Abstract  In domains such as nuclear power, industrialprocess control, and space shuttle missioncontrol, there is increased interest inreducing personnel during nominal operations. An essential element in maintaining safeoperations in high risk environments with this`on-call' organizational architecture is tounderstand how to bring called-in practitionersup to speed quickly during escalatingsituations. Targeted field observations wereconducted to investigate what it means toupdate a supervisory controller on the statusof a continuous, anomaly-driven process in acomplex, distributed environment. Sixteenshift changes, or handovers, at the NASAJohnson Space Center were observed during theSTS-76 Space Shuttle mission. The findingsfrom this observational study highlight theimportance of prior knowledge in the updatesand demonstrate how missing updates can leaveflight controllers vulnerable to beingunprepared. Implications for mitigating riskin the transition to `on-call' architecturesare discussed.