If Airbus keeps to its preliminary schedule for A320neo transition then, from the second quarter of 2017, it will start producing more of the re-engined twinjet than the baseline A320.
The crossover point will come only 18 months after the A320neo enters service, and Airbus expects to achieve a monthly production rate of 42 aircraft from the beginning of 2018. A320neo chief engineer Pierre-Henri Brousse says that the transition between the two types is "secured and top priority" for the airframer.
Airbus is developing eight flight-test aircraft - four A320neos, two A321neos and two A319neos - in order to certificate each of the three variants with both powerplant options, the Pratt & Whitney PW1100G and the CFM International Leap-1A.
However, the manufacturer is also going to build eight pre-series aircraft from the beginning of 2015, according to the Airbus transition schedule.
"These will feature exactly the same specification as the [full production] faircraft but with a specific lead time, to fix any industrial issues