How Do Aircraft Engines Work?
The air is sucked into a turbine engine via the fan.
This passes through a compressor which spins at very high speed, raising the pressure of the air by compressing it. The squeezed air is then sprayed with fuel and an electrical spark combusts the mixture, which expands again and forces its way out of the back of the engine through the nozzle (in the case of a jet engine), providing the airplane with its thrust.
For turboprop engines the process is the same, except that the majority of expanding air forcing its way through the powerplant is harnessed to drive the propeller.
The multiple parts of the jet and turboprop engine’s components are exposed to extreme heat and pressure and require careful maintenance.
What are the Basics of Aircaft Engine Maintenance?
Here is a guide to the basic terms. Aircraft owner/operators should keep comprehensive, up-to-date logs of all aspects aircraft engine maintenance.
What is an Aircraft Overhaul?
An overhaul is where the aircraft’s engines are disassembled, its parts are inspected and measured, and certain parts are replaced (see Life Limited Components, below).
What is the Time Between Overhaul (TBO)?
The amount of time (hours) an aircraft’s engines should fly before an overhaul is performed.
Most aircraft engines come with a recommended Time Between Overhaul from the manufacturer.
How does Time Between Overhaul (TBO) affect Price/Value?
Aircraft with a shorter TBO will usually have less value than an aircraft that has undergone a major overhaul more recently.
What is a Hot Section Inspection (HSI)?
The Hot Section Inspection generally happens after a set time period (and usually at the mid-point between zero hours and the TBO limit).
The inspection focuses on engine’s components that are subjected to the extreme pressures and heat of fuel combustion.
It helps to confirm that all hot section components of the engine are in good working order, and that they will continue to produce the rated power in the engine, operating efficiently and safely until the next scheduled inspection.
Among the components subjected to an HSI are:
What Happens if Aircraft Engine Components Fail the HSI?
Those components will need to be replaced or repaired, while other items may simply be logged for future attention if they don’t directly impact the integrity of the powerplant.
If significant deterioration isn’t found in the engine’s hot section components, an HSI tends to be a relatively low-cost major maintenance event – and the shortest, with some engines down for only a couple of days.
What are Life Limited Aircraft Engine Components?
Life Limited Components (LLCs) – come with life-limits, as set by the OEM. Those limits may be measured in hours or cycles (an aircraft take-off and landing represents one cycle). Once that limit is reached, they must be replaced.
How to Keep it Aircraft Engine Maintenance Predictable?
An aircraft engine maintenance event is one of the most expensive aspects to owning a business aircraft.
It’s possible to keep the costs predictable. Aircraft owners can enrol their aircraft on an hourly maintenance program – either with the engine manufacturer, or from a third-party program provider.
You can read more about jet engine maintenance programs here on this hub or visit our jet engine maintenance articles.
1. Don’t scrimp on replacement Life Limited Components (LLCs)…
2. Are you monitoring your engine performance data closely?
3. How good are your engine preservation methods?
4. An unscheduled event is an opportunity for a scheduled inspection!
5. Don't neglect the APUs...
There are many MRO facilities that could do your aircraft engine maintenance work. But you should make sure the one you choose can handle all the associated MRO work on the engine's accessories and components as well as the engine itself.
If a facility needs to outsource any component/accessory MRO work, then the overall time taken to overhaul the engine will increase, along with the possible costs.
You should also ensure the engine maintenance facility has a proven track-record for working on your engine type and you should ask to see references from previous customers who have had work completed on the same engine type.
Finally, consider the proximity of the engine maintenance provider to your operating base. Much time, expense and complication can be saved if you are available and present at the maintenance facility when needed.
In the case of a complete aircraft engine overhaul, engine maintenance can take anywhere from three to six weeks, or more.
You can control the costs of aircraft engine maintenance. All of the engine manufacturers and some third-party providers offer Hourly Engine Maintenance Cost Programs, removing the nasty surprises of engine maintenance.
These programs require you to pay a set amount into an account for every hour that your aircraft flies. That accrues, so that when scheduled or unscheduled engine maintenance is required, the program provider covers some, if not all the costs – including, in some cases, the expense of borrowing loaner engines while your regular powerplants are being repaired or overhauled.
You are advised to check with the relevant program provider what is covered by their program, and the hourly payment that will be required.
Smaller business jet engines can cost in the region of $200k-$300k each to overhaul. At the other end of the scale, modern large business jet engines can each cost between $1m-$3m to overhaul.
Turboprop engines tend to cost less to maintain than jet engines. The costs for turboprop engines overhaul in Business Aviation tends to range between $100k-$300k each.
Helicopter turboshaft engine maintenance costs are similar to turboprops. Operators can expect to pay $100k to $300k per engine, per shop visit.
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Jeremy Cox is president, JetValues-Jeremy LLC and enjoys direct interface between aircraft purchaser...
Mike Saathoff has over 20 years of experience in corporate aircraft maintenance. He has held several...
