How many minutes before an aircraft reaches the clearance limit fix should holding instructions be issued when a delay is expected?

Holding instructions should be issued to an aircraft expected to encounter a delay at the clearance limit fix at least 5 minutes before they reach that point. This timeframe allows the pilot sufficient opportunity to prepare for the holding procedure, ensuring a smooth transition into the holding pattern if necessary.

Issuing instructions too close to the clearance limit could lead to confusion or impede the pilot's ability to safely enter the hold, especially if they are busy managing other flight tasks. By giving the pilots a 5-minute heads-up, air traffic controllers can enhance safety and efficiency, allowing for better coordination and adherence to air traffic procedures.

In most air traffic control operations, clear and timely communication about holding patterns is essential, and the 5-minute guideline is standardized to promote operational consistency.