The Difference Between Contained & Uncontained Engine Failures

Modern commercial aviation is among the world’s most safety-driven industries. As a result, accidents are thankfully very rare, and, even in the event of engine failures, aircraft can often land safely. When one hears about incidents involving engine failures, they are generally classed as either contained or uncontained. But what is the difference between these terms?

Antonov An-124 Uncontained Engine Failure Getty
Uncontained engine failures are far more visually conspicuous. The fast-moving debris that results from them can be dangerous for people on the ground, and sometimes even those onboard. Photo: Getty Images

Contained engine failures

According to Skybrary, most engine failures that occur on contemporary commercial aircraft are of the contained variety. However, as these incidents are not as visually striking as their uncontained counterparts, it can be the case that one hears about these less often.

An engine failure will generally involve a component or multiple components disintegrating, or becoming separated from the engine’s main body. The difference between contained and uncontained engine failures is where these components end up. Specifically, Skybrary reports:

“This term [contained] means that, even if components disintegrate or separate inside the engine, they either safely remain within the engine case, or exit the engine case via the tailpipe as intended by the engineers.”

SWISS A220-100
Engine failure incidents caused Swiss to temporarily ground its Airbus A220 fleet in 2019. Photo: Getty Images

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The ability for debris to exit via the tailpipe is a common safety feature among aircraft engines. It helps ensure that “the failure of a single engine on a multi-engine aircraft will not present an immediate risk to the safety of the occupants or the aircraft.”

Uncontained engine failures

Meanwhile, the distribution of debris in an uncontained engine failure is far more random and dangerous. In these instances, the damaged components can break away from the engine in any direction, rather than merely exiting via the tailpipe as intended. Some incidents will be so violent that they compromise the structural integrity of the engine casing itself. Skybrary states:

“An ‘uncontained’ engine failure is likely to be a violent one, and can be much more serious because engine debris exits it at high speeds in other directions, posing potential danger to the pressurized aircraft structure, adjacent engines, the integrity of the flight control system and, possibly, directly to the aircraft occupants.”

The Difference Between Contained & Uncontained Engine Failures
A United Airlines Boeing 777 experienced an engine failure after departing Denver yesterday. Photo: @speedbird5280 (Hayden Smith) via Instagram

These incidents can also pose significant danger to people and property on the ground if larger debris falls from altitude. However, although these incidents must make for an incredibly alarming sight for window-seat passengers near the affected engine, they will, more often than not, also end with a safe landing.

Two similar incidents yesterday

In an incredible coincidence, yesterday saw debris from two separate aircraft fall from the sky after departure. The first saw fragments from a Longtail Aviation Boeing 747-400F fall onto a Dutch village following an engine failure after it departed from Maastricht, causing injuries and property damage on the ground.

Then, later on, a Honolulu-bound United 777 suffered a spectacular engine failure after departing Denver. It landed safely, but not before large pieces of engine casing had fallen into gardens and parks in the district of Broomfield. The NTSB is said to have dispatched a team to examine the debris.

What do you make of the incidents yesterday? Have you ever been on a flight that has experienced either kind of engine failure? Let us know your thoughts and experiences in the comments.