It took an unexplained air disaster to help this South Asian country shift from dictatorship to democracy. The Pakistani Air Force plane had been in the air less than five minutes when it exploded on Aug. 17, 1988, killing all 30 passengers, including Pakistan’s president, a U.S. ambassador and the systems of power that had been ruling Pakistan for 11 years. President Muhammad Zia-ul-Haq, 64, was returning from Bahawalpur, almost 400 miles south of the capital city, Islamabad, where he’d been paying his respects to a recently deceased American nun. With him on the plane were the U.S. ambassador to Pakistan, Arnold Raphel, and the top American military adviser to the region, Gen. Herbert M. Wassom. Most of Zia’s top commanders were also killed. | 