The Problem
When attemping to start a flight in smartCARS, a popup message saying "You must be at the departure airport to start your flight" displays and the flight cannot start.

The Resolution
If you are an airline administrator, check and correct the latitude and longitude of the airport that you experienced the issue for via your website's back-end.
If you are a pilot, contact your virtual airline's administration. and provide this article to them.

The
 Explanation
Assuming you are indeed at the correct airport according to your simulator, this occurs when the location of the airport according to your website does not correspond with its location in the simulator.
As a virtual airline administrator, to check if an airport is correct, look up its location on http://airnav.com and compare to your website's information for it. If it is incorrect, you can use the location given by AirNav to correct it.

In some cases, the scenery in the simulator itself may not match the real location, which can cause this issue to persist even after correcting the latitude and longitude. In that case, as a virtual airline administrator, you must either decide to match the scenery or require different scenery.