Aircraft Maintenance Schedule
Arleen Jerdee
Aircraft maintenance checks are periodic inspections that have to be done on all commercial and civil aircraft after a certain amount of time or usage. Military aircraft normally follow specific maintenance programmes which may, or may not, be similar to those of commercial and civil operators.[citation needed]
Airlines and other commercial operators of large, or turbine-powered, aircraft follow a continuous inspection program approved by the Federal Aviation Administration (FAA) in the United States,[1] or by other airworthiness authorities such as the Transport Canada Civil Aviation Directorate (TCCA), or the European Aviation Safety Agency (EASA). Each operator prepares a Continuous Airworthiness Maintenance Program (CAMP) under its Operations Specifications or "OpSpecs".[2]The CAMP includes both routine and detailed inspections.
Airlines and airworthiness authorities casually refer to the detailed inspections as "checks", commonly one of the following: A check, B check, C check, or D check. A and B checks are lighter checks, while C and D are considered heavier checks. Aircraft operators may perform some work at their own facilities, but often checks, and especially the heavier checks, take place at maintenance, repair and overhaul (MRO) company sites.[4]
Some authorities use a type of check, known as a 3C check or Intermediate Layover (IL), which typically includes light structural maintenance, including checks for corrosion, or on specific high-load parts of the airframe.[7] The 3C check may also be used as the opportunity for cabin upgrades, e.g. new seats, entertainment systems, carpeting. This shortens the time the aircraft is out of service, by performing two distinct tasks simultaneously. As component reliability has improved, some MROs now spread the workload across several C checks, or incorporate this 3C check into D checks instead.[8]
The D check, sometimes known as a "heavy maintenance visit" (HMV),[9] is by far the most comprehensive and demanding check for an airplane. This check occurs approximately every 6-10 years.[8] It is a check that more or less takes the entire airplane apart for inspection and overhaul. Even the paint may need to be completely removed for complete inspection of the fuselage metal skin. Such a check can generally take up to 50,000 man-hours, and 2 months to complete depending on the number of technicians involved.[10] It also requires the most space of all maintenance checks, and as such must be performed at a suitable maintenance base. The requirements and the tremendous effort involved in this maintenance check make it by far the most expensive, with total costs for a single D check in the million-dollar range.[11]
Manufacturers often underestimate the cost of the D check. Boeing underestimates the cost for four of its aircraft, and the expectation is that it has underestimated it for the B787-9 which in 2018 had not been in service for long enough to have been put through a D check.[14]
As of 2015, there are 731 foreign repair shops certified by the FAA performing critical maintenance inspections and repairs for airplanes operating in the United States. This includes repair facilities performing the "heavy maintenance", D Checks, such as the Aeroman facility located in El Salvador, where one in eight mechanics are FAA certified. At a major overhaul base used by United Airlines in China, the ratio is one FAA-certified mechanic for every 31 non-certified mechanics.[15]
All aircraft need periodic inspections and maintenance in order to ensure they are airworthy and safe to fly. Some of that maintenance is pre-scheduled and known to both the pilot and aircraft technician. Other types of maintenance are sudden and unscheduled, which can be due to problems found by the pilot or by the A&P performing an inspection. For pilots and aircraft owners, it is important to understand the differences between scheduled and unscheduled aircraft maintenance.
Scheduled aircraft maintenance is preventative maintenance that is performed at regular intervals. This type of maintenance generally includes 100-hour inspections, annual inspections, and progressive inspections as well as preflight checks to ensure the aircraft is airworthy and ready to be flown.
Every pilot is required to perform certain preflight checks in order to make sure the aircraft is ready to be flown and that there are no obvious defects or malfunctions. When a pilot or student pilot performs a preflight check, he or she must use a checklist in order to ensure nothing is forgotten. Preflight checks include walking around the aircraft and inspecting all the major components of the fuselage and flight control surfaces for defects, wear and tear, and other deformities that may impede the safety of the flight. The cockpit, cabin, avionics, and battery are also checked and tested for proper operation and function prior to the flight. If any abnormalities are found, the pilot does not depart and instead contacts a maintenance technician for repairs.
