What is the maximum permissible difference between designated DME and aircraft equipment?

What is the maximum permissible difference between designated DME and aircraft equipment?

• A. 0.1 NM
• B. 0.5 NM
• C. 1.0 NM
• D. 2.0 NM

Answer: (B)

Distance measuring equipment is used to determine how far the aircraft is from a specific ground station, and a cross-check is often performed against the distance calculated by the aircraft’s own navigation equipment. The allowable discrepancy between these two distance readings is limited to 0.5 nautical miles. This tolerance reflects the typical accuracy of DME systems and onboard navigation calculations, while still being practical for maintenance and routine checks. If the difference is within 0.5 NM, the DME and the aircraft’s distance measurement are considered in good agreement for IFR navigation. A larger difference could indicate a fault in the DME installation or in the aircraft’s distance measurement, prompting further inspection.

Distance measuring equipment is used to determine how far the aircraft is from a specific ground station, and a cross-check is often performed against the distance calculated by the aircraft’s own navigation equipment. The allowable discrepancy between these two distance readings is limited to 0.5 nautical miles. This tolerance reflects the typical accuracy of DME systems and onboard navigation calculations, while still being practical for maintenance and routine checks. If the difference is within 0.5 NM, the DME and the aircraft’s distance measurement are considered in good agreement for IFR navigation. A larger difference could indicate a fault in the DME installation or in the aircraft’s distance measurement, prompting further inspection.