Indicated airspeed, DBS 5,3 message

    Args:
        msg (String): 28 bytes hexadecimal message

    Returns:
        int: indicated arispeed in knots

def ias53(msg):
    """Indicated airspeed, DBS 5,3 message

    Args:
        msg (String): 28 bytes hexadecimal message

    Returns:
        int: indicated arispeed in knots
    """
    d = hex2bin(data(msg))

    if d[12] == '0':
        return None

    ias = bin2int(d[13:23])    # knots
    return ias