{{Short description|Type of airspace at airports in the United States}}
'''Mode C veil''' refers to a kind of airspace which currently surrounds all primary Class B airports within the United States. This airspace extends horizontally to a circle of 30 NM radius centered on the airport, and extends vertically from the surface up to 10,000 feet MSL.<ref name="USCFR91.215"/> The name refers to the mode of transponder operation which is required within this airspace — that is, with very limited exceptions, all aircraft operating within this airspace must have an altitude-reporting Mode C transponder in operation. An additional requirement for the transponder to have ADS-B Out became effective January 1, 2020.<ref name="USCFR91.225"/>
{{As of|August 2017}}, all 37 Class B airports in the United States<ref name="ClassB"/> have Mode C veils centered on them.<ref name="USCFR91.D"/> Prior to November 2014, two Class B airports did not have a Mode C veil (at least ''de jure''): William P. Hobby Airport in Houston<ref name="Note2"/> and Marine Corps Air Station Miramar in San Diego.<ref name="Note1"/>
Mode C veils were implemented after the collision of Aeroméxico Flight 498 and a Piper Archer on August 31, 1986, within the terminal control area of Los Angeles airport.
==References== <references>
<ref name="USCFR91.215">{{cite web |url=https://www.ecfr.gov/cgi-bin/text-idx?node=se14.2.91_1215 |title=USCFR Title 14 Part 91.215(b) (2) |accessdate=2024-06-06}}</ref>
<ref name="USCFR91.225">{{cite web |url=https://www.ecfr.gov/cgi-bin/text-idx?node=se14.2.91_1225 |title=USCFR Title 14 Part 91.225 |accessdate=2024-06-06}}</ref>
<ref name="ClassB">{{cite web |url=https://www.faa.gov/documentLibrary/media/Order/JO_7400.11B.pdf |title=FAA order JO 7400.11B, Airspace Designations and Reporting Points, effective 2017-09-15 |accessdate=2024-06-06}}</ref>
<ref name="USCFR91.D">{{cite web |url=https://www.ecfr.gov/cgi-bin/text-idx?node=ap14.2.91_11721.d |title=USCFR Title 14 Part 91, Appendix D |accessdate=2024-06-06}}</ref>
<ref name="Note2">Which had it ''de facto'', although not necessarily ''de jure'': {{USFR|78|14910}} ("the FAA plans to add the William P. Hobby Airport to the list of airports identified in Title 14 of the Code of Federal Regulations, Part 91, Appendix D, Section 1").</ref>
<ref name="Note1">For many years, both of these exceptions had Mode C veils centered on them on the sectional, WAC, and Low IFR charts, which was inconsistent with CFR and as such was either a cartographic mistake, a regulatory mistake, or both. In a separate action ({{USFR|79|57431}}, published 2014-09-25 and effective 2014-11-13), the FAA updated CFR Title 14 Appendix D to Part 91, Section 1, to include both Hobby and Miramar.</ref>
</references>
Category:Air traffic control in the United States