* Length of the delay in deliveries unknown
* Norwegian Air looking to secure backup planes
* Norwegian Air has eight Dreamliners on order
OSLO, Feb 8 (Reuters) - Norwegian Air Shuttle said it will lease aircraft to replace Boeing's 787 Dreamliners if they are not delivered in time to launch its long-haul service.
Boeing has notified the Nordic carrier that its delivery schedule was at risk because of an investigation by the U.S. National Transportation Safety Board into the aircraft and the extent of the possible delay was not yet known.
"In the event that the 787 is not operational in time for Norwegian's services to New York and Bangkok replacement long-haul aircraft will be leased to ensure flights are operated as scheduled," the firm said on Friday.
Norwegian was scheduled to receive the first of eight Dreamliners in April and the firm has already sold deeply discounted ticket for its first overseas flights as it aims to take on traditional legacy carriers.
Authorities grounded the Dreamliner worldwide on Jan. 16, after a series of battery incidents, including a fire on board a parked 787 in Boston and an in-flight problem on another plane in Japan. The groundings have cost airlines tens of millions of dollars, with no end in sight.