On Saturday, about five minutes after taking off from Denver International Airport for a flight to Honolulu, United Airlines flight 328 has suffered an uncontained engine failure on its starboard engine. Fragment perforated Wing-body fairing and engine debris rained down over a mile-long area of ​​a Denver suburb, with the nearly intact engine inlet narrowly missing a home.

Following the incident, the Boeing 777-200 immediately returned to Denver and landed safely approximately half an hour after departure. No injuries were reported among the 231 passengers and 10 crew on board the aircraft, or anyone on the ground.

Images of the failure were captured by the passengers of the plane and the observers on the ground. A passenger video which has been widely shared on Twitter shows that the engine is missing most of its nacelle (the housing that contains and protects the engine) and the fire of what is likely a fuel leak. The video and photos from the ground show the engine seems to explode so what smoke trail.

According to a preliminary investigation from the National Transportation Safety Board, two engine fan blades were fractured. While the agency prepares its final report, the FAA requested further inspection of all 777s with similar engines, and United have grounded their 777s using it. Here’s what we know so far about what happened.

What is an uncontained engine failure?

Jet engine failure occurs when parts inside the engine fragment or disintegrate while the engine is running. In the event of a contained fault, the broken parts do not pierce the engine nacelle and / or are ejected through the engine nozzle.

In the event of an uncontained failure, the parts explode with such force that they enter the nacelle or destroy it completely. Although less common than contained failures, unconfined failures are much more dangerous. They can be so violent – remember that a jet engine’s turbines spin at an extremely high speed of thousands of revolutions per minute – that parts tear into the plane’s fuselage, causing much bigger problems. or what is sometimes called a catastrophic failure.

For example, on April 17, 2018, an engine on a Southwest Airlines Boeing 737 flight between New York LaGuardia and Dallas Love Field stranded so violently that fragments of the hood damaged the aircraft fuselage, causing explosive depressurization. A passenger was sucked out of the plane and killed.

And in a more notable incident, a United McDonnell Douglas DC-10 was flying from Denver to Chicago on July 19, 1989, when the fan on its rear engine exploded disintegrated. Engine parts cut off the flight control lines in the tail, leaving pilots unable to control the aircraft using conventional methods (instead, the flight crew maneuvered the aircraft by applying alternative thrust to the remaining wing-mounted engines). Although 112 people died in a forced landing in Sioux City, Iowa, 185 passengers and crew survived.

What causes an engine failure?

A few things including undetected wear or engine faults, metal fatigue, mistakes in maintenance, and fuel contamination. External factors like bird strike, ice, or flying through volcanic ash can also cause engine failure.

Failure can also occur due to blade separation, where one of the motor fan blades (it’s the thing that spins in front of the motor) breaks while the motor is running. It can then ricochet through the engine like a bullet, causing extensive damage.

It is also the probable cause here. In his preliminary report published on Sunday, the agency found that two of the engine’s 22 fan blades were fractured. Investigators found one of the broken blades on the ground and the other was encased in the engine containment ring, which is a housing that surrounds the engine (see more images in a NTSB Tweet).

Are the engines tested for failure?

Yes. When new jet engines are designed, the FAA and other aviation safety agencies require that they pass certain safety tests before they are certified. These tests include firing scoops of ice and dead birds into a running engine while it is attached to a ground test stand. Manufacturers also perform a stall test in which a small explosive is attached to one of the blades to separate it from the shaft.

The desired result of all of these tests is contained failure, and engines are designed to deliver this result as much as possible. But sometimes things happen that are beyond the design parameters.

In the passenger video, why is the engine still running?

As a result of the failure, the flight crew reportedly cut off the fuel and supply lines to the engine. So while it may seem like it was still running, it is simply a “windmill” effect of air flowing at high speed through the fan, causing it to spin. It’s like a breeze blowing in a wind turbine.

What type of engine was it?

It was a PW-40077 turbojet engine, produced by Connecticut-based Pratt & Whitney for nearly 20 years. This is only one version of the Pratt & Whitney PW-4000 engine family. The 777-200, a long-range widebody airliner, flies on two of the engines.

