AN UNPLANNED ROOF FALL WAS DISCOVERED DURING A PRESHIFT EXAMINATION. THE FALL OCCURRED IN THE NO. 1 ENTRY OF TG 101, BETWEEN X-CUTS 22 AND 23. THE FALL AREA IS APPROX 19 FT WIDE, 50 FT LONG AN D 10 FT HIGH. THE FALL DID NOT OBSTRUCT TRAVEL THROUGH THE TAILGATE ENTRY, NOR DID IT OBSTRUCT VENTILATION.