"Columbia"'s main engines were throttled down to 65% thrust to transit the region of Max Q, the point during ascent when the shuttle undergoes maximum aerodynamic stress. This occurred 56 seconds into the flight at Mach 1.06. The wind corrected value was (predicted , limit ). The two SRBs performed better than expected causing a lofted trajectory, and were jettisoned after burnout at 2 minutes and 12 seconds (at altitude, higher than planned). After 8 minutes and 34 seconds Mission Elapsed Time (MET) the main engines were shut down (MECO, at altitude ) and the external tank (ET) was jettisoned 18 seconds later to eventually break up and impact in the Indian Ocean. Two twin-engined Orbital Maneuvering System (OMS) engine burns of 86 seconds duration initiated at 10 minutes and 34 seconds MET and 75 seconds duration at 44 minutes 2 seconds MET inserted "Columbia" into a orbit. This subtle deviation from the original plan of circular went largely unnoticed. In fact it adjusted the spacecraft's orbital period to take account of the 10 April scrub, so that attempts could still be made to use KH-11 reconnaissance satellites to image "Columbia" on orbit. Overall Young commented that there was a lot less vibration and noise during launch than they had expected. However, the sensations accompanying the first firing of the large Reaction Control System (RCS) jets surprised the crew. Crippen commented "it's like a big cannon just fired ... you don't like them the first time you hear them". Young reported that "the entire cabin vibrates ... it felt like the nose was being bent".