§ 91.217 Data correspondence between automatically reported pressure altitude data and the pilot's altitude reference
14 CFR Part 91 — Subpart C—Equipment, Instrument, and Certificate Requirements
Official text — 14 CFR § 91.217
REGULATION — LEGALLY BINDING(a) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder—
(1) When deactivation of that equipment is directed by ATC;
(2) Unless, as installed, that equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95 percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft; or
(3) Unless the altimeters and digitizers in that equipment meet the standards of TSO-C10b and TSO-C88, respectively.
(b) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder or with ADS-B Out equipment unless the pressure altitude reported for ADS-B Out and Mode C/S is derived from the same source for aircraft equipped with both a transponder and ADS-B Out.
Reproduced from the eCFR. Text as amended through 2026-07-31. Verify against the official source before relying on it operationally.
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Is this a regulation?
Yes — this is regulatory text and is legally binding.
Text published in the Code of Federal Regulations. Regulations are legally binding on pilots and operators.