There are certain monitoring, inspection and detection procedures which enable the maintenance personnel to predict and prevent failures in aircraft components well before their actual occurrence. Collectively these activities and practices form the preventive maintenance procedures in aviation.
Understanding the Principle of Preventive Maintenance
The underlying principle of all preventive maintenance procedures is to establish a set of checks and monitoring mechanisms that will ensure that the replacement or repair of components and systems is undertaken well before they approach the stage of imminent malfunction. This can be achieved through a series of planned maintenance activities which are both time based as well as condition based. Condition monitoring is a relatively new concept that requires withdrawal of components from service before completing their life cycle based on their actual condition. This method also permits life extension of components that display healthy characteristics beyond their stipulated life cycle. Whereas corrective maintenance involves repair activities post failure, preventive maintenance methods aim to be able to take action before the actual malfunction occurs so as to avoid accidents in the air.
Preventive Maintenance Objectives
The basic aim of all kinds of maintenance activities is to keep the equipment serviceable, but the scope of preventive maintenance is focused on those measures that help predict failure and thereby allow pre-emptive counter measures. The key objectives of such practices all over the world encompass the following aspects:
Enhance safety in the operations of aviation related equipment or systems.
- Enhance reliability of maintenance schedules and practices.
- Reduce the down time of aircraft and enhance the availability state by pro-active maintenance management.
- Create a useful database of performance-related information for future reference.
- Cut down high costs of post accident damage or salvage through predictive repairs and replacements.
- Most importantly, to save valuable human lives and costly aircraft.
Tools for Identifying the Need
For any preventive program to be effective, its schedule and periodicity must be based on accurate and timely information regarding the current status of the components it is meant to cater. Such information is collected and collated on an ongoing basis to provide the maintenance personnel with an updated analysis of the situation and physical state of the components. The decision regarding premature replacement and repairs can be generated through study of this data. The vital information regarding aircraft and its allied systems is continuously gathered through the following tools:
- Scheduled inspections at periodic intervals.
Flight data recording.
- Advanced simulations of material stress characteristics.
- Vibration analysis.
- Spectrometric analysis of oils and lubricants.
- Crack detection tests on critical components.
- Operators’ report on abnormal indications during operations.
Cost Savings Through Preventive Practices
Apart from being an essential method of ensuring safety in the operating envelope of aircraft and its associated systems, preventive maintenance can also have a significant bearing on the overall maintenance costs both at the operator as well as manufacturer’s level. The most prominent contribution to cost savings comes from the minimized grounding of aircraft. Through pro-active maintenance, failures are avoided by repairs and replacement of suspect components during scheduled servicing itself, which translates directly into an improved serviceability state and greater availability of aircraft for operations.
Through periodic monitoring of the components, their actual condition is ascertained on a regular basis. This permits the grant of life extension to components that display good health despite completing their life cycle. This increases the life period of a component and thereby reduces the life cycle cost per component which has a huge cumulative effect on the total reduction in maintenance costs.
Since preventative maintenance aims to eliminate unpredicted failures, it automatically cuts down on unplanned maintenance activities which are mostly a result of accidents. Such post-accident repairs often contribute the maximum to servicing costs. Failure of the components during critical stage of operations not only causes damage to that system but also causes huge collateral damage to multiple associated systems, thereby increasing the cost of repair and replacement.
Limitations on Preventive Practices in Aviation
Despite its numerous advantages, preventive maintenance methods cannot be applied to all the systems related to aircraft operations at the operator’s level, primarily due to the complexities of the processes involved. The Federal Aviation Authority (FAA) categorically stipulates the systems and components that can be covered through preventive practices at the operator level. For example: FAA, FAR Part -43, Appendix- A, Paragraph – C (Preventive Maintenance). The publication also enlists the extent of works that can be undertaken on the approved components so as to ensure that the available equipment, tools and software at the operator’s maintenance setup are capable of said activities. Additionally, specific clearance and authorization of the personnel has to be obtained after due training and certification before they can undertake preventive maintenance schedules.
Latest Trends in Preventive Maintenance
Currently, most manufacturers employ extremely sophisticated software in this field to accurately track and predict failures in the systems. This software takes into account a large quantity and variety of data packages regarding the status of the system. They simultaneously process them to be able to predict impending failures. The algorithms of the software also cater to cross functional impacts of the various systems so as to maintain vigil even on the non-critical areas related to operations. While most of the software is generic and based on typical system requirements, there is also some highly specialized software catering to the specific needs of advanced models and types of equipment. The most common preventive actions include crack detection tests on load bearing bolts and attachments and structural members of the airframe. Spectrometric analysis of hydraulic and engine oils and leakage detection of pressurization systems are also importan. Such checks provide essential insight into the health and condition of the critical systems of which failure in-flight can have disastrous consequences. These preventive checks are conducted on a regular basis by all airlines and private operators for all aircraft and components that indicate deterioration below safe acceptable limits are immediately replaced prior to takeoff.
Enhancing Flight Safety
Preventive maintenance procedures are increasingly becoming indispensible tools to ensure flight safety in the ever-increasing complexities of aviation operations. It has been globally accepted that through such predictive measures, the accident rates can be significantly reduced and the flight envelope expanded within safe limits. It is mandatory for operators across the world to undertake such specialized maintenance activities apart from regular servicing schedules of flying machines.
AOPA, Pilot's Guide to Preventive Maintenance, http://www.watsonvillepilots.org/articles/DIYmaint.htm
FAA, Regulations - Policies, http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.list/parentTopicID/114
Image: Boeing Vertol CH-113 by A Hunt under Public domain