Aircraft Engine Age Deterioration

In Service Condition Inspection of N6937Y, PA23-250

• Compression: Excellent
• Oil Consumption: Good
• Oil Analysis: Clean
• Oil Filter Examination: OK
• Engine Operation: Smooth

Based on above findings aircraft was operated on June 23, 1996. Aircraft crashed during flight killing all aboard.

• Fatigue crack at corrosion pit between cylinder fins
• In flight fire
• Wing separated in flight
• 5 fatalities

Lycoming connecting rod with rust

Overhaul Condition Inspections that WERE NOT DONE but recommended (Factory overhaul inspections after 12 years; engine time-in-service: 21 years):

• Corrosion and Pitting Inspection
• Magnetic Particle Inspection
• Florescent Penetrant Inspection
• Eddy Current Inspection
• Visual Inspection
• Dimensional and run-out inspection
• Wear and surface damage

These more thorough inspections were not performed presumably because In Service Condition Inspections were all that were required (in the opinion of some airplane owners and mechanics) to determine the safety of the engine. Unfortunately, In Service Condition Inspections were not adequate given the age of the engine. "Bad practices that result in no immediate ill effects wind up becoming the norm."

 Age related deterioration may result in sudden and catastrophic engine failure as this example illustrates. This accident, and other age-related-failures, may be prevented on high calender time engines by using more thorough Overhaul Condition Inspections that better inspect for corrosion pitting, fatigue cracks, and other deterioration both external and internal.

Links to accidents related to corrosion pitting:

Lycoming fuel injector lines

Crankshaft Failure of antique engine

Navion Crankshaft Failure - pitting on fillet


A 150 µm deep (0.010 inch) corrosion pit
A post-mortem examination found evidence of soot  in the airway of the pilot, which indicated that he had  been breathing during exposure to smoke.  Toxicology  results showed the presence of cyanide in the pilot’s  blood at a significantly elevated level; cyanide is a  common combustion product of some materials  found in aircraft construction. 


Cessna 152 Cylinder Failure

Engine Failure/Fire Piston Pin Pitting

Propeller Loss "Had the failed engine been overhauled within the manufacturer’s recommended time of 2000 hours, or even within 2200 hours had it met the manufacturer’s 200-hour extension requirements, the overhaul would have occurred before the flange cracking had reached a critical stage and the crankshaft should have been scrapped."


The occupants were fatally injured. "A fatigue crack developed in the engine crankshaft as a result of corrosion pitting and the absence of a case-hardened layer on the fillet radius of the number six connecting rod journal. The fatigue failure of this section of the engine crankshaft resulted in a complete loss of power."


 Both occupants were fatally injured. The helicopter was completely destroyed in the post-impact fire. Enstrom F-28C Helicopter C-GVQQ total time in service of 611 hours over the 27 years since the 1982 overhaul. "The fracture of the check ball retainer in the exhaust valve hydraulic tappet..."

Calender time and Hours (stress cycles) are both considerations for continued safe operation

I0-520 Cylinder with combustion chamber cracks

"Old designs are never proven for fatigue simply by virture of their longevity. Fatigue is wear-out. There is no guarantee that future failures will be confined to those seen in the past." Steve Swift,GNATS AND CAMELS - 30 Years of Regulating Structural Fatigue in Light Aircraft"


Crankshaft Fatigue Failure in TIO-540 Engines operarating past TBO