Aircraft FAQ
The plane shows that it's following the route perfectly, but it's actually deviated from it!
Since the 737 Classic is not equipped with GPS, you may encounter Map Shift.
Updated Latest published version
If your EHSI is showing you following the route line but a flight tracker shows you deviating,
You're probably experiencing map shift.
Inertial Reference Systems (IRS) drift over time, which causes the IRS position to disagree with the actual aircraft position. With no GPS, the 737 Classic relies on DME/DME position updating to counter this.
When position updating isn't performed, your aircraft's perceived position (FMC position) will not match with its actual position.
For more information, check out the Flying without GPS chapter of the Aircraft Features doc.
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Source: CSS Launcher User Manual, Rev. 5 — December 2025.