Life-Limited Parts: Assumptions to Avoid

Aircraft engines contain various Life-Limited Parts (LLPs) with OEM-imposed restrictions on the number of cycles they are permitted to fly before they need to be replaced. These restrictions can be measured in hours or in cycles, with one cycle equalling start, taxi, take-off, landing and shutdown.

An aircraft buyer or operator can face significant financial and operational headaches if they fail to keep track of such parts. With that in mind, what exactly are the potential risks associated with LLPs, and how can these be addressed?

Stacy Hollis is an Engine Service Sales Specialist at Duncan Aviation, an MRO provider that offers a range of services for engines and other elements of business aircraft.

He says that if you have an LLP nearing the end of its lifecycle, it is important to replace it with a part that has enough time or cycles remaining to make it to the next major engine event, such as a Hot Section Inspection (HSI), a Major Periodic Inspection (MPI) or the more in-depth Core Zone Inspection (CZI).

“Trust the engine shop that you’re working with to provide options, based on price and cycles remaining,” Hollis recommends.

Don’t Just Assume Life-Limited Parts are Covered Delray Dobbins, Associate Director, Eagle Service Plan (ESP) Sales and Strategy at Pratt & Whitney Canada, says the main assumption that buyers should avoid is to think that engine maintenance programs cover everything.

While most programs always cover the HSI, Mid-Life Inspection and the overhaul, some components like LLPs may or may not be covered. Some programs do not cover them as a default, he highlights.

The ESP hourly maintenance program, for example, gives customers the choice of whether to include this type of coverage or not. Buyers of older aircraft should understand that this one item can have a dramatic effect on the aircraft’s value, he adds.

“Any buyer of a used aircraft should exercise due diligence and assess any upcoming maintenance exposure,” he recommends. “They should also consider the life cycle of the main components of the aircraft, such as engines, gear, whether there is a calendar wing de-mate, etc. These types of items should fall under this type of analysis.”

Life-Limited Parts Cannot be Overhauled

It is important to realise that LLPs cannot be overhauled, even though engines can be. An LLP will typically survive two or three overhauls before it is scrapped due to hitting the cyclical limit, Dobbins says.

“A buyer using the internet as his or her trusted advisor (as opposed to an experienced industry professional) may overlook this nuance. Such an oversight will often create a maintenance exposure down the road that will be quite uncomfortable, financially.”

The Cost is More Than the Sum of the [Life-Limited] Parts

It is vital that operators consider more than just the cost of the replacement part, according to Greg Ryan, Senior Sales Director for Business Aviation at GE Aerospace.

“Evaluating when [the LLPs] will expire is critical to maximizing time on wing and optimizing operating costs,” he suggests. “The ‘best price’ LLP may not have sufficient life remaining to get you to the next scheduled engine event. A shop visit that comes earlier than anticipated due to an expired LLP reduces the useful TBO and can be financially burdening.”

As some of the iconic business jets begin to age, the market becomes more difficult to navigate without the assistance of sound expertise, Ryan highlights. For example, it is important to be diligent in reviewing records, because LLPs could drive significant engine events that are not necessarily aligned with your mission profile.

“Someone who operates an average flight leg of three hours has a lot more flexibility than an operator typically with a one-hour flight leg,” he illustrates. “The same aircraft could be a great buy for one customer and not even a realistic consideration for another.”

It is vital to separate the emotional part of an aircraft purchase from the technical and economic analysis, Ryan warns. “If you don’t have prior experience with a particular aircraft model or are [buying] an aircraft for the first time, hire a trustworthy expert to guide you,” he says.

“The person you hire should have no association with the aircraft or be part of the potential sale transaction. If you work with a Fixed-Based Operator (FBO), ask the Director of Maintenance for advice, as they will often have great options you can consider.”

And don’t overlook having a candid conversation with someone who owns the type of aircraft you are considering. They can share a lot of the pros and cons as well as potential surprises they may have encountered. “Remember this is an investment so you need to do your homework,” Ryan adds.

Check the Logbooks for Life-Limited Part Status

James Becker, who heads up the Aircraft Appraisal Department at Elliott Aviation, says he has seen scenarios where a new owner buys an airplane where the engine may have thousands of hours TBO and think that they are safe. Unfortunately, they have not looked at the engine logbooks for the status of the LLPs. 

Such owners can take the engines apart, take the LLPs out, replace them and keep going. However, “when you send an engine out to have it opened up internally, you’re likely going to end up with some kind of an overhaul,” he adds.

This is something he considers in his role as an appraiser, asking not only how many hours remain until overhaul, but also the status of ‘rotables’ (parts that must be rotated out).

Make Sure All Life-Limited Parts Are Correctly Documented

Janine K. Iannarelli, President of Par Avion Ltd, says that traceability is very important for all components installed on an aircraft. A new part will come with the required paperwork specific to that component, substantiating its origin and authenticity. But you should ensure that previously used components do as well, she adds.

“Refurbished or overhauled parts must be properly documented, too, especially if they are engine components as it is critical to know the times and/or cycles accrued, as well as those remaining.”

The person responsible for the care and maintenance of the aircraft will want to see documentation demonstrating that the entity that overhauled – or otherwise repaired – a component for an aircraft is authorized to do so, Iannarelli adds.

“It is particularly important with engine components that an accurate, detailed record of each installed component showing cycles since new, cycles remaining and the time between overhaul along with the part and serial number is maintained.”

Work With an Expert Who Understands the Paperwork

Sean Lynch, Managing Director of Engine Assurance Program (EAP) says it is vital to work with an expert who knows how to read engine logbooks. “You need someone who knows what they’re looking at when it comes to Service Bulletins and Airworthiness Directives,” he adds.

There may be 2,500 hours remaining until your next shop visit for an MPI, he illustrates, but if you have a compressor disc that is due early, you will not make the 2,500 hours.

“If you have an AD that needs to be complied with either immediately or at some point before the regular interval, then you’re also going to be putting that engine down early,” he concludes.

More information from:
Duncan Aviation: www.duncanaviation.aero
Elliott Aviation: www.elliottaviation.com
Engine Assurance Program: www.eap.aero
GE Aerospace: www.geaerospace.com
Par Avion Ltd: www.paravionltd.com
Pratt & Whitney Canada: www.prattwhitney.com