For an alternate with two navigational facilities, each providing approaches to different runways, what are the additive values for ceiling and visibility?

• A. Ceiling: add 300 ft to higher CAT I HAT; Visibility: add 1/2 statute mile to higher authorized CAT I landing minimums.
• B. Ceiling: add 200 feet to higher Category 1 Height Above Threshold (HAT) for the two approaches used, and a visibility is derived by adding 1/2 statute mile to the higher authorized category 1 landing minimums of the two approaches used.
• C. Ceiling: add 150 ft; Visibility: add 1/4 mile
• D. Ceiling: add 200 ft; Visibility: add 1 statute mile

Answer: (B)

When planning an alternate that uses two different navigational facilities, each with its own instrument approach to a different runway, you must apply the more restrictive minima from the two approaches and add margins to them. The added margins are fixed: 200 feet to the higher CAT I height above threshold (HAT) and 1/2 statute mile to the higher CAT I landing minimums. This gives you a conservative, safe baseline that ensures altitude and visibility are enough for either approach if conditions demand using the less favorable option.

So you take the higher HAT among the two approaches, add 200 feet, and take the higher landing minimum visibility among the two approaches, then add 1/2 mile. For example, if one approach has a HAT of 300 ft with a minimum visibility of 1/2 mile and the other has a HAT of 480 ft with a minimum visibility of 1 mile, the alternate minimums become 680 ft ceiling (480 + 200) and 1.5 miles visibility (1.0 + 0.5). This aligns with using the higher of the two CAT I minima plus the specified margins.

The other choices don’t match these standard additive values, which is why the correct approach uses 200 ft and 1/2 mile.