The PW-4077 is one of the biggest and most powerful engines on a commercial airliner. Its fan is 9.3 feet in diameter, almost as wide as the passenger cabin of a Boeing 737, and it is almost 16 feet long. It produces a maximum of 98,000 pounds of takeoff confidence, which is equivalent to two engines used on the early models 747.

Boeing doesn’t make engines?

No. Boeing, like Airbus and all other modern aircraft manufacturers, does not design or build jet engines. It builds the aircraft, and airline customers choose an engine made by a third party. Besides the PW4077, the 777 also flies with engines manufactured by Rolls-Royce and General Electric. the General Electric Motors on the new 777X are the biggest business drivers of all time.

How old was the engine?

It is not clear at the moment. Although the 777-200 is 26 years old (which is old, but not old for an airliner), engines are regularly replaced on airplanes during maintenance overhauls.

Have there ever been faults with PW-4000 family engines?

Yes. In December, a Japan Airlines 777 connecting Okinawa to Tokyo suffered damage to the fan blades and lost part of an engine cover shortly after takeoff. The plane returned to Okinawa and landed safely.

On February 13, 2018, another United 777 with PW-4077 engines experienced an uncontained engine failure about 40 minutes from landing on a flight from San Francisco to Honolulu. The NTSB discovered that a fractured fan blade was the cause. The plane also landed safely without any injuries.

Can the 777 drive a single engine?

Yes. Like all multi-engine aircraft, the 777 can still fly safely if one of its engines fails. The plane will fly at a slower speed, of course, and the thrust on just one side of the plane will affect the way it behaves. But pilots are well trained to handle such incidents using the rudder to compensate. Boeing has also designed a flight control system that will automatically adjust the rudder. The pilots are trained for all kinds of engine failures in simulation sessions.

What would have happened if the engine had failed over the Pacific Ocean?

The 777 would have continued to Hawaii or turned back to a West Coast airport, whichever was nearest. It is because it is certified for ETOPS, which stands for Extended Twin Engine Operations. This rating means that a twin-engine aircraft can fly on one engine for as long as it takes to get to an airport. The maximum distance depends on the aircraft, but it can range from 2 hours to 5.5 hours.

And now?

The NTSB will continue its investigation. Depending on its findings, the FAA may issue a airworthiness directive which would order airlines to repair or modify all PW-4000 engines.

Pratt & Whitney said immediately after the incident that he dispatched a team to work with the investigators.

Sunday, the FAA administrator Steve dickson ordered increased inspections of all 777 aircraft equipped with PW4000 engines. “We looked at all the safety data available after yesterday’s incident,” Dickson said in a press release. “Based on the initial information, we concluded that the inspection interval should be accelerated for the hollow fan blades which are unique to this engine model.” The agency followed with a more complete order Tuesday.

In a statement issued the same day, Boeing said it was actively monitoring the investigation. “While the NTSB investigation is ongoing, we have recommended that the operations of the 69,777 in service and 59 in storage powered by Pratt & Whitney 4000-112 engines be suspended until the FAA identifies the protocol for appropriate inspection. “

Also on Sunday, United said he was temporarily deleting 24 of its 777 aircraft powered by PW4000 engines on its schedule. “We will continue to work closely with regulators to determine any further steps and expect only a small number of customers to be disturbed,” the airline said. “Safety remains our top priority, which is why our crews participate in extensive training to prepare for and manage incidents like the UA328.”

And in other developments:

• the Japan Civil Aviation Bureau ordered Japan Airlines and All Nippon Airways to ground its 777 aircraft that use the engines.
• Grant Shapps, UK Secretary of State for Transport, has forbidden 777 affected to enter British airspace.
• Korean Air and Asiana Airlines have stated that they will temporarily ground their plane.

Now playing:
Check this out:

Boeing’s Huge 777X Fold-Wing Jet Completes Its …

3:00