The assure vs. insure vs. ensure has been discussed frequently on this site. But I came across a New Yorker article, which has excellent editing, which uses "insure" when it seemingly should have used "ensure." Here's the sentence in question, talking about a jumpshot in basketball:
The shooting elbow travels upward on a narrow path within inches of the torso, to insure an efficient and steady glide; the other arm folds over, framing the face of the shooter.
I hesitate to second guess the editors at the New Yorker, but shouldn't that be "ensure"?