Aircraft maintenance planning and control pdf
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- NetLine/Ops ++ MaintenanceControl
- NetLine/Ops ++ MaintenanceControl
- Aircraft maintenance planning and scheduling : an integrated framework
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NetLine/Ops ++ MaintenanceControl
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Consideration of aircraft operations, including inspection, maintenance, and repair procedures is crucial in the development and application of new materials and structures. This part of the committee's report focuses on the operation and monitoring of materials and structures in a service environment. Chapter 7 , "Aircraft Maintenance and Repair," describes the issues related to maintenance of commercial transport aircraft.
The lessons learned from the aging of metal and composite structure are discussed. Chapter 8 , "Nondestructive Evaluation," describes current aircraft inspection practices and identifies needs for improved nondestructive evaluation techniques and promising technologies for the future.
The successful utilization of new materials and structural concepts relies on maintenance programs that cost-effectively ensure passenger safety. This chapter is an overview of the current experience in aircraft maintenance programs, including inspection and repair processes, lessons learned from aging aircraft, and future needs to support new materials and structural concepts.
Maintenance programs are evolved and developed for each new type of aircraft based on previous experience with similar materials, engines, components, or structures. New materials or structures, for which experience is limited, are observed more frequently until a basic level of confidence is established.
Time extensions to inspection intervals are based on observations made during routine service checks. A typical airline maintenance and service plan is outlined in table The objectives of an effective maintenance program are as follows Edwards, :. Ensure, through maintenance activity, that the inherent safety and reliability imparted to an aircraft by its design are sustained.
Provide opportunities to restore levels of safety and reliability when deterioration occurs. Obtain information for design modification when inherent reliability is not adequate.
Any new aircraft program is based on assessing structural design information, fatigue and damage tolerance evaluations, service experience with similar aircraft structures, and pertinent test results. Generally, the maintenance task evaluates sources of structural deterioration including accidental damage, environmental deterioration, and fatigue damage; susceptibility of the structure to each source of deterioration; the consequences of structural deterioration to continuing airworthiness including effect on aircraft e.
The application of new materials will not cause undue maintenance difficulties or hardship for the airlines provided the aircraft designer is familiar with component experience. Airline experience indicates that hardware items wear out, but statistical old-age wear-out in complex mechanical, electrical, and avionic components is not a dominant pattern of failure.
In fact, over 90 percent of generic part types show either random distribution of failure or gradually increasing probability of failure with age Edwards, The reliability of a part or component of aircraft hardware is only as good as its inherent design supported by adequate maintenance allows it to be. Hence, it is generally accepted that 1 good maintenance allows parts to reach their potential reliability; 2 overmaintaining does not improve reliability, but does waste money; and 3 undermaintaining can degrade reliability.
In general, fundamental design changes are required to correct inherent component reliability problems. There are three approaches to preventative maintenance that have proven to be effective.
The first method, hard time , involves removing a unit from service when it reaches a pre-ordained parameter value. The third method, functional verification , requires performing an operational check of hardware function s to determine each function's availability if it is normally hidden from the scrutiny of the flight and operating crew. There are many components for which measurement of deterioration, periodic removal for maintenance, and hidden function verification are not economically feasible or beneficial.
Such parts require routine performance or reliability. Specific checks on engine oils, hydraulics, oxygen, and specified unique aircraft requirements. Major structural inspections with attention to fatigue damage, corrosion, etc.
Aircraft is dismantled, repaired, and rebuilt. Aircraft is repainted as needed. Modern aircraft are more tolerant of failures than older aircraft designs because of the increased redundancy provided in the design. Generally, most airlines classify specific component maintenance tasks as follows:. Malfunctions of components should be evident to the operating crew, have no direct adverse effect on safety whether they occur as a single or multiple event , and minimize the effect on the operation of the aircraft itself.
Effective application of new materials on commercial aircraft requires the designer to consider potential sources of damage or degradation in operating environments and to develop a maintenance and repair approach to address them.
Damage may occur due to flight loads, thermal and environmental cycles, and aircraft operation and servicing activities. A number of valuable lessons have been learned from.
These lessons provide evaluation criteria in the application and servicing of new materials and structures. An International Air Transport Association survey estimates that 36—40 percent of damage to aircraft is from ramp and maintenance damage, sometimes called friendly foreign object damage IATA, Figure shows a diagram of the Boeing aircraft interfaces with servicing and other equipment Boeing, b.
These areas are especially prone to damage and require robust material performance in these locations. To determine the extent of groundhandling damage, 11 airline operators were queried for ground damage history during the years to Boeing, a. Of the 2, incidents reported, more than a third were from unknown causes. A tabulation of the causes of damage is given in table Ramp and maintenance damage can represent significant costs to the airlines.
The repair of a damaged component is only part of the cost. The airline also bears the cost of flight delay or cancellation and the effects on connections and aircraft rotations. In April , an Aloha Airlines Boeing experienced an in-flight structural failure in which a large section of the upper fuselage ripped open and separated from the aircraft.
The failure resulted from multiple-site damage MSD and corrosion. In this case, MSD was the link-up of. The accident focused international attention on the problems of operating an aging commercial fleet. In approximately 46 percent of the U.
If current usage and replacement trends continue, the number of aircraft over 20 years old will double by the year Currently some 3, aircraft are affected by FAA Airworthiness Directives that concern operation and maintenance of the aging fleet. The review of experience with aging aircraft has caused an increase in the emphasis on stress corrosion, corrosion, fatigue, and MSD issues.
This experience has caused, in turn, the selection of new aircraft alloys with better constituent chemistry control or changes in heat treatment tempers. Also, it has stimulated the development of new organic finishes that significantly retard corrosion, as well as the implementation of design practices to vastly improve corrosion resistance.
