IATA Aircraft Lease Guidance

Guidance Material and Best Practices for Aircraft Leases
come to a conclusion if the demonstration flight was completed satisfactorily or if any follow up action or
retest is required, based on any findings during the demonstration flight.
The final stage of aircraft’s physical inspection is a borescope inspection of the engines and APU, where
Lessee should check on condition basis and confirm to its satisfaction that there is no internal damage or
defect, which would cause the premature removal of the Engine or APU with reference to both the agreed
minimum life remaining in respect of the Engine and APU, and with reference to the expected on-wing time
remaining based on time since last shop visit and remaining LLP life. Borescope inspection should be
recorded on video. This can be useful in case of any disputes with Lessor or insurance companies in case of
an engine malfunction or damages during the aircraft operation by Lessee. It may be helpful as a reference
upon the aircraft redelivery as well. However such inspection is not required by manufacturer and is driven by
Lessee’s “on condition” requirement. The Lessee should have the right under the lease agreement and is
advised to attend these inspections with their own specialists to verify that the engines and APU satisfy the
delivery conditions, thus avoiding any later issues or discussions.
A full borescope is generally understood to involve a complete video borescope inspection of the compressor,
combustion, and turbine sections, in accordance with the procedures, including with respect to applicable
limits and tooling, of the relevant manufacturer’s manual. It is essential that the applicable manual is
referenced, as e.g. the Aircraft Maintenance Manual (AMM) for an on-wing borescope inspection will usually
state less stringent limits than the Engine Shop Manual (ESM). In most cases, since the borescope inspection
will occur whilst the engine is installed, the AMM “on wing” limits should be applied and should be clearly
specified under the lease agreement. The engine should not reveal any condition which would cause the
engine to be unserviceable, serviceable with an increased frequency inspection, or otherwise not meet the
operational requirements as defined in the lease agreement.
It is also important to ensure that the scope of inspection and the tooling used to conduct the borescope are
consistent with the manufacturer’s recommendations. In recent years the use of flexible probes coupled with
an unlimited scope of inspection undertaken by specialist inspectors for the purposes of lease transition have
resulted in many premature and ultimately unnecessary removals with corresponding costs and delivery
delays suffered by all parties. The use of flexible probes has also been known to result in internal damage to
the engine resulting from tips being broken or caught between blades. AMM guidelines will specify the kind
of borescope probe which should be used for routine inspection, and will usually only call out the use of
flexible probes for further examination on initial findings.
Because the borescope inspection usually occurs towards the end of the delivery inspection process, the risk
of delay due to adverse borescope findings can be significant. This risk tends to increase relative to the
maintenance status of the engine (i.e. a “high time” engine with more flight hours and cycles consumed will
have an increased risk of adverse findings relative to an engine which is “low time” or fresh from shop visit). It
is often in the interests of all parties for the outgoing Lessee to schedule a preliminary borescope inspection
prior to, or at commencement of the redelivery check to identify any potential defects and to allow sufficient
time for resolution without impacting the transition timeline.
28 4 th Edition 2017