It is not possible to talk about airworthiness of aircraft without mentioning the aircraft’s Approved Maintenance Program (or AMP). This document is the basis for airworthiness management, it has to be available for every aircraft and it needs to be consulted with regards to every maintenance action to be performed. Let’s take a closer look at what an AMP actually is, where it comes from and how it must be used to ensure continuous, safe flights.
What is an Approved Maintenance Program (AMP)?
In short, an approved maintenance program is a list (in the form of a long table) of all maintenance tasks which need to be performed on an aircraft from time to time. In other words, based on the AMP an airworthiness engineer knows exactly what tasks need to be performed after an aircraft reaches a certain point in life, be it calculated based on calendar age, flight hours of flight cycles.
The AMP for large aircraft consists of several hundreds of pages and is generally divided into some major sections, such as zonal inspections, airworthiness limitations, etc. It will also contain guidelines on whether there is a certain threshold on a task (a “threshold” is the first instance in which a task is to be carried out, for example a certain inspection may need to be done after the aircraft has flown for 20.000 flight hours and thereafter repeated at 2.000 flight hours intervals).
The typical structure of an entry in the AMP table will be as follows: AMP task number, MPD task number, brief task description, interval and threshold information and notes. Sometimes an AMM reference is also provided. Why there is an AMP and MPD number available (and what an MPD number is), I will try to explain further in this post.
What is very important to understand is that an AMP is always aircraft specific – it reflects one aircraft, and one aircraft and only during a given time, while the aircraft is being flown by a specific operator. This is sometimes causing confusion – an AMP is never a generic document (i.e. for a fleet of 30 different Airbus A320 aircraft). It does happen that operators place different AMPs into one document (in which case there would be one more column stating the tail number of serial number to which a given task applies), but formally those are still separate AMPs approved for different aircraft, only presented in one book.
Who creates an Approved Maintenance Program and How Can They Do It?
Creating an AMP is the responsibility of the operator. In particular, it should be created by the CAMO PH (or under his/her supervision). The document needs to be created and approved by the competent authority before the aircraft is brought under the operators CAMO. It also constitutes the foundation for populating the company’s digital airworthiness management system.
The AMP is written based on several source documents, which I will briefly describe below, but also on a given operator’s experience with the type and the results of the company’s reliability program.
In short, the CAMO PH should analyze all the source documents and create a list of tasks applicable to a given aircraft. Furthermore, he or she should then consider all the variables which are specific to the given operator. Those may include things like procedures for sampling the operation of emergency escape slides, which don’t need to be performed on every aircraft but rather on a fleet. The post holder should also analyze the operator’s reliability program to determine whether there are any repetitive defects which would require an additional inspection or a shortening of the manufacturer recommended inspection interval. On the other hand, it may also happen that some intervals can be escalated if company experience shows that no defect has ever been found while using the original interval (for example some corrosion inspections for aircraft which rarely ever fly in humid weather).
As you can see, the Approved Maintenance Program should be highly operator specific and can be used only by one company.
What are the Source Documents for an Approved Maintenance Program?
The AMP can (and should) be based on several documents which define the aircraft’s maintenance requirements. Let’s go through them one by one:
- Maintenance Planning Document (MPD) – on first sight, the MPD looks exactly like an AMP. Just like the AMP, it contains a long table with entries for different maintenance tasks. Therefore, there may be some confusion as to what it is, and I even met people who believed that a copy of the MPD can be approved as an AMP. However there is one huge difference – the MPD is generic. It is being issued by the aircraft manufacturer and applies to many aircraft in the world wide fleet. Therefore, it is not customized and several (hundreds of) tasks are dependent for example on the aircraft modification status and its serial number. It cannot be considered as a final list of tasks for a given tail number.
- Aircraft modification status – as I already mentioned, the applicability of several tasks is dependent on the aircraft modification status. In several cases, the MPD may list a task as “pre mod” or “post mod”. The author of the AMP must know whether the aircraft is “pre” or “post” in order to know which task applies and should be carried out. Also, the aircraft may have custom modifications embodied, which often come with their own maintenance tasks. Of course, the manufacturer will not include such tasks in the MPD, but the AMP must conform to them.
- Aircraft AD status – the final AMP should include all repetitive tasks which need to be performed on the aircraft. This includes repetitive inspections called for by airworthiness directives. All available and applicable, repetitive ADs should be included in the AMP.
- Aircraft SB status – similarly to the modification status, the applicability of some tasks may be dependent on whether a specific service bulletin has been performed. Also, some SBs may require repetitive inspections in which case, similarly as with the ADs, such inspections should be included in the AMP.
- Operator Reliability Program – based on an analysis of the operator’s reliability program, the author of the AMP can decide to shorten some maintenance intervals for given tasks, or – on the contrary – extend them. In both cases, he or she will need to convince the appropriate aviation authority that such a decision is well supported by maintenance but this can (and, in fact, should) be done to fully account for the type of operations in a given airline.
- Company procedures, customer experience values, and similar requirements – these are things which also may affect the AMP. Perhaps the company wishes to have carpets replaced every 6 months or would like to inspect and repair some commercial decals once every week? Those are also maintenance tasks, which need to be supported by proper documentation and should be included in the AMP.
As you can see, creating an Approved Maintenance Program is not quick and easy. However, this is the only way to ensure that all performed maintenance and its intervals truly reflect the operating conditions of the aircraft.
How Does an Approved Maintenance Program Change Over Time?
This may have already become clear, but an AMP is a living organism. It changes over time and it has to change. In fact, a regular (at least twice a year) review of the AMP and implication of relevant changes is a legal requirement under EASA. So why and how can an AMP change?
First of all, an AMP will need to change because the source documents change. Top aircraft manufacturers, like Airbus or Boeing release new revisions of the MPD at least twice a year. This alone will force operators to change their AMPs in order to reflect the manufacturer induced changes.
The same applies for all remaining documents. Throughout their lives aircraft are modified and have new service bulletins embodied. In many cases, this will impose changes on the AMP. Also new ADs are being issued continuously and they, also, affect the AMP.
Last but not least, the operator’s reliability program continues to work and bring in new reliability data. This data should be regularly analyzed and proper conclusions should be drawn with respect to aircraft maintenance and airworthiness. This is why there is a requirement to analyze the effectiveness of an AMP at least twice a year. The CAMO PH must be convinced that the AMP indeed “foresees” aircraft damage and provides appropriate maintenance tasks at appropriate intervals.
How is an Approved Maintenance Program Actually “Approved”?
Each AMP and also every AMP revision needs to be approved by the competent aviation authority. This can be a lengthy process, as the authority will need to time to (at least briefly) ensure that the AMP is corresponding to the source documents.
Also, every deviation from the source documents (like interval changes for certain tasks) need to be applied for from the authority and only with their approval can they be changed to suit the operator’s needs.
As you can see, creating and monitoring of an AMP can be a tedious process, but the Approved Maintenance Program is the most vital document in airworthiness, after all.