* Company gives no forecasts for "challenging" 2010
* Keeps 2009 revenue, operating margin goals
* A400M engine ready for maiden flight by year-end
* Shares fall, partner GE reports later on Friday (Adds detail, share price)
PARIS, Oct 16 (Reuters) - French aerospace and defence group Safranforecast a challenging 2010 as it posted flat third-quarter revenue on Friday, pressured by underused business jets and lower-than-expected sales of spare parts.
The company, which partners General Electric in the world's largest engine maker for civil jetliners, CFM International, reiterated forecasts for 2009 revenue "on the same scale" as 2008 and an operating margin of about 6 percent.
But it did not give a specific outlook for next year.
"It is too early to make detailed predictions, but 2010 will be a challenging year and we intend to face the challenges," Chief Executive Jean-Paul Herteman told reporters.
Safran shares were down 5.2 percent to 12.07 euros at 1016 GMT.
GE is due to publish third-quarter results later on Friday, with Wall Street expecting profit to fall over half to 20 cents per share, according to Thomson Reuters I/B/E/S, with revenue forecast to drop about 15 percent to $40 billion.
Safran third-quarter sales fell 0.2 percent to 2.38 billion euros ($3.55 billion), with core aerospace propulsion falling 1.5 percent.
Analysts had predicted revenue closer to 2.5 billion euros.
Natixis Securities analyst Olivier Brochet said sales of spare parts of CFM56 engines, the workhorse of most airline short-haul fleets, which fell 2.6 percent in dollar terms over nine months, had fared worse than an expected decline of 2 percent.
The CFM56 is the engine built and sold in a joint venture with GE, the world's largest jet engine manufacturer.
Shares in Rolls-Royce, which some analysts say is better shielded from market variations through flexible "TotalCare" engine support contracts, rose around 0.4 percent on Friday.
Safran said it had also been hurt by a slump in business jet travel, hit by recent publicity over unpopular executive perks.
"Revenue was affected by the depressed market conditions in the business aircraft segment, which account for 10 percent of aircraft equipment business," the company said.
Falls in the aero-engine sector were dampened by higher defence and security spending.
Engine makers clinched a wave of new orders over the summer tied to aircraft deals negotiated before the financial crisis exacerbated a cyclical downturn last year. But fresh demand is waning, putting more focus on servicing older engines.
Safran was created from a merger of French state engine maker Snecma and telecoms equipment group Sagem in 2004, and has a market value around 5 billion euros.
The company is also part of a consortium building the West's largest turbo-prop engine for the Airbus A400M military transport plane, Europe's largest defence project, which has been hit by both engine and software delays.
Herteman said recent trials had gone smoothly and that the engine was not standing in the way of a first flight for the aircraft by the end of the year, as Airbus plans.
Delays of up to two years in the maiden flight have caused friction between EADS unit Airbus and its engine suppliers, which also include Rolls-Royce and Germany's MTU.
Herteman declined to comment on whether Safran would take financial provisions for either the A400M or delays to the Boeing 787 Dreamliner, which is also two years late. (Reporting by Matthias Blamont, Tim Hepher and James Regan; Editing by Rupert Winchester) ($1=.6702 Euro)