Under what condition is the minimum described for a black dashed line on a NDB approach?

The correct understanding of the minimum described for a black dashed line on a NDB (Non-Directional Beacon) approach is that it is valid only with ADF (Automatic Direction Finder) navigation. This means that in order to conduct the approach safely and effectively, the pilot must be relying on ADF equipment specifically designed to receive signals from NDBs.

The black dashed line indicates that the approach procedure requires the use of ADF for navigation, as this type of navigation equipment is essential for accurately following the course to the NDB. The ADF allows the pilot to determine the aircraft's bearing relative to the NDB and fly the approach accordingly.

Other navigation aids such as GPS or VOR are not applicable for this specific approach minimums. Therefore, it is critical to have functioning ADF equipment to ensure that the requirements for the approach are met and to maintain safety during the landing process.