The U.S. Air Force on Tuesday ordered a deeper inspection of the engines similar to those on a Boeing 777 aircraft that suffered a spectacular crash over Denver days earlier.
The incident, in which a Pratt & Whitney engine burst into flames and scattered debris over a suburb of Denver shortly after the start of Honolulu, led to many Boeing 777s being grounded worldwide for safety issues.
“U.S. aircraft operators equipped with certain Pratt & Whitney PW4000 engines (must) inspect those engines before further flight,” the Federal Aviation Administration (FAA) said.
The regulator said it issued the order “as a result of a fan blade failure that occurred on Saturday on a Boeing 777-200 that had just departed from Denver International Airport.”
Before returning to the sky, operators must perform a thermal acoustic image (TAI) inspection of the large titanium fan blades located on the front of each engine. “TAI technology can detect cracks on the inner surfaces of the hollow fan blades, or in areas that cannot be seen during a visual inspection,” it said in a statement.
Metal fatigue has emerged as the main suspect in the engine failure, which did not cause any injuries.
Steve Dickson, the FAA chief, had told a meeting of the Aviation Safety Council earlier Tuesday that “we want to understand what happened and take the necessary steps to prevent a similar recurrence.”
“We are fortunate that there were no deaths or injuries,” Dickson added.
Near miss over Denver was a new setback for Boeing, which recently resumed deliveries of the long-ground 737 MAX after two fatal crashes.
It also raises new questions about the FAA, which was attacked around for its oversight of Boeing at the certification of the 737 MAX, and about whether the maintenance was adequate on the plane, aviation experts said.
Even before the Denver incident, U.S. aviation safety regulators had weighed stricter inspections on the jets and their Pratt & Whitney engines, U.S. officials said Tuesday.
The FAA reviewed inspection records and maintenance history following an incident with Japan Airlines fan blades on December 4 last year “to determine the cause of the fracture and evaluated whether the blade inspections should be adjusted,” an FAA spokesman said Tuesday. The flight landed in Japan without damage.
Following an incident in February 2018 on another United jet, the FAA reviewed 9000 fan blade inspection reports and issued an Airworthiness Directive with new inspection rules.
At a news conference on Monday, the National Transportation Safety Board said it was too early to know if the issue in Denver was similar to those in the Japan Airlines flight or the February 2018 incident, which involved another Boeing 777 and Pratt & Whitney engine.
“A preliminary site investigation indicates damage consistent with metal fatigue,” said NTSB President Robert Sumwalt.
He said two fan blades broke on engine number two on the Boeing 777-200 on Saturday. One of them was later found on a football field, while the other remained in the engine.
The NTSB also plans to look at the inspection register on the United plane to see “who knew what when, what could have been done and what should have been done,” Sumwalt said.
“Fatigue means you can get a crack in the material and when you recharge it over and over again, the crack grows slowly,” says Robert Kielb, a professor at Duke University’s School of Engineering.
“This is an example of an event where we learn something about the design 20 years after it was put into use, and then we immediately ground the fleet, figure out what’s going on and fix it.”
Headache for Boeing
In the wake of the Denver incident, Boeing said all 128 of the 777s with Pratt & Whitney engines were grounded.
Of the 128 aircraft, only 69 were in operation while 59 were stored.
In addition to United, which removed 24 aircraft from traffic, the affected airlines included the Japanese airlines Japan Airlines and All Nippon, as well as South Korea’s Asiana and Korean Air.
On Monday night, a Delta Air Lines flight on a Boeing 757 en route to Seattle from Atlanta to Salt Lake City was diverted “by an abundance of caution following an indicator warning of a possible problem with one of its engines,” a Delta spokesman said. .
“The flight landed safely without incident and was taxed to the gate without assistance.”
Boeing recently resumed deliveries of the 737 MAX after a 20-month global grounding after two crashes killed 346 people.
MAX began returning to commercial service in late 2020, with airlines’ travel still depressed due to the coronavirus pandemic.
Boeing executives said last month that they expected it to take about three years for the activity to return to pre-pandemic levels.
Michel Merluzeau, an expert at the consulting company AIR, agreed that the latest problem did not seem to be due to poor floor design.
“It’s not really a problem for Boeing,” he said. “It’s more a matter of maintenance – how United or Pratt & Whitney maintain engines that have been used for a while.”
The section “is an embarrassing headline, but as a practical issue it will not affect Boeing,” Scott Hamilton told Leeham News, an aviation news website.