What is the slant range error significance at 1 NM above the DME station?

The significance of slant range error at 1 nautical mile (NM) above the DME (Distance Measuring Equipment) station is considered negligible. Slant range error refers to the difference between the horizontal distance from the aircraft to the DME station and the actual straight-line distance, which includes both the horizontal distance and the aircraft's altitude above sea level.

At an altitude of 1 NM above the DME station, the vertical component is minimal compared to the horizontal distance. Since the DME provides distance information based on the line-of-sight measurement to the ground station, the impact of altitude on the accuracy of the distance reading becomes less significant. Therefore, any potential error in slant range is small relative to the overall range measurement.

In contrast, at higher altitudes or greater distances, the slant range error might become more pronounced due to the increasing angle of the line between the aircraft and the DME station, leading to larger discrepancies in the calculated distance. Hence, the consideration of slant range error being negligible at low altitudes, such as 1 NM above the station, is accurate and reflects how DME systems function in practical scenarios.