Aircraft Maintenance Programs - The Fundamentals

An Aircraft Maintenance Program (Commonly referred to as an AMP) is probably the most important document in Continuing Airworthiness. Requirements for an AMP are encapsulated in EASA CAMO.A.315 (b) and Part-M, M.A.302.?It is also a requirement both from ICAO Annex 6,8 & FAA Part 121.367 & Airworthiness Circular AC 120-16F.

What sometimes is missed in the quagmire of regulatory requirements is that an AMP is not just about regulatory compliance. An effectively managed AMP using a well-defined Reliability Program can lead to significant Cost Saving on Scheduled Maintenance.

AMP is a topic on which reams of pages can be written, in the interest of brevity for today’s article I will try to restrain myself to some informative FAQ’s pertaining to AMPs.

Q: What is an Aircraft Maintenance Program?

An AMP is an approved document that includes all the Scheduled Maintenance Requirements for an Operators fleet. The AMP is prepared by Fleet type and includes all the aircraft included in that particular fleet. For eg. an Operator with an A320 and B737 Fleet will have separate AMPs for each fleet type.

The purpose of an AMP is to ensure the realization of the inherent safety and reliability levels of the equipment.

These Scheduled Maintenance usually originate from the ICA (Instructions for Continued Airworthiness) issued by Type Certificate and Supplemental Type Certificate holders.

Another term that is often used is the Maintenance Schedule, the primary difference is that a Maintenance Schedule is the list of all the tasks along with their Thresholds/Intervals of Compliance whereas a Maintenance Program includes the Maintenance Schedule and the associated procedures and standard Maintenance Practices.

Q: What documents are to be reviewed while drafting an AMP?

All ICAs issued by STC and TC holders need to be considered for inclusion in the AMP. These typically include Maintenance Review Board Report (MRBR), AWL (Airworthiness Limitations), CMR (Certification Maintenance Requirements), FAL (Fuel Airworthiness Limitations), CPCP (Corrosion Prevention and Control Program), EWIS & Zonal Inspection documents and Scheduled Maintenance ETOPS requirements.?Normally all these different ICAs are included and compiled by Aircraft OEM into an MPD (Maintenance Planning Document).

One should also include Time Limits from Engine and APU Manuals and also any Scheduled Maintenance Requirements emerging out of STC requirements.

Q: How is an AMP Structured and what are its contents?

This varies greatly from Organization to Organization however all AMPs have some common elements. First would be the Preface or Introduction which have Scope and associated Procedures. ?Then it is preferable to have multiple sections such as Systems Maintenance, Structures Inspection (covering Widespread Fatigue Damage and Corrosion Prevention & Control Tasks), Zonal Inspections, Engine/APU, Time Controlled Items, Life Limits, and In-House Tasks. However some Operators keep the entire Maintenance Schedule as one document, some even divide it ATA wise. There is no one size fits all system here and it really boils down to how an Organization feels is the best way to present this information.

Q: Do ADs and SBs with repetitive Inspection requirements need to be included in the AMP?

The simple answer is, it is not necessary as long as you have a separate approved procedure for controlling these documents and the maintenance arising out of these. At most, a cross reference to the procedure can be provided in the AMP. Nevertheless, some operators do prefer to integrate these into their AMPs and once again there is no right or wrong way, it is just what model fits best for the organization. Whatever model one chooses to follow, the associated procedures should be clearly documented.

Q: Is it enough to consult just the MPD for preparation of the AMP?

A very critical point to be understood is that an MPD is not an approved document rather it is a repository document for many different sources primary among them being MRBR, AWLs, CMRs & FALs. However we still need to consult other mandatory documents such as Engine and APU Time Limit Manuals. If an aircraft has any STC based modification embodied on the Aircraft, any ICAs originating out of that would also need to be included.

Applicable source document review needs to be a thorough and precise endeavor, it is a tedious task and a duplicate review can limit Human errors.

Q: Does an AMP need to be approved by the regulator?

The answer depends upon whether your NAA follows an EASA system or an FAA system.

In an EASA System the initial AMP needs to be approved by the NAA, however subsequent revisions if agreed to by the NAA can be “Indirectly Approved” by a designated personnel from the CAMO; normally the CAMO Manager. This must be documented in the CAMO manuals. Even in such cases the NAA may stipulate certain conditions where indirect approval may not apply e.g. Escalation of intervals, addition of new aircraft, deletion of tasks.

However if the NAA does not approve the Indirect Approval procedure then all revision must be approved by the regulator. ???

In an FAA System the FAA does not directly approve the Maintenance Program however the maintenance program forms a part of OpSpecs and OpSpecs are made mandatory through the issue of an Operating Certificate. The FAA approves the Maintenance Program through the OpSpecs.

Q: What is the relationship between Maintenance Programs & Reliability?

Any maintenance program that has Maintenance Tasks emerging as a result of MSG logic or has condition monitored components needs to be managed via a Reliability Program. This implies we need to measure and monitor the reliability of Systems as well as the non-routine findings emerging out of scheduled maintenance Tasks and adjust the intervals based on the Reliability Reports.

Furthermore maintenance Tasks can even be Deleted from or Added to the maintenance Program based on Reliability and In-Service Experience.

An important consideration here is that reduction of intervals and deletion of tasks from the AMP based on the reliability program is applicable only from tasks arising out of non-mandatory sources.

Note: In an FAA System a Reliability Program is referred as CASS (Continuing Analysis and Surveillance System) program

Q: How often should an AMP be revised?

An AMP should be revised at least Annually to comply with regulatory requirements. However a best practice would be to initiate an immediate update as soon as any of the major source documents are updated.

Q: Are the Intervals that are initially defined in the AMP fixed or can they be adjusted?

It depends upon what is the origin of those Tasks and Intervals. Tasks emerging from the MRB report form only the baseline and can be definitely adjusted. As a rule of thumb all intervals arising out of MRB Report can be adjusted based on an approved Reliability Program.

However mandatory requirements such as AWLs/CMRs/FALs/Life Limits cannot be escalated, nevertheless there are no restrictions on reducing the interval and making them more restrictive.

Q: What is the difference between an Interval Escalation & Variation?

An Escalation is an increase in interval of a Task initiated at time of AMP revision as part of Reliability Review.

However a Variation is a one-time exceptional interval extension of a maintenance task interval for an Approved period due to exigent circumstances. The allowable Variations are defined in the Preface to the approved AMP and each variation on a Task needs to go through an approval process which is defined in the Operator’s CAME.

Q: Where do the concept of Letter Checks such as A check , C check and D check fall into the AMP Concept?

Operators/CAMO/Maintenance Planning Department may prefer to group the individual maintenance tasks with similar intervals together and assign them letter designators for ease of planning of maintenance. ?They may choose to define these as Part of the AMP however it is not really a regulatory requirement and with the use of MSG-3 is probably an antiquated concept. (I do promise that I will deal with this in one of the later articles).

Q: What is the origin of the tasks that are included in the AMP?

The tasks are derived from an approved report published by the Aircraft OEM called MRBR or Maintenance Review Board Report. The establishment of tasks and Intervals by MRB is based on a process called MSG-3. This is an entirely differently discussion in itself and I will embark on a detailed discussion in future articles.