TWR COULD NOT SEE END OF RWY DUE TO LOW VISIBILITY. ACFT X ON RWY TAXIED OFF JUST AS ANOTHER ACFT Z ON APCH DID GAR. ACFT X THEN TAXIED BACK AND TOOK OFF. ACFT Y STATES THAT TWR DID NOT KNOW OF ACFT Z ON APCH.

Narrative

WE WERE GIVEN POS AND HOLD BY STL TWR BEHIND A X ACFT ON RWY 30L AT TXWY S. WE WERE OVER THE HOLD SHORT LINE WHEN THE X ACFT SUDDENLY ADDED A LARGE AMOUNT OF PWR AND EXITED THE RWY ON THE OTHER SIDE. WE STOPPED AND AT THIS TIME WE COULD SEE A DC-9 ON A GAR AT APPROX 100 FT. WE WERE OVER THE HOLD LINE BUT CLR OF THE RWY. ATIS WAS M5 OVCST 3 BUT THE TWR SAID THAT HE HAD US ON RADAR BUT COULD NOT SEE US. HE ASKED IF WE WERE ON THE RWY OR WAS THE X ACFT TWR AT STL IS APPROX 120 FT AND COULD NOT SEE THE END OF RWY 30L. THE X ACFT TURNED AROUND AND DEPARTED THEN WE DID WITH NO FURTHER INCIDENT. THE TWR OPERATOR SAID THAT HE HAD NO KNOWLEDGE ABOUT THE DC-9 AND IT WOULD BE INVESTIGATED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR AND THE SAAB WERE TO DEPART FROM RWY 30L AND THE INBOUND DC-9 WAS TO LAND ON RWY 30R. FOR SOME UNKNOWN REASON; THE DC-9 WAS LINED UP ON THE WRONG RWY; RWY 30L. ALL 3 ACFT REACTED CORRECTLY WHEN THEY SAW THE PROB. THE RPTR HAS NOT HEARD ANYTHING MORE FROM HIS ACR OR THE FAA ON THIS MATTER.