Minimum Turning Altitude (MTA)

Minimum turning altitude (MTA) is a charted altitude providing vertical and lateral obstruction clearance based on turn criteria over certain fi xes, NAVAIDs, waypoints, and on charted route segments. When a VHF airway or route terminates at a NAVAID or fi x, the primary area extends beyond that termination point. When a change of course on VHF airways and routes is necessary, the enroute obstacle clearance turning area extends the primary and secondary obstacle clearance areas to accommodate the turn radius of the aircraft. Since turns at or after fi x passage may exceed airway and route boundaries, pilots are expected to adhere to airway and route protected airspace by leading turns early before a fi x. The turn area provides obstacle clearance for both turn anticipation (turning prior to the fi x) and fl yover protection (turning after crossing the fi x). Turning fi xes requiring a higher MTA are charted with a fl ag along with accompanying text describing the MTA restriction.

Source: FAA Aeronautical Chart User's Guide