Ticket prices
To calculate the ticket prices, you multiply your route length (L) with specific values. Those values depend on your high cost carrier percentage (HCC%) (go to Menu -> Airline -> Settings to change that)

Let´s first make clear how the suggested ticket prices (Autoprices) are calculated.
The percentage is the respective HCC%, L is the route length in km.
0-9%: E= L*0.70 B=L*0.98 F=L*1.40
10-19%: E= L*0.75 B=L*1.05 F=L*1.50
20-29%: E= L*0.80 B=L*1.12 F=L*1.60
30-39%: E= L*0.85 B=L*1.19 F=L*1.70
40-49%: E= L*0.90 B=L*1.26 F=L*1.80
50-59%: E= L*0.93 B=L*1.30 F=L*1.86
60-69%: E= L*0.95 B=L*1.33 F=L*1.90
70-79%: E= L*0.96 B=L*1.34 F=L*1.92
80-89%: E= L*1.00 B=L*1.40 F=L*2.00
90-99%: E= L*1.05 B=L*1.47 F=L*2.10
To earn the most profit though, you multiply the suggested ticket prices with 1.74(9).
You have to be careful when doing this since hitting or exceeding the ticket limit (suggested ticket price x 1.75) always leads to zero pax. Round down if you multiply with 1.749 or use 1.74 to be on the safe side.
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NOTE!: When the game first came out, multiplying with 1.74 lead to 0 pax if you were not a 90%+ high cost carrier. This seems to be patched now, at least it worked also with lower % when I just tested that. (22.11.2018)
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Route:
Finding the perfect stopover and destination is a very difficult task because there are many factors that you must consider.
First of all, you should know that the routes should be as long as possible (to keep the on-ground time as low as possible) while still fitting to your playing schedule (if you depart a route when you wake up it should not arrive while you are sleeping again etc.) If you are able to, I would suggest keeping routes around 6, 8, 12, 16 or 24h long (including your turnaround time of course!).

There is one main demand (the overall demand of a route) and 3 sub demands.
The 3 sub demands are:
Economy (e)
Business (b)
First class (f)

Since both the demand of Stopover and Destination count to the route demand, you also have to pay attention to finding good airports. The overall demands should not be lower than 90% and the economy demands should not be lower than 80%.
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NOTE! The route demand is the average of stopover and destination demand. This applies to the overall- and the sub-demands (E, B, F).
Route Demand (O, E, B, F) = (Stopover demand (O, E, B, F) + destination demand(O, E, B, F) / 2
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Of course, you also must consider your planes specs like Range, Runway requirement etc.

Additional info:
You can only create 10 routes from the same hub to the same destination.
If you already filled all good destinations in your range, you can simply change your hub and create 10 additional routes to that destination.
The cost of hubs is based on your current overall balance (all bank accounts together). So think about spending as much money as you can before purchasing a new one, but leave enough money to afford it.
You should aim for max. economy since it gives the most profit.
If you just started playing the game and want to grow fast, do not buy new planes and do not reconfigure used planes. Used planes are mainly economy configured which is exactly what you want, and they are not worth the money you have to pay to exactly match your seat config with the route demand. Instead rather think about investing that money into a new plane.
If you have difficulties finding good airports or understanding how to calculate ticket prices and seat configs, visit am3info.com and check out our demand map + calculators.

Example (just a simple example to show how it would be perfect, this will not completely add up in the game!)
Let´s say you have a DC-9-10 with a runway requirement of 2,000ft, a range of 2000km and a velocity of 800kmh. It´s full economy configured.
The hub is Berlin (EDDT). We use “Esenboga” (LTAC) as stopover and “Riga” (EVRA) as destination. (found using the demand map at am3info.com)
Demand Esenboga: O=99% E=83% B=9% F=8%
Demand Riga: O=96% E=81% B=11% F=8%
Route demand (average of both): O=(99+96)/2 = 97,5% E=(83+81)/2 = 82% B=(9+11)/2 = 10% F=(8+8)/2 = 8%.
Berlin to Esenboga are 2000km and Esenboga to Riga are also 2000km, adds up to 4000km.
Our ticket price formula as a 99% high cost carrier is E= L*1.05 B=L*1.47 F=L*2.10
Calculated: E=4200$ B:5880$ F:8400$
Since the plane is 100% economy configured, only the e price matters. For best profit we multiply it with 1.749 which would be 4200$*1.749=7345.8$. Round down to not hit the ticket limit = 7345$ per ticket.
With 800kmh the DC-9-10 takes 5 hours for that flight. Perfect! Why? Because as a 99% high cost carrier, our turnaround time is 1 hour which gets us to exactly 6h per flight.

If you want to learn more about AM3, have a look at the game guides section or our website at am3info.com
If you have anything to add or found a mistake, please share it in the comments.