Incident of pain with undetermined etiology in hypobaric chamber operations.

On a routine, low-pressure chamber training flight to 25,000 ft (7,620.0 m/282.4 mm Hg), a subject experienced moderate to severe pain in the right hip while descending through an altitude of 9,500 ft (2,895.6 m/532.9 mm Hg). Standard operating procedures for dealing with such reactions were initiated resulting in the diminishing of symptoms as the chamber was reascended to an altitude of 12,000 ft (3,657.6 m/483.4 mm Hg). The symptoms reappeared upon descent through 7,500 ft (2286.0 m/575.6 mm Hg). After three relief attempts, descent was commenced at a rate of 1,000 ft/min (304.8 m/min), and the subject was asymptomatic at sea level. A subsequent reevaluation flight was scheduled for the following day and produced similar results. Medical evaluation produced no data that could be used to determine the etiology of this reaction that took place under hypobaric conditions.