There is no doubt that one of the reasons which allow aviation to be one of the safest means of transport is the existence of strict aircraft maintenance protocols. These are regulated procedures which are specific to each kind of aircraft and subject to the approval and monitoring of each country’s aviation authorities.
Any aeroplane’s maintenance programme is a basic pillar to ensure not only its safety but also the aircraft’s longevity under the best possible reliability conditions.
It is assumed that the average useful life of a commercial aeroplane is around 25 years, though this depends on a variety of circumstances. Nonetheless, this figure can be misleading. Firstly, because it really depends on the number of the aeroplane’s flight hours over the years and also because it could vary on the basis of other factors like the aircraft model, strict fulfilment of maintenance plans, etc.
It is not very common for an airline to keep an aircraft for such a long time. In reality, the average life of an aircraft in an airline is around 10 years (Air Europe 4.3; Emirates, 6.1; Iberia 9.4; KLM 10.4; Lufthansa 11.2; Air France 11.3 and British Airways 12.5) (1). They are then sold on to other airlines and may finally be reconverted into cargo aircraft. In any case, each aeroplane will, over the course of its life, have undergone thousands of hours of maintenance and checks by mechanics, technicians and engineers. They are in charge of overhauling aircraft in highly specialised facilities to ensure they can fly as if they were newly built despite their age.
But exactly what does aircraft maintenance consist of?
Any aircraft has to follow a scheduled servicing plan based on the number of hours it has flown, which includes concrete specifications for each model. The purpose of these plans is to attain the highest possible safety rates and, in any event, they are based on maintaining the aircraft’s airworthiness certificate and ensuring maximum reliability.
In other words, the aircraft is immediately repaired in the event of it suffering a breakdown. This is known as an unscheduled procedure.
For their part, scheduled maintenance actions are any which have to be carried out once an aircraft has completed a certain number of flight hours. These are geared at preventive actions. They include all the necessary operations needed to keep aircraft in perfect working order, ensure their useful life and reduce as much as possible the costs of any breakdowns. They are as follows:
Transit or pre-flight check.
A rapid check performed before any flight or stopover. The aircraft’s general state, landing gear, fuel and oil levels, hydraulics, access panels, etc. are checked.
Daily check.
Performed before the day’s first flight. Apart from the actions mentioned above, systems and equipment are checked.
Service check.
Takes place every 100 flight hours (approximately a week). All aspects related to the aircraft’s safety are checked, any incident detected is put right and all fluid levels needed for it to fly are verified and optimised.
A check.
Performed when the aircraft has between 500 and 800 flight hours or between 200 and 400 cycles (take-off and landing is considered as an aircraft cycle). It includes a general inspection of the aircraft’s structure, systems and components. The check affects both the aircraft’s interior and exterior and it has to remain in the appropriate hangar overnight.
B check.
This check is complementary to and more extensive than the aforementioned check. It tends to be done on older aeroplanes (modern ones do not generally need it). It is carried out every 4-6 months and lasts between 1 and 3 days.
C check.
It takes place every 20-24 months and involves a layover in the hangar of between one and two weeks. An extensive complete maintenance procedure is carried out by areas on all the aircraft’s internal and external elements. Some airlines take advantage of this check to introduce certain innovations and renew the cabin (multimedia elements, lighting systems, reordering classes, etc.).
D check.
Also known as the “Intermediate Layover” (IL) or “Heavy Maintenance Visit” (HMV). It is carried out every 6 years. It is the most comprehensive maintenance process an aircraft has to undergo over the course of its life. Depending on the type of aircraft, up to 300 specialised workers (A380) may be involved, who dedicate around 60,000 man-hours to the check. The aircraft is put out of service for between 45 and 60 days. This check costs around 2 million euros.
Practically the entire aircraft is taken apart during the Intermediate Layover and the paint may be completely removed. A structural check of all the aircraft’s parts is done. Its surfaces are analysed with X-rays. Engines are dismantled and some parts are replaced by other original parts, even if they are in good condition. This check comes to an end with functional ground checks and a test flight, during which all systems are tested and the aircraft is subjected to extreme flight conditions for 6 hours under the supervision of pilots, technicians and engineers.
Such is the exhaustiveness of these checks that airlines almost always take advantage of them to completely replace systems with other more recent and more advanced systems, which in all likelihood did not exist when they acquired the aircraft. It is also true that some companies take advantage of these checks to sell the aircraft and replace it with another new aeroplane due to their costs and layover times.
The end result of the Intermediate Layover is an aircraft with zero flight hours, which is the same as if it had just left the factory.
Airlines have no other option than fulfilling these maintenance procedures, regardless of the aeroplanes’ apparent condition. Should this not be the case, they would lose the relevant airworthiness certificate and the aeroplane would be grounded.
Aviation safety is no trivial matter. It is an obligation accepted by all parties. There is no doubt that fulfilling aircraft maintenance protocols is essential to gain the trust and ensure to the greatest extent possible the safety of those who keep this business going: namely the passengers.
(1) Source: Airfleets and Planespotters (oct. 2016)
