NTSB Factual Report

HISTORY OF FLIGHT

On January 3, 2017, about 0930 mountain standard time, an experimental amateur-built Softex Investment LLC V-24L airplane, N710XP, collided with terrain during an off-airport landing near Paradise, Montana. The airline transport pilot and passenger were seriously injured. The airplane sustained substantial damage. The airplane was registered to Summit International American and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The cross-country flight originated from Missoula, Montana, about 0830 and was destined for Seattle, Washington.

The pilot reported that the purpose of the flight was to return the airplane to its home base in Seattle. The day before the flight, the pilot checked the airplane as it had been in a heated hangar for about 10 to 14 days. The pilot started both engines and conducted checks of all the systems including the operation of the propellers. All was normal, and the airplane was put back in the hangar.

The next day, the pilot again checked the airplane and did an engine run-up and all systems showed normal. After departure and about 25 to 30 minutes into cruise flight, the airplane was about 1,500 to 1,800 ft above ground level when a vibration developed. The pilot did not see anything abnormal with the engine instruments. He noted that the airspeed was rapidly decreasing along with a loss of altitude, so he applied maximum power to both engines. The airplane continued to descend, and he decided to perform an emergency forced landing in an open area of a railroad yard.

AIRCRAFT INFORMATION

The 4-seat low-wing, retractable-gear, multi-engine pusher experimental airplane, serial number 14-03-05, was manufactured in 2014. According to the maintenance logbooks, the airplane received its first and only condition inspection on June 30, 2016.

The left engine was a Lycoming, fuel-injected YIO-320-D1B engine, serial number EL-6259-55E. Total time recorded on the engine at the time of the condition inspection was 62.5 hours.

The right engine was a Lycoming, fuel-injected YIO-320-D1B engine, serial number EL-6260-55E. Total time recorded on the engine at the time of the condition inspection was 62.5 hours.

Fueling records at Northstar Jet, Missoula, Montana, established that the airplane was last fueled on September 2, 2016 with the addition of 24.7 gallons of aviation fuel. The general manager reported that each morning, before aircraft fueling, a fuel sample is tested from the facility fuel sump. On the morning of September 2, 2016, the fuel sample retained received a rating of "1A", meaning clear and bright and water-free.

METEOROLOGICAL CONDITIONS

An automated surface weather observation at Mullan Pass VOR/DME (MLP), Mullan Pass, Idaho (elevation 6,074 ft msl, 34 miles west of the accident site) was issued 23 minutes after the accident. It indicated wind from 130° at 7 knots, 10 miles or greater visibility, with an overcast ceiling at 5,500 ft, temperature at -17°C, dew point -21°C, and an altimeter setting of 29.96 inches of mercury.

An automated surface weather observation at Missoula International Airport (MSO), Missoula, Montana (elevation 3,204 ft msl, 41 miles southeast of the accident site) was issued 23 minutes after the accident. It indicated wind from 110° at 9 knots, 10 miles or greater visibility, few clouds at 6,500 ft, with an overcast ceiling at 9,000 ft, temperature at -14°C, dew point -19°C, and an altimeter setting of 30.26 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

The wreckage came to rest at the end of a snow-covered field after impacting a ditch. The landing gear appeared to be in the retracted position. The path of the airplane could be determined by tire marks in the snow.

The airplane remained relatively intact, with all four corners of the airplane present at the wreckage site. The empennage separated from the fuselage near the trailing edge of the wings. The left wingtip separated after impacting the ditch. The right-wing spar was damaged near the right wing, which separated from the wing. The left engine remained attached to the left wing. The three propeller blades on each engine were fractured and separated about midspan.

Flight control continuity of both ailerons was established to the wing separation point and from the wing separation points on the fuselage to the yoke. Rudder and elevator control continuity was established from the rudder and elevator to the empennage separation point and from the empennage separation point to the rudder pedals and yoke, respectively.

The fuel selector valves within the cockpit were in the off positions. The throttle arm, mixture arm, carburetor heat arm, and governor arm followed control movement, and moved freely from stop to stop.

The crankshaft rotated freely in both engines and the valves moved approximately the same amount of lift in firing order. Thumb compression was obtained on all cylinders in firing order.

All center electrodes of all the spark plugs were circular and clean with no mechanical deformation.

The spark plugs were connected to their respective ignition leads and were grounded. The magnetos were manually rotated on the left engine, and both magnetos produced sparks at all plugs except the top spark plug in cylinder No. 2 and the bottom spark plug in cylinder No. 1. The magnetos on the right engine were also rotated, and both magnetos produced sparks at all plugs.

Both engine fuel filters were disassembled. A pale blue fluid was inside both filters that smelled similar, but slightly different than 100LL aviation fuel, and contained "sand-like" debris. The same "sand-like" debris remained within the fuel filter container after the fluid was drained. A sample of the fluid was retained for further examination, but the fluid was unable to be tested due to the small quantity. The overall effect and or correlation of the trace amounts of debris in the fuel system and engine performance could not be determined.

NTSB Probable Cause

A partial loss of power during cruise flight for reasons that could not be determined because postaccident examination of the engines did not reveal evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.