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 geometry.

The Turn Calculator:

• Allows the user to make the following inputs by means of the input fields in bold dark blue:

  • aircraft speed data (can be either IAS, Mach or TAS; after input of one of these variables, the other two are automatically computed taking into account Flight Level and ISA deviation)

  • Route data (Flight Level, inbound and outbound courses): the inbound and outbound courses are defined by dragging the inbound and outbound turn segments

  • Weather data (Wind, ISA deviation)

• The tool then computes and displays the turn geometry of the ‘Fly-By Transition Boundary’ (displayed in green) for the given turn angle and Flight Level

• The tool also computes and displays the turn geometry of a constant radius turn (displayed in red) defined by a turn radius (see the bold dark blue input field) and the entered speed, Flight Level and weather data.

• The tool provides information on aircraft performance through the turn defined by the constant radius, which includes the evolution of bank angle and calculated groundspeed.

Purpose

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 tool and any derivative works including but not limited to, any express or implied warranty of fitness for a particular purpose.

Turn Performance

Aircraft turn performance is commonly influenced by the following factors:

• The fact whether the aircraft flies a Fly-By or a constant radius turn: the aircraft will fly a constant radius turn if it is coded as such in the database (either through the use of the Radius-to-Fix (RF) path terminator for terminal area operations or the specification of a turn radius at a waypoint along an airway for en-route Fixed Radius Transitions)

• Prevailing wind conditions

• Design of the ATS routes - angle of turn

• Controller instructions

• Aircraft type, altitude, speed, avionics and software, as well as pilot input

Constant radius versus Fly-By turns

Constant radius turns, if correctly applied, will ensure all aircraft follow the same path in a highly repeatable fashion. Fly-By turns produce a wide variety of turn performance and the earliest turn can be up to 20NM before the waypoint. Fly-By turns should remain within the Fly-By Transition Boundary which is defined in RTCA DO-236C / EUROCAE ED-75D and calculated by this tool, as follows:

Low Altitude Transitions (below Flight Level 195):

• Groundspeed = 500 kts

• Bank Angle = Minimum(Turn Angle / 2, 23º)

High Altitude Transitions (above Flight Level 195):

• Groundspeed = 750 kts

• Bank Angle = 5º

• Turn initiation distance ≤ 20 NM