Top reasons for taking aircraft engine on a stand
Maintaining aircraft engines takes various scheduled shop visits, depending on how long it is in operation. They prevent the majority of failures, but now and then aircraft engine has to be removed and put on the stand for unscheduled repairs. What are the main reasons (1) for such incidents?
Exhaust Gas Temperature (EGT) margin deterioration
EGT margin deterioration is often caused by the gradual increase in the clearance between the turbine blade tips and surrounding static seals or shrouds. Rate of deterioration is influenced by several factors – thrust rating, engine derate, average flight leg flown, ambient temperatures and environment (2). As deterioration increases, so does the fuel burn and gas flow losses, meaning that the overall efficiency of the engine gets significantly reduced.
For first-run engines in short-haul operations, this cause generates up to 50 per cent of shop visit removals while decreasing below 40 per cent. In medium and long haul operations, EGT margin deterioration cases increase in mature-run aircraft engines and make between 40-50 per cent of shop visit removals.
For aircraft engines in medium and long – haul operations, hardware deterioration can be as often a reason for removal as EGT margin deterioration. These mechanical problems occur after certain parts are exposed to extreme operating conditions for a prolonged period. They can result in blade distress (particularly on High-pressure turbine blades), parts cracking and chipping, and in extreme situations, part failures.
For engines in short-haul operations it’s still one of most often cases of shop visit removals, but twice rarer than for long haul operations, making about 20 per cent of removals.
Life limited part (LLP) expiry
While hardware or EGT margin deterioration depends on many external factors, life-limited parts have clear due-to dates and are required to be changed as soon as they reach the term. Aircraft engines in short-haul operations are more sensitive for this cause and in mature-run engines, it makes up to 60 per cent of shop visit removals. For medium and long haul operations, it takes around 10-20 per cent of the reasons for removal.
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