Aircraft callsign

    Args:
        msg (string): 28 bytes hexadecimal message string

    Returns:
        string: callsign

def callsign(msg):
    """Aircraft callsign

    Args:
        msg (string): 28 bytes hexadecimal message string

    Returns:
        string: callsign
    """

    if common.typecode(msg) < 1 or common.typecode(msg) > 4:
        raise RuntimeError("%s: Not a identification message" % msg)

    chars = '#ABCDEFGHIJKLMNOPQRSTUVWXYZ#####_###############0123456789######'
    msgbin = common.hex2bin(msg)
    csbin = msgbin[40:96]

    cs = ''
    cs += chars[common.bin2int(csbin[0:6])]
    cs += chars[common.bin2int(csbin[6:12])]
    cs += chars[common.bin2int(csbin[12:18])]
    cs += chars[common.bin2int(csbin[18:24])]
    cs += chars[common.bin2int(csbin[24:30])]
    cs += chars[common.bin2int(csbin[30:36])]
    cs += chars[common.bin2int(csbin[36:42])]
    cs += chars[common.bin2int(csbin[42:48])]

    # clean string, remove spaces and marks, if any.
    # cs = cs.replace('_', '')
    cs = cs.replace('#', '')
    return cs