MONTREAL - Bombardier Inc. shares fell to a new low Tuesday after Spirit AeroSystems said some closing conditions on its planned acquisition of Bombardier's aerostructures business remain unmet, injecting a degree of uncertainty into the deal.

The US$500-million sale of facilities in Belfast and Morocco forms a key part of Bombardier's shift from a commercial plane-and-train maker to a pure-play manufacturer of private jets.

The deal is also critical to buoying the Montreal-based company's balance sheet, which is currently weighed down by more than US$9 billion in debt.

Spirit says the agreement will automatically terminate if conditions are not satisfied by Oct. 31, according to filings it submitted Tuesday to the U.S. Securities and Exchange Commission.

The Kansas-based company says the conditions include an absence of legal barriers, receipt of third-party consents and no major adverse changes to the business, which includes fuselage and wing factories.

Bombardier shares fell by two cents or five per cent to close at 38 cents on the Toronto Stock Exchange, a new 25-year-low for the Quebec mainstay.

“While we believe that Bombardier has sufficient time remaining to satisfy the closing conditions laid out in the purchase agreement, we view the announcement this morning by Spirit as lowering the probability of a successful close,” analyst Walter Spracklin of RBC Dominion Securities said in a research note.

“Bombardier and Spirit are actively working to meet the closing conditions and complete the transaction this fall,” Bombardier spokesman Olivier Marcil said in an email.

The agreement was initially anticipated to wrap up in May of this year.