During the era which the aircraft and aviation industry largely growth up, the aircraft manufacturer, and selected industry participants form groups called Maintenance Steering Groups (MSG).

This Maintenance Steering Group MSG aim to determine an appropriate time and to overhaul in fact all component (whether they need it or not was not a consideration). During the latter part of the 1960’s a task force was created to investigate more cost effective (but equally safe processes) from this, led the concept we now call “on condition maintenance”.

A document was produced during 1968 by ATA (Air Transport Association) -titled Maintenance Evaluation and Program Development, which also became known as “MSG-1” The process was trialed on the Boeing 747. The MSG-1 process used decision logic to develop scheduled maintenance.

MSG-2 was developed and used for developing scheduled maintenance for 1970’s, MSG-2 was process orientated and for first time introduced ‘condition monitored maintenance’ concept.

MSG-3 was first published in 1980 is a task orientated and the main idea behind this concept is to recognize the inherent reliability of aircraft systems and components, avoid unnecessary maintenance tasks and achieve increased efficiency.

Control Processes

  1. Hard Time: life limit or maximum interval gave to the component until performing maintenance tasks on a part or unit. Such intervals apply to overhaul, but also to the total life of the part or unit.
  2. On condition: mean we not left the component until it’s failure, but during its life we do repetitive inspections, test and analysis to measure part integrity and determine the conditions, then we can take the proper decision.So, we can define as maintenance process having repetitive inspections or tests to determine the condition of units, systems, or portions of structure with regard to continued service-ability (corrective action is taken when required by item condition.)
  3. Condition Monitoring: means we left the component / part until it’s failure, but we pay attention to the part without any regular inspections, tests…etc.Simply we can define as a maintenance process which allows a unit to operate until failure. Condition monitoring is not permitted for units whose failure has an adverse effect on operational safety.
  4. Zonal Inspection Programs: means to do regular inspection to the aircraft component according to different inspection programs like: Corrosion Protection Program CPP, sampling program…etc. these programs replace the condition monitoring in MSG3.The zonal inspection programs are very important and need to be done carefully to be effective because if not it may affect the safety.

Below table give brief difference between 3 revisions of MSG






used decision logic to develop scheduled maintenance.


process orientated and introduced ‘condition monitored maintenance’ concept

Task orientated, recognize the inherent reliability of aircraft systems and components, avoid unnecessary maintenance tasks and achieve increased efficiency

Hard Time HD

(less components than MSG 2)

On Condition

Condition Monitoring



(Replaced by zonal inspection program)

zonal inspection programs



What’s next?

After Maintenance Steering Groups (MSG) and Industry Steering Committees (ISC). through numerous meetings determine the frequency and scope of aircraft inspections to be performed. This information is provided to another group called the maintenance review board (MRB) group led by the Airworthiness Authority. The MRB will issue their final recommendations as a MRB Report (MRBR) to the manufacturer on how an aircraft should be maintained. The manufacturer then publishes this information in Maintenance Planning Documents (MPD) to be provided to the customer. For airline or commercial operators, the recommendations of the MRB and subsequent MPD are used to develop its Customized Maintenance Program (CMP).

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