On January 26, 2024, about 1329 Pacific standard time, a Piper PA-18A-150, N7473D, was substantially damaged when it was involved in an accident near Eden, Oregon. The pilot was seriously injured, and the passenger received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.   Both the pilot and passenger stated that they had a limited recollection of the accident flight. The pilot reported that they departed Joseph State Airport (JSY), Joseph, Oregon, at 0955 with 36 gallons of fuel on board, for a scenic flight. At an unknown point during the flight they landed on a private airstrip owned by the passenger. The passenger reported that they were returning from his property when they impacted the ground, about three hours into the flight. The pilot and passenger could not remember any further details.

According to first responders, the fuel selector was in the OFF position at the accident site. A representative of the recovery team reported that he drained about 2-3 gallons from the right-wing fuel tank and about 7 gallons from the left-wing fuel tank.

Postaccident examination of the airplane and engine revealed no preimpact mechanical anomalies that would have precluded normal operation. Both propeller blades were straight and remained attached to the crankshaft at the propeller hub. One blade tip was bent towards the camber side of the blade and the other blade tip was bent towards the blade face. The engine ran smooth and continuously during an engine test run and the fuel system (from the fuel lines at the wing roots to the engine) functioned normally when fuel was plumbed into the lines. A small oil leak was observed at the No. 3 cylinder exhaust tube and the engine was subsequently shut down for safety reasons. The fuel tanks were not compromised.

The airplane impacted mountainous terrain at a field elevation of about 2,900 ft mean sea level (msl) and was about 30 nm from the nearest airport with an onsite weather reporting station. A High-Resolution Rapid Refresh (HRRR) model sounding was created for the accident time and location. As the pilot and passenger were unable to recall their altitude before the airplane crashed, the model sounding was created from various altitudes. At an elevation of 3,900 ft msl, the HRRR sounding indicated the temperature was about 38° F and the dewpoint was about 29° F (“1” in Figure 1); the wind was from 207° at 3 kts.

At an elevation of 4,900 ft msl, the HRRR sounding indicated the temperature was about 32° F and the dewpoint was about 23° F (“2” in Figure 1); the wind was from 204° at 9 kts.

At an elevation of 5,900 ft msl, the HRRR sounding indicated the temperature was about 31° F and the dewpoint was about 20° F (“3” in Figure 1); the wind was from 201° at 11.5 kts.

According to the model sounding, the airplane was operating in conditions conducive to serious icing at cruise power at 3,900 ft msl (1,000 ft above ground level). At higher altitudes, the conditions were conducive to icing at both glide and cruise power.

Figure 1: Carburetor icing probability chart from Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35

According to the airplane manufacturer, a manual was not developed for this airplane as it was not required when it was certificated under Civil Aviation Regulations 3. In addition, no fuel consumption information was found in the airplane’s type certificate. Fuel computations were derived from the Lycoming engine manual, which listed fuel consumption of 16.1 gph at 2,700 rpm and 200 hp, 12.3 gph at 75% power and 150 hp, and 9.5 gph at 65% power and 130 hp. The fuel consumption for the accident flight was computed based on the fuel quantity determined by recovery personnel at the accident site and the total time in flight (216 minutes). The total calculated rate of consumption from the accident flight was about 8 gph.

The airplane crashed about 40 nm miles north of its departure airport. The estimated time en route from the accident site to the pilot’s departure airport was calculated using a normal cruise airspeed of about 85 kts, and the rate of fuel consumption during the accident flight. If the pilot had elected to proceed home from the accident site, the engine would have consumed about 3-4 gallons of fuel.