By Bjorn Fehrm

June 02, 2017, ©. Leeham Co: We last week got an understanding of the maintenance task types that a Maintenance Planning Document (MPD) for the Airbus A320 contains.

We now use this knowledge to build an operator’s maintenance program for our A320-based airline.

Figure 1. The first modern maintenance program was formed around the Boeing 747. Source: Wikipedia.

Operator’s Approved Maintenance Plan

We already know that we, as the aircraft’s operator, are responsible for keeping the aircraft airworthy. We do that according to the rules and regulations of our local Airworthiness Authority.

The MPD is the aircraft OEM’s recommendation for a minimum level of tasks we shall include in our maintenance plan. We also know that we must include:

• Certification Maintenance Requirements (CMR) tasks.
• different Airworthiness Limitations (AL) prescribed tasks.

To that we will add:

• The MPD tasks that are relevant for our aircraft and our operation;
• Service Bulletins (SB) from the OEM;
• Service Letters from the OEM;
• Airworthiness Directives (AD) from our Airworthiness authority;
• Engine and APU service tasks from their OEMs; and
• Any other vendor service tasks (e.g. for our Buyer Furnished Equipment (BFE)).

As seen, it’s no little job to compile our maintenance program. But we must satisfy all these requirements. Without an approved plan by our local authorities, there is no flying.

In practice, our maintenance specialists start with the aircraft’s MPD. They then add the other tasks until we have an Operator’s Approved Maintenance Plan (OAMP), accepted by our authorities.

 Grouping of checks

An OAMP has typically something like 4,000 tasks that shall be performed before the different limits run out. To make sure our aircraft spend their time flying passengers, instead of at maintenance, we must cluster these tasks in a smart way.

We must combine tasks that have the same limits and need the same access (like to the avionics bay or behind the cargo bay lining). This might mean we won’t use the maximum limits for the flight hours/cycles for several tasks, but it’s still better to do the task when access is opened.

The grouping will differ between different types of operators. Some fly many short flights during a day, with a return to home base several times a week, like we do. Others fly longer legs and are seldom at their home bases during the week.

We will assume that our operation has an average of seven flights a day of 1.43 hours, making for 10 hours a day. We operate 350 days a year for 3,500 flight hours and 2,450 flight cycles.

We will build a typical Operator’s Approved Maintenance Plan (OAMP) with these values. It suits our operation to group the tasks in the classical: Line, Ramp, A, C and D check pattern.

Other operators would cluster the tasks differently, as their operations makes a more continuous check style suit them better.

Line checks

We would make the pre-flight check thin (a minimum of tasks performed by our flight crews before each flight, essentially a walk-around) and then we group tasks like engine oil checks, brake checks, tire pressure checks, etc., at our home bases, as overnight checks by our line mechanics. To the home station job, we would add any repair jobs that crop up during the week (like avionics warnings/malfunctions or broken cabin items).

Another type of airline would group tasks for a fatter pre-flight check, with the flight crew doing for example brake checks, tire pressure checks and checking cabin emergency equipment besides the visual walk-around inspection.

Outstation mechanics would be tasked to drain the fuel system, do engine oil checks/fills and any other heavier tasks for the aircraft (the aircraft doesn’t see the home base during the week). Any simpler repair jobs would be carried out as well, but most would be deferred to the weekly Ramp check at home base.

Ramp checks

Each week, our home station mechanics would do a more extensive Ramp check inspection of the aircraft’s emergency equipment (like flight crew emergency oxygen), check and fill APU oil, check critical cabin functions and clear any faults that has been deferred from the week’s flying.

There is a Minimum Equipment List (MEL) issued by the aircraft OEM, which prescribes what minimum level of avionics and other equipment that must be functional for continued flight. As most systems have redundancies, the MEL can allow an aircraft to continue flying with items reported as faulty. Such faults are then handled at the weekly Ramp checks.

A checks

The A check, which is performed by our contracted A to D check maintenance supplier, groups tasks which have maximum 600 flight hour intervals or 450 flight cycles.

To not pass these limits, it’s typically done after 400 flight cycles for our A320s. With 10 flight hours a day, the A check is typically a bimonthly check. The A320 has several Zonal inspection tasks with a 100-day limit. Many of these are scheduled into the A check, to stay below 100 days and to do the inspections when hatches/linings are opened anyway.

About two man-weeks are required to perform the tasks grouped into our A check. Many times, operators have, like we, contracted the A to D checks (or equivalent tasks) with an aircraft maintenance provider (like Delta Techops, Lufthansa Technik…). Our airline hires and trains Line/Ramp mechanics, but outsources more advanced jobs to industry specialists.

C checks

The C checks (also called the first “Base checks”) are the heavy systems checks. Systems gets tested and units that are time or cycle limited (like pumps; actuators) are replaced with units overhauled by specialists (the units are called Rotables).

For our A320s, the checks are done at or before passing 6,000 flight hours or 20 months, and then at multiples of these limits. With our utilization of 3,500 flight hours per 12 months, we would hit the 20-month limit at 5,800 flight hours.

At the first C check, there is a list of tasks that form the first C check job list. Then for each repeat at 12,000, 18,000 hours, etc., tasks are added to form fatter C checks. As our aircraft gets older, more and more items reach their use limits.

The first C check needs about 800 man-hours for the C check tasks. To that come non-routine repairs or Service Bulletins/Airworthiness Directives that shall be done and that get grouped with the C checks.

D checks

The D checks are also called the Heavy checks. This is when the aircraft are more or less completely teared down, including paint stripping, so detailed structural inspections can be done.

For our A320s, this is done every six years and repeated at the aircraft’s next sixth year. These are time-consuming and expensive checks, especially the 12-year ones (once again the check gets fatter, the aircraft gets older and tasks are added as the checks are repeated).

Next week

Next week, we will give example of items that get replaced on our A320s during these checks and what their typical costs are. We will also look at the costs for the checks themselves.