Cold Death by Kenneth Robeson

Doc could easily have freed himself. His enormous lung capacity made him as nearly an amphibian as it is possible for any man to be. As the plane cracked up and sank, Doc had absorbed enough air to keep him alive for several minutes.

Instead of pulling himself out he let go his supporting hold. Scraggs's first scream died in a gasping gurgle. Doc groped his way to the confined space where the little man was trapped. Gripping fingers fastened on a bony ankle.