Pinnacle Airlines has restricted flights to a maximum of FL370.
In May, National Helicopter sued the city, charging that the Council had no right to restrict flights.
A separate agreement with National and other operators restricts flights mainly to areas away from residential neighborhoods.
By restricting flights from only towered airports, federal authorities can directly determine who's in the system.
A second proposed rule would restrict flights by student pilots in "terminal control areas" around these airports unless they had special flight and ground training.
It does not restrict flights to an efficient hub-and-spoke system.
One solution might be to restrict flights to certain hours or places, said several people who sent in comments.
It is also possible that some airlines will restrict flights over the election period.
The agreement does not restrict flights at Manchester.
Citing extreme shortages in America's air traffic control system, it has issued an urgent recommendation to restrict rush-hour flights at 22 major airports this summer.
