Accident Overview
On April 27, 2019, at approximately 0945 central daylight time, a Piper PA-23 airplane, registration N233P, was substantially damaged during a forced landing near Sulphur Springs Municipal Airport (SLR) in Sulphur Springs, Texas. The pilot, the sole occupant, was not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Pilot Report
The pilot reported that before departure from Mount Pleasant Regional Airport (OSA), the airplane's main fuel tanks were topped off. While overflying SLR, the pilot noticed a slight drop in rpm on the left engine. He increased the left engine manifold pressure to full, but the engine speed continued to decrease. A small amount of black smoke was observed coming from the left engine. The pilot checked that the fuel primer was locked. As airspeed decreased, he decided to turn back to SLR. He activated the boost pumps, checked fuel quantity, verified the fuel selector was set to main tanks, and checked engine gauges. The left engine tachometer indicated only 2,000 rpm at full throttle. The airplane was at about 3,000 ft mean sea level (msl) and descending 100 to 200 ft per minute with decreasing airspeed. The pilot stated that, without warning, the right engine died. Attempts to restart it failed, and the propeller went to the feathered position.
Unable to maintain altitude or airspeed, the pilot located a field for a forced landing. As he descended, the left engine lost power. The pilot reported that the left engine continued to windmill but was unresponsive to throttle changes. After the forced landing, the pilot secured the fuel pumps, fuel, avionics, and master switch. The airplane sustained substantial damage to the left and right wings and the fuselage.
Post-Accident Examination
Following recovery, an examination of the engines and airframe was conducted. Approximately 45 gallons of fuel was recovered from the main fuel tanks. The left-wing main fuel tank appeared intact, and fluid was visible in the fuel cell from the filler opening. A fuel sample from the left tank separated into two layers: the top part blue, consistent with 100 LL avgas, and the lower portion clear with brown sediment at the interface. The fuel strainer bowl contained rust-colored liquid and sediment; the strainer screen had numerous small flakes of unidentified material. A sample from the left tank tested positive for water using Kolor-Kut water-finding paste. In contrast, a fuel sample from the right-wing tank was blue and consistent with 100 LL avgas, with no debris or contaminants in the strainer bowl or screen.
Examination of the right engine revealed magneto timing set at 12.5°, while the data plate specifies 25°. No other preimpact abnormalities were noted. The right engine's two-bladed propeller was in the feathered position; both blades were straight with no bending.
Examination of the left engine found magneto timing at 23° (data plate specifies 25°). The bolts securing the upper and lower halves of the carburetor were loose. Upon opening the carburetor, the bowl was dry, and the gasket appeared worn, consistent with rubbing between the two halves. The top set of spark plugs exhibited heavy carbon coating, consistent with a rich fuel setting. A non-original equipment manufacturer air induction system was observed and appeared free of blockages. The left engine's two-bladed propeller was not feathered; both blades showed polishing and slight S-bending.
Engine Test Runs
The left engine was mounted on a test stand with the bent propeller replaced by the right engine's propeller. During a test run, the left engine would not produce rated power and ran rich. When the fuel mixture control was leaned, the engine smoothed out and ran normally. The carburetor was bench tested and operated as expected. Disassembly of the carburetor revealed evidence of water staining.