NTSB Factual Report

On October 15, 2016, about 1430 central daylight time, a Piper PA 18-150 airplane, N9473D, conducted a forced landing near Jasper, Texas. The private rated pilot received minor injuries and the airplane was substantially damaged during the accident. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time.

The pilot reported the flight had just departed from the Jasper County Airport (KJAS), Jasper, Texas. After reaching an altitude of about 1,000 ft, the engine starting "missing." He switched fuel tanks and pumped the throttle; the engine continued to run, but was not making power. Unable to maintain altitude, he turned back towards the airport. Realizing he would not clear trees, he selected an area for the forced landing. The airplane came to rest with in a slight right wing down, nose low attitude among several trees.

Substantial damage was noted to the airplane's fuselage and wings. Fuel was present on site.

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.

A review of aircraft records revealed the last annual inspection was completed on August 31, 2016. At the time of the inspection, the engine had accrued 44.87 hours since a top overhaul. The aircraft's tachometer had accumulated 1.49 hours, since the last annual inspection.

Examination of the airplane noted that the wood under the battery box, located in the aft section of the airplane, appeared rotted. The engine's muffler had hole(s) rusted through it; 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 was noted on each cylinder; engine continuity was also 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 any debris and contamination, the bowl contained a small amount of liquid; light blue in color, consistent with 100LL avgas. Both wing fuel tank gas caps were an aftermarket type, and were absent an FAA-PMA marking; additionally, the fuel caps appeared to be a 'non-vented' type. Air was blown into the fuel lines near the fuselage/wing root, both left and right fuel lines were clear to the gascolator.

At 1415, the automated weather station at KJAS recorded; temperature 92.5 degrees F, and a dew point of 69.6 degrees F, 10-mile visibility, wind from 170 degrees at 7 knots, and altimeter setting of 30.06.

The carburetor icing probability chart included in Federal Aviation Administration Special Airworthiness Information Bulletin No. CE-09-35, Carburetor Icing Prevention, indicated that the airplane was operating in an area that was associated with a risk of carburetor ice formation, at glide and cruise power settings.

The examination did not find a specific reason for the loss of engine power.

NTSB Probable Cause

A partial loss of engine power for reasons that could not be determined, because an examination of the airplane did not identify a specific reason for the loss of engine power.