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How can the time for daily maintenance or A Check be calculated for different aircraft types?
Is there any exact formulation depending on the aircraft specifications?
P.S.,I'm very new to the aviation field.

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The time taken for the daily maintenance or 'A' checks (or any other checks for that matter) depends on a number of parameters like:

  • The aircraft configuration.

  • The experience and skill level of the aircrew.

  • The condition (or age) of the aircraft and its components.

  • Requirement of any special checks (whether manufacturer/regulator mandated or operator requirement)

Usually, the checks to be carried out during each schedule (hourly or calender based) are determined by the manufacturer (sometimes in co-ordination with the operator) and laid down. The time required is then calculated by actually timing the operations and adding correction factors or by statistical analysis over a period of time.

One thing to note is that this is not exact and will vary based on a number of factors. For the same checks, different operators (and manufacturer) may allot different time periods. If two different checks (for e.g. airframe and the engine) are required to be carried out at the same time, the time required will differ.

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This answer is not specific for A-checks, but covers the whole maintenance effort.

Try Eddins-Earles, Mary: Factors, Formulas and Structures for Life Cycle Costing, Eddins-Earles, 89 Lee Drive, Concord MA 01742, USA, 1981

It's a bit dated, but has a wealth of data.

Another source would be Fabrycky, Wolter J.; Blanchard, Benjamin S.: Life-Cycle Cost and Economic Analysis, Prentice-Hall International. ISBN 0135383234.

Also, the white volume (I think it is No 8) of Jan Roskam's collection is a good start. Roskam, Dr. Jan: Airplane Design, Roskam Aviation and Engineering Corporation, Ottawa, Kansas 66067, USA, 1990.

Generally, this is not exact science, so exact times cannot be expected. With experience, each operator will be able to estimate how long things take, but you do these checks to find possible damage which needs to be taken care of. A lot depends on the training and experience of the maintenance crew. The best way to approach this is with statistics.

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To answer your first question:

The manufacturer (OEM) usually publishes an estimate of maintenance man-hours (MH) needed for each task within their Maintenance Planning Document (MPD). For non-MPD tasks, source documents such as Service Bulletins usually also have an estimate.

When an A- or C-Check work package is created, the OEM's estimates for each task can simply be added up to get a rough idea of the total number of MH needed. HOWEVER: this is just an estimate! The OEM's figures assume that the work is being carried out in ideal conditions, i.e. the tools are all at hand; paperwork is printed out; access to the aircraft is readily available; and the mechanic is well versed in doing that task. The OEM's estimate therefore needs to be adjusted. I've seen various organizations use factors varying between 2 to 4 i.e. if the OEM says one hour, you plan for between two to four hours. The factor will typically vary depending on factors such as: - facilities / equipment available at the maintenance location; - experience and skill levels of the technicians; - age and condition of the aircraft; - and even the type of check (e.g. A-Check vs C-Check).

Once the total MH for the A- or C-Check package is calculated, you can get a rough estimate of the ground-time you'll need for the check, based on the manpower you have available.

HOWEVER, a word of caution! As Peter says, this is not an exact science! Remember that the number of MH is different from the actual time it takes to do the task (known as "elapsed time")... E.g. time for a sealant to cure doesn't count towards the MH, but does still need time in the real world. Remember, just because a woman can deliver a baby in nine months, doesn't mean nine women can deliver a baby in one month!

Ideally, the company should have a process in place to gather and analyze data on planned MH vs utilized MH and planned vs utilized ground-time and incorporate this into their production planning activities.

To answer your second question:

As can be seen above, there is no "exact formulation". The calculations based on the OEM's MPD and source documents provide a ballpark figure, to which you then need to apply your engineering judgement and experience. This is where data gathering and analyses can be invaluable to an organization's planning process.

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