no speed tape

Hi to all . I love flying Queen 747 8 f version however shame there isn't back up secondary speed gauge if this happened . It all started when Airhauler wanted it to have a fun so gave me this failure while cruising .It all whent ok up until approuch. Lucky all my app doing manualy so as this time . Honestly I wanted to do autoland but somehow on approuch she wouldn't spool to keep app speed set and engage ,so had to fly manual . Little scarry as my manual lending is always some nice some not to mention ,but this time no speed just watch TAS and GS . well all finish ok agent took cargo . So I would like to ask if such failurer is realistic? thanks Petr