This paper extends a random preventive maintenance scheme, called repair alert model, when there exist environmental variables which effect on system lifetimes. It can be used for implementing age-dependent maintenance policies on engineering devices. In other words, consider a device which works for a job and is subject to failure at a random time X, and the maintenance crew can avoid the failure by a possible replacement at some random time Z. The new model is flexible to including covariates with both fixed and random effects. The problem of estimating parameters is also investigated in details. Here, the observations are in the form of random signs censoring data (RSCD) with covariates. Therefore, this paper generalizes derived statistical inferences on the basis of RSCD albeit without covariates in past literature. To do this, it is assumed that the system lifetime distribution belongs to the log-location- scale family of distributions. A real data set is also analysed on basis of the results obtained.

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