The Boeing 767-400ER is an unpopular but exciting variant. Effectively designed to replace old tri-engine equipment, just 38 aircraft were built. The first flight was nearly 25 years ago, in October 1999. Aside from one aircraft in Bahrain, all are operated by Delta Air Lines (21) and United Airlines (16). I have fond memories of flying the -400ER with both US operators, and it remains among my favorite widebodies.