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Pooja Gupta
by on May 16, 2012
623 views

Aircraft maintenance is one of the most important subject when we talk about the safety of an aircraft. Aircraft maintenance is the overhaul, repair, inspection or modification of an aircraft or aircraft component.

Maintenance includes the installation or removal of a component from an aircraft or aircraft subassembly, but does not include:-

  • Elementary work, such as removing and replacing tires, inspection plates, spark plugs, checking cylinder compression, etc.
  • Servicing, such as refueling, washing windows.
  • Any work done on an aircraft or aircraft component as part of the manufacturing process, prior to issue of a certificate of airworthiness or other certification document.

Maintenance may include such tasks as ensuring compliance with Airworthiness Directives or Service Bulletins. Since aircraft maintenance is so important to safety, there are even numerous Aircraft maintenance institutions which have been setup worldwide which trains students to be certified airplane technicians. These mechanics works with airplane manufacturers and airlines to build, repair, and inspect aircraft to make sure they are safe for flight. Almost 200 aircraft maintenance schools across the country provide two and four-year programs that cover engineering, mechanics, electronics, plumbing, welding, and machining in a complete educational package.

Aircraft maintenance may be categorized into two:-

  • Preventive Aircraft Maintenance, where equipment is maintained before break down occurs. This type of maintenance has many different variations and is subject of various researches to determine best and most efficient way to maintain equipment. Recent studies have shown that Preventive maintenance is effective in preventing age related failures of the equipment. For random failure patterns which amount to 80% of the failure patterns, condition monitoring proves to be effective.
  • Corrective Aircraft Maintenance, where equipment is maintained after break down. This maintenance is often most expensive because worn equipment can damage other parts and cause multiple damage.

 

Preventive aircraft maintenance

Preventive aircraft maintenance is maintenance performed in an attempt to avoid failures, unnecessary production loss and safety violations. As equipment cannot be maintained at all times, some way is needed to decide when it is proper to perform maintenance. Normally, this is done by deciding some inspection/maintenance intervals, and sticking to this interval more or less affected by what you find during these activities. The result of this is that most of the maintenance performed is unnecessary and it even adds substantial wear to the aircraft equipment. Also, you have no guarantee that the equipment will continue to work even if you are maintaining it according to the maintenance plan.

 

Corrective aircraft maintenance

Corrective aircraft maintenance is probably the most commonly used approach, but it is easy to see its limitations. When aircraft equipment fails, it often leads to downtime in production. In most cases this is a costly business. Also, if the equipment needs to be replaced, the cost of replacing it alone can be substantial. It is also important to consider health, safety and environment (HSE) issues related to malfunctioning equipment.

Corrective aircraft maintenance can be defined as the maintenance which is required when an item has failed or worn out, to bring it back to working order. Corrective maintenance is carried out on all items where the consequences of failure or wearing out are not significant and the cost of this maintenance is not greater than preventive maintenance.

Aircraft maintenance is highly regulated. There are various airworthiness authorities around the world. The major airworthiness authorities include:-

  • Civil Aviation Safety Authority (CASA) Australia
  • European Aviation Safety Agency (EASA) Europe
  • Federal Aviation Administration (FAA) United States
  • Transport Canada (TC) Canada
  • Directorate General of Civil Aviation (DGCA) India

At the completion of any maintenance task a person authorized by the national airworthiness authority signs a release stating that "The described maintenance has been performed in accordance with the applicable airworthiness requirements." In the case of a certified aircraft this may be an Aircraft Maintenance Engineer or Aircraft Maintenance Technician, while for amateur-built aircraft this may be the owner or builder of the aircraft.

The maintenance of an aircraft mainly rests in the hands of the Aircraft Maintenance Technicians and the Aircraft Maintenance Engineers with high responsibilities on their shoulders. An aircraft maintenance technician, as used in the United States, refers to an individual who holds a mechanic certificate issued by the Federal Aviation Administration; the rules for certification, and for certificate-holders, are detailed in Sub part D of Part 65 of the Federal Aviation Regulations (FAR's), which are part of Title 14 of the Code of Federal Regulations. Aircraft Maintenance Technicians (AMT's) inspect and perform or supervise maintenance, preventive maintenance, and alteration of aircraft and aircraft systems. In the US, aircraft maintenance technicians usually refer to themselves as A&Ps, for airframe and powerplant mechanics.

