Background - An aircraft landing gear shipset consist of a nose gear assembly plus two to four main gear assemblies, depending on the aircraft type. The main components of each gear assembly consist of the inner and outer cylinders, drag braces and struts, and various hydraulic actuation mechanisms that serve to lower and retract the gears.
Landing gear overhaul intervals are determined by the need to inspect, and if required, treat for corrosion. Overhaul intervals for landing gears are generally calendar & flight cycle limited, and for most models are in the region of 10-12 years and 18,000-20,000 flight cycles.
The timing of when the overhaul occurs is based on which of the performance intervals is more limiting. For example, a landing gear with overhaul intervals of 10 years and 20,000 flight cycles, which is operating 2,500 flight cycles per year will occasion its overhaul at the eight-year anniversary. Landing gears that are operating below 2,000 flight cycles per year will have their overhaul calendar-limited to 10 years.
Maintenance Cost Drivers:- Factors driving Landing gear overhaul cost consist of:
Size and complexity
Number of modifications to incorporate
Operational environment and maintenance practices
Market penetration - number of MROs supporting the gear
Cost of exchange fee.
Labor required to overhaul a gear shipset is generally predictable since most of the work scope is routine. The majority of the total cost of an overhaul is material related ; bushings account for the biggest cost of parts and material, as do seals, bearings, and parts containing special alloy materials such as nickel, cadmium and chrome. Downtime for a narrow body overhaul process is in the range of 30-40 days, while widebody gears are in the range of 50-60 days.
Few airlines have their own landing gear overhaul shops given that most do not have sufficient volumes to financially justify it, therefore most use third-party specialist overhaul facilities. These overhaul facilities typically carry spare gear inventory for multiple aircraft types, which they offer under either an exchange or loan program.
Under a loan program, the overhaul specialist provides the airline with a designated spare gear, which is fitted to an aircraft while the airline’s gear is overhauled. Upon completion of an overhaul, the spare set is removed and replaced with the original gear. The cost to the airline general reflects both the cost to overhaul the original gear plus a loan fee.
Under an exchange program, a spare gear is installed on an aircraft while the original gear is transferred to an overhaul facility. Once the airline’s gear has been overhauled it then becomes a spare set, and subsequently an exchange unit. The cost to the airline general reflects both the cost to overhaul the original gear plus an exchange fee.
Typical Qualifying Work : Overhaul of a Landing Gear assembly in accordance with the Manufacturer's repair manual that restores such Landing Gear to a "zero time since overhaul" condition in accordance with the Manufacturer's repair manual and is performed in accordance with the Manufacturer's overhaul specifications and operating criteria (excluding any rotable components such as wheels, tires, brakes and consumable items). Most lessors include loan and/or exchange fees into their standard reserves.
Typical Excluded Work : Work related to Service Bulletins (SBs), Service Letters (SLs), Airworthiness Directives (ADs), exchange & handling fees, packaging and shipping charges are not eligible for reimbursement from Landing gear reserves.
Example Landing Gear Reserve Rate Estimations
Equipment : A320 Landing Gear
Overhaul Intervals : 120 Months & 20,000 FC, whichever is more limiting
Overhaul Cost : $420,000
Reserve Rate: US $21.00 per Cycle but not less than US $3,500 per Month
EASA Part 145 & Part 21
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