What is the maximum allowable CDI error when checking a VOR/TACAN at a designated ground checkpoint?

The maximum allowable Course Deviation Indicator (CDI) error when checking a VOR (VHF Omni-directional Range) or TACAN (Tactical Air Navigation) at a designated ground checkpoint is established to ensure that navigational aids are operating accurately, thus maintaining safety and precision in flight operations.

In this context, the correct choice reflects the standards set forth by regulatory authorities, which indicate that when performing a ground check, the CDI error must not exceed ±4 degrees. This tolerance is crucial for pilots who rely on accurate navigation data to ensure they are on the correct course, especially when operating under instrument flight rules. Adhering to this standard helps to minimize the risk of navigation errors that could lead to hazardous situations in flight.

In contrast, the other options reflect tolerances that do not meet the established standards for VOR/TACAN checks. A smaller allowable CDI error would be overly stringent and may not be practical, while a larger error allowance would not provide the precision necessary for safe operation. Understanding this standard will assist pilots in maintaining their proficiency and ensuring optimal use of navigational aids.