Reliability, Availability, Maintainability and Safety in Aircaft Maintenance
The principles that govern the desired operational functioning within an airline’s
fleet are in many cases dependent on factors, such as: airline culture, financial and
commercial pressures and measures of performance, therefore it can sometimes be
difficult to achieve a balance between them. However, it is essential for the industry
and more specifically for airlines to perform in the safest and most commercially viable
way and still comply with regulatory requirements.
In the assembling of good practices and procedures within the continuing
aircraft airworthiness endeavour, it is necessary to identify how the interaction between
key four elements (Availability, Reliability, Maintainability and Safety) affects the final
objective which is to ensure that the industry is safe, continuing its effort to keep aircraft
airworthy, available, reliable and therefore profitable.
Safety is the number one driver in the maintenance planning effort, indented to
ensure continuing airworthiness of commercial aircraft, this is also due to the ethic
commitment from the airline industry to the public, into keeping it as the safest mode of
transport and lowering its vulnerability, keeping the industry alive. In many cases it has
been seen how airlines banish from the airline business scene due to safety flaws within
their maintenance organisations, which resulted in incidents or accidents.
However, maintenance is also about ensuring aircraft/fleet can cope with the
technical and operational requirements of an airline’s flight schedule, which generates
revenue, being the core of airlines as a business, therefore being efficiency and
commercially driven as well.
In order to achieve a safe and efficient operation where aircraft are available
according to an airline’s flight schedule (allocated time and place) - that is when
aircraft are to make revenue – aircraft maintenance planning must be factored in. The
relationship between Safety, Availability, Reliability and Maintainability is that these four
independent but complementary elements are the result of a maintenance planning
effort by operators, aircraft manufacturers and airworthiness regulations at different
stages in the life of a given aircraft model. That is from its design, through to its
certification and finally its operation.
, These elements are independent in their nature as each of them aims at
achieving a primary goal, i.e. [1]Safety “integrity”: to ensure a given aircraft system
performs its safety function during a given period of time. Availability: to ensure
aircraft/fleet is safe and fully operational within the desired time intervals. Reliability: to
ensure aircraft/fleet is able of performing to a determined standard, such as: aircraft
inherited reliability (as reliable as it can be). Maintainability: to ensure an aircraft,
engine or part can be restored to its original operating condition by (pre-established
procedures) repair, replacement, etc, within a given period of time.
However, these elements also complement each other, as they to some extent
input practical limitations. For instance, aircraft reliability and maintainability can
directly affect availability and ultimately safety. Therefore, for availability and safety to
be achieved, reliability and maintainability considerations must be taken into account,
completing a practical balance between them.
Perhaps the only exception can be observed in the relationship between
reliability and maintainability where an increase or decrease in either of the two will not
necessarily have any effect. While maintainability can directly increase and/or affect
safety and availability it does not necessarily pose any significant implications to the
reliability of a component/aircraft/fleet, as reliability in itself is attributable to other
factors.
In airline terms, these four elements (Availability – reliability – Maintainability and
Safety) translate into the coordination of scheduling constrains, commercial and
economic pressures, technical limitations and safety standards set by regulatory bodies
and aircraft manufactures, therefore facing requirements to comply with and
constrains to deal with.
The maintenance effort also translates into economic values. The survivability of
an airline as a business depends on several performance factors. The airline industry is
perhaps one of the most competitive businesses in the world, where its most valuable
tangible asset – aircraft – must be available to meet airlines’ requirements as a business.
Therefore the availability of an airline’s fleet is to be kept at maximum to ensure
an efficient operation, which translates into efficient commercial performance. Such
1 C Turkoglu, 2009, Maintenance Planning Lecture Notes 2, Slide 13 – 14.
