This study examines users’ perceptions (Capability, Value, Timing, and Acceptance) of an ERP implementation at a major aircraft manufacturing company in the pre-Implementation phase (T1) and the immediate post-Implementation phase (T2), which is referred to in the literature as the Shakedown Phase. Our study is one of only a few that looks at users’ perceptions over time, and that focuses on the Shakedown phase. We obtained 205 T1-T2 matched responses and 120 open ended comments at the post-implementation phase (T2). A comparison of the four key perceptions shows a statistically significant drop for all of the perceptions, except for User Acceptance. This is an interesting finding, implying that users continue to perceive the ERP system as important even though their perceptions regarding capability, value, and timing drop significantly from pre-implementation to post-implementation stage. We further explore the variations in these perceptions across tenure with the company and job profiles.