Can you depart or land without an altimeter setting?

• A. No, unless the IAP specifies a suitable alternative (minimums with the (blank) altimeter setting)
• B. Yes, always
• C. Only for VFR
• D. Only for departures

Answer: (A)

Having the correct altimeter setting is essential for accurate altitude information during takeoff and approach. The altimeter measures pressure and then converts it to your indicated altitude, so without a valid setting you could be higher or lower than you think, risking terrain or obstacle clearance.

You generally must have the local altimeter setting before departing or landing. There is an exception only if the instrument approach procedure’s minimums explicitly call for a suitable alternative altimeter setting. In that case, the minimums will indicate which setting to use (often shown as “minimums with the [blank] altimeter setting”). If no such alternative is published, you can’t depart or land without a valid altimeter setting.

So the correct approach is that you cannot depart or land without an altimeter setting unless the IAP minimums specify a different, approved setting.