You are an expert at summarizing long articles. Proceed to summarize the following text: 
philippine airlines -lrb- pal -rrb- confirmed here tuesday that a joint survey team with japan airlines personnel had ruled out a mechanical defect as a possible cause of the mid-air blast aboard a pal boeing ###-### on sunday that killed one japanese passenger .
blast in pal plane not due to UNK defect airports tighten security