What should you do with all MDAs when using the Rockford altimeter setting?

When using the Rockford altimeter setting, it is essential to increase all Minimum Descent Altitudes (MDAs) by 80 feet. This adjustment accounts for the difference in altimeter settings between standard pressure (29.92 inHg) and the local altimeter setting. The Rockford altimeter setting is typically lower than standard pressure, and maintaining the appropriate clearance above terrain and obstacles is critical for safety in instrument approaches. Therefore, increasing the MDAs ensures that the aircraft maintains safe vertical separation in compliance with the altered pressure altitude.

Other options do not correctly address the requirements of changing altitudes when modifying altimeter settings. Keeping the MDAs the same would not account for the need to increase altitude due to changes in pressure. Decreasing the MDAs would potentially place the aircraft at an unsafe altitude, while only increasing the MDA for approach procedures neglects the need to adjust all MDAs uniformly for various stages of flight.