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x-c without ADSB

Asked by: 1579 views Airspace

How are you suppose to fly over mountainous terrain without ADSB? I understand you can go above 10K without ADSB as long as you are over mountains (2500 AGL), but does that mean you should descend over a valley and then climb again over the mountains? Seems counter productive. Is there a lateral limit on ADBS? 

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1 Answers



  1. Jeff Baum on Apr 18, 2022

    You have been required to have a transponder with Mode C when operating above 10,000 unless within 2,500 agl for years.

    14 CFR 91.215 (b)(i) “In all airspace of the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface”

    So, the ADS-B rule simply adds ADS-B Out to the existing Mode C requirement. There is no listed “lateral limit” for either requirement. My guess is that a momentary, slight exceedance due to variations in terrain would probably not be an issue. Sustained flight above 10,000 when terrain avoidance is not an issue, different story.

    To remain completely in compliance with he regulation, best plan is to find a route which allows you to remain below 10,000 or allows you to safely remain within 2,500 of the surface (or have ADS-B installed).

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