Boeing has revealed more about its thinking regarding a possible new 737 variant powered by advanced turbofans, but says it will not decide on any move until after July's Farnborough air show.
Meanwhile, Airbus's similar studies of an upgraded A320 appear more advanced, with suggestions that a formal launch is imminent.
Boeing Commercial Airplanes president Jim Albaugh says that the airframer is evaluating whether and how to execute a re-engined 737, and wants to ensure it is not "a me-too airplane".
Speaking at the JP Morgan Aviation, Transportation & Defense Conference in New York on 9 March, Albaugh said that Boeing has always competed on value rather than price "and we want to make sure if we do re-engine we have an airplane that enjoys a 5%, 6%, or 7% efficiency or value capability above the competition".
Albaugh says that Boeing "right now" is in talks with all three engine manufacturers, and thinks they will all be able to deliver efficiency improvements in the 10-15% range. The airframer is also looking at ways of "scaling down" 787 technologies for the 737, he adds.
Any decision to go ahead with the upgrade will be after Farnborough, says Albaugh, "probably towards the end of the year".
Meanwhile, industry sources say Airbus is courting potential launch customers for its planned re-engined A320 family, and the boss of one of the prospects - Qatar Airways chief executive Akbar Al Baker - believes that a go-ahead could be imminent.
"I believe that Airbus is going to make an important announcement this month," he says. "And I think they will come up with a programme similar to the [Bombardier] CSeries and install the [Pratt & Whitney] GTF."
In response, Airbus says its position on the timing remains unchanged - that it aims to make a decision this year.
However, the airframer's chief salesman John Leahy recently said that he hoped to get the plan finalised by Farnborough. Service entry is targeted for 2015.