code: def alt40mcp(msg):
      
      d = hex2bin(data(msg))
  
      if d[0] == '0':
          return None
  
      alt = bin2int(d[1:13]) * 16    # ft
      return alt
docs: Selected altitude, MCP/FCU
  
      Args:
          msg (String): 28 bytes hexadecimal message (BDS40) string
  
      Returns:
          int: altitude in feet