Maintenance is work that is carried out to preserve an asset (such as a
roof or a heating boiler), in order to enable its continued use and
function, above a minimum acceptable level of performance, over its
design service life, without unforeseen renewal or major repair
Reasons for Maintenance
Maintenance serves to protect the owners’ real estate investment in a number of ways
To keep the assets in good working order so as to minimize disruptions and downtimes.
To keep the assets in a state of good repair for the owners’ health and safety.
To keep the assets from deteriorating in appearance and becoming unsightly.
To ensure that the assets achieve their full potential service life.
Duty of Care
To satisfy a legislated duty that is owed to owners, occupants and guest on the property.
Duty to Mitigate
To prevent unnecessary damage to assets that may result in their premature failure.
Types Of Maintenance
1. Periodic maintenance ( Time based maintenance - TBM)
2. Predictive maintenance
I. Condition Monitoring
Break Down Maintenance
It means that people waits until equipment fails and repair it. Such a thing could be used when
the equipment failure does not significantly affect the operation or production or generate any
significant loss other than repair cost.
It is a daily maintenance ( cleaning, inspection, oiling and re-tightening ), design to retain the
healthy condition of equipment and prevent failure through the prevention of
deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration. It
is further divided into periodic maintenance and predictive maintenance. Just like human life is
extended by preventive medicine, the equipment service life can be prolonged by doing
Time based maintenance consists of periodically inspecting, servicing and cleaning equipment
and replacing parts to prevent sudden failure and process problems
This is a method in which the service life of important part is predicted based on inspection or
diagnosis, in order to use the parts to the limit of their service life. Compared to periodic
maintenance, predictive maintenance is condition based maintenance. It manages trend
values, by measuring and analysing data about deterioration.
Condition monitoring is the process of determining the condition of machinery while in
The key to a successful condition monitoring programme includes:
1. Knowing what to listen for
2. How to interpret it
3. When to put this knowledge to use
Successfully using this programme enables the repair of problem components prior to
Condition monitoring not only helps plant personnel reduce the possibility of catastrophic
failure, but also allows them to order parts in advance, schedule manpower, and plan other
repairs during the downtime.
It improves equipment and its components so that preventive maintenance can be carried out
reliably. Equipment with design weakness must be redesigned to improve reliability or
Advantages And Disadvantages
Break Down Maintenance
Lower start up cost Unpredictability
Limited personnel requirement Equipment not maximised
Reduced maintenance costs Indirect costs
Potentially increased margins
Over all very cost effective Catastrophic failure still a risk
Flexibility can allow for adjustment of
schedule to accommodate other work
Increased equipment life Performance of maintenance based on
schedule not required
Saved energy cost resulting from
equipment running from pick efficiency
Risk of damage when conducting
Reduced equipment or process failure Saving not readily visible without a base
Over all saving between 12% to 18%
Increased component operational
Increased investment of diagnostic
Allows for pre-emptive corrective action Increased staff training for analysing data
Decreased part and labour cost Saving not readily visible without a
Improved safety and environment
Over all saving between 8% to 12% over
Extend bearing service life Monitoring equipment costs
Maximise machine productivity Operational costs (running the program)
Minimise unscheduled downtime Skilled personnel needed
Safely extend overhaul intervals Strong management commitment
Improve repair time A significant run-in time to collect
machine histories and trends is usually
Increased machine life
Improve product quality
Reduce product cost
Enhance product safety
Lower short-term costs Increased long-term costs due to
unplanned equipment downtime.
Requires less staff since less work is
Possible secondary equipment or process
Prone to neglect of assets
Aircraft maintenance is the overhaul, repair, inspection or modification of an aircraft and
Airlines authorities casually refer to the detailed inspections as "checks―
Different Types of checks
1. A check
2. B check
3. C check
4. D check
Among all the checks A and B checks are lighter checks, while C and D are considered
This is performed approximately every 500 - 800 flight hours or 200 - 400 cycles. It needs
about 20 - 50 man-hours and is usually performed overnight at an airport gate or hangar. The
actual occurrence of this check varies by aircraft type, the cycle count (take off and landing is
considered an aircraft "cycle"), or the number of hours flown since the last check.
This is performed approximately every 4–6 months. It needs about 150 man-hours and is
usually performed within 1–3 days at an airport hangar. A similar occurrence schedule applies
to the B check as to the A check. B checks may be incorporated into successive A checks
This is performed approximately every 20–24 months or a specific amount of actual flight
hours (FH) as defined by the manufacturer. This maintenance check is much more extensive
than a B Check, requiring a large majority of the aircraft's components to be inspected. This
check puts the aircraft out of service and until it is completed, the aircraft must not leave the
maintenance site. It also requires more space than A and B Checks—usually a hangar at a
maintenance base. The time needed to complete such a check is generally 1–2 weeks and the
effort involved can require up to 6000 man-hours
This is by far the most comprehensive and demanding check for an airplane. It is also known
as a Heavy Maintenance Visit (HMV). This check occurs approximately every 5 years. It is a
check that, more or less, takes the entire airplane apart for inspection and overhaul. Also, if
required, the paint may need to be completely removed for further inspection on the fuselage
metal skin. Such a check can usually demand up to 50,000 man-hours and it can generally take
up to 2 months to complete, depending on the aircraft and the number of technicians involved.
It also requires the most space of all maintenance checks, and as such must be performed at a
suitable maintenance base. Given the elevated requirements of this check and the tremendous
effort involved in it, it is also by far the most expensive maintenance check of all, with total
costs for a single visit ending up well within the million-dollar range.
NDT In Aircraft Maintenance
During aircraft maintenance 'NONDESTRUCTIVE TESTING' (NDT) is the most
economical way of performing inspection and this is the only way of discovering defects.
In order to maintain the aircraft defects free and ensure a high degree of quality &
reliability and as a part of inspection programme, usually following NDT methods are
1) Liquid penetrant
2) Magnetic particle
3) Eddy current
5) Radiography (x-ray/gamma ray)
8) Infrared Thermography.