NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brian Walton
Date: 2025 Aug 31, 00:31 -0700
Boeings on autopilot fly great circle tracks; it's all they can do.
The North Atlantic Track System is planned on Mercators. If you fly from say N60W40 to N60W30, half way along you will see a cross track error shown of some miles towards the N Pole.
Approaching a NATS waypoint, the autopilot anticipates the turn, and turns left to the next track. The aircraft is NEVER on the Mercator ground track. The bank angle used is around 23°, depending on ground speed which may be anywhere between 300 and 700kts depending on wind.
On routes nearer the N Pole, say London-Tokyo, the display changes automatically from magnetic to true. No paper charts are needed. Back up is provided by crew's personal lap-tops, issued by the company, and updated automatically.
Anyone can draw a Mercator on ruled notepaper, in a boat, or aircraft cockpit.
