A problem with the plane's newly developed Pratt & Whitney geared turbofan (GTF) engine during stationary maintenance testing last Thursday has sparked concerns about further delays in the already-overdue CSeries development.

"We still very much believe in this aircraft," spokesman Nils Haupt said in an email. "Lufthansa is fully confident that Bombardier will be able to solve the issue ... but we hope that no further delays will occur."

Germany's Lufthansa signed a letter of interest in 2008 for 30 planes, with options for 30 more, and firmed the order in March 2009. The planes are for its Swiss airline subsidiary.

Montreal-based Bombardier said on Tuesday that there were no developments with the investigation into what went wrong with the engine.

On Monday, the company's aerospace unit president told Reuters that the probe had narrowed to a few possible causes and the plane could soon be back flying if the problem was what Bombardier suspected.

The Transportation Safety Board of Canada, which sent an investigator to Bombardier's flight testing facility outside Montreal, said on Tuesday it had nothing new to report.

UBS analysts were told in meetings with Pratt & Whitney parent United Technologies Corp on Monday that the incident was relatively minor.

United Technologies does not see the incident as related to the the gearbox, analyst David Struass wrote in a research note, adding that the company "expects to know root cause by the end of this week."

Bombardier shares gained 1.9 percent on Tuesday to end at C$3.71 on the Toronto Stock Exchange. News of the engine failure on Friday sent Bombardier stock down 1.9 percent on worries over the cause and whether it could require a costly, time-consuming redesign.

Multiple delays have disappointed investors and added to competition concerns as the CSeries takes on smaller jetliners made by industry leaders Boeing Co and Airbus Group NV.

Bombardier wants to dominate the 100- to 149-seat plane market with the CSeries, built with lightweight composite materials and other technologies designed to make it burn less fuel and operate more quietly, with lower operating costs.

(Reporting by Susan Taylor and Solarina Ho; editing by Andrew Hay)