FOS Instrument Science Report #109 "FOS Calibration Plan for Cycle 4" by A. Koratkar, C. Keyes, A. Kinney, I. Evans, and C. Taylor Abstract excerpted from the report: This instrument science report describes in detail the Cycle 4 calibration program for the Faint Object Spectograph (FOS). A summary description of each program is given that includes proposal identification; estimated spacecraft time' primary targets (if any); detectors, apertures, and spectral elements used; and target acquisition techniques (if required). Also provided are the program abstract and scientific justification, a description of the observations, a summary of the primary program objective, and a listing of prerequisites and special requirements. Companion FOS Instrument Science Report CAL/FOS-108 provides similar information for the Servicing Mission Orbital Verification (SMOV) FOS Calibration program. These two documents provide the complete description of all calibration programs deemed necessary to provide an inital working calibration of the FOS in the post-COSTAR era. For more information, please contact the above authors.