Maintenance Planning Document (MPD): The Essential Repository for Developing an Aircraft Maintenance Program

Every effective Aircraft Maintenance Program (AMP) starts with a solid foundation—and that foundation is often the Maintenance Planning Document (MPD).

But what exactly is the MPD, and how does it support compliance?

In simple terms, the MPD is a repository document issued by the aircraft’s Type Certificate Holder (TCH). It typically brings together the Primary Sources of the Aircraft Maintenance Program:

• Airworthiness Limitations (ALS)

• Certification Maintenance Requirements (CMR)

• Maintenance Review Board Report (MRBR)

The MPD may also include tasks from Secondary Sources:

• Regulatory requirements

• Airworthiness Directives (ADs)

• Operational requirements

• Low Utilization Recommendations (LUR)

• Supplemental Structural Inspection Documents (SSID)

• Life Extension Programs (LEP)

• Service Bulletins (SBs) and Service Letters (SLs)

• Modifications and repair-related repetitive tasks

• Component manufacturer recommendations

Smaller aircraft manufacturers often include more of these Secondary Sources directly in the MPD to make life easier for their operators. Larger manufacturers, on the other hand, may leave the evaluation and inclusion of these Secondary Sources into the AMP to the operators, allowing for greater flexibility and customization.

Aircraft Maintenance Program Sources

It's important to be clear: complying with the MPD alone does not guarantee regulatory compliance. While the MPD is a valuable compilation, it is not the authoritative source—compliance comes from the original documents such as the ALS, CMR, MRBR, and ADs. I'll explain why that matters shortly.

A Structure Rooted in MSG-3

The structure of the MPD typically aligns with the Maintenance Review Board Report (MRBR), which forms the foundation of most modern maintenance programs, and, usually, with the MSG-3 methodology, organized into four working portions, each with its own decision logic:

1. Systems and Powerplant

2. Aircraft Structures

3. Zonal Inspections

4. L/HIRF (Lightning/High-Intensity Radiated Fields) – this fourth category is often integrated into the others.

This structure reflects the preventive and risk-based philosophy of MSG-3, helping ensure that maintenance tasks are effective and efficient throughout the aircraft lifecycle.

🔍 The latest MSG-3 evolution considers elements like Aircraft Health Monitoring (AHM), enabling more predictive and condition-based maintenance strategies.

How to Use It

In addition to listing tasks, the MPD provides critical planning information, such as:

• Reference to the instructions,

• Estimated man-hours and workforce size (*),

• Required skills and qualifications,

• Access panel locations,

• Necessary tools, parts, and equipment.

(*) These values are generalized and may not reflect the operator's actual performance. Each organization should determine its own labor efficiency factor, adjusted from historical data, to schedule tasks more accurately and optimize manpower.

The Instructions

Most task instructions referenced in the MPD are found in the Aircraft Maintenance Manual (AMM).

The Aircraft Maintenance Manual (AMM) is the document that contains most of the necessary tasks and procedures for the maintenance of the aircraft (scheduled and unscheduled): information on aircraft features, systems, structures, installations, basic control, servicing procedures, maintenance instructions, access procedures, removal/installation of parts and components, methods and equipment, and instructions to apply protective treatments after structural inspections.

In short, the AMM provides the step-by-step guidance for most routine maintenance activities.

For tasks requiring more advanced techniques, such as inspections involving specialized tools or skills, references may be made to other manuals—like the Non-Destructive Testing (NDT) Manual or specific component maintenance manuals.

Why Do Inconsistencies Occur Between the MPD and the Source Documents?

Compliance with the MPD doesn't necessarily ensures compliance with regulatory requirements. For example, Airworthiness Life Limitations, not considered as repetitive maintenance tasks, may not be incorporated in the MPD but are an essential part of the Aircraft Maintenance Program. Even if the MPD contains all the Primary and Secondary Sources, the operator is still responsible for controlling, analyzing, and implementing each source document, as applicable.

Inconsistencies between the MPD and source documents are more common than you might imagine. These errors usually originate from the Type Certificate Holder during the compilation of the MPD, particularly when interpreting or transposing data from documents like the ALS, CMR, MRBR, or others, into the MPD. While the MPD serves as the foundation for an AMP, the process of transferring maintenance requirements between various documents isn't always error-free.

For instance, over a two-year period, I identified and documented more than 75 discrepancies between the MPD and its original source documents for a single aircraft type. Several of these differences could have compromised continuing airworthiness if the source documents had not been carefully reviewed and validated.

If you spot one, please, inform the Type Certificate Holder (TCH). Addressing these issues helps improve the accuracy of the MPD and supports the entire industry’s commitment to safety and compliance.

Final Thoughts

The MPD is an essential bridge between maintenance requirements, maintenance instructions and planning information. However, never forget: the MPD is a starting point, not a guarantee of compliance. Real compliance comes from diligently cross-checking each MPD entry against its original source document. That’s the key to building an Aircraft Maintenance Program that’s both efficient and fully compliant.