Also in the cards for Airbus narrowbodies is an electronic flight bag (EFB) upgrade and an onboard airport navigation system.

For its part, Boeing also is stressing the need to keep MAX's upgrade features simple. Its redesign is focused on accommodating the Leap-1B, which has a 69.4-in.-dia. fan, while instituting modest aerodynamic changes to enhance the engine's improvement in fuel burn. The aircraft will feature radial tires on its main and nose-wheel landing gear.

Boeing is introducing a Class 2 EFB to the NG series this year; this incorporates a built-in interface for a bring-aboard laptop system. Still under discussion is whether to include a Class 1 EFB that is built into the flight deck on MAX.

A “slimline” lavatory, which uses thinner walls, and saves enough space to add three additional seats, will be basic to the MAX and available on the NG in 2014, says Wyse.

But as it considers such incremental improvements, Boeing does not want the switch to the new airplane to threaten current production rates of the 737 NG. It wants to protect its supply chain and its own workforce in Renton as the MAX is introduced into the factory's two final assembly lines. Memories of the costly delays of the 787 and 747-8 programs are still raw. “The issues we've had on some of our recent development programs [have been] taken incredibly seriously,” says Wyse.

Among them is the bad publicity generated by program delays. So Wyse and other senior officials speak only in general terms about schedules and have offered no details about what is planned for flight testing.

Comac's C919 program assumes an eventual production rate of 150 a year, based on supplying 30-40% of Chinese demand for aircraft of its size and 10% of international demand. Claimed orders rose to 235 at the Singapore show in February, when Comac announced a contract for 20 C919s from BOC Aviation, a Singapore-based lessor that belongs to the Bank of China.

Comac is not, however, following the scrupulous rules of Western suppliers in announcing its deals. Options are being announced as orders, and even the orders have little binding force, presumably because the inexperienced manufacturer is reluctant to guarantee deliveries on time.

Comac remains committed to its target of certifying and delivering the C919 by 2016. Some industry executives familiar with the program wonder whether that can be achieved. A Comac official acknowledges that the schedule is now very tight.

Airbus's president for China, Laurence Barron, said in June that Comac will have done very well if it achieves its eight-year development schedule.