History of Flight
On August 24, 2014, about 1305 Alaska daylight time, a Ryan Navion A, N4827K, was substantially damaged when it impacted terrain while maneuvering in mountainous terrain approximately 56 nautical miles north-northeast of Coldfoot, Alaska. The airplane was operated by Kirst Aviation as an on-demand sightseeing flight under 14 CFR Part 135. The commercial pilot and three passengers were seriously injured. The right-front seat passenger died 35 days after the accident as a result of his injuries. Visual meteorological conditions prevailed, and a VFR flight plan was filed. The flight originated at Fairbanks International Airport (PAFA) about 1003.
Earlier that day, the pilot filed a flight plan indicating stops at Bettles Airport (PABT), Deadhorse Airport (PASC), and Barter Island LRRS Airport (PABA) before returning to PAFA, with about 7 hours 20 minutes of fuel on board.
The accident occurred between PABT and PASC in Atigun Pass, a high mountain pass crossing the Brooks Range at 4,739 feet msl. FAA charts for the area contained a warning: "RAPIDLY RISING TERRAIN" and "USE CAUTION DURING PERIODS OF LOW CEILING AND VISIBILITY."
During an interview, the pilot stated that the male passenger (right front seat) had requested the flight about two weeks prior. The flight to PABT was uneventful. On the leg from PABT to Atigun Pass, the pilot was climbing through 5,500 to 5,700 feet with a target of 6,000 feet when the male passenger slumped into the yoke, blocking throttle and landing gear controls as they encountered rising terrain and a downdraft. Airspeed increased from 130 to 160 knots. The pilot lowered flaps halfway and opened the canopy 6 inches for post-crash exit. Post-impact, the pilot shut off fuel, master switch, and magnetos and exited. Passengers were unresponsive. Alyeska Pipeline personnel arrived; one female passenger was airlifted; the pilot and two remaining passengers were transported to Galbraith Lake.
The pilot reported no mechanical malfunctions precluding normal operation. On a subsequent form (NTSB 6120.1), he stated encountering "abrupt and unexpected aircraft instability" and noted a "propeller bolt failure causing blade to become unindexed and blade separation in flight," checking the box for mechanical failure.
Passenger interviews: The right-front passenger remembered a clear blue sky and taking photos; he could not recall the impact. One rear-seat passenger felt a bank and drop as if "into an air pocket" after taking motion sickness pills. Another rear-seat passenger felt a downward pull after taking a pill.
Witnesses observed the airplane flying slowly at low altitude following terrain. The engine sounded strong. The airplane impacted sloping terrain at about 4,600 feet, slid 35 feet, and came to rest. First responders found all occupants conscious; the pilot instructed canopy unlatching. The pilot later told a first responder that a strong downdraft caused altitude loss and he added power and lowered flaps.
Personnel Information
The pilot held a commercial pilot certificate with single-engine land/sea and instrument ratings, a flight instructor certificate, and a mechanic certificate with airframe/powerplant ratings and inspection authorization. His most recent FAA second-class medical was issued April 3, 2014. He reported 4,759 total flight hours, 657 in the accident make and model. He had two previous accidents: a December 2007 forced landing after loss of engine power for undetermined reason (NTSB probable cause), and a November 2008 midair collision with a Cessna 182R (probable cause: failure to maintain separation and follow tower instructions).
Aircraft Information
The airplane was a single-engine, four-seat, low-wing metal aircraft powered by a 225 hp Continental E-225-4 engine driving a two-blade Hartzell constant-speed propeller. Manufactured in 1949, its most recent annual inspection was completed by the pilot on June 14, 2014, at 4,027.4 total hours and 334.1 hours since engine major overhaul. The propeller was overhauled May 31, 2011, and installed by the pilot. It had been removed and remounted three times for hydraulic bladder diaphragm inspections.
Weight and balance: The pilot reported calculating weight about 40 pounds below gross weight before departure. Review of fuel flow data indicated a minimum fuel load of about 100 gallons to have 7 hours 20 minutes fuel on board. Calculated weights (pilot 160 lbs, right front passenger 230 lbs, two rear passengers 180 and 150 lbs, baggage 30 lbs, fuel 100 gallons) showed the airplane was about 187 pounds above max gross weight on takeoff from PAFA, 37 pounds over on landing at PABT, and at max gross weight 30 minutes into the accident flight from PABT.
Meteorological Information
At 1253, PABT reported wind 030 at 9 knots, temperature 17°C, dew point 5°C, altimeter 29.87 inHg. At 1344, Chandalar Shelf Airport (5CD), 4 nm southwest, reported wind west-northwest at 1 knot, temperature 7°C, dew point 4°C, altimeter 30.04 inHg. FAA weather camera images at 5CD showed VMC with scattered to broken clouds at about 8,000 feet. A SNOTEL site at 4,800 feet near the accident site reported wind from 059 degrees, peak 9 knots, average 4 knots at 1300. First responders reported visibility over 10 miles, scattered clouds at 12,000 feet, wind northeast at 4-7 knots.
Wreckage and Impact Information
The airplane came to rest near mile marker 244.5 of the Dalton Highway, about 100 feet below the highway on a 45-50 degree rocky slope. It sustained substantial impact, crush, and compression damage to wings, fuselage, empennage, and firewall. The engine was canted 10 degrees down. Landing gear was up; flaps switch was full down with partial extension; magneto switch at "BOTH"; throttle idle and bent up; propeller pitch high rpm; mixture full rich; carburetor heat off.
Engine examination: Both magnetos attached and produced spark when rotated. One magneto had a loose housing. Ignition harness and spark plugs undamaged; plugs showed normal operating signatures except some oil-coated (consistent with engine position) and normal wear. Fuel pump attached and functional; carburetor inlet screen contaminated with rubber material and particulates; fuel present in carburetor chambers. Induction and exhaust systems damaged from impact. Oil cooler and sump undamaged; oil pick-up tube screen clear. Oil pump housing showed scoring consistent with hard particles.