Navigational tolerance for DME is +/- how many nautical miles?

• A. +/- 1 nm
• B. +/- 2 nm
• C. +/- 3 nm
• D. +/- 5 nm

Answer: (B)

DME distance readings have inherent measurement errors due to signal propagation and equipment limits, so pilots use a practical tolerance for navigation. For DME, the standard navigational tolerance is about two nautical miles. This means the actual distance to the station is expected to be within plus or minus two nautical miles of the indicated readout. This margin reflects typical DME performance across common operating ranges, keeping guidance useful without being unrealistically precise. Tolerances of one mile are typically too optimistic for everyday practice, while tolerances of three or five miles would be too loose for reliable navigation and sequencing.