Definition
In RNAV (area navigation) operations, the maximum allowable lateral deviation from the centerline of a desired course. It defines how far an aircraft may drift left or right of the programmed track while still being considered on course for navigation accuracy purposes.
Plain English
How far off to the side of your intended course you are allowed to be before you are considered off course.
Context Anchor
Seen in navigation, instrument procedures, and moving-map or flight-management displays that show whether the aircraft is left or right of its intended path.
Derivation
Cross-track' refers to the sideways direction across your course line, as opposed to 'along-track' which is forward or backward along it. 'Tolerance' means the allowable amount of error. Together: the allowable sideways error from the course.
Why Pilots Care
Staying inside cross-track tolerance keeps the aircraft within protected airspace and ensures obstacle clearance and procedure compliance.
Grounding Statement
Picture the intended path as a centerline in the sky; cross-track tolerance is the allowed space to either side of that centerline.
Intuition Check
Tolerance does not mean “roughly okay” or “pilot preference” here. It means a specific allowed left-or-right error from the intended ground path.
Example Sentence 1
The RNAV approach required a cross-track tolerance of 0.3 nautical miles, so the pilot monitored the GPS deviation indicator closely.
Example Sentence 2
On the approach, the pilot corrected heading to remain inside the published cross-track tolerance.