The Federal Aviation Administration on Tuesday ordered airlines in the United States to ground planes with the type of engine that blew apart after takeoff from Denver this past weekend until they can be inspected for stress cracks.
The FAA's order applies to U.S. operators of airplanes equipped with certain Pratt & Whitney PW4000 engines, which are used solely on Boeing 777s. Before the planes can fly again, operators must conduct a thermal acoustic image inspection of the large titanium fan blades at the front of each engine.
The technology can detect cracks on the interior surfaces of the blades that can't be seen by the naked eye, according to the order.
Pratt & Whitney said in a statement that the inspection process will involve having fan blades shipped to them so they can perform the TAI inspection. The company said there are approximately 125 Boeing 777 aircraft with its PW4000-112” engine
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"Pratt & Whitney is coordinating all actions with Boeing, airline operators and regulators. The safe operation of the fleet is our top priority. Pratt & Whitney commends the flight crew operating United Airlines flight 328 for their professionalism. Further investigative updates regarding United Airlines flight 328 will be at the discretion of the NTSB," the statement reads.
The FAA directive is a blow to United Airlines, which had 24 of the planes in service and is the only U.S. airline with the engine in its fleet.
“On Sunday, we voluntarily removed 24 Boeing 777 aircraft powered by Pratt & Whitney 4000 series engines from our schedule," said United spokesman David Gonzalez. "We’ve been working with the NTSB on their investigation and will comply with the FAA’s Emergency Airworthiness Directive to ensure all 52 of the impacted aircraft in our fleet meet our rigorous safety standards.”
A United flight from Denver to Honolulu made an emergency landing shortly after takeoff Saturday as pieces of the engine’s casing rained on suburban neighborhoods. None of the 231 passengers or 10 crew were hurt, and the flight landed safely.
Robert Sumwalt, chairman of the National Transportation Safety Board, said during a virtual news conference Monday night that a fractured fan blade found in the engine had visible signs of “damage consistent with metal fatigue.” The broken blade hit and fractured the blade next to it as the engine broke apart, according to a preliminary investigation.
Sumwalt said the blade that fractured first was flown on a private jet to Pratt & Whitney’s headquarters Monday night to be examined under the supervision of NTSB investigators.
“Our mission is to understand not only what happened, but why it happened, so that we can keep it from happening again,” he said.
The FAA directive said the agency would review the results of the inspections “on a rolling basis.”
“Based on the initial results as we receive them, as well as other data gained from the ongoing investigation, the FAA may revise this directive to set a new interval for this inspection or subsequent ones,” the directive said.
The previous inspection interval for Pratt & Whitney PW4000 engines was 6,500 flight cycles. A flight cycle is defined as one takeoff and landing.
Video posted on Twitter from Saturday’s emergency showed the engine fully engulfed in flames as the plane flew. Freeze frames from a different video taken by a passenger sitting slightly in front of the engine and also posted on Twitter appeared to show a broken fan blade in the engine.
Passengers said they feared the plane would crash after an explosion and flash of light, while people on the ground saw huge chunks of the aircraft pour down, just missing one home and crushing a truck. The explosion, visible from the ground, left a trail of black smoke in the sky.
The FAA has issued an Emergency Airworthiness Directive ordering U.S. operators of airplanes with Pratt & Whitney PW400 engines to inspect these engines before flight.
The FAA made the order after a Boeing 777 operated by United Airlines had to make an emergency landing in Denver Saturday after one of its engines blew apart due to a fan-blade failure. The plane dropped chunks of debris that landed in neighborhoods and sports fields, but it was able to make the landing without any reported injuries.
The FAA instructions require operators to do what's called a thermal acoustic image (TAI) inspection of the large titanium fan blades at the front of each engine. A TAI can detect cracks in the interior or in areas that cannot be seen during a visual inspection.
The FAA will review the results of the inspections and issue additional guidance based on the data.
The investigation into the Denver incident is ongoing. Already, 69 planes and another 59 in storage were grounded in the U.S., Japan and South Korea, the only countries with planes using this particular engine.
Safety experts say the focus of the investigation is on why the fan blades snapped and whether mistakes were made in manufacturing or maintenance or if problems were missed during inspections. The Denver incident will be compared to other similar ones over the last few years.