Improvements can be purchase on the Buy Improvements screen. There are ticket cost improvements, cargo load improvements, fuel cost improvements, and passenger amount improvements. Each type of improvement has multiple levels that unlock once purchasing the each successive improvement. Each successive improvement has a higher rating requirement and costs more money.
The percentages stack on top of each other for each level. If level 1 gives you %5 and level 2 gives you 7%, you will then have 12% in that improvement.
Itzamna 07:26, 17 April 2008 (UTC)