ETOPS — how twins were allowed over oceans

ETOPS stands for Extended-range Twin-engine Operational Performance Standards, and it answers one question: how far from a diversion airport may a two-engine aircraft fly? Before it existed, the answer was 60 minutes — which effectively barred twins from crossing oceans and made three or four engines mandatory for long-haul.

As engines became dramatically more reliable, regulators extended the limit: 120 minutes, then 180, then beyond. An ETOPS-330 aircraft may fly up to five and a half hours from the nearest suitable runway on one engine. The Boeing 767 pioneered the regime in the 1980s; the 777 and A350 perfected it.

The consequence reshaped aviation. Two engines burn less fuel than four, so once twins were allowed everywhere, the four-engine airliner became economically indefensible. The A340, the 747 and ultimately the A380 were all killed by a rule change, not by a better aircraft. Pilots have a grim joke about the acronym: Engines Turn Or Passengers Swim.