100-hour inspections are required by the FAA, and those regulations can be found under FAR 91.409b. During a 100-hour inspection, all inspection plates, access doors, cowlings and fairings are removed, and all of the major components of the aircraft are inspected. This typically includes the fabric and skin of the fuselage, the windows, cabin and cargo doors and the flight control surfaces as well as the tires, brakes, struts and landing gear.
Inside the aircraft, the cabin and cockpit are inspected for any potential issues such as loose controls and objects and seat and seat belts malfunctions. The avionics, yoke, fuel switches, flight controls and battery are also inspected and tested. The engine and engine area are also inspected and routine maintenance is performed, such as cleaning the spark plugs and changing the oil. If defect or damage is found, repairs are made to ensure the aircraft remains airworthy in accordance with all applicable FAA regulations.
Annual inspections are performed once every 12 calendar months and are required for all aircraft, regardless of whether they are used for hire, flight instruction or for recreational use. FAR 91.409a sets up the requirement for an Annual Inspection while FAR 43 Appendix D outlines the detail and scope of the inspection itself.
Annual inspections are typically more detailed than 100-hour inspections. The annual commonly includes all of the inspections performed in the 100-hour, such as, review of all the aircraft logbooks and testing and inspecting the engine, flight surfaces, flight controls and avionics. If obvious defects and/or problems are found during the annual inspection, they are noted so that they can be repaired and the aircraft airworthiness restored.
Unscheduled aircraft maintenance occurs anytime a component has malfunctioned or is suspected of malfunctioning, and by definition, this maintenance is unforeseen. It can occur after the pilot finds a problem during the preflight inspection, as the result of an in-flight malfunction, or as the result of problems found during 100-hour, annual, and progressive inspections.
Examples of unscheduled maintenance could be anything from a worn tire, low landing gear strut, or sheared vacuum pump to in-flight issues such as a rough running engine or high magneto drop during run-up. Upon discovery, the pilot would report the problem to the A&P technician and fill out a maintenance request. At this point, the aircraft would be grounded until the problems are repaired and the aircraft is deemed to be airworthy by the technician.
Our A&Ps at Double M Aviation in Lakeland can perform all of your scheduled and unscheduled maintenance in a timely and affordable manner. We offer 50-hour, 100-hour, annual, and progressive inspections as well as efficient responses to all unscheduled maintenance. Every aircraft is personally flown by our IA after each scheduled inspection so you can be confident that your aircraft is airworthy and ready for your next flight.
The aircraft maintenance scheduling is one among the major decisions an airline has to make during its operation. Though maintenance scheduling comes as an end stage in an airline operation, it has potential for cost savings. Maintenance scheduling is an easily understood but difficult to solve problem. Given a flight schedule with aircraft assigned to it, the aircraft maintenance-scheduling problem is to determine which aircraft should fly which segment and when and where each aircraft should undergo different levels of maintenance check required by the Federal Aviation Administration. The objective is to minimize the maintenance cost and any costs incurred during the re-assignment of aircraft to the flight segments.
This paper provides a complete formulation for maintenance scheduling and a heuristic approach to solve the problem. The heuristic procedure provides good solutions in reasonable computation time. This model can be used by mid-sized airline corporations to optimize their maintenance costs.
Consideration of maintenance constraints has long been recognized to be a cornerstone in aircraft scheduling. The development of aircraft maintenance schedule is a complicated task involving the synthesis of a range of economic, political, legal and technical factors. Demand for service, aircraft utilization and operational cost of aircraft are the principal drivers. The goal is to achieve a balanced pattern of flights that results in a timetable consistent with the FAA regulations and airline policies. The major airlines have witnessed significant changes in their operating environment after the airline deregulation act of 1978. As a result of fierce competition the airlines had to cut their prices down and this led to more passengers flying than ever before. More than 80% of passengers are now traveling on tickets priced at less than base fare. This accompanying downward pressure on revenues has led many carriers to focus their attention on controlling maintenance and personnel costs.
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