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The Hindu Explains | What are the concerns around the ‘engine failure’ of a Boeing 777, and why is the aircraft maker under scrutiny?

The damaged starboard engine of United Airlines flight 328, a Boeing 777-200, is seen following a February 20 engine failure incident, in a hangar at Denver International Airport in Denver, Colorado.   | Photo Credit: NTSB

The story so far: Regulatory moves have come into effect following an “uncontained engine failure” on a United Airlines Boeing 777 during a scheduled domestic flight in the United States. Dozens of Boeing 777 aircraft with a Pratt and Whitney engine variant have been grounded and subjected to further checks.

What happened to the United Airlines flight?

On February 20, 2021, Flight UA 328, from Denver to Honolulu, with over 200 passengers and 10 crew had just departed and was in the initial climb phase, when the inlet on the right turbofan engine, a Pratt and Whitney PW4077 build, separated in what is technically known as an engine failure event. The crew stopped the climb, levelled off the aircraft, and declared an emergency. The plane touched down safely within 25 minutes of take-off.

The engine failure was a dramatic event with many eyewitnesses on the ground, as debris rained down on some neighbourhoods under its flight path. There were police reports of the debris field extending to over one nautical mile. This is being investigated by the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB). Some of the passengers also filmed the remains of the engine wobbling on the engine pylon in a fiery blaze. The FAA and the NTSB have determined that there was damage to the engine and the fuselage of the plane (a machine a little over 26 years old) as well as an inflight engine fire. The initial examination has shown up two stressed and fractured blades.

How common is an engine failure?

Given the technological advances made by engine manufacturers, the modern jet engine seldom fails, says a senior Boeing 777 pilot. Statistics show that the number of inflight engine shutdowns are very low in this day and age, says another senior Boeing 777 pilot. Nevertheless, there have been events. In recent examples, on February 26, a Rossiya cargo Boeing 777 flight on the Hong Kong-Moscow-Madrid sector had an engine electronic control issue in one of its General Electric (GE) engines while it was about to land. The plane touched down in Moscow without any further eventuality.

In 2018, a United Airlines Boeing 777 flight had a fan blade fracture. Some of the blade debris impacted the fuselage, but the aircraft was safe. In the same year, engine failure on a Southwest Boeing 737 flight caused fragments to rupture a part of the fuselage. A passenger lost her life.

In 2017, an Air France Airbus A380 had an extreme engine failure that left behind only a metal stub. Experts determined this to be an “uncontained failure” after much investigation involving multiple agencies as the debris was scattered over the icy expanse of Greenland.

In December 2020, a Japan Airlines 777 suffered fan-blade damage but made a safe landing.

However, the most dramatic incident occurred in November 2010, when a Qantas Airbus A380 with 459 passengers and crew on a scheduled flight from London to Sydney via Singapore experienced engine failure in one of its four Rolls-Royce Trent 900 engines just after leaving Singapore. At that time, it was the first-of-its-kind incident involving the Airbus A380. After the aircraft returned to Singapore safely, inspections showed that a turbine disc in the number two engine had disintegrated, in turn damaging a part of the wing, fuel system, landing gear and destroying some of the flight and engine controls. It was eventually traced to a manufacturing defect in an oil pipe. The aircraft underwent extensive repairs and was returned to service. The case also led to more detailed checks on the Airbus A380.

Engine failures can occur at any stage in the flight, says the senior 777 commander. Take off and the climb-out are critical phases as the aircraft is heavy due to the fuel load and also gathering momentum to attain sustained flight, he adds.

What are the kinds of engine failure?

Engines are designed to handle issues such as damaged blades and bird hits. Engine failure, in general, is classified as contained or uncontained. In the first, even if engine components disintegrate or separate, they remain within the engine, or as designed by the engine manufacturer, exit the engine case.

In the second, there is a “random, violent event, and one that is usually beyond the design parameters”. Damaged components can pose a danger to the aircraft, its fuselage, and in some cases, as in a four-engine aircraft, threaten the adjacent engine. They can affect crucial flight and engine control systems and, in turn, passengers and crew and also people on the ground. The senior 777 commander says pieces could also rupture other surfaces or hydraulic lines or fuel lines leading to fuel or hydraulic-related failures.

The second senior 777 pilot says there are minor failures such as surge or stall conditions that may not require the engine to be shut down but run at a lowered power setting. There can also be a flame-out, where the engine shuts down but is not necessarily damaged and may be restarted while the aircraft is still in flight. Engine damage or an engine fire is where the engine must be shut down as soon as possible, he adds.

The first senior 777 pilot says manufacturers have specific checklists that systematically guide pilots to safely handle the situation. Carrying these out can be intricate and pilots need to ensure good coordination and decision-making. The priority is to continue flying the aircraft safely. Only after this is established, can the pilots start with the checklists.

There is the “engine limit surge stall” checklist for contained failure and “engine severe damage separation” or the “fire engine” checklists for uncontained failure, says the pilot.

The second senior 777 pilot says there are also lists related to the fuel or hydraulics, then an overweight landing checklist, or if the fire is contained, then a fuel jettison checklist.

Pilots, he says, are rigorously trained to handle such scenarios. The training starts with thorough system knowledge taught to them in ground school, followed by repetitive simulator training, where these emergencies are simulated. In addition, pilots are also checked for their proficiency in the flight simulator every six months to ensure that the highest standards are maintained, he adds.

Pilots, says the senior 777 commander, are checked and assessed by senior trainers; even the senior trainers go through these checks at specified requisite intervals. On the 777, pilots are trained to fly it back safely on a single engine. Though it does require skill and concentration, it is perfectly possible, adds the senior 777 pilot.

Every engine manufacturer has published the limits which should not be crossed and pilots have to ensure this. The pilot says the United Airlines incident was handled well, adding that it takes great skill and training to handle such a case of severe engine failure and bring the aircraft back safely.

The first senior 777 pilot says the Boeing 777 has an EICAS, or the Engine Indicating and Crew Alerting System, which assists the crew in fault-finding and makes recommendations on what must be done. So, a very thorough assessment is done on the steps and on how to go about them.

After the United Airlines incident, what are the regulatory measures now?

On February 21, Boeing, the aircraft manufacturer, said it has recommended “suspending operations of the 69 in-service and 59 in-storage 777s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol”. This will now affect 69 planes in service and 59 craft in storage.

In an initial statement, FAA administrator Steve Dickson said the FAA after consulting its experts, had issued an Emergency Airworthiness Directive that would need immediate or enhanced inspections of Boeing 777s with certain Pratt & Whitney PW4000 engine variants. The order affected ANA, Japan Airlines, Asiana Airlines, Korean Air, EgyptAir, and Vietnam Airlines. In an Emergency Airworthiness Directive issued on February 24, the FAA now requires U.S. operators to conduct immediate thermal acoustic image (TAI) inspection of the engine blades for the PW4074/D, 4077/D, 4084/D and 4090/-3 engines. It says TAI technology can detect cracks on the interior surfaces of hollow fan blades, or in areas that cannot be seen during a visual inspection. The hollow fan blades are unique to this engine model. The FAA is to review the results and set new engine and aircraft inspection intervals. Cracks in the blades can be a problem and airlines use technologies such as ultrasound to detect such fissures beneath the blade surface.

So far, Japan, New Zealand and the United Kingdom have stopped operators using the Boeing 777 with this engine variant from entering their airspace.

 

Will the directive affect India?

Flag carrier Air India, which is the only Boeing 777 operator in India, uses GE-manufactured engines (GE90). The two new Boeing 777 aircraft for the transportation of India’s VVIPs are also unaffected as they, too, have GE engines.

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