To add a search, basically you modify this:
/core/modules/Schedules/Schedules.php, around line 166 is:
public function FindFlight()
There's a bunch of if statements looking at that search form.
So let's assume the field you added was name'd "airline", you'd add:
if($this->post->airline!= '')
{
$routes = SchedulesData::GetSchedulesWithCode($this->post->airline);
Template::Set('allroutes', $routes);
}
Basically you need the Template::Set('allroutes', ...); portion so the template has routes to display. The GetSchedulesWithCode will work with the latest beta.
But that's basically how you would build up that search.
You can add additional fields/search parameters that way too. The only thing would be is you might need to write some SQL.