Time-honored traditions

For aircraft owners, every hour flown reduces the value of the aircraft with a significant financial decision looming when the engine reaches time between overhauls (TBO). There is also a TBO spec measured by trips around the sun regardless of how many hours the engine has been spinning.

TBO is the original equipment manufacturer’s recommendation for overhaul based on tens of thousands of testing hours and data analysis compiled from engines in service. The objective of the TBO milestone is to provide guidance for preventive maintenance with plenty of safety margin built in. What is commonly misunderstood is whether the OEM’s recommended TBO triggers FAA-mandated maintenance. It may be misunderstood because the answer is: It depends on the application.

The good news is that for most general aviation operations, TBO is merely an OEM recommendation, not a required maintenance interval. Required maintenance at TBO falls under FAR Part 135 operations (air taxi).

Regardless of when the engine’s productive life draws to a close, there are a variety of options to consider, each with a unique value proposition.

Option 1: Fly beyond TBO (deferred decision)

Except for the Part 135 scenarios, neither the engine OEM nor the FAA requires service upon reaching TBO. Based on engine condition, the powerplant can be operated beyond the recommended TBO insofar as the engine continues to be maintained in accordance with mandatory service bulletins, airworthiness directives, and FAA requirements like 100-hour and annual inspections.

Savvy aircraft operators use oil analysis to track and monitor engine condition. Compression checks are also a good indication of top-end engine condition. Owners deciding to operate beyond TBO may consider doing both more frequently for early detection of accelerating engine component wear.

While continuing to operate beyond TBO is perfectly acceptable for most, it only defers the inevitable engine maintenance decision. From an aircraft value perspective, once the engine exceeds its published TBO, additional operational hours likely will not continue to diminish aircraft value because the engine will already be deemed to be “run-out” regardless of actual engine condition. Keep this in mind for Option 6 at the end.

Option 2: Engine overhaul (cumulative engine time/zero SMOH)

The overhaul option has the most variability. Price, quality, downtime, warranty, and perhaps peace of mind vary greatly when opting for an engine overhaul. The spectrum of alternatives ranges from factory overhaul to highly specialized maintenance, repair, and overhaul (MRO) facilities, independent maintenance shops, and individual A&Ps.

Reputable engine overhaulers have excellent processes, procedures, trained staff, and quality control. Some overhaulers use only OEM parts and specs. Others may use aftermarket parts and may claim to improve the engine in the overhaul process. An A&P occasionally overhauling engines as needed may or may not have the same level of subject matter expertise, familiarity, or quality control as a facility that does overhauls all day, every day. Equally important considerations are aircraft downtime (versus the installation of a complete engine) and engine warranty (coverage, length, and service network).

Keep in mind that an engine overhaul does not reset the engine time to zero—only the manufacturer can do that. The overhaul, regardless of how extensive, is maintenance performed as a continuation of the engine’s life since new. For example, if an engine had 2,875 hours before the overhaul, it still has 2,875 hours after the overhaul. However, an overhauled engine will commonly be considered as X hours since major overhaul to indicate the freshness of an engine post-overhaul.

Option 3: Factory remanufactured engine (zero SFRM)

Factory remanufactured engines are built by the OEM, use OEM parts, include a factory warranty, and start at zero time. In most cases, all new parts are installed with the possible exception of crankcases and crankshafts.

There are some key benefits to selecting a remanufactured engine. Remanufactured engines are built in the factory by OEM-trained workers and are assembled to current standards reflecting any enhancements or modifications that may have occurred since the engine was originally built. The warranty will typically be longer than an overhauled engine and should be readily honored at any OEM-authorized service center nationwide. And best of all, downtime is significantly reduced.

In most cases, you can purchase a remanufactured engine and continue flying until the replacement engine arrives. Upon returning your run-out engine to the OEM, a core value will be reimbursed if the engine being returned is complete, assembled, and serviceable as a future factory-remanufactured engine.

Option 4: Factory-new engine (zero SN)

If money is no object, the decision to install a factory-new engine is an easy one. The factory-new engine includes 100-percent genuine OEM parts, offers the longest warranty, and includes any enhancements or modifications that may have occurred to the engine variant over time.Don't get discouraged by the process, but rather enjoy the experience of owning and operating an aircraft.

Those opting to install an engine rather than overhaul can also explore whether any STCs apply to the aircraft make and model that may include upgrading the powerplant to one with more horsepower or perhaps even a different engine altogether like a Jet A-burning diesel. STC upgrade or not, choosing a new engine will also have the highest price tag.

Option 5: Salvaged engine (TBD)

Purchasing an engine from an aircraft salvage company requires considerable due diligence. While the purchase price will undoubtedly be very attractive, the value proposition may be uncertain.

Typically, the buyer assumes the risk on a salvaged engine if purchased “as is.” There may be unknown or undisclosed issues, and it may or may not have logbooks. Some known problems may be noted by the seller, but without an engine tear-down for inspection, there is no definitive way of knowing the condition of the engine.

For example, an engine listed as “10 SMOH” that was removed from an airframe destroyed in a hurricane may sound like a great find. But the engine should be torn down and inspected for rust (caused by water ingestion or stagnation), bent crankshaft (if the hangar collapsed and struck the propeller or if the aircraft was blown over), or any number of scenarios that could render a salvaged engine to be unfit.

Consequently, the total cost of purchasing a salvaged engine should include the cost of teardown, inspection, and repair if necessary. When budgeting for a salvaged engine, consider a worst-case scenario, like discovering a bent crankshaft upon inspection. If cost of purchasing a salvaged engine, tearing it down, and possibly replacing major components like the crankshaft or all cylinders and a cam is still cheaper than purchasing a remanufactured engine, then it may be good value. If an engine fails prematurely, it may cost you dearly.

Option 6: Sell the aircraft

The final option is to avoid the engine refresh decision and sell the aircraft as-is with a run-out engine. Doing so allows the new owner to consider the options. Any number of scenarios may be the catalyst for an aircraft owner to step up or step down, selling an aircraft when the engine is run-out is as good as any.

Whenever the time comes for an engine overhaul or replacement, explore the options and value propositions and seek advice from subject matter experts. Don’t get discouraged by the process, but rather enjoy the experience of owning and operating an aircraft—it’s a privilege that a small percentage of the population will ever know.

Randy S. Bolinger is a marketing, communications, and brand management leader in the aviation, auto, and powersports industries. He is an instrument-rated pilot, has been flying for more than 30 years, and owns a Cessna 177 Cardinal.