NTSB Factual Report

On June 19, 2009, about 1100 eastern daylight time, a Cessna 170B, N8339A, collided with a hill during an emergency landing in Mahwah, New Jersey. The private pilot was seriously injured, and the airplane was substantially damaged by impact forces. The flight was operated as a personal flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, and a visual flight rules flight plan was filed. Visual meteorological conditions prevailed for the planned flight to Greenwood Lake Airport (4N1), West Milford, New Jersey. The flight originated from Barnes Municipal Airport (BAF), Westfield, Massachusetts.

The pilot stated that during a cross-country flight, the airplane’s engine began to vibrate heavily. She attempted to continue her flight to the destination airport, but lost total engine power. She then attempted an emergency landing in a field, but collided with a hill during the landing roll.

The pilot recalled that during a previous cross-country flight she experienced a vague vibration while enroute. After she landed she informed her mechanic of the anomaly, and an inspection was performed. The mechanic was unable to identify the source of the vibration. An assumption was made by the mechanic that the carburetor may have developed carburetor ice.

Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the airplane overshot a field during landing roll out and collided with a hill. The airframe and flight control system components revealed no evidence of preimpact mechanical malfunction. The examination of the engine revealed that the No.1 cylinder was separated from the engine case. Six of the eight cylinder attachment thru bolts were separated at the cylinder attachment flange. The bolt nuts were not found. The other thru bolts were still attached to the case but loosely held by the nuts to the bolts. The threads on one of the thru bolts exhibited corrosion and discoloration. Review of logbooks revealed that the last annual inspection was conducted on March 06, 2009, at 3,258.6 hours total engine time. A log entry was made on June 10, 2009 at 3,263.1 engine total time, for an inspection for a "possible rough running engine." A "no defects noted" statement was entered after various component checks, and the airplane was returned to service. The engine had a top overhaul on March 1, 2001, at a tachometer time of 116.5 hours.

NTSB Probable Cause

A loss of engine power due to the failure of the No. 1 cylinder thru bolt hold down nuts due to corrosion.