Last week we noted landing gear LLP (Life Limited Part) and some considerations, while a similar concept to landing gear, an engine LLP have some additional factors to be aware of.
An engine can operate at multiple different thrust levels, for example, the CFM56-7 on the Boeing 737 NG series where one engine can be used on different variants and the thrust changed accordingly. Often the LLP life is based on a thrust setting – the higher the thrust rating the lower the life.
Service Bulletins commonly referred to as “SB’s” are airworthiness documents that originate from the original equipment manufacturer (OEM).
The purpose of these documents is a work instruction that may be anything from an inspection right through to a change of parts or the actual design.
The purpose of the Service Bulletin (SB) can vary and they aim to achieve many purposes including:
* Improve reliability
* Improve safety by reducing the risk
* Change a configuration – example thrust rating for an engine.
* Address an issue found to affect airworthiness – enforced by an AD (Airworthiness Directive)
* Change a process or maintenance task.
Consider a Landing Gear which during a shop visit when a LLP (Life Limited Part) is replaced, the ongoing part can be one of two conditions:
New – The item has not yet been used.
Part-Life – The item is not new and has been used before; but will have some remaining life.
During operation of an aircraft there are times when the short-term maintenance changes due to factors such as damage for example. If we think about an aircraft fuselage getting damaged in a turnaround at an airport, the aircraft might be allowed to continue in service for a number of cycles before the repair has to be completed; while this allows operation to continue, this is a maintenance action which we would not accept at a lease transition.
During an aircraft transition a delay is always going to have a negative impact for one party be it the lessor or lessee depending on which transition is occurring (Delivery & Re-Delivery).
With lease costs and delay clauses, the financial exposure can fast become large; it is an important consideration when considering factors such as the physical observations or findings from the review.