Turn Calculator

The Turn Calculator has been developed by EUROCONTROL to enable ATM specialists, including airspace planners, to visualise and comprehend the impact of aircraft turn performance primarily in the en route.

The Turn Calculator allows the user to input appropriate aircraft, route and weather data to then predict the turn performance (colour coded in blue).

The tool then computes the geometry of both the ‘Fixed Radius Transition’ and ‘Fly By’ for the given turn angle and displays the expected earliest ‘Fly By’ turn as well as the FRT. 

The tool provides information on aircraft performance through the turn which includes the evolution of bank angle, calculated groundspeed and load factor.


The Turn Calculator is not intended to be used as a route design tool although it may be useful during the planning (pre-design) and validation (post-design) phases.

The Turn Calculator is provided on the clear understanding that EUROCONTROL makes no warranty, whether express or implied, arising by law or otherwise, assumes no responsibility to any person or persons, and disclaims any liability with respect to the use of the software and any derivative works including but not limited to, any express or implied warranty of fitness for a particular purpose.


The Turn Calculator was developed to run on MS Excel for Windows XP or Windows Vista. Contact us to request the Turn Calculator, or to give your feedback on the tool.

Request tool


Aircraft turn performance is commonly influenced by the following factors:

  • Prevailing wind conditions
  • Design of the ATS routes
  • Controller instructions
  • Aircraft type, altitude, speed, avionics and software, as well as pilot input

In en route operations the aircraft can transition between the route legs either using ‘Fly By’ turns or by Fixed Radius Transition (FRT).  ‘Fly By’ turns produce a wide variety of turn performance and the earliest turn can be up to 20NM before the waypoint.  The FRT, if correctly applied, will ensure all aircraft follow the same path in a highly repeatable fashion.

Turn Calculator user interface

Navigation support team

If you wish to have specific information on a particular navigation topic, please contact us