Pratt & Whitney admits the first 18 months of commercial operations with the PW1100G engine could have gone better.
After dealing with a succession of minor crises, including bowed rotors, parts shortages, prematurely deteriorating components and one in-flight shutdown, the question facing the company as the Paris air show begins is simple: 18 months after entering service, are the geared turbofan's most serious technical and production problems in the past?
P&W officials are still meeting with airframers to decide how many GTF engines must be built next year. With the A320neo and CSeries continuing to ramp up and the Embraer 190-E2 entering service next year, P&W needs to be ready to build hundreds more engines in 2018 than the 350-400 stated as a goal this year.
"We're putting the capital in place today in anticipation of the rate going up. I'm not worried about that. I think the capital is in place," P&W president Bob Leduc tells FlightGlobal.
To stay on schedule for 350-400 deliveries this year, P&W needed to hand over 88-100 GTFs to customers in the first quarter. Instead, the company delivered 70. Although the number was below trend, Leduc points to the positive trend line from the first quarter of 2016 to the same period in 2017.
"In the first quarter last year, we made 26 GTFs. This year we built 70," Leduc says.
"If you can double the rate in 12 months you're doing really good. And we more than doubled. We just need to stay on that trajectory and we'll be fine."
Yield management
To improve the pace of deliveries, P&W needs to improve yields on dozens of parts. Last October, P&W parent United Technologies reported chronic shortages of around 40 parts in the supply chain.
One of the most critical deficiencies was P&W's hybrid metallic fan blades, composed of titanium leading edges and hollow aluminium bodies. P&W's sole fan blade plant could not produce them fast enough. As the GTF entered the production ramp-up, workers were still learning how to manufacture the exotic items. As of a year ago, one out of every two blades had to be scrapped because of defects.
Yields of the original fan blade for GTF engines are now at 85%, Leduc says.
That is well above the company's original production plan, which assumed a 75% yield for the component, Leduc says. Since April, two more facilities have opened in Michigan and Japan to build the blades, adding quantity to the improving quality of the production system.
"Fan blades are not going to be in our way anymore," Leduc says.
Another sign of P&W's improving production system is the mid-turbine frame, one of the most important structural elements in any engine. The part is made as a single piece using a casting process. As the metallic structure is formed, great care must be taken to eliminate voids at the molecular level. Too many voids, or porosity, causes the entire part to be scrapped.
"The yield on that part [a year ago] was 40%," Leduc says. "And today it's 97%."
P&W solved the problem by changing the tooling in production and altering the heat treating process in post production, he says.
Such improvements suggest P&W's supply chain has stabilised at current production levels. By raising yields and adding production capacity, the company has positioned the GTF programme to catch up on production commitments this year.
"There's nothing in our way to deliver 350" engines, Leduc says.
For customers, the steadily increasing delivery rate is helpful, but is still complicated by how the engines are applied. About one-seventh to one-eighth of all deliveries this year must be diverted into an expanded pool of spares. The extra supply of engines is needed to keep the aircraft already in service flying while P&W rolls out a series of durability upgrades.
Teething troubles
The GTF entered service in January 2016 with several defects that would require almost two years to resolve. The most glaring issue that emerged after entry into service for the PW1100G was a rotor bow problem. All large turbofan engines are affected to some degree by the effect of differential heating on the rotor shaft.
The phenomenon requires airlines to motor the fan on each engine for about 1min to cool off the heated section of the shaft. The PW1100G, however, initially required crews to cool the engines for several minutes each. P&W solved that problem across the fleet by October 2016 by strengthening the shaft bearings, making them less susceptible to the thermal bowing effect.
As that issue was fixed, P&W released details of two more defects in the engine design. Two major parts – combustor liners and carbon air seal assemblies in the No. 3 bearing – proved to degrade prematurely.
P&W completed retrofits of an improved seal for the No. 3 bearing in May, and production engines are now being delivered with the improved design.
P&W rolled out an improved combustor liner design last year, but it was not enough to fix the problem. A third-generation combustor liner – internally dubbed the Block C design – is now scheduled to be rolled out in the fourth quarter. The new version tweaks the layout of the internal cooling passages embedded into the combustor liner.
"We will be okay with the combustor that comes into production in the fourth quarter timeframe," Leduc says.
P&W has proceeded with key certification tests, such as extended twin-engine operations (ETOPS), with the existing combustor configuration. The absence of a final combustor liner design until the fourth quarter will not delay ETOPS certification, Leduc says. ETOPS is a critical certification for Hawaiian Airlines, which has already delayed entry into service of its PW1100G-powered A321neos until next year.
"We're cautiously optimistic [ETOPS certification] is in the fourth quarter timeframe," says Chris Calio, president of P&W Commercial Engines. "We've provided everything we can to the regulatory agencies."
As this report went to press, an investigation in India was continuing into an 8 February engine failure involving a GoAir Airbus A320neo. The aircraft landed on one engine but the incident prompted immediate, fleetwide inspections of the main accessory gearbox on the PW1100G.
ETOPS certification should remain on track, however, Calio says. The fleet in-flight shutdown rate remains above the US Federal Aviation Administration threshold for ETOPS – 0.02 incidents per 100,000 flight hours.
India's civil aviation authority has not yet released a preliminary report on the investigation, but P&W executives do not believe the shutdown will reveal a new design problem.
"It's still under investigation, but we do not believe it's a design issue," Calio says.
Adds Leduc: "I believe this is the only event that we've ever seen. Data would tell us it's not a design issue, but, until the regulators are done, I better say we can't say one way or the other."
The GTF's troublesome debut masks several of P&W's proudest achievements. The company spent more than two decades and $10 billion to invent the fan drive gear system, a reduction gear that decouples the rotation speed of the fan and the low-pressure turbine, allowing both systems to rotate at the most efficient speed.
To date, the fan drive gear system has performed exactly as P&W promised. By all accounts, the engine is meeting or slightly exceeding targets for fuel burn production. Notwithstanding the durability issues, the engine's measured dispatch reliability has also met P&W's promised rates, Leduc says.
Despite those achievements, CFM International continues to enjoy a slight advantage in market share among announced engine selections for the A320neo family. Once the in-flight shutdown investigation and the combustor liner durability problems are finally resolved, P&W can start working to fix the geared turbofan's market share problem.
Source: Cirium Dashboard
