How to unlock jumbo jets

When you first play, I would suggest NOT upgrading airports or planes. Bucks are used to buy parts for new planes. As you gain levels, the planes you can develop are gradually better. Develop better planes based on carrying more passengers, or the same passengers with a plane that has more speed / range.

Upgrading airports seems to me to be best kept for poor airports (0.4 style airports), so that when you have a few planes there, there are still jobs available.

Another important thing to remember is, try to keep a fleet of planes with a good mix of passengers / cargo. As in, don't just have all your planes for passengers. Try and keep a level mix between ability to carry cargo AND passengers, being as airports have a seemingly equal mix of passengers and cargo.

For early on - consider this:

1. 'Watching' a plane fly earns you the most stuff. Regularly, coins and bucks fly across the screen to 'earn' by clicking them. (best way to earn bucks).
2. Airports range from class 1-3. When you reach the point to develop a class 2 aircraft, they can only fly to class 2+ airports (blue & red). Not ideal unless you have a LOT of airports.
3. When filling up your plane, don't just pick the first ones available. See how much profit you'll earn, go back and then try a different set of options for the best profit.
4. Whenever a combo is available (i.e. your plane holds 3 passengers, and you can take 3 passengers to 1 single place) take it. The 25% bonus, plus the single destination gives a lot more profit.
5. Whenever a buck passenger / cargo is available - take it. Even if it means a loss. Bucks are worth far more than a loss of coins.

Distance, plane Weight, and plane Speed are the 3 variables used to determine a plane's flight expense. (The higher these values, the higher the total cost.)

You can spend "Bux" to upgrade an individual plane to lower its Weight 3 times, by 5%, 10%, and 15%. These upgrades names (in game) are slightly misleading: they represent your total weight reduction, so each upgrade is only giving 5% for a total of 15% weight reduction, and 15% reduction in cost. See "Napkin Math" below for details...

Please note that increasing a plane's Speed via upgrades will increase flight costs, but lower flight durations.

Also note that adding/removing passengers and cargo currently has no impact on a plane's weight. (as of v1.0.3 anyway)

Napkin Math:

I tried out a few Speed and Weight upgrades... Each time I lowered my plane Weight by 5%, it consistently lowered the route cost (from original cost) by another 5%. Increasing the Speed by 5% increased the route cost by 5%. When I combined the two, the results showed the effects multiplied.

Thus, the game appears to follow a simple formula for cost:

Weight(W) * Speed(S) * Distance(D) * SomeConstant(SC) = Cost(C)

So, if we reduce weight by 15% and increase speed by 5%... (0.85*W) * (1.05*S) * D * SC = 0.85*1.05 * C = approx. 89.25% change in Cost.