March 17, 2017, ©. Leeham Co: In the last Corner, we showed graphs of the yearly flight hours for engines on single-aisle aircraft. Now we will deduce the market for engine overhauls from these graphs.
These will show which engines generate a maintenance volume that is interesting for engine overhaul companies and which engines are niche.
Based on the market size, we will then go through how an engine is maintained when new, mature and at end-of-life.
To understand the engine maintenance market, we need to deduce the number of shop visits per year from the different engines we graphed last week. The graphs were in Engine Flight Hours (EFH). To get to Engine Flight Cycles (EFC, which is the primary driver for engine overhaul for single-aisle engines), we establish the ratio Engine Flight Hours to Engine Flight Cycles.
EFH to EFC ratios vary from below one to up to four for single-aisle engines. Our scope is not to conduct an accurate engine maintenance survey but to get a feel for the maintenance market. We can therefore assume an average flight hour to flight cycle ratio of 1.5 without doing a large fault.
We can also assume that engine families with only mature engines in the market are now in a phase were they typically stay on wing for 7,500-10,000 cycles (time on wing decrease for later shop visits). The cycles on wing within a family will vary, with the highest-rated engine reaching EGT limits quicker. Low-rated engines will stay on wing until the first LLP limit will force the removal for first shop visit.
The time on wing is also dependent on the environment. Hot and dusty areas (like North Africa, Middle East) will deteriorate the engine’s compressor parts. This will reduce the flight cycles before a removal or change to a lower rated use on a smaller aircraft variant
With the described assumptions, the flight hour tables of last week translates to the shop visits per year table in Figure 2.
I have clustered engine families as maintenance shops certify to handle a whole family with its variants. There is a physical difference in the CFM56-5 and -7 engines, but the technologies used for the engines are the same.
It’s obvious there is a large difference between the CFM56/V2500 engine overhaul markets and the rest.
If we assume that an engine maintenance company would like to have at least 50 overhauls of an engine family per year, with an absolute minimum of 10-20, there can’t be too many shops competing for jobs for the PW2000 and RB211-535 engines. The PW6000 is only maintained by MTU in Hannover. The BR715 family is present on Business jets, which improves the situation.
For the CFM56 and V2500, there exists a real engine maintenance market. Competing for overhaul work are engine OEM shops (pure OEM or Joint Ventures with airlines/industrial partners) and independent shops.
Independent shops divides in airline-affiliated shops (like Delta TechOps, United Services, Air France Industries/KLM Engineering & Maintenance, Lufthansa Technik..) and technology companies (like MTU Germany/China, BEDEK Israel, GA Telesis…).
The choice of the overhaul strategy is dependent on the age of the engine family and the individual engine. When an engine family is new, most jobs will be around OEM guarantee cases. There are also few shop visits, as the engine is in its honeymoon phase. There are no scheduled shop visits until past 10,000 flight cycles (and then only for highest rated variants).
With typical 1,500 flight cycles per year for a single-aisle engine, there will be 10 years or more before the an overhaul market is created for engines like CFM LEAP and Pratt & Whitney GTF. During this phase, the OEM is the maintenance partner and power-by-the-hour maintenance agreements are norm.
As an engine family matures, the engines have typically passed the first shop visit and time on wing is shorter. The engines are now in the main overhaul cycle, with shop visits planned to coincide with LLP limits for major modules. Duration of shop visits is an important factor; this places the jobs with engine shops that are geographically close.
When engines passed the mature phase and are in their last years, either as a family or as individuals, the maintenance strategy changes. It’s time to match the component life of the LLPs to the engine’s remaining life. Spare parts and complete engines are used from part-out aircraft.
Workscopes are planned with used parts so the engines different parts have a matched life until next visit or scrap time. As used engines are available on the market, these can be swapped for the engine going off wing. The removed engine might be restored to go into the replacement cycle or dismantled for spares.