ACR X CFTT AFTER GAR DUE TO OCCUPIED RWY.

Narrative

ACR X ON APCH TO RWY 5R AT MEX; IN NIGHTTIME CONDITIONS WITH LIGHT TO MODERATE RAIN FALLING; IT WAS NECESSARY TO EXECUTE A GAR. THE GAR WAS CAUSED BY THE PRECEDING ACFT NOT CLRING THE RWY PRIOR TO OUR TOUCHDOWN. AS THE FO ESTABLISHED THE ACFT IN A CLB; AN ACFT WAS LIFTING OFF OF RWY 5L. WE RECEIVED A 070 DEG HDG FROM THE MEX TWR CTLR. I ACKNOWLEDGED THE CLRNC AND ASKED FOR AN ALT TO CLB TO. WE RECEIVED NO RESPONSE FROM THE TWR CTLR. I MADE 2 MORE REQUESTS FOR AN ALT WITH NO RESPONSE FROM THE TWR. I TOLD THE FO TO CLB TO 12000 FT. FINALLY; TWR GAVE US A CHANGE OF FREQS TO DEP CTL; BUT AGAIN NO ALT. MY MAIN CONCERN AT THIS POINT WAS THE HIGH TERRAIN TO THE E OF THE ARPT. WE ESTABLISHED CONTACT WITH THE DEP CTLR (I BELIEVE THE CTLR WAS THE FINAL CTLR FOR ARRS). THIS CTLR DID NOT KNOW WHO WE WERE; OR WHERE WE WERE. AFTER I TOLD HIM OUR POS HE GAVE US ANOTHER FREQ TO CALL. BY THIS TIME; I HAD TOLD THE FO TO TURN R; BACK TO THE MEX VOR. WE EXECUTED THIS TURN ON OUR OWN TO AVOID THE MOUNTAINS TO THE E OF THE ARPT WHICH WERE OBSCURED BY THE DARKNESS; CLOUDS AND RAIN. WHEN WE ESTABLISHED CONTACT ON THIS NEW FREQ; THE CTLR WAS ALSO SURPRISED TO HEAR FROM US; AND DID NOT KNOW WHERE WE WERE. AT THIS TIME; WE WERE APPROX ON THE 080 DEG RADIAL; AT APPROX 8 MI. AT APPROX 6 MI E OF THE MEX VOR; WE RECEIVED A SQUAWK; AND WERE CLRED TO RWY 5R BY THE MEX 2 TRANSITION. WE LANDED SUCCESSFULLY FROM THIS APCH. THE MAIN AREA OF CONCERN WAS THE CTLR'S APPARENT LACK OF AN ACTION PLAN DURING A RWY 5R GAR WITH AN ACFT SIMULTANEOUSLY DEPARTING RWY 5L. BY USING A CLRNC WITH HDG ONLY; AN UNSUSPECTING CREW COULD CONCEIVABLY FLY THE 070 DEG HDG DIRECTLY INTO HIGH TERRAIN WHILE WAITING FOR THE CTLRS TO RADAR IDENT THE ACFT AND ISSUE A VALID CLRNC. THIS SIT COULD LEAD TO A CFIT ACCIDENT. FINALLY; THE PUBLISHED MISSED APCH FOR RWY 5R WAS UNAVAILABLE TO US DUE TO THE AIRSPACE BEING OCCUPIED BY THE ACFT DEPARTING RWY 5L.