This would be a great feature ... imagine this:
Airline B needs to operate flights from certain airport, where none of its planes can operate from, so he ACMI leases plane from Airline A, and they agree per-block hour price. Airline B pays per block our, pays landing fee, pays navigation fee, pays catering and passenger handling. Airline A pays wages, cost of capital, fuel and maintenance. It would be upon the Airline A to determine a block hour cost it wants to charge, and maybe a minimum contract can be enforced (similar as with terminals, a flat fee per week regardless if the capacities are used).
How would scheduling work:
After the aircraft is ACMI leased, Airline A sees all scheduled flights but cannot change them. Airline A also sees flight costing for those flights related to its own costs (aircraft cost of capital, wages, maintenance, fuel). Airline B can make full schedule changes but cannot go under 100% maintenance ratio (because then the re-up costs for maintenance would be higher on player A). Airline B would see its flight costing related to block hour cost, wages of its own personnel (non-crew wages), pax handling, navigation and landing fees, and catering.
How would lease process work:
An airline would publish its offer on its enterprise game site or in the forums.
A price is agreed between Airline A and Airline B.
Through Asset management tool, ACMI lease is set up, by entering enterprise ID of Airline B, ACMI rate per hour, and hours per week contracted (in further advanced mode overages for usage over contracted block hours can be implemented). An in-game message is sent to Airline B, which it needs to accept for ACMI lease to start (same as with terminal offers).
Seating:
The seating would be implemented by Airline A, and Airline B cannot change the seating. Basically, what airline B can do with the ACMI leased aircraft, is only to schedule it, and schedule only within the 100% maintenance ratio AND within the number of block hours contracted.
Ratings:
Ratings for a flight would be calculated based on seating from Airline A, catering from Airline B, and an average of images of Airline A (operating airline) and Airline B (marketing airline).
Advantages:
Further cooperation among players
Lower need for additional maintenance categories
More dynamic in aircraft movements
Option for unused planes to do some work
Great feature to have when maintenance checks (such as C, and D) are implemented in game ... two weeks time spent on C check or over a month on a D check,