"What has propelled the market to record growth are two factors: cheap cash and expensive fuel," said Richard Aboulafia, an aerospace analyst with the Teal Group in suburban Washington. "Now something has changed."

Whether the continued fall in price of oil represents something more significant than a short-term imbalance of global supply and demand remains to be seen, some analysts warn. But if it continues, airlines would be motivated to keep their older, fuel-guzzling jets flying for a few more years and delay new orders in hopes of saving money.

"We can't yet predict if it will last or how the air carriers will react," Mr. Aboulafia said, "but I think now would be an excellent time for caution."

Airline start-ups may find it tough to attract funding at a time when the largest U.S. carriers have endured bankruptcies and consolidation to emerge as disciplined competitors, said Richard Aboulafia, aerospace analyst with Teal Group, a Fairfax, Virginia-based consultant. "Investors realize the big guys are getting their act together and are no longer egg-laying dinosaurs," Aboulafia said. "The idea of adding more to the fray when everybody seems to have their costs in line with market reality — that's just a very bad idea."