Selected altitude, MCP/FCU

    Args:
        msg (String): 28 bytes hexadecimal message (BDS40) string

    Returns:
        int: altitude in feet

def alt40mcp(msg):
    """Selected altitude, MCP/FCU

    Args:
        msg (String): 28 bytes hexadecimal message (BDS40) string

    Returns:
        int: altitude in feet
    """
    d = hex2bin(data(msg))

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

    alt = bin2int(d[1:13]) * 16    # ft
    return alt