<div class="htmlview paragraph">Phased planar array radars represent a class of equipment employing hundreds or thousands of individually steerable radiating and receiving elements.</div> <div class="htmlview paragraph">In the operation of such systems, it is necessary to keep continually ahead of an advancing failure accumulation through maintenance policies geared to replacement-while-in-operation concepts.</div> <div class="htmlview paragraph">Several practical maintenance polices are considered: <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">Immediate maintenance</div></li> <li class="list-item"> <div class="htmlview paragraph">Delayed maintenance</div></li> <li class="list-item"> <div class="htmlview paragraph">Cyclic maintenance</div></li></ul></div> <div class="htmlview paragraph">The effects of these policies on the outage availability are considered and it is shown that each has certain advantages.</div> <div class="htmlview paragraph">Immediate maintenance yields the highest system availability, but requires the continued presence of a moderate size maintenance force. Increasing the number of maintenance crews increases the availability of phased array systems, but the added contribution to satisfactory system states shrinks rapidly with the growth of crews.</div> <div class="htmlview paragraph">Delayed and cyclic maintenance both involve a more leisurely, planned work pace characterized by periods of relatively low service activity, followed by periods of intense activity to restore the system. At the expense of some system availability, these policies require only part-time presence of maintenance personnel and may well be the most attractive alternatives for phased array radar systems possessing some degree of surplus performance.</div>