B757-200 FIRST OFFICER REPORTS LOW ALTITUDE ALERT RECEIVED FROM ATC DURING NIGHT VISUAL APPROACH TO RUNWAY 11L AT TUS.

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ON A NE ARR TO TUS WHILE ON VECTORS; WE WERE GIVEN A DSCNT TO 7000 FT FOLLOWED BY A FURTHER DSCNT TO 5000 FT. WHEN WE CALLED THE ARPT IN SIGHT WE WERE CLRED FOR A VISUAL APCH TO RWY 11L AND TOLD TO SWITCH TO TWR. THE ILS WAS OTS; BUT FOR SITUATIONAL AWARENESS WE HAD LOADED THE APCH IN THE FMC; EXTENDED FROM THE OM POCIB AND ALSO PUT CALLS ON THE FIX PAGE. AT 5000 FT WE INITIATED THE TURN TO FINAL; HALF WAY BTWN POCIB AND CALLS AND APPROX 2.5 NM E OF THE EXTENDED CTRLINE AT ABOUT 180 KIAS. THE CAPT (PNF) THEN SELECTED 4600 FT IN THE ALT WINDOW AND WHILE IN THE TURN APCHING 4900 FT; THE TWR ABRUPTLY SOUNDED A LOW ALT ALERT AND STATED THAT MVA IN OUR AREA WAS 5300 FT. I WAS STARTLED AND I IMMEDIATELY DISCONNECTED THE AUTOPLT AND CLBED BACK UP TO 5000 FT. WHILE CONTINUING THE L TURN AND NOW SLIGHTLY NOSE HIGH; I ALSO MOMENTARILY LOST SIGHT OF THE RWY; OVERSHOT AND ROLLED OUT POINTING SLIGHTLY L OF CTRLINE. THE CAPT INFORMED THE TWR THAT WE HAD BEEN CLRED FOR A VISUAL APCH; TO WHICH THE CTLR DID NOT RESPOND. AFTER DETERMINING THAT WE NOW WERE HIGH ON THE PAPI; WE RESUMED OUR DSCNT TOWARDS THE RWY AND LANDED. IN HINDSIGHT LOOKING AT THE APCH PLATE; I BELIEVE WHAT MAY HAVE CAUSED THE PROB IS THE LOCATION OF A 4260 FT ANTENNA JUST W OF THE APCH PATH WHERE WE INITIATED OUR TURN TO FINAL. I HAD NOT NOTICED THE LOCATION OF THE ANTENNA WHILE BRIEFING THE APCH. I AM ALSO GUESSING THAT WITH US BEING AT APPROX 180 KIAS AND HEADED DIRECTLY TOWARDS THE ANTENNA MAY HAVE TRIGGERED AN ALARM IN THE TWR TO WHICH THE CTLR HAD TO RESPOND. IT WOULD HAVE BEEN NICE; HOWEVER; IF THE CTLR HAD GIVEN US A CLR OF CONFLICT CALL BECAUSE NEITHER THE CAPT NOR MYSELF AT THAT POINT UNDERSTOOD WHY WE RECEIVED THE ABRUPT; DISRUPTIVE AND ALARMING CALL FROM THE TWR. IT HAD BEEN OVER 1 YR SINCE I HAD FLOWN INTO TUCSON AND THE LESSON I LEARNED IS TO ALWAYS SLOW THINGS DOWN EARLIER; BECAUSE THAT WILL GIVE ME MORE TIME TO DEAL WITH UNEXPECTED CIRCUMSTANCES IF AND WHEN THEY OCCUR.