Piper PA 23 N233P accident near Sulphur Spring, Texas

Probable cause

The pilot’s inadequate preflight inspection, during which he failed to detect the water contamination in the left fuel, which resulted in a partial loss of power in the left engine. Contributing to the accident was the total loss of power in the right engine for undetermined reasons.

NTSB analysis

The pilot of a twin-engine airplane was in cruise flight when the left engine lost partial power. He turned on the boost pumps, checked the fuel quantity and engine gauges, verified fuel tank selection, and added throttle. However, the left engine continued to lose power. The pilot reported that, without warning, the right engine lost total power and would not restart. The right propeller went to the feathered position. The pilot initiated a forced landing to a field. During the descent, the left engine lost total power but the propeller continued to rotate, and the left engine was unresponsive to throttle input. During the forced landing, the airplane sustained substantial damage to the left and right wings and the fuselage.

Examination of the right engine found the magneto timing at 12.5º (data plate specifies 25º). Otherwise, no preimpact abnormalities were noted during the right engine examination that would have precluded normal operations. The investigation was not able to determine why the right propeller was stopped in the feathered position.

Examination of the left engine found the magneto timing at 23º. 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 left engine running at a rich fuel setting. During a test run, the left engine would not produce rated power and ran rich. When the mixture was leaned, the left engine ran smooth and ran normally. The carburetor was bench tested and operated as expected. The carburetor was disassembled, and evidence of water staining was present.

A fuel sample 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 revealed rust colored liquid and sediment in the bowl. The fuel strainer screen contained numerous small flakes of an unidentified contaminant. A sample of fuel drained from the left-wing tank tested positive for water when tested with water-finding paste. The loss of power on the left engine is likely due to water contamination.

Text from the NTSB. Open the NTSB docket for CEN19LA129 for the full record.