Incident Details
On March 16, 2012, at approximately 1015 central daylight time, a Cessna 172K (registration N79509) suffered a total loss of engine power while maneuvering near Pensacola, Florida. The pilot performed a ditching into Pensacola Bay. The aircraft was operated by a local flight school under Title 14 Code of Federal Regulations Part 91 as a local instructional flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed from Pensacola Gulf Coast Regional Airport (PNS) around 0915.
According to both the certified flight instructor (CFI) and the student pilot, while cruising at about 1,000 feet above ground level, the engine hesitated and then quit. The CFI took control, attempted an engine restart during descent, but the restart was unsuccessful. The airplane was ditched in the bay. The airplane struck the water, both occupants egressed, and the airplane subsequently sank. The airplane sustained substantial damage to the windshield and was submerged in salt water.
Occupants and Crew
The CFI held a commercial pilot certificate with ratings for airplane single-engine land, multiengine land, and instrument airplane, as well as a flight instructor certificate with ratings for airplane single-engine land, multiengine land, and instrument airplane. The CFI reported over 4,000 total hours of flight experience, with over 2,000 hours in the accident airplane make and model.
The student pilot held a student pilot certificate issued on February 5, 2012, and reported 3 total hours of flight experience, all in the accident airplane make and model.
Aircraft and Engine Examination
Post-accident examination by the NTSB investigator revealed that the engine remained attached to the airframe via the engine mounts. The engine was rotated by hand using the propeller, which remained attached to the propeller flange. Thumb compression was confirmed on the No. 4 cylinder; no compression was noted on the other cylinders. After removing engine accessories, the engine was rotated by hand using the attached propeller, but continuity was not obtained to the rear accessory pad. Removal of the accessory pad revealed that the crankshaft gear lockplate and bolt were absent from the crankshaft gear attached to the aft end of the crankshaft. The lockplate and bolt were not located throughout the engine. Rotation of the crankshaft gear revealed a fractured stepped dowel. The crankshaft, step dowel, and crankshaft gear were sent to the NTSB's Materials Laboratory for further examination. No other defects were noted with the engine.
Maintenance Records
Airframe and engine maintenance records showed that a 50-hour inspection had been performed on February 23, 2012. At that time, the engine had 534.39 hours total time since overhaul. An entry dated August 8, 2010, recorded that the engine was rebuilt in accordance with Lycoming factory recommended procedures and that all recommended parts listed in the Lycoming overhaul manual and service bulletins were installed.
According to Lycoming Service Bulletin 475C, procedures include assembling the gear to the crankshaft using a new lockplate and bolt, tightening the bolt to 125 in-lbs torque, tapping around the pilot flange to check seating, bending the lockplate against the bolt head, and making a logbook entry specifying final bolt torque. No such entry was found in the engine logbook.
NTSB Laboratory Findings
The NTSB's Materials Laboratory visually examined the crankshaft gear. No witness marks or wear were noted where the lockplate and bolt contact the gear. The threaded bolt hole in the end of the crankshaft showed no deformation, fracture, or wear. Examination of the dowel and pilot hole on the gear revealed matching wear marks. The wear mark covered about one-third of the dowel's cross-sectional area, and the remaining area was fractured with ratchet and crank arrest marks and individual fatigue striations. The crankshaft, dowel, and gear were measured and found to be within manufacturer limits.