The 727 has landing flaps of 30 and 40. Early in the operation of the airplane a UAL flight made a very hard landing at KSLC that is resulted in an accident:
https://en.wikisource.org/wiki/Aircr...nes_Flight_227
One of the conclusion was with 30 flaps the high descent rate approach might have been arrested. Because of this accident 30 flaps became the standard landing flap. Some airlines even blocked out 40 flaps.