On April 27, 2019, about 0945 central daylight time, a Piper PA-23 airplane, N233P, was substantially damaged when it was involved in an accident near Sulphur Springs Municipal Airport (SLR), Sulphur Springs, Texas. The pilot was not injured. The flight was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that before departure from Mount Pleasant Regional Airport (OSA), the airplane’s main fuel tanks were “topped off.” The pilot added that as he passed over SLR, he 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. He observed a small amount of black smoke coming from left engine and checked that the fuel primer was still locked. The airspeed was decreasing, so he decided to turn back to SLR. He turned on the boost pumps, then checked the fuel quantity, verified the fuel selector was set to the main tanks, and checked the engine gauges. The left engine tachometer showed only 2,000 rpm, with full throttle. The airplane was about 3,000 ft mean sea level (msl) and descended 100 to 200 ft per minute while the airspeed decreased. The pilot stated that, "with no warning, the right engine died." He attempted to restart it, but the right engine would not restart, and the propeller went to the feathered position. The airplane was not able to maintain altitude or airspeed, so the pilot located a field to perform a forced landing. As he descended to the field, the left engine lost power. The pilot stated that the “left engine continued to windmill but was not responsive to throttle changes.” After the forced landing and the airplane came to rest, the pilot turned off the fuel pumps, fuel, avionics, and the master switch. During the forced landing, the airplane sustained substantial damage to the left and right wings and the fuselage. After the airplane was recovered, an examination was conducted on the engines and airframe. About 45 gallons of fuel was recovered from the airplane’s main fuel tanks. The left-wing main fuel tank appeared intact, and fluid was observed in the fuel cell when viewed from the filler opening. A sample of fuel collected from the left side fuel tank appeared divided with the top part blue, consistent with 100 LL avgas, and the lower portion of the liquid was clear with brown sediment visible at the intersection of the two liquids. The fuel strainer bowl contained rust colored liquid and sediment. The fuel strainer screen contained numerous small flakes of an unidentified material. A sample of fuel drained from the left tank tested positive for water when tested with Kolor-Kut water finding paste. A fuel sample taken from the right-wing tank appeared blue; consistent with 100 LL avgas. The fuel strainer bowl and screen were absent debris/contaminants.

Examination of the right engine found the magneto timing at 12.5º (data plate specifies 25º). Otherwise no preimpact abnormalities were noted during the engine examination. The right engine’s two-bladed propeller was found in the feathered position. Both blades appeared straight absent bending.

Examination of the left engine found the magneto timing at 23º (data plate specifies 25º). The bolts that secured the upper and lower halves of the carburetor were found loose. When the carburetor was opened, the inside of the bowl was dry, and the gasket appeared worn, consistent with rubbing between the two carburetor halves. The top set of spark plugs displayed heavy carbon coating consistent with the engine running at a rich fuel setting. A non-original equipment manufacturer air induction system was observed and appeared free of any blockages. The left engine’s two-bladed propeller was not in the feathered position. Both blades showed signs of polishing with slight S-bending of the blades.

The left engine was mounted on a test stand, the bent propeller was replaced with the propeller from the right engine. An engine test run was completed and noted that the left engine would not produce rated power and ran rich. The fuel mixture control was leaned, and the left engine smoothed out and ran normally. The carburetor was bench tested and operated as expected. The carburetor was disassembled, and evidence of water staining was present.