The first incident with a Boeing 777 with the same engine type was recorded midway over the Pacific Ocean on another United Airlines flight to Honolulu on February 13, 2018
The Federal Aviation Administration in the United States issued an emergency order on sunday saying it would be stepping up inspections of Boeing 777 aircrafts with certain Pratt & Whitney PW4000 engines. This is the same engine, that fell apart on the United Airlines flight yesterday.
Since entering revenue service in 1987, Pratt & Whitney has delivered more than 2,500 PW4000-94” engines that have collectively logged more than 120 million dependable flight hours on commercial aircraft around the world.
On 2 October 2015, while in cruise at 33,000 feet, Delta Air Lines Boeing 747-451 N662US experienced a loss of power from its Number 3 engine, a Pratt & Whitney PW4056.
The US National Transportation Safety Board (NTSB) say in their safety investigation report that the flight crew heard a loud “pop” that was followed by the engine’s N1 (fan speed) decreasing while the exhaust gas temperature (EGT) increased. The engine was shut down and the aircraft diverted safely.
The aircraft suffered minor damage (nicks and dents to the underside of the right wing, inboard aileron and the leading edge of the right horizontal stabilizer). The NTSB say the engine failure was ‘contained’ i.e. no debris was released radially (only axially).
A United Airlines B 777 -200 on February 2018 with 378 passengers on Board and also on a flight to Honolulu had another incident relating to the Pratt & Whitney PW4000 engine.
US investigators believe prolonged absence of formal training and certification for a fan-blade inspection technique resulted in a flawed blade being returned to service and subsequently fracturing on a United Airlines Boeing 777-200.
The fracture in the right-hand Pratt & Whitney PW4000 fan blade, during cruise at 36,000ft on 13 February 2018, led to the loss of most of the inlet duct and all of the left and right fan cowls.
It also resulted in debris – believed to be from a blade – puncturing the right-hand side of the fuselage, just below the window line.
ational Transportation Safety Board investigators found that Pratt & Whitney developed a new inspection process, known as thermal acoustic imaging, around 2005.
This process was designed to inspect the interior surfaces of the PW4000 fan blades, and detect cracking in the hollow core, using sound energy to generate friction across any discontinuities which can then be picked up by thermal sensors.
Pratt & Whitney classified the process as ‘new and emerging technology’, in line with industry practice for newly-introduced non-destructive inspection methods. This meant it did not need to develop a formal initial and recurrent training programme.
But the inquiry found that – even after 13 years – the manufacturer was using the same classification for the technique, despite having inspected over 9,000 blades, and did not have a defined training and certification regime.
Two shift inspectors, including the one who last inspected the blade, told the inquiry that their training on the technique amounted to 40h on-the-job training, whereas certification for eddy current and ultrasonic inspection involved extensive classroom training and up to 1,600h of practical experience.
“At one point [Pratt & Whitney] did provide training on [the technique],” says the inquiry. “However, neither of the two inspectors were permitted to attend the training so that they could work to clear out a backlog of blades in the shop.”
The inspector who worked on the blade also claimed that there was no feedback from engineers about whether any blade rejections were valid or false.
Investigators determined that thermal acoustic imaging inspections of the United 777 blade in March 2010 and in July 2015 revealed indications in the same location as the subsequent low-cycle fatigue crack.
This finding, after the incident, spurred Pratt & Whitney to order a review of over 9,600 previously-inspected blades. Pratt & Whitney also reported that they had developed a curriculum for initial and recurrent training on the inspection technique following the event.
It covers a range of 52,000 to 62,000 pounds of thrust and has five major aircraft applications. Approved for 180-minute Extended-range Twin-engine Operations (ETOPS), the engine provide airlines with excellent operational flexibility and high reliability. Advanced, service-proven technologies, such as single-crystal superalloy materials and its Full-Authority Digital Electronic Control (FADEC), contribute to superior fuel economy and reliability. The engine’s benefits are further enhanced by excellent performance retention, long on-wing times and low maintenance costs.
The PW4000’s noise and emissions parameters are lower than levels required for all current and anticipated emissions and noise regulations. For a further reduction in emissions, Pratt & Whitney’s TALON (Technology for Advanced Low NOx) combustor technology is now available for the PW4000. Derived from the 112-inch fan model, TALON has segmented, replaceable liner panels for easy maintainability and air blast fuel nozzles for excellent fuel atomization and mixing resulting in clearer burning and low emissions.
A discussion if it was safe to operate a twin engine aircraft to Hawaii was answered by a captain as follows:
Every twin-engine flight is planned so that the loss of an engine will result in a safe landing. Modern twin-jets are specially certified for extended overwater operations. Engine failures are very, very rare, but should one occur, the airplane can safely fly to an alternate airport, the airport of origin or the airport of destination.