The general requirements for eligibility for a mechanic certificate include the following:

  • Be 18 or older;
  • Be able to read, speak, and understand English;
  • Meet the experience or educational requirement; and
  • Pass a set of required tests within a maximum of 24 months.

The required tests include, first, a set of knowledge tests; these are followed by a practical test, which includes an oral examination component, and which is administered by a Designated Mechanic Examiner (DME).

A person who fulfills the necessary requirements is issued a mechanic certificate with either an airframe or powerplant rating, or both. It is these ratings which together account for the common practice of referring to mechanics as "A&P's." Until 1952, instead of the Powerplant rating, an Engine rating was issued, so the abbreviation "A&E" may appear in older documents.

Eligibility for the mechanic tests depends on the applicant's ability to document their knowledge of required subject matter and ability to perform maintenance tasks. The FAA recognizes two ways of demonstrating the needed knowledge and skills: Practical experience or completion of a training program at a school certificated under Part 147 of the FAR's.

 

Aircraft Maintenance Checks:-

Aircraft maintenance checks are periodic checks that have to be done on all aircraft after a certain amount of time or usage. Airlines and other commercial operators of large or turbine-powered aircraft follow a continuous inspection program approved by the Federal Aviation Administration (FAA) in the United States, or by other airworthiness authorities such as Transport Canada or the European Aviation Safety Agency (EASA). Under FAA oversight, each operator prepares a Continuous Airworthiness Maintenance Program (CAMP) under its Operations Specifications or "OpSpecs". The CAMP includes both routine and detailed inspections. Airlines and airworthiness authorities casually refer to the detailed inspections as "checks", commonly one of the following: A check, B check, C check, or D check. A and B checks are lighter checks, while C and D are considered heavier checks.

A Check

This is performed approximately every 500 - 800 flight hours. It is usually done overnight at an airport gate. The actual occurrence of this check varies by aircraft type, the cycle count (takeoff and landing is considered an aircraft "cycle"), or the number of hours flown since the last check. The occurrence can be delayed by the airline if certain predetermined conditions are met.

B Check

This is performed approximately every 3-6 months. It is usually done in 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, ie: A-1 through A-10 complete all the B check items.

C Check

This is performed approximately every 15–21 months or a specific amount of actual Flight Hours (FH) as defined by the manufacturer. This maintenance check is more extensive than a B Check, as pretty much the whole aircraft is 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. The schedule of occurrence has many factors and components as has been described, and thus varies by aircraft category and type.

D Check

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 5–6 years. It is a check that, more or less, takes the entire airplane apart for inspection and overhaul. Such a check can generally take from 3 weeks to 2 months, depending on the aircraft and number of technicians involved (it is not uncommon to have as many as 100 technicians working on a Boeing 747 at the same time). It also requires the most space of all maintenance checks, and as such must be performed at a suitable maintenance base.

Because of the nature and the cost of such a check, most airlines - especially those with a large fleet - have to plan D Checks for their aircraft years in advance. Often, older aircraft being phased out of a particular airline's fleet are stored or scrapped upon reaching their next D Check, due to the high costs involved in it in comparison to the aircraft's value. Many Maintenance, Repair and Overhaul (MRO) shops state that it is virtually impossible to perform a D Check profitably at a shop located within the United States. As such, only few of these shops offer D checks.

 

Maintenance Review Board

Initial aircraft maintenance requirements are proposed in a Maintenance Review Board (MRB) report based on Air Transport Association (ATA) publication MSG-3.

Modern transport category airplanes with MSG-3 derived maintenance programs employ usage parameters for each maintenance requirement such as flight hours, calendar time, or flight cycles. Maintenance intervals based on usage parameters allow more flexibility in scheduling the maintenance program to optimize aircraft utilization and minimize aircraft downtime.

SIJU GEORGE
nice work.........
PRANJAL MATHUR
great work ,,,
Harut
Nice,useful...
Stewart
Always nice to be reminded what we are and what we stand for! thank you.
dave davidson
just an FYI preventive maintenance is also called routine maintenance since it is something that is ongoing. just terminology. all that you stated above is 100% true

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