Typical MRO Operations

1. Typical MRO Operations 

Keeping aircraft in excellent condition requires many types of maintenance activities. These areas require different skill sets and services, and not all MRO organizations perform them all. MRO services are generally provided by the airlines, by original equipment manufacturers (OEMs) like Boeing, and independent enterprises. Some independent organizations specialize in one or two MRO services. 

Airlines must perform both scheduled and unscheduled maintenance. Scheduled maintenance is performed periodically depending on flight hours to maintain the inherent safety and reliability levels of the aircraft. However, sometimes unscheduled maintenance must be performed to restore the safety and reliability of an aircraft that has experienced deterioration or failure of capability. Both types of required maintenance can be broken down into the following four activities. Line maintenance is typically done on in-service aircraft while the other three types of maintenance are done on out-of-service aircraft: 

1) Line maintenance involves the trouble-shooting and repair of maintenance problems that can be performed without taking the aircraft out of service, and includes minor and major aircraft checks. Line maintenance is usually performed at a certified MRO location, often at the airport. Tasks may include the A checks described below, as well as any less-than-A checks such as daily checks or 48-hour checks. 

2) Component maintenance includes repairs to major aircraft components, such as brakes and wheels, that are critical to the airworthiness of the aircraft. Component maintenance is typically performed in a hangar at an approved MRO location. 

3) Engine maintenance involves the dismantling, inspecting, assembling and testing of aircraft engines. Engine maintenance is typically performed at a certified engine overhaul shop. 

4) Heavy maintenance includes major items such as structural modifications, landing gear repair, engine changes and regular calendar checks. Heavy maintenance is typically performed at a specialized facility away from the airport. 

The above aircraft maintenance tasks are also categorized by maintenance check levels as follows: 

a) Walk around (or “less-than-A”) inspection. This entails a visual inspection of the aircraft exterior in order to check for leaks, worn tires, and other damage. 

b) A Check. Every three to five days, the aircraft’s landing gear, control surfaces, fluid levels, oxygen systems, lighting, and auxiliary power systems are checked at the airport gate. 

c) B Check. Every eight months, internal control systems, hydraulic systems, and cabin and cockpit emergency equipment, as well as A-level check items, are inspected. 

d) C Check. Every 12 to 17 months, the aircraft is opened for inspection of wear, corrosion and cracks. C checks typically take place in a maintenance hangar, often at an airline’s hub airport. 

e) D Check. Every four or 5 years, depending on flight hours, an aircraft is completely disassembled, inspected, and re-assembled at a specialized facility. A D check takes 30 days to complete. 

Each of the above maintenance tasks has a well-defined process and expected performance time. Usually these processes go smoothly but they can be disrupted by various events such as the finding of non-routine maintenance problems during routine maintenance checks, as well as the lack of suitable parts. Chasing parts is a particular problem, especially with non-routine maintenance problems. Meeting the flight schedule is a high priority and when spare parts are not available it is sometime necessary to borrow that part from another aircraft being serviced at the same time, often leading a delay in returning the second aircraft to service. 

To avoid “borrowing” parts, it is important to implement inventory controls that assure both availability and quality of parts. The ordering, storing, controlling and handling of materials such as repair and spare parts is critical to the smooth functioning of an MRO facility. The number of parts required, when to order them, and where to position them affect the efficiency with which maintenance tasks are able to be performed and, in turn, impact the footprint of the overall operations. 

A typical “C” check might proceed as follows. In preparation for arrival of the aircraft, the hangar area is cleaned and any needed equipment such as scaffolding is brought to the work area. The required parts are identified and located nearby so they can be delivered just-in-time. After the aircraft is washed, it is towed to the work area where it is parked so that visual inspections can begin. After inspection, the required work items are determined and mechanics are assigned to allow for efficient completion of the tasks around the aircraft. If additional parts are needed that were not included in the original list, they are requested. A quality control inspector monitors the quality of the parts and work. When all tasks are completed, the aircraft is moved out of the hangar and the space is cleaned for the next assignment. 

Maintenance activities that will be performed at the BSAS facility at Pudong Airport include line and heavy airframe maintenance, such as “C” checks, as well as modifications for the 747 and 777 aircraft, and passenger-to-freighter conversions.