Mode C veil
Mode C veil refers to a kind of airspace which surrounds most primary Class B airports within 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. The name refers to the mode of transponder operation which is required within this airspace (i.e., with very limited exceptions, all aircraft operating within this airspace must have an altitude reporting Mode C transponder in operation). All 37 existing (as of late 2014) Class B airports in the United States, have Mode C veil centered on them. This was not the case for many years, whereas two airports did not have it (at least de jure): Houston Hobby Airport and Miramar Naval Air Station.
- 14 C.F.R. 91.215(b)(2)
- FAA's order JO 7400.9Y "Airspace Designations and Reporting Points", effective 2014-09-15, accessed 2014-10-29
- CFR Title 14 Appendix D to Part 91, Section 1
- Which had it de facto, although not necessarily de jure: 78 FR 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").
- 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 cartographic mistake, or regulatory mistake, or both.
- In a separate action (79 FR 57431) FAA updated CFR Title 14 Appendix D to Part 91, Section 1 to include Houston–Hobby and Miramar on the list, effective 2014-11-13.