The engine shutdown was determined to be caused by severe pogo oscillations measured at a strength of 68 g and a frequency of 16 hertz, flexing the thrust frame by 3 inches (76 mm). The vehicle's guidance system shut the engine down in response to sensed thrust chamber pressure fluctuations. Pogo oscillations had been seen on previous Titan rockets, and also on the Saturn V during Apollo 6, but on Apollo 13, they were amplified by an unexpected interaction with turbopump cavitation.