Cessna 172K N79509

Summary

On 16 March 2012 at about 15:15 local time, a Cessna 172K registered N79509, operated by Skywarrior Inc, was involved in an accident near Pensacola, Florida, United States. 2 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

16 March 2012 at 15:15

Classification

Accident

Location

Pensacola, Florida, United States

Coordinates

30.4197, -87.1931

Aircraft

Cessna 172K

Registration

N79509

Category

Airplane

Engines

1

Operator

Skywarrior Inc

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

Pensacola → Pensacola

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA12LA234

Nobody was injured.

A total loss of engine power due to the improper installation of the crankshaft gear bolt or lockplate by maintenance personnel. Contributing to the accident was the lack of suitable terrain for a forced landing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

During the training flight, the single-engine airplane was in cruise flight about 1,000 feet above ground level when the engine stopped operating. The flight instructor assumed control of the airplane and unsuccessfully attempted to restart the engine while descending for an emergency landing. He ditched the airplane into a nearby bay. The airplane sustained substantial damage to the windshield during the accident sequence and was submerged in salt water. Postaccident examination of the engine revealed that the bolt or lockplate, which attaches the crankshaft gear to the aft end of the crankshaft, was missing. Further, the alignment dowel was fractured across about one-third of the cross-sectional area. The bolt and lockplate were likely either not installed or were improperly installed, which would allow the bolt to loosen and become disengaged. Measurements of the dowel, pilot flange, and counterbore recess diameters were all within the manufacturer's specifications; the dowel also met the manufacturer's hardness requirement. Because the components were within manufacturer's specifications, it is likely that the components did not have any preexisting wear or manufacturing issues. Additionally, wear marks on the crankshaft, dowel, and gear were likely caused by the newly installed gear and were consistent with either no installation or improper installation of the bolt or lockplate. Therefore, it is likely that when the wear on the dowel had proceeded through about one-third of the cross-section, the stresses in the dowel became sufficiently high to initiate fatigue cracks at the base of the worn part of the dowel and eventually led to a fatigue fracture. The evidence is consistent with the failure of maintenance personnel to install, or properly install, the bolt and lockplate during the engine’s last overhaul, which resulted in the crankshaft gear becoming separated from the crankshaft and a total loss of engine power. If the engine had failed at a point that would have allowed the pilot to land the airplane on land, the airplane damage is less likely to have been substantial; therefore, contributing to the accident was the lack of suitable terrain.

Quoted verbatim from the NTSB record.