Accident Details
On August 7, 2012, at approximately 0945 central daylight time, a Cessna 177B, registration N17201, impacted terrain during a forced landing following a loss of engine power near Carthage, Texas. The commercial pilot reported no injuries. The airplane sustained substantial fuselage damage. The aircraft was registered to a private individual and operated by Hawkeye Helicopters under 14 CFR Part 91 as an aerial observation flight. Day VFR conditions prevailed, and the flight did not operate on a VFR flight plan. The flight departed Shreveport Regional Airport, Louisiana, at about 0830.
Pilot Actions
The pilot stated he had been flying at 500 feet above ground level following a pipeline for about 1.5 hours when the engine lost over 50 percent power without warning. He searched for a landing area and managed to climb about 50 feet. He activated the electric fuel pump and adjusted the propeller and mixture. The descent rate was about 50 feet per minute. He selected an old logging site for the forced landing, and the airplane impacted logs and stumps during rollout.
Examination Findings
An FAA inspector examined the wreckage and confirmed substantial damage. The engine propeller turned when rotated by hand. A teardown examination of the Lycoming O-360-A1F6D engine revealed that the number one cylinder intake valve was not present under its rocker arm tip. The valve keepers were worn, deformed, and segmented in the rocker box. The rocker arm tip exhibited wear consistent with contact against the valve stem and keeper, and the rocker arm showed a wear mark from contact with the valve spring retainer. The piston had impact marks from valve contact, and the cylinder intake port had a hole from the liberated valve stem. The valve was found in pieces in the number three and four intake tubes.
Component Analysis
Components were examined at Engine Components International (ECI) in San Antonio, Texas. The number one intake valve showed no fatigue fractures and no erosion or wear on the face. The push rod was straight, and there was no evidence of a sticking valve. The rocker arms are made of low carbon alloy steel with carburized tips. The failed rocker arm tip was too damaged for metallurgical analysis, and the carburized layer depth could not be determined. The remaining intake valve rocker arms met overhaul hardness requirements but had a shallow carburized layer.
Maintenance History
The engine had accumulated about 878.5 hours time since overhaul. A compression check on June 6, 2012, showed pressures of 79/72/72/79. On July 13, 2012, at 779 hours TSO, a rough running engine issue was corrected by replacing the magneto, harness, and ignition switch. The rocker arm with the worn tip was marked with numbers 5829-2 and 69443-D, corresponding to Lycoming part number 69444. According to a work order, this rocker arm was "rebrushed and refaced" by Aircraft Specialties Services. A representative from that repair station stated they use the Lycoming overhaul manual for guidance on rocker arm reconditioning.
Manual Specifications
The Lycoming overhaul manual (Section 6-34) specifies that damaged, badly worn, pitted, or scored rocker arm tips warrant replacement. However, it does not list quantitative limitations or a gage for determining tip serviceability. Lycoming Service Table Of Limits And Torque Value Recommendations (SSP1776) also lacks quantitative specifications for rocker arm tip wear. Magnetic particle inspection, as per ASTM E1444/E1444M-12, can detect subsurface defects. Both the repair station and Lycoming reported using magnetic particle inspection during rocker arm reconditioning.