Canada's Bombardier Inc reported slightly weaker than expected results on Thursday, prompting some analysts to express concerns about the aircraft and train maker's cash burn rate as it continues to pour money into its CSeries aircraft program.

Montreal-based Bombardier posted lower-than-expected first- quarter revenue, which some analysts attributed in part to weaker pricing in business aviation.

"Overall, we view these results negatively, mainly due to the significant and unexpected free cash flow usage in the quarter," said RBC Capital Markets analyst Walter Spracklin, in a note to clients.

"Key will be whether or not the recent debt capital raise will be enough to get the company through the next several years of capital expenditure spend on the CSeries."

Bombardier, which has poured billions of dollars into its CSeries aerospace program, said free cash flow usage during the quarter came to $915 million, compared to $590 million a year ago.

"We don't anticipate to have to go back to any sources to increase our liquidity. We have ample liquidity to meet our plan," said Chief Executive Pierre Beaudoin, noting the company was reaffirming its full-year capital expenditure of between $1.6 billion and $1.9 billion.

"We don't think we need to borrow government money on this program, that's already been done," he said, reiterating the company's expectation it will reduce investment spending as the year progresses and have good cash flow by the fourth quarter, a typically strong delivery period.

Bombardier shares sank as much as 6.6 percent in early morning trading on the Toronto Stock Exchange, reversing big gains from the previous session.

Revenue in the aerospace division fell 9 percent to $2.1 billion in the first quarter.

Total revenue rose about 2 percent to $4.35 billion, but fell short of the average analyst estimate of $4.58 billion, according to Thomson Reuters I/B/E/S.

Bombardier, which also makes trains, said revenue rose nearly 10 percent to $2.3 billion in the transportation business.

The company delivered a total of 56 aircraft in the quarter, compared to 53 a year earlier.

Bombardier said it was making progress with the CSeries program, with 280 hours of flight testing so far, and the fourth flight test vehicle was expected to complete its first flight in the coming weeks.

The costly CSeries could be Bombardier's ticket into the big leagues, with its CS100 and CS300 models suited to compete with the smaller planes made by rival Boeing Co and Airbus Group.

Bombardier Aerospace's backlog totaled $38.5 billion, higher than the $37.3 billion at the end of December. Order backlog in the transportation business totaled $38.4 billion, up from $32.4 billion at the end of December.

The company's net income fell to $115 million, or 6 cents per share, in the quarter ended March 31, from $148 million, or 8 cents per share, a year earlier.

Excluding one-time items, Bombardier earned 8 cents per share, in line with the average analyst estimate.