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    Interface CommBAltitudeReply

    A DF20 Comm-B altitude reply - the same altitude payload as SurveillanceAltitudeReply (DF4), extended with a 56-bit MB field carrying an Enhanced Surveillance Comm-B register. Like SurveillanceAltitudeReply, this is a targeted response whose CRC is XORed with the responding aircraft's ICAO address rather than being a plain checksum - candidateIcaoHex needs cross-checking against known traffic before it can be trusted.

    interface CommBAltitudeReply {
        altitudeFt: number | undefined;
        candidateIcaoHex: string;
        commBRegisters: CommBRegister[];
        identActive: boolean | undefined;
        kind: "commBAltitudeReply";
        squawkAlert: boolean | undefined;
    }
    Index
    altitudeFt candidateIcaoHex commBRegisters identActive kind squawkAlert
    altitudeFt: number | undefined

    Decoded altitude in feet, or undefined if the AC field is empty or invalid.

    candidateIcaoHex: string

    Candidate 24-bit ICAO hex address, recovered from the CRC field - verify against known traffic before trusting it.

    commBRegisters: CommBRegister[]

    Every Enhanced Surveillance Comm-B register the MB field plausibly holds - see inferCommBRegisters. Empty if none matched.

    identActive: boolean | undefined

    True when the transponder's Ident (SPI) pulse is active, from the Flight Status field. Undefined for a reserved Flight Status value.

    kind: "commBAltitudeReply"

    Discriminant tag identifying this as a decoded DF20 Comm-B altitude reply.

    squawkAlert: boolean | undefined

    True when the transponder is flagging a recent squawk code change, from the Flight Status field. Undefined for a reserved Flight Status value.

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