What is the mnemonic?
1-2-3 / 1500 + 2 / 2000 + 3 / MMOISTRS / 3585
The basic 1-2-3 rule: 1 hour before to 1 hour after ETA, ceilings 2,000 or more, vis 3 SM or more.
1500 + 2 / 2000 + 3
For flag operations, 1500 feet / 2 miles above lowest approach mins, or 2,000 AFE / 3 miles, whichever is greater.
- within 100 OR ½ of Cat 1 mins at destination
- AND within 100 OR ½ of DERIVED mins at 1st alternate
- then 2nd alternate required.
Method 2 Engine failure at cruise, clear all obstacles by 2,000 feet, 5 SM either side of route — but if failure occurs before reaching cruising alt, we need to be able to return to departure airport, or divert to a takeoff alternate using Method 1 calculations.
- destination = not less than ½ the vis for the expected approach
- 1st alternate = not less than ½ the DERIVED ceiling AND vis
- 2nd alternate = at or above DERIVED mins