 In 1987 and 1988, NASA conducted atmospheric ozone-layer depletion studies using two piloted NASA aircraft, a modified Douglas DC-8 jetliner and a Lockheed ER-2, a civilian version of the U-2 spy plane.However, operating the ER-2 over Antarctica, where ozone depletion took place, was regarded as risky, since if the pilot had to bail out, survival was unlikely.In addition, the ER-2 had a ceiling of 20 kilometers (65,000 feet), while ozone depletion takes place at 30 kilometers (100,000 feet), and the ER-2 could not stay aloft long enough to study ozone changes during a full day-night cycle.