Engine Overhaul: What you Need to Understand

Any mistaken assumptions by an aircraft owner about an overhaul can add even more cost to an already-expensive process. But what do owners need to understand before the overhaul begins? Chris Kjelgaard looks at engine maintenance plans, life-limited parts, and over-reliance on maintenance tracking software.

Chris Kjelgaard  |  11th July 2022
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Chris Kjelgaard
Chris Kjelgaard

Chris Kjelgaard has been an aviation journalist for more than 40 years and has written on multiple topics...

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A private jet engine mechanic surveys a powerplant at StandardAero


It is all too easy for a Business Aircraft owner to not fully understand the extent of the repair and replacement work that might be required during a scheduled engine overhaul.

It’s even easier to underestimate how much work might be required when an engine must undergo a shop visit for unscheduled maintenance after a fault is detected, or a part fails.

Misunderstandings on the part of aircraft owners can easily happen when too much is taken for granted regarding their engine maintenance plan coverage, or an over-reliance on maintenance tracking software for information on engine status exists.

Preparatory homework is required, allowing the owner to review their assumptions before the engine enters the shop for maintenance, scheduled or otherwise.

“We find operators are typically unfamiliar with many factors surrounding major maintenance events like overhauls,” says Joe Capra, Senior Commercial Director, Pratt & Whitney Turbofans for StandardAero Business Aviation. But if the owner realizes that, as with most things ‘information is power’...it is easy for the owner to prevent themselves being surprised.

“Those who take the time to visit the facility where their engines will undergo the maintenance benefit from meeting the technical team, learning the process, reviewing choices regarding parts, cost and supplemental support, and understanding anticipated turn-around-times for their event,” he adds.

“Our OEM-authorized engine service centers have technical experts with experience from overhauling or repairing hundreds of engines and will provide all the tips and suggestions to navigate the process,” Capra assures.

“This includes establishing a budget, or in the example of pre-paid maintenance plans, a review of what is and isn’t covered.”

Engine Maintenance Plan Familiarization

To prevent expensive misunderstandings, it’s particularly important for owners to know exactly what they are buying when either they contract for new engine maintenance plans for their aircraft or buy an aircraft with engine maintenance coverage already in place, according to Sean Lynch, Program Coordinator for Engine Assurance Program (EAP).

“Before you buy the aircraft [with an engine maintenance program supposedly already attached], you need to make sure the program is fully transferable and paid-up, or you’ll end up in a fight with the seller over the bill or lose the engine coverage,” Lynch warns.

As Capra indicates, it is vital for aircraft owners in possession of pre-paid engine maintenance plans to know exactly what their plans cover. For instance, several engine OEMs — and at least one well-known independent pre-paid plan provider — offer different levels of maintenance coverage, each being priced to suit different owners’ budgets. The different levels offered by any given provider don’t all offer the same coverage.

For example, cheaper monthly plans often don’t provide engine rentals when the engines covered under the plan are in the shop for maintenance.

Nor do they cover the costs of shipping those engines to and from the maintenance shop. And they’re less likely to provide engine condition trend monitoring or cover the replacement of Life Limited Parts (LLPs), or routine line maintenance.

Indeed, some plans only cover engine maintenance following a catastrophic part failure. On the other hand, comprehensive programs — offered optionally by some engine OEMs and as the only choice by others — cover just about every cost incurred when an engine enters the shop for scheduled or unscheduled maintenance, including short-term engine rentals, transport costs, and even (in some cases) charters of an alternative aircraft.

Those few maintenance-related cost items not covered by some of the comprehensive plans are either left out to provide a little wiggle room for plan cost savings at the owner’s option — the providers offering even more comprehensive coverage to owners willing to pay the full amounts — or are excluded because they can only arise owing to negligence on the aircraft owner’s part.

Over-reliance on Maintenance Tracking Software

For engines not covered by pre-paid maintenance programs, another misunderstanding that can mislead owners on each engine’s part life and condition is for them to place too much faith in the information provided by the maintenance tracking software program used for the engine.

“If the engine is not on a program, you need to familiarize yourself with the [aircraft’s maintenance] logbooks, because with engine maintenance tracking programs the data is only as good as what has been inputted,” notes Lynch.

“You need to verify [from the detailed information on completed maintenance tasks] in the logbooks that the engine status matches up with what the tracking program says.”

Capra agrees. “We think maintenance tracking software programs and databases are excellent for tracking when maintenance is required,” he says.

“We do, however, strongly believe that looking through the logbooks and understanding what the total run time has been on non- cycle or hour-life items helps to understand whether these items will have a higher susceptibility for replacement during the next maintenance event.

“An example might be the total time since installation of a set of turbine blades,” Capra highlights. “Were they installed new or used at the last major shop event? Or were they original to new manufacture and reinstalled at the last hot section inspection?”

The logbook information is critical to understanding the history of what was accomplished on the engine, he explains, and it shouldn’t be taken for granted that maintenance time-tracking software alone provides these insights.

Know your Life-Limited Parts

From a maintenance-cost viewpoint, it is critical for aircraft owners to know how much life any given Life-Limited Part (LLP) has, both before and after full overhaul or major mid-term inspection, according to Lynch. LLPs (such as fuel control units, turbine disks and even individual turbine blades) are enormously expensive to replace.

The cost of having to do so can be ruinous for an owner who has relied entirely on what the maintenance tracking software says regarding engine life, but suddenly finds during a major scheduled inspection conferring, say, another 1,000 hours of engine time until the next full overhaul, that the engine contains LLPs which only have 100 hours of running life remaining.

This happened in one specific example Lynch encountered, of a Gulfstream G100 whose engines were covered under a plan which neither included the cost of LLP replacement nor the cost of renting replacement engines while the recently inspected engines were inducted again for LLP replacement.

Another even more extreme example Lynch cites from his personal experience is that of a critical part failing in an engine which had emerged from a mid-point inspection (MPI) only a few months earlier. Unknown to the owner, the engine contained a part which had been installed eight years earlier during a compressor zone inspection and was years out of warranty.

The failure of that part when the engine was still fresh out of its MPI led to the engine having to be removed from the aircraft and inducted for unscheduled maintenance, at a total cost of $240k. Luckily for the owner, the engine was fully covered under an EAP comprehensive program.

In some cases (not those cited above) the additional engine maintenance costs resulting from a misunderstanding over remaining part life can be so high that they exceed the actual market value of the aircraft in good condition.

This effectively renders the aircraft immediately obsolete, fit only to be scrapped except possibly for a little price recovery available from some non-limited engine parts which may be resaleable.

That said, Capra reckons most owners are aware of how expensive misunderstandings regarding remaining LLP life can be and pay particular attention to knowing just what the LLP ‘green time’ situation is in their engines.

“In major maintenance events, where access to life limited parts is performed, we make owners and buyers aware of any short hour/cycle situations and offer the decision to replace these items with new or used parts with sufficient time remaining to suit their operational requirements.”

Another bit of good news for owners is that “manufacturers’ warranty terms, and conditions and elements of maintenance plan cost coverage, are well understood by OEM-approved engine MRO facilities,” according to Capra.

“These programs can change from time to time, so involving the pre-paid maintenance plan provider and the MRO is very beneficial to understanding plan coverage.”

More information from
Engine Assurance Program: www.eap.aero
StandardAero: https://standardaero.com

Don’t miss the second part to this article, Engine Overhaul: Seek Expert Advice on AvBuyer!

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