Accident Overview
On October 15, 2016, at approximately 1430 central daylight time, a Piper PA-18-150, registration N9473D, performed a forced landing near Jasper, Texas. The airplane was privately owned and operated under 14 Code of Federal Regulations Part 91 as a personal flight. The private-rated pilot reported minor injuries, and the aircraft sustained substantial damage. Visual meteorological conditions prevailed at the time.
Pilot Report
According to the pilot, the flight had just departed from Jasper County Airport (KJAS), Jasper, Texas. After reaching an altitude of about 1,000 feet, the engine began "missing." The pilot switched fuel tanks and pumped the throttle; the engine continued to run but did not produce sufficient power. Unable to maintain altitude, he turned back toward the airport. Realizing he would not clear trees, he selected an area for the forced landing. The airplane came to rest in a slight right-wing-down, nose-low attitude among several trees.
Examination Findings
The airplane was recovered and transported to a salvage facility, where an examination was conducted by the NTSB Investigator in Charge and an FAA inspector. Substantial damage was noted to the fuselage and wings. Fuel was present at the accident site. A review of records showed the last annual inspection was completed on August 31, 2016. At that time, the engine had accrued 44.87 hours since a top overhaul. The tachometer indicated 1.49 hours since the last annual inspection.
Examination revealed that the wood under the battery box, located in the aft section, appeared rotted. The engine's muffler had holes rusted through it, and exhaust signatures on the inside of the muffler shroud and cabin heat duct were consistent with exhaust gas leakage. Welding on the muffler-exhaust pipe appeared to have holes in and around the weld. When the engine was rotated by hand, thumb compression and suction were noted on each cylinder, and engine continuity was established through the valve train and engine. The intake and exhaust rocker arms were removed from each cylinder; two of the four cylinders had the exhaust rocker arm on the intake valve and/or the intake rocker on the exhaust valve. Both left and right magnetos were removed and produced a spark at each terminal when rotated by hand. The carburetor inlet screen was removed, and the carburetor separated; the carburetor bowl and screen were clear of debris and contamination, with the bowl containing a small amount of light blue liquid consistent with 100LL avgas. Both wing fuel tank gas caps were aftermarket type, absent an FAA-PMA marking, and appeared to be non-vented type. Air blown into the fuel lines near the fuselage/wing root confirmed that both left and right fuel lines were clear to the gascolator.
Weather Conditions
At 1415, the automated weather station at KJAS recorded temperature 92.5°F, dew point 69.6°F, 10-mile visibility, wind from 170° at 7 knots, and an altimeter setting of 30.06 inches of mercury. The carburetor icing probability chart included in FAA Special Airworthiness Information Bulletin No. CE-09-35 indicated that the airplane was operating in an area associated with a risk of carburetor ice formation at glide and cruise power settings.
Investigation Outcome
The examination did not identify a specific reason for the loss of engine power.