The FAA and NASA developed a cooperative research effort aimed at providing a technological basis for ensuring the continued safe operation of the aging commercial aircraft fleet. Each agency developed a program consistent with its mission. The FAA's National Aging Aircraft Research Program addresses the aging aircraft structural safety concerns and provides certification authorities and operators with the tools to meet those concerns.
NASA's Airframe Structural Integrity Program is focused on developing advanced integrated technologies to economically inspect for damage and to analytically predict the residual strength of older airplanes. Together these programs form the technological basis for a cooperative effort with U. MSD is a form of widespread fatigue damage that is characterized by small cracks emanating from structural details such as fastener holes Sampath, If cracks emanate from adjacent fastener holes, they have the potential to link up and lead to unexpected catastrophic failures as described in the previous section.
Also, even without link-up, multiple-site cracks can severely degrade the capability of the structure to withstand major damage from other discrete sources as is described later in this section. In the past, the standard industry practice was to visually inspect the airframe for damage. Various levels of inspections ranging from daily walk-around inspections to detailed tear-down inspections were performed. Instrumented nondestructive evaluation NDE methods such as eddy current probes were used only to inspect local regions of the structure where previous cracking problems had occurred.
While these inspection methods were labor intensive and highly subjective, they were acceptable because the airframe was designed to survive a two-bay skin crack with a severed frame or stiffener.
This design criterion was established to enable the airplane to tolerate major discrete source damage i. Such damage is large enough that it should be easily detected, and the operator does not need to search for small cracks to ensure the structural integrity of the airframe.
However, this "fail-safe" philosophy assumed that the structure adjacent to the major damage e. Design residual strength requirements were based on this assumption. However, the existence of very small cracks e. Therefore, inspection of aging aircraft has become much more onerous than for newer aircraft because safety is vitally dependent on the detection of the very small cracks associated with this onset of MSD. This represents a major challenge to the inspection and aircraft industries.
The principal technical needs are 1 to develop and verify advanced NDE technology that can reliably and economically detect disbonds, small MSD fatigue cracks, and corrosion and characterize their effect on the residual strength; and 2 to develop and verify advanced fracture mechanics and structural analysis methodology to predict fatigue crack growth and residual strength of airframe structures to determine in-service inspection thresholds and repeat intervals, quantitatively evaluate inspection findings, and design and certify structural repairs.
NDE methods related to MSD are described in chapter 8 , and fracture mechanics and structural analysis methods are described in chapter 6. Corrosion of aging aircraft has been described as an insidious problem Marceau, While other aging mechanisms, such as wear and fatigue, are somewhat predictable and can be addressed by the airline maintenance programs to preclude major structural problems, corrosion—especially in its localized forms—is very difficult to predict and detect. Factors that influence the extent of corrosion on aircraft are materials selection, design, component processing and finishing, operational environments, and maintenance programs.
It is anticipated that airplanes manufactured today will experience fewer corrosion problems than those in the current aged fleet because of significant design and corrosion protection improvements that have been implemented and because of operators' increased awareness of the role of these improvements in preventive maintenance.
Clearly, maintenance. Some examples of design improvements to reduce corrosion on the Boeing Marceau, include:. Major airline fleets include aircraft ranging in age from new to 25 years old. Consequently, the degree of corrosion protection incorporated into the airplane varies from limited protection for older aircraft to fairly extensive protection for newer aircraft.
Corrosion control programs are tailored to individual fleets, depending on age, prior experience, flight environment and degrees of corrosion protection incorporated prior to the delivery of the aircraft DeRosa, All protective finishes are maintained and corrosion prevention compounds are applied during periodic maintenance. Critical areas that are prone to excessive corrosion include areas below the galleys, doorways, lavatories, cargo compartment subfloors, inside external fairings, and the bilges which are all treated at four-year intervals.
Landing gear wheel wells and wing spars are treated yearly. Longer intervals of time are allowed between reapplications of corrosion prevention compounds in the case of less-severe environments. Aging aircraft repairs have typically involved upper-skin lap fastener replacement, nonbonded skin panel replacement, skin lap doubler repairs, frame reinforcement, entryway door and scuff-plate doublers, replacement bushings and clevis joints, bulkhead forging replacement, and selected landing gear component replacement.
Based on service experience, the airlines have expectations that manufacturers of new aircraft will DeRosa, :. The objective of aging aircraft programs is to ensure the continued airworthiness of large transport aircraft as long as they remain in commercial service Curtis and Lewis, Because new materials and fabrication processes may yield different degradation and damage mechanisms, a preproduction review should ensure that the new aircraft design includes lessons learned from the existing aging fleet.
Many of the steps needed to improve aging performance are detailed below.
NetLine/Ops ++ MaintenanceControl
Typically a good maintenance Planning Engineer has a strong aviation background, such background knowledge aids and supports the Maintenance Planning role and enables a strong understanding of how to comply with the various tasks. The primary output from Maintenance Planning is a Check Pack, work Pack or Engineering Order, the inputs into Maintenance Planning are many and varied and need to me measured and managed. Typically the main functions of Maintenance Planning include configuration management to ensure that the integrity of the modification status of the aircraft is managed correctly. The maintenance program is the source document for generating the work package. As well as the basic work package it is normal to manage an ongoing modification program which improves the reliability or economic viability of the aircraft. Because of the critical nature of the planning role it is typical to see very strong process driven by detailed procedures. It is important that these procedures are well understood and reflect not just best practice, but that they are also efficient.
within the context of manufacturing planning and control, is further enhanced for aircraft heavy maintenance applications, taking into account the uncertainty.
Aircraft maintenance planning and scheduling : an integrated framework
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