PDX TWR CTLR CONCERNED WITH AREAS OF INHIBITED VISIBILITY OF TXWY A; PARALLEL TO RWY 10L-28R; DURING ARPT CONSTRUCTION PHASE. TWR ASDE EQUIP ALSO OTS.

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DUE TO CONSTRUCTION OF NEW PARKING GARAGE AND ELEVATOR SHAFTS; PARTS OF FBO RAMP; TXWYS A4; A3 AND A ARE NOT VISIBLE FROM THE TWR. THE ARPT SURVEILLANCE DETECTION EQUIP IS OUT FOR MAINT UNTIL AUG/99 OR SEP/99. THERE IS A REMOTE TV CAMERA WITH ZOOM FEATURE; BUT THIS CAMERA HAS TO LOOK AT AN AREA MORE THAN 1/2 MI; AND DOESN'T ALWAYS WORK. ON SEVERAL OCCASIONS; NUMEROUS GA ACFT HAVE CALLED TO TAXI TO THE ACTIVE RWY. SOMETIMES THEY AREN'T FAMILIAR WITH THE TXWYS. SOMETIMES THEY DON'T TAXI RIGHT AWAY. THE TXWY A4 AND TXWY A INTXN IS NOT VISIBLE FROM THE TWR AND YOU CAN'T SEE THEM UNTIL THEY ARE ESTABLISHED ON TXWY A. YOU CAN SEE THE TXWY A3 AND TXWY A INTXN; BUT YOU LOSE THEM AGAIN EBOUND ON TXWY A. YOU CANNOT SEE THEM MOVE AROUND THE FBO RAMP. WHEN SEVERAL OF THEM CALL AT ONCE; BECAUSE OF THE NON VISIBILITY; YOU DO NOT KNOW WHERE THEY ARE. WHEN THE PLT IS CONFUSED; IT IS HARD TO GUIDE THEM; BECAUSE YOU CAN'T SEE THEM. TXWY A4 INTXN IS ABOUT 1/2 WAY DOWN RWY 10L/28R; A POINT OF CRITICAL OP IN DEP OR LNDG ROLL; AND THAT RWY IS USED BY MANY ACR ACFT. YOU CANNOT TELL A PLT HAS TAXIED THE WRONG WAY UNTIL THE LAST FEW FT OF ENCROACHING TOWARDS THE RWY BECAUSE YOU CAN'T SEE THEM. I BELIEVE THIS TO BE A VERY DANGEROUS SIT. WITH OPERATIONAL ACFT SURVEILLANCE EQUIP YOU CAN SEE AT A GLANCE THE POS OF ALL ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE NEW PARKING GARAGE BEING BUILT IS THE VISUAL OBSTRUCTION BLOCKING PORTIONS OF TXWY A; BTWN TXWY A4 AND TXWY A3; ADJOINING GA PARKING. ALTHOUGH THE PARKING GARAGE IS 7 STORIES TALL; AND THE OLD TWR IS BTWN 7 AND 8 STORIES; IT IS THE ADDITION OF THE ELEVATOR SHAFTS ON THE PARKING GARAGE THAT ARE THE VISUAL OBSTRUCTIONS. THE NEW TWR CONSTRUCTION; LOCATED TO THE E OF THE NEW PARKING GARAGE; IS PROJECTED FOR COMPLETION DEC/99; 1 MONTH EARLY. ANALYST ASKED IF THE ATIS ADVISES ACFT IN THE REDUCED VISUAL AREA THAT PORTIONS OF THEIR TAXI RTE MAY NOT BE VISIBLE FROM THE TWR; THE CTLR ADVISED NO. THE CTLR STATED THAT THE TOUCHDOWN AREA FOR RWY 28R IS VISIBLE FROM THE OLD TWR LOCATION. THE ASDE IS DOWN FOR RELOCATION INTO THE NEW TWR AND BEING INSTALLED WITH SYS UPGRADES.