Altimeters on Approach

Reader David Novelli asked an innocent but probing question. His primary airport has an approach that says if the local altimeter setting is unavailable you should use one from a nearby field and adjust the minimums. Weve all seen that, although few of us have actually had to take advantage of it.

IFR Staff

Saturday, November 11, 2017 at 12:00 AM ET

Verified

Key Takeaways:

Per regulations, an instrument approach is legally unusable if a certified altimeter setting (local or from a designated nearby airport) is unavailable.
In dire, Part 91 emergencies, pilots might hypothetically "guesstimate" an altimeter setting using uncertified sources (e.g., another pilot or nearby airport trends) only if the weather is comfortably above minimums.
This emergency "guesstimate" method requires significant safety margins added to minimums and is an intellectual exercise, not official guidance; the proper procedure is always to divert when a certified altimeter setting is unavailable.

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Reader David Novelli asked an innocent but probing question. His primary airport has an approach that says if the local altimeter setting is unavailable you should use one from a nearby field and adjust the minimums. We’ve all seen that, although few of us have actually had to take advantage of it.

Philosophically digging deeper, Novelli’s question was what to do when both the primary and the secondary airport aren’t reporting an altimeter. This yielded some interesting discussions of both the legal and the practical that are just the stuff we’re known for.