The CEOs of Delta Air Lines (DL, Atlanta Hartsfield Jackson) and United Airlines (UA, Chicago O'Hare) both said they were interested in the proposed Boeing "New Mid-Market Airplane" (NMA) as a replacement for their B757 and B767 jets, Flightglobal has reported.

"Boeing hasn't decided if it's going to launch that aircraft - we hope they will," Delta CEO Ed Bastian said during the J.P. Morgan Aviation, Transportation & Industrials Conference.

The American carrier currently has 111 B757-200s (inlcuding eleven in its VIP charters division), sixteen B757-300s, two B767-300s, fifty-six B767-300(ER)s, and twenty-one B767-400(ER)s. The NMA could potentially replace all of these types. Delta's B757-200s are 22.4 years old on average, its -300s - 16.1 years old, 767-300(ER)s - 22.8 years, and -400(ER)s - 18.2 years.

Delta is planning to invest heavily in its fleet over the coming years with some USD4 billion earmarked for this purpose in 2019 alone.

For its part, United will be looking to replace its fifty-five B757-200s, twenty-one -300s, thirty-eight B767-300(ER)s, and sixteen -400(ER)s. Some of the B757-200s used on short-haul flights will be replaced with B737-10s.

"Dennis [Muilenburg, Boeing CEO] and I talk about this all the time - speed up the process, we're growing, we need aircraft and they make great aircraft. Having it in a little bit shorter timeframe would be helpful," United CEO Oscar Munoz said during the US Chamber of Commerce Aviation Summit.

The carrier is alternatively evaluating adding more B787s or ordering either A321-200neo(LR) or A330neo from Airbus.

Boeing currently plans to make a decision whether to develop the NMA, a type tentatively seating up to 270 passengers, in 2020. If the manufacturer proceeds with the project, it would target 2025 for the entry into service.