What Happens When a Plane Engine Fails? What This Week's United Diversion Shows

Early Monday morning, a United Airlines flight from Washington Dulles to Amsterdam turned back over the Atlantic after one of its two engines developed a problem — exactly the situation most people picture when they think about what could go wrong on a long flight over water. The plane landed safely in Newfoundland a few hours later, and every one of the 131 people on board walked off normally. It's a good moment to look at what actually happens when an airliner loses an engine, and why the outcome here was never really in doubt.

What happened on United Flight 946

United Flight 946, a Boeing 767-300 built in the early 1990s, departed Dulles for Amsterdam on the night of October 11 with 122 passengers and nine crew aboard. About 370 nautical miles east of St. John's, Newfoundland, cruising at 37,000 feet, one of its two Pratt & Whitney engines developed a problem, according to The Aviation Herald, via AeroCorner. The crew declared an emergency, descended to 26,000 feet, and turned the aircraft back toward Newfoundland.

The jet landed safely at St. John's International Airport at 3:29 a.m. local time, and passengers disembarked normally, the Canadian Press reported. United arranged overnight hotel rooms and flew out a replacement aircraft to carry passengers on to Amsterdam. The airline has described the cause only as an "engine issue" and hasn't said which engine was affected or whether it was shut down in flight.

Why a twin-engine jet doesn't need both engines

This is the part that surprises a lot of nervous flyers: a modern twin-engine airliner is designed, tested, and certified to fly safely on a single engine — including over open ocean, for hours at a time. That capability has a name, ETOPS (Extended-range Twin-engine Operations Performance Standards), and it's the whole reason airlines are allowed to fly twin-engine jets like the 767, A330, or 787 across the Atlantic and Pacific instead of routing them near land.

To earn an ETOPS rating, an aircraft type has to prove its systems can keep running for a set number of minutes on one engine alone, with margin to spare. Depending on the aircraft, that rating now stretches past 300 minutes — well beyond what most diversions actually need. Ratings have climbed steadily since the standard was introduced in the 1980s: from 120 minutes in 1985, to 180 in 1988, up to 330 minutes for some 777s and 370 for the A350. A plane doesn't need both engines running to be safe. It needs to be able to reach a runway on one, and that's exactly the standard it's built and tested to meet.

How often does this actually happen?

Engine problems serious enough to divert a flight are uncommon, but at the scale of global aviation they're not vanishingly rare either. One widely cited estimate puts in-flight jet engine failures at roughly once every 375,000 engine flight hours, which — given that more than 27,000 flights depart U.S. airports every day — works out to something happening somewhere in the system every few days. The reason this rarely makes headlines is also the reason it rarely matters much to the passengers involved: the aircraft is built with exactly this scenario in mind, and the standard outcome is what happened on UA946 — a controlled diversion and a safe landing.

What a diversion like this actually looks like from your seat

If you'd been on this flight, here's roughly what you would have experienced: a change in engine sound or vibration, an announcement from the flight deck that the crew is diverting as a precaution, a noticeably longer descent than usual, and then a normal landing — followed by the inconvenience of an overnight delay and a rebooked flight the next day. That's genuinely the whole story for the vast majority of these events. The "emergency" you might read about in a news headline is a procedural step that gives a diverting aircraft priority handling from air traffic control. It isn't a sign that the landing itself was ever in doubt.

Putting it in perspective

Stories like this travel fast because "engine failure" sounds dramatic in a headline. But the underlying event — one engine of two developing a problem, and the aircraft completing a safe, unremarkable landing on the other — is close to a textbook case of the redundancy commercial aviation is built around. Nobody was hurt. The system worked exactly as designed, from the engineering of the aircraft, to the training of the crew, to the airline's plan for getting passengers to a hotel and onward the next morning.

If the sounds and sensations of flight are the part that gets to you — an unfamiliar engine note, a change in vibration, a noise you've never noticed before — it often helps to know what's normal before you're in the air wondering about it. Our Sounds Decoder guide walks through the everyday noises a flight makes, from engines to hydraulics to landing gear, so an unfamiliar sound is a lot less likely to catch you off guard.

Frequently asked questions

Can a plane actually fly safely with only one engine?

Yes. Twin-engine airliners are certified under ETOPS rules specifically to fly for hours on a single engine if needed, including on long routes over open ocean. This isn't an emergency workaround — it's a standard part of how these aircraft are designed and tested before they're ever approved to fly a route.

Does an engine problem mean the plane could crash?

No. Commercial jets occasionally lose power from one engine, and the near-universal outcome is a precautionary diversion and a normal landing, exactly as happened with UA946. Both the aircraft's systems and its pilots' training are built around this exact scenario.

Why did the crew declare an emergency if it wasn't a crisis?

Declaring an emergency is a procedural tool, not a sign of danger. It gives air traffic control the authority to clear airspace and runways for the aircraft and prioritize its landing, the same way an ambulance gets priority at an intersection whether or not the situation turns out to be serious.

How often do engine problems like this happen?

Not often, but not never. Estimates put in-flight jet engine failures at roughly once every 375,000 engine flight hours, which across the scale of global aviation adds up to an occasional event somewhere in the system. Because aircraft are built to handle it, these events are overwhelmingly non-events for passengers: a diversion, an inconvenience, and a safe landing.