Really, it's okay if your airliner loses an engine

Over the weekend, both engines on a Singapore Airlines Airbus A330-343 lost power while cruising at 39,000 ft.

The crew was able to restart the engines but not before the aircraft lost 13,000 feet of altitude.

Fortunately, no one was injured, and the flight continued safely to its destination. 

Airliner do sometimes lose power to both engines.

But it's a rare occurrence - these days, virtually unheard of. What does happen with slightly greater frequency is the loss of a single engine.

Most of the time, the pilot diverts to an emergency landing location, and no one is injured.

However, there have been occasions in which pilots chose to fly on to their destination instead of turning around.

In 2005, British Airways Flight 268, routed to London, lost one of its four engines while taking off from Los Angeles International Airport.

Instead of returning to LAX, the pilot and his Boeing 747-400 continued toward Heathrow Airport. But because of unfavorable winds and operating conditions that caused the plane to burn too much fuel, the jumbo jet didn't have the gas to reach London and made an emergency landing in Manchester.

Long-distance and transoceanic flights have traditionally been flown by three- or four-engine wide-body airliners. This is because when it comes to the engine count on an airliner, aviation thinking dictates that there is safety in numbers. 

But as modern turbofan engines have become more reliable, engine failures have become far less common. As a result, most airlines have turned to twin-engined mini-jumbos that are more fuel-efficient. 

These days, the three-engine airliner has gone the way of the dinosaur, and the four-engine jumbo jets that once dominated the skies are well on their way toward extinction.  

But engine failures do still happen. As terrifying as they may be for many of the passengers, though, losing one engine on a twin-engined airliner like the Boeing 787 isn't as serious as one might think.

When an aircraft is flying without one of its engines, it tends to fly at a lower altitude and work the remaining engine(s) harder. This makes the plane less fuel-efficient and reduces range. However, the vast majority of twin-engine long-haul airliners can perform this maneuver with no significant reduction in capabilities. 

Before a twin-engine airliner is allowed fly long-distance routes over large bodies of water or through uninhabited regions like the Arctic, it must be certified by the Federal Aviation Administration (FAA) for ETOPS or Extended range Twin Operations. 

When an aircraft is certified, part of the assessment is based on the plane's performance when flying on a single engine.

For example, the 787Dreamliner is certified for ETOPS-330. This means that the aircraft can fly routes that take it as far as 330 minutes (five and a half hours) of single-engine flying time from the nearest viable airport.

Other twin-engine airliners, like the Boeing 777, are also certified for ETOPS 330. Airbus' popular A330 has been certified for 180 minutes of ETOPS flying, while the company's coming A350 is currently seeking 420 minutes of ETOPS certification.