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Aircraft or missiles are flown for missions of varying durations. Data are collected at the end of each mission which indicate the mission duration and whether the equipment failed. The data are considered as multiple s-independent grouped censored samples with failure times unknown. The underlying failure model considered is the 2-parameter Weibull distribution. Maximum likelihood estimates are derived. The exponential distribution is used for comparison. Monte Carlo simulations are used to compare s-efficiency of estimates for grouped data with estimates if failure times were known. The asymptotic variance-covariance matrix was computed for the sampling conditions studied and was used to obtain lower s-confidence bounds on the system reliability.