An aircraft flying over a hydrophone in the sea produces a noise signature whose magnitude and duration depend on such parameters as hydrophone depth, water depth, and flight altitude. This signature represents sound reaching the hydrophone in four different ways: via a direct refracted path, via one or more bottom reflections, via the so‐called lateral wave, and via sea scattering. Of these, the refracted path is the most important and easiest to evaluate. Generalized contours for the nearfield of this component are given; in the farfield it is shown that the source in air can be replaced by an equivalent in‐water source having a cosine‐squared directivity pattern and a source level 7 dB less than that of the real source. In a field experiment, a Navy P3 Orion turboprop aircraft flew over hydrophones at two depths in deep water. The brief noise signature, lasting but a few seconds, was found to be accounted for statisfactorily by the refracted sound field. However, under conditions not existing in the field experiment, such as in shallow water, in rough seas, or at very shallow depths, it is conceivable that the other contributors to the total underwater sound field may become important.