward the southeast before turning to the northwest. The airplane continued on the northwesterly heading until crossing Beacon Point on Kupreanof Island and then turning west-northwest. The airplane continued on this heading until it entered Pybus Bay at 1,861 ft msl. The airplane then made four 360° turns, exited Pybus Bay while descending, and then leveled off about 215 ft msl. After exiting Pybus Bay, the airplane flew between Grave Island and Admiralty Island at 261 ft msl before entering Little Pybus Bay on a west-northwest heading at 940 ft msl. The airplane then turned 360° and continued heading west-northwest. The last recorded GPS data plot was at 1314:05 when the airplane was at 2,405 ft msl, heading 299°, and at 74 miles per hour. A flight track map overlay and tabular data corresponding to the accident flight are available in the public docket for this accident. MEDICAL AND PATHOLOGICAL INFORMATIONThe Alaska State Medical Examiner, Anchorage, Alaska, conducted an autopsy of the pilot. The cause of death for the pilot was attributed to "multiple blunt force injuries." The FAA Bioaeronautical Sciences Research Laboratory performed toxicology testing of the pilot's specimens on July 06, 2016, which was negative for ethanol, drugs, and carbon monoxide. TESTS AND RESEARCHOn October 18, 2016, an engine examination was performed by Continental Motors, Mobile, Alabama, under the supervision of the NTSB. Due to limited damage, an engine test run was conducted following the replacement of impact-damaged components. The engine was fitted with a test club propeller for the IO-550 series engine. The engine started normally on the first attempt without hesitation or stumbling in the observed rpm. The engine rpm was advanced in steps for warm-up in preparation for full-power operation. The warm-up sequence was completed over 15 minutes before the engine throttle was advanced to the full-open position and then held for 5 minutes to stabilize. Throughout the test phase, the engine accelerated normally without any hesitation, stumbling, or interruption in power, and it demonstrated the ability to produce rated horsepower. During the engine test, the magnetos were checked, and a drop of 44 rpm was noted for the left magneto, and a drop of 32 rpm was noted for the right magneto.
The pilot's inadvertent turn toward terrain that was higher-than-expected while trying to avoid poor visibility conditions and his subsequent attempt to clear terrain, which reduced the airspeed and led to the exceedance of the airplane's critical angle of attack and an aerodynamic stall and spin.
Source: NTSB Aviation Accident Database
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