NTSB Factual Report

On September 27, 2001, at 0905 central daylight time, a Cessna T188C agricultural airplane, N4629J, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Aiken, Texas. The airplane was registered to a private individual and was operated by Addison Spraying Service, of Plainview, Texas. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The local flight originated from the Hale County Airport, Plainview, Texas, at 0900.

According to the pilot, the flight was part of the boll weevil eradication program. The pilot was maneuvering the airplane to enter a field and commence spraying, when at 120 feet agl, the engine lost power. The pilot attempted to restart the engine; however, the engine did not restart. During the ensuing forced landing, the airplane contacted circular rows of cotton, the left main landing gear separated from the airplane, and the left wing's rear spar was damaged. The airplane came to rest upright.

The Teledyne Continental Motors (TCM) TSIO-520-T engine was examined by an FAA inspector. The propeller rotated when it was manipulated by hand; however, none of the accessory drive gears rotated as the propeller was turned. The engine was sent to the TCM Factory in Mobile, Alabama, for further examination.

The engine was examined under supervision of an NTSB investigator at TCM. The oil sump was removed and ferrous debris was observed in the sump. The oil pump was removed, disassembled, and observed to be lubricated and intact. The engine crankcase and cylinders were disassembled. A silicon residue was observed on the base flanges of the #1, #2, #4, and #6 cylinders and on the mating surface of the crankcase halves (backbone). Fretting was observed on the base flanges of the cylinders, on the crankcase mating surfaces, and on the main bearing bosses. The crankshaft was observed to be fractured between the #2 main bearing and #3 crankshaft cheek. According to a TCM metallurgist the fatigue fracture's origin was determined to be at the aft radius of the #2 main bearing. The #2 main bearing was fragmented, and the bearing's bore was cracked and damaged.

According to the engine maintenance logbook, on May 3, 1999, the engine underwent its last field overhaul, during which the crankshaft was installed in the engine. On May 10, 2001, the engine underwent its most recent annual inspection at a time of 664.0 hours since overhaul. At the time of the accident, the engine had accumulated 777.0 hours since overhaul.

NTSB Probable Cause

the application of silicon sealant to the crankcase mating surfaces by maintenance personnel, which resulted in improper torque on the bolts which mate the crankcase halves, vibration, and the subsequent failure of the #2 main crankshaft bearing. A factor was the lack of suitable terrain for the forced landing.