Jumbo, I probably did not explain myself very well, because I keep talking about figures per a/c added and you keep talking about general data.
So, let's do first things first.
Cost of the fleet (all monthly values): Total monthly cost = (Fixed Admin Cost Type + Admin costs* Na) + (Fixed Maint Cost + Main Cost * Na) + (Crew Training Cost * Nc) + (Fixed Maint Cost per Engine Type + Maint Cost * Ne).
Na=number of a/c in fleet
Nc=number of crew needed for the a/c
Ne=number of engine owned by the airline
If you split up these costs you'll see why formulas are limiting and also why my model works better (if nothing else, it is simpler). Moreover, all those figures can be fitted in an expanded chart for every a/c you buy (either new or used) so that "anyuser" can make his/her own calculations and get a rough estimate of how much money he/she's going to pay for that additional a/c in his/her fleet.
I would also like to point out that airlines suffer of very high overhead costs (as railroads, if Sigma is reading) and that:Fixed Admin Costs Type
: is often in the range of multiples of 100.000€/USD (the bigger the a/c, the higher the costs, but the increase is surprisingly quite flat) because you need to hire a fleet/type manager who is a licensed engineer, usually with seniority and needs some people working for him. They have to liase with the a/c manufacturer and keep the a/c tech docs updated and do all the peperwork that Civil Aviaiton Authorities need/ask. Much of this work is indipendent from the number of a/c you have in fleet
. You only have additional work for updating the paperwork related to any single a/c of the type.Fixed Maint Costs
: we talk about the A, B, C and D checks plus all the wearing parts that will be used to keep a/c in airworthy condition. It also includes the HUGE COSTS for mantaining a warehouse with all the spare parts you need
. This warehouse has a cost (the building itself) and must be manned by licensed technician, not by the first worker that walks in front of the building. These costs are around figures close to 1mln€/USD for a/c like A32X/B73NG. Usually these costs include spare engines.Crew Training Costs
: quite easy to calculate but are still pretty high, because of the number of crews involved and the costs of training structures and related staff.Fixed Maint Costs Engine Type
: high costs because the airline needs certified engineers and dedicated workshops. Plus the spare parts for every engine. (I'm not considering the spare engines).
All you wrote is nice, but in the end what people want to know are those few figures you can fit together with the price of line checks... Truste me. Nobody cares about nice indexes, percentages, etc...