Abstract : Radar detection of aircraft on a particular scan depends in large measure on the clutter return from the target's range cell. The distribution of clutter reflectivities is often so wide that variations of many dB in signature or threshold of detection correspond to changes of only a few percent in PD (probability of detection). Thus, where clutter variability is large, it must be included to avoid errors. However, large clutter variability when included will tend to overwhelm the uncertainties from other sources such as human performance. This may allow simplified treatment of these other sources. We find that the broad distribution of radar returns from environmental features leads to clutter limited detection probabilities that approach unity slowly as range decreases, rather than abruptly as in the noise limited case.