Running Past TBO: Smart Economics or Owner Negligence?

Aircraft engine manufacturers recommend that owners overhaul their engines when they accumulate a certain amount of operating time, usually between 1200 and 2400 hours depending on the engine's make and model. For example, Teledyne Continental Motors suggests that owners overhaul its IO-550 model engine at 2000 hours. Textron LycLycoming Engine - photo by wirelizardoming suggests that owners overhaul its O-235 engine, like the one pictured, at 2400 hours.

Overhauls are expensive.  Some can cost $40,000 or more.  An increasing number of owners opt to run their engines 200, 400 or more hours past the manufacturer's recommended "time between overhauls," or TBO.  Once past TBO, they may take extra precautions by, for example, regularly sending out engine oil samples for spectrographic analysis, checking the engine’s compression, and looking inside certain parts of the engine with a boroscope to insure that  things look good. They feel the manufacturer's TBO recommendations are somewhat arbitrary. By running their engines past TBO they are squeezing more life out of them, and that just makes good economic sense.

The FAA does not require private owners to comply with the manufacturer’s stated TBO interval. The manufacturer's TBO is therefore advisory only.  As long as a properly certified mechanic has

within the previous twelve months certified that the engine is airworthy, then the owner is, from a regulatory standpoint, free to operate the engine as many hours as he wishes.

But if an owner does operate past TBO, and the engine fails, and a passenger is hurt as a result, could the owner be held accountable despite the fact he was in compliance with all FAA regulations?

You bet.

An owner can be held accountable for an accident after TBO if a judge or jury decides that:

1.  in not complying with the manufacturer's overhaul recommendations, the owner was negligent (not "reasonably careful" under the circumstances) and

2.  the negligence was a cause of the accident. 

The FAA regulations are minimum standards only.  Many would argue that more can and should be expected of a reasonably careful owner or operator.  If a judge or jury agrees, then the operator would be held responsible for the harm resulting from running the engine past TBO, even though the regulations allowed him to.


How would the aviation attorney representing the injured passenger establish the owner's liability?  Through expert testimony.  Let's say that at 100 hours past TBO an exhaust valve failed, the engine lost power, and an accident resulted.  It wouldn't be difficult to establish a causal link between the owner's decision to run the engine past TBO and the engine failure. 

Q: Mr. Metallurgist, did you find any defect in the exhaust valve?


A: No, it was manufactured properly and was a fine example of an exhaust valve in all respects.


Q: Then why did it fail?


A: It failed in fatigue. It took all the vibration, bending, and heat that it could and then it finally quit.


Q: Would it have broken if the owner had not continued to run the engine past the manufacturer's 2000 hour overhaul interval?


A: No, sir, it would not have broken had the owner followed the manufacturer's recommendation.


Q: How do you know that?


A: Well, for one thing, it completed the manufacturer's service interval without breaking. It broke only when the owner asked more of it than the manufacturer recommended. Certainly, had the engine been overhauled at 2000 hours and a new valve installed, one would not expect it to have failed in fatigue 100 hours later. Rather, one would have expected the valve to continue in service well beyond that.


The injured passenger's attorney would next call to the stand the owner of an FBO (aircraft rental agency).  The FBO owner would testify that he never runs engines beyond TBO because he doesn't assume that he is smarter than the manufacturer.  He would testify that some things, like whether internal parts are worn beyond safe limits, cannot be determined without tearing down the engine. The witness might then suggest that the costs saved by running an engine beyond TBO are marginal and just aren't worth the risk to human life. 

With the testimony of those two witnesses, a judge or jury could well decide that the owner was negligent in operating his engine past TBO and that the negligence caused the passenger's injuries.

Some proponents of running an aircraft engine beyond TBO downplay the risks.  They argue that the manufacturer's TBO is a "made up" number, and few engine failures have actually been attributed to the owner's decision to run past it.  One prominent aviation maintenance expert even suggests that there have been no cases where running past TBO resulted in an owner being held responsible for a passenger's resulting injuries.

Not so.  

There may be good economic reasons to run an engine past TBO.  But an owner who does so should expect to be held responsible if an accident results. 

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Comments (1) Read through and enter the discussion with the form at the end
Dan Akerman - December 29, 2009 1:13 AM

Interesting article.
However, I think a good defense lawyer could contest the notion that the engine manufacturer can predict the life of a component to within 100 hours. A different metalurgist witness could, based on examples of varying fatigue lifes of seemingly identical parts, show that the valve could just as easily have failed at say 1900 hours, and that the vast majority of identical valves make it well beyond TBO.

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