The McDonnell Douglas MD-11 is the most common trijet flying today (sort of). At least that’s true if one ignores the fact that the MD-11s are currently grounded following the 2025 UPS crash, and UPS has hurriedly retired its jets while FedEx wants to start flying them again by the end of May 2026. The aircraft is notoriously difficult to land, and it is easy to point to its tail engine (engine #2) and assume that is the issue. But the truth is more complicated than that, with its difficulty coming from efficiency-led redesign more than the engine itself.