IFR Airport Basics

Recently, a reader asked about a puzzling approach at Chatham, MA (KCQX). The RNAV (GPS)-B is perfectly aligned with Runway 24 and the descent angle is a routine 3.05 degrees, yet it has only circling minimums. Approaches most often just have circling minimums if the alignment to the runway exceeds 30 degrees (for most procedure types) or the descent angle is greater than 3.77 degrees (for Category C and below). So, whats up at Chatham?

Editorial Staff

Friday, January 08, 2016 at 12:00 AM ET

Verified

Key Takeaways:

Instrument approach minimums, such as straight-in versus circling-only, are significantly determined by physical airport infrastructure like runway markings, not just approach alignment or descent angle.
Weather reporting systems and reliable altimeter sources are crucial, as their absence or reliance on remote sources can restrict commercial operations, invalidate alternate planning, and lead to increased minimums.
The monitoring status of navigation facilities and the presence of adequate lighting also dictate an approach's usability, particularly for alternate planning and night operations, underscoring the importance of comprehensive infrastructure health.

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This procedure has only circling minimums because of the runway markings, of all things. The runway has basic, visual markings; straight-in minimums require at least non-precision instrument runway markings. This little detail isn’t found on the chart or in the Airport/Facility Directory, but can be found in online sources, such as Airnav.com, which are based on FAA airport survey data.