Quadjet airliners are among the most striking aircraft found in the skies. They represent a stark contrast compared to the twin-engine aircraft of varying shapes and sizes that constitute the majority of commercial planes today.

Yet, does their design mean that four-engine aircraft such as the Airbus A380 are better equipped for engine failures? Also, would such an aircraft be able to fly under the power of just one engine?

What might cause an engine to fail?

Engine failures can occur as a result of one or more of a number of reasons. The result can generally be categorized as either a contained engine failure or an uncontained engine failure. A contained engine failure is where something goes wrong in the engine, but it all remains in place inside the engine casing. Power supply issues are an example of a failure in which the engine remains intact.

Meanwhile, an uncontained engine failure is where one or more components break away from the engine. These occurrences are visually far more conspicuous and can make for an alarming sight for passengers seated near an aircraft's wing. In a worst-case scenario, there is even a risk that the whole engine can fall apart to the ground below.

For instance, An Qantas A380 sustained an uncontained engine rotor failure (UERF) of its number two engine while climbing out of Singapore Changi in November 2010.

"A Rolls-Royce Trent 900. Debris from the UERF impacted the aircraft, resulting in significant structural and systems damage. The flight crew managed the situation and, after completing the required actions for the multitude of system failures, safely returned to and landed at Changi Airport." - Australian Transport Safety Bureau (ATSB).

Despite all these possible causes, it is improbable that, on a four-engined aircraft, that all but one engine would fail. But what if it did? Let us consider the impact that this would have on the aircraft.

Can an A380 operate on a single engine?

A plane has three different possible forms of movement while in the air: ascending, descending, and level flight. An A380 has four engines, each of which provides around 356.81 kN (80,210 lbf) of thrust. These four engines' combined thrust equates to around 1,427.24 kN (320,840 lbf), which powers the aircraft to lift it into the sky.

To maintain level flight with a single engine, its thrust of 356.81 kN (80,210 lbf) would need to produce sufficient power to maintain a cruise speed of Mach 0.85 (903 km/h; 488 knots).

However, this speed is impossible for a single-engine to provide. As a result, the aircraft will start to slow and drag, losing altitude. In this instance, it would be of utmost importance to the crew to restart the other engines.

If not, they would need to promptly find a suitable nearby airport to divert to for an emergency landing. This could prove particularly difficult with the A380, which can only fly in and out of certain airports due to its sheer size.

On the whole, flying an A380 with the power of just one engine seems a precarious prospect. Indeed, even flying the A380 under the power of two engines is something that Federal Aviation Regulations state should only be done in extreme cases.

Other quadjets with multiple failures - BA9

Despite many airlines already retiring the Airbus A380, it is still a relatively young aircraft. However, looking further back in history at the Boeing 747 against which it was designed to compete, one can find instances of multiple engine failures involving the 'Queen of the Skies.'

In June 1982, a 747 operating British Airways flight BA9 from London to Auckland encountered a thick cloud of volcanic ash near Jakarta, Indonesia. Back then, crews had little experience in dealing with such a rare event.

Unfortunately, flying through a thick volcanic cloud of ash is more like being in a thick sandstorm than a snowstorm. Instead of ice that melts in the engine, the ash particles became more like sandpaper, jamming up components. This caused all four engines to fail and the aircraft to become the world's biggest flying glider.

The captain of the Galunggung Glider, Eric Moody, is famously quoted as having then announced:

"Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress."

The plane glided onwards for 15 km per kilometer of altitude lost, slowly descending in preparation for a water landing. Once out of the ash cloud, the flight engineer was able to restart a single-engine that was enough to power the aircraft back up to a height of 12,000 feet.

Shortly afterward, the crew succeeded in restarting the other three engines, but one failed again. In the end, the aircraft was able to return to Jakarta. It landed there safely despite the ash having rendered the windscreen almost opaque.

KLM flight 867

Before the 1980s were over, a similar incident would befall a KLM Boeing 747-400 flying from Amsterdam to Tokyo via Anchorage, Alaska. In December 1989, KLM flight 867 flew through a cloud of ash from Mount Redoubt. This had erupted the previous day. Once again, this led to all four of the aircraft's engines failing.

In this instance, the aircraft had to descend for more than 14,000 feet before its crew could restart its engines. Having succeeded in doing so, KLM flight 867 made a safe landing back in Anchorage.

A National Transportation Safety Board (NTSB) report concluded:

"Inadvertent encounter with volcanic ash cloud, which resulted in damage from foreign material (foreign object) and subsequent compressor stalling of all engines. A factor related to the accident was: the lack of available information about the ash cloud to all personnel involved."

The incident resulted in more than $80 million of damage to the aircraft, which had to have all of its engines replaced. However, at the end of the day, the fact that, on both these occasions, the 747s in question landed without any loss of life despite losing all engine power far outweighs these costs in importance.

Altogether, these cases prove that a quadjet can land safely with fewer engines. Airbus once controversially touted the benefits of having four engines on long-haul flights after the introduction of the A340. Its advert once stated, "If you're over the middle of the Pacific, you want to be in the middle of four engines."

Airbus also soon launched its "4 engines 4 long haul" campaign." This was a little dig at Boeing's 767 and 777 jets amid their popularity on transoceanic missions. Unsurprisingly, these promotions were pulled as they implied that twin engines weren't as safe as quadjets.

Still, the chances of an A380 being left with one engine midflight are incredibly small. Flight crews would undoubtedly be keen to land the plane safely as soon as possible, even if one engine goes.

What are your thoughts about the prospects of an Airbus A380 operating on one engine? What do you make of the overall factors involved across the industry in this field? Let us know what you think of the situation in the comment section.

Sources: ECFR, ATSB, NTSB