According to this New York Times article (via Kottke), FedEx launches five mostly-empty jets every night — from Las Vegas, Duluth, Laredo, Fort Myers, and Portland (ME) — all heading for Memphis through various meandering routes. These flying spares often end up diverting mid-flight to deal with package overflows at hubs or with equipment failures on other FedEx flights. Constant diversion sounds like an interesting challenge both for the flight crews and for the dispatchers.