When should an aircraft begin to slow down when entering a hold?

The correct approach to slowing down an aircraft when entering a hold is to do so 3 minutes before arrival at the holding point. This timing allows the pilot to adjust the speed adequately to enter the hold at the appropriate airspeed, ensuring a safe and stable entry into the holding pattern. It also helps ensure that the aircraft is within the required speed parameters to allow for proper maneuvering as it approaches the fix.

Slowing down earlier provides the additional benefit of accommodating any necessary adjustments due to air traffic control instructions or environmental factors, which might require the aircraft to hold for a longer duration. Achieving the right speed before reaching the holding fix allows for smooth transitions into the holding pattern, especially when factoring in the potential for needing to make tight turns or adjustments during the entry.

The other options, while they might suggest varying points at which to slow down, do not offer the same strategic planning and preparation, which is crucial when managing the approach to a hold. For instance, slowing immediately upon entering the hold or at the holding fix may not provide the necessary margin needed for managing speed effectively, which can lead to complications in the maneuvering process.