UPS flies -100's with Rolls Royce Tays in all 3 positions. They re-engined their entire -100 fleet (49) to meet stage 3 requirements. The Tays put out 15,000 lbs each which is equivalent to -17'JT8D's. they also burn 25% less gas. Down low the Tays are great, but they run out of air by FL220, overall, a real nice mod.