CFM56 Shop Visit

Can we shift gears a bit and really dive into the CFM56 and, specifically, a shop visit and how a shop visit works? Can we walk through the process, from start to finish? When the engine is due a shop visit, what is the process from there?

It starts before the engine arrives and that is an agreement between the engine owner and the engine overhaul shop, as to what is the scope of work to be done on the engine. Different airlines have different approaches. Some people take the standard OEMs work scope and just ask them the engine shop to apply the recipe, if you like, with any additional modifications that they want incorporated, at the time. Others have very specific work scopes; an evolution of what the OEMs have prepared.

So first of all, there is a negotiation and an agreement for the work scope on the engine. That’s typically for a package of engines, because there will not be one. There will be a series of engines to go through the shop. Then as the engine is scheduled to be removed from the aircraft, there will be an initial communication between the engine owner and the shop, as to exactly the latest status of the engine, as it comes off the aircraft. The engine will be pulled from the wing, replaced with another one, put on a transport trolley and transported to the engine overhaul shop.

It arrives at the engine overhaul shop. It’s in a very stout bag, or sometimes a box, on a transport stand. It gets wheeled in, they open it up and there’s an initial check, just to make sure it’s the right engine. Engine serial number, engine model and make. Make sure it really does belong to who people say it does. Then the engine overhaul shop will have prepared a set of work instructions for their team, which starts with removal of all the externals. There’s components and there’s parts. Components that function and parts that don’t. A pipe doesn’t function, so they will remove it. An air starter valve functions, it moves, so they will take that off and that will be put in a different category.

Everything will be removed and it’s looked at as they take it off. If anything looks visibly broken, it’s immediately identified. Each group of parts gets sent to the appropriate part of the shop that is responsible for those groups of parts. Then you’re down to the bare engine, without the components on the outside and the engine is broken into its component modules. There will be a fan module, a compressor module, a combustor module and a couple of turbine modules. Depending on the engine, there may be a few other modules. Each of those modules is then dismantled. Sometimes, there are mini visits, when not all the modules are dismantled. The turbines and the combustor wear faster than the compressors. If it’s the right time to do an overhaul, because the aircraft is not flying very much, but the engine has still got some life left in it, an operator might choose to have a mini visit. That’s part of the negotiation, up front.

The modules get taken apart and inspected, as they go along. All the components that are dissembled, go off to their respected parts of the shop. Everything is inspected and cleaned where necessary. Parts that are within tolerance and are acceptable, are usually put back in for rebuild. Those that have some kind of wear, there is a determination concerning, when it’s put back in the engine, will that component wear out before the next visit? In other words, do we need to change it now, to avoid an early visit, or not? Once everything has been inspected, typically, there is a review, with the customer. This is what we’ve found; this is what we expect to find. This is the difference. These things are more worn than we expected. These things are less worn than we expected. The review discusses what to do about it.