SAN ANTONIO: The FAA may not approve of a TWA pilot's newest safety technique, but it's hard to quarrel with success. Late Tuesday, when Flight 199 was 15 miles southwest of the San Antonio International Airport, a cockpit light indicated that the tail stairwell door of the Boeing 727 had fallen open about two feet. (The 70 or so passengers would have noticed even faster but for a bulkhead between the gaping hole and their compartment.) Incredibly, the crew wasted no time in selecting one of its number to fix the problem. "They did use a rope and tied it around this individual," said airport spokeswoman Linda Wasserman. "Just for safety, they kept a hold of him by this rope and he did reach out and pull this door closed." A few passengers later revealed that seat belts were used to tie the door shut. So far, neither TWA nor Boeing have commented.