* Pratt & Whitney says making progress on supply chain
* Fan-blade manufacturing pressure adds to delays - sources
* Some Airbus jets also affected by new delay -sources
By Tim Hepher and Allison Lampert
PARIS/MONTREAL, Sept 6 (Reuters) - Further delays in deliveries of the latest jet engine from Pratt & Whitney underline the challenges of speeding up manufacturing for multiple planemakers as well as pressure on an already taut supply chain, industry sources said.
Canada's Bombardier said it was cutting forecasts for CSeries jet deliveries because of delays in getting engines from Pratt & Whitney, one of a handful of engine makers whose efficient new designs have triggered a boom in aircraft sales.
Pratt & Whitney did not say what had caused the delays, but suggested it was grappling with problems at its own suppliers.
"In terms of production, we've made significant headway in the supply chain, but there is some pressure on new engine deliveries for this year," a spokeswoman said in a statement.
Three industry sources said the U.S. engine maker also faces challenges in bedding down the manufacturing techniques for the engines' novel "hybrid-metallic" fan blades, the world's first to be made mainly from aluminium alloy.
While the sources said there is nothing technically wrong with the lightweight blades, one said the problem was linked to perfecting advanced new industrial methods, leading to some quality problems and slowing down deliveries.
"The process is not yet automated enough; it remains too much of an artisan process," the source said.
The reported fan-blade manufacturing problem is at least partly responsible for delays that prompted Bombardier to more than halve its forecast for deliveries, two of the sources said.
It has also contributed to delays in some deliveries from Pratt to Airbus, though those are dwarfed by other technical issues now being resolved, a person close to the matter said.
Airbus declined comment.
Pratt & Whitney declined to add to its earlier statement.
Similar engines are being developed for planemakers in Brazil, Japan and Russia. Brazil's Embrarer said its E-Jets E2 programme was not affected.
The new Geared Turbofan engine relies on a larger fan than previous comparable models to help burn less fuel.
Pratt & Whitney is ramping up output of the fan blades and other parts quickly to meet demand, and earlier this year opened a secondary manufacturing facility in Singapore.
In 2014, Pratt & Whitney signed a 10-year, $1.1 billion deal with Alcoa for parts including forgings for aluminium fan blades. The blades are manufactured using a process that has not been disclosed. Alcoa was not immediately available for comment.
Shares in Pratt & Whitney parent United Technologies fell 0.8 percent.
Analysts said the delays added to pressure on Pratt & Whitney to ramp up production but did not drastically alter the balance of risks involved in record jetliner production.
"It is a question of time and money, not a question of if," said a specialist who closely follows aerospace manufacturing. (Editing by Ruth Pitchford)