A Part 121 flag operation is planned in a two-engine turbojet airplane. The destination forecast calls for a 2,000-foot broken ceiling and 4 statute miles visibility for the period from 1 hour before to 1 hour after the ETA. The lowest applicable visibility minimum for the available instrument approach is 3/4 statute mile, and there is no acceptable circling MDA published. Under 14 CFR 121.621, is a destination alternate required?
- AYes, because the forecast ceiling is below 3,000 feet
- BNo, because forecast ceiling and visibility meet the 1,500-foot/greater-of-3-SM-or-approach-plus-2-SM criteria
- CNo, because two-engine airplanes are automatically exempt from alternate requirements
- DYes, because visibility is less than the approach minimum plus 2 statute miles
Show answer & explanationAnswer & explanation
Correct answer: B. No, because forecast ceiling and visibility meet the 1,500-foot/greater-of-3-SM-or-approach-plus-2-SM criteria
Under 121.621, no alternate is required if, for the period 1 hour before to 1 hour after ETA, the ceiling will be at least 1,500 feet above the lowest circling MDA (or 1,500 feet above the airport elevation if no circling minimums) and visibility will be at least 3 SM or 2 SM more than the lowest applicable visibility minimum, whichever is greater. Here, 3/4 SM + 2 SM = 2.75 SM, so the greater value is 3 SM; forecast visibility of 4 SM meets this, and the 2,000-foot ceiling exceeds the 1,500-foot requirement, so no alternate is required.
Why the other options are wrong
- A. 3,000 feet is not the regulatory ceiling threshold; 1,500 feet above minimums is.
- C. Engine count does not exempt an operator from alternate weather requirements.
- D. The correct comparison uses the greater of 3 SM or approach-plus-2-SM, which is 3 SM here—forecast 4 SM exceeds it.
Flag Alternate Weather Rule (121.621)
Defines when a destination alternate is not required for flag operations based on forecast ceiling and visibility during the arrival window.
- Applies 1 hour before to 1 hour after ETA
- Ceiling must be 1,500 ft above lowest circling MDA (or airport elevation)
- Visibility must be greater of 3 SM or approach minimum + 2 SM
Memory trick: 1500 above, 3 or plus-2 — clear enough means skip the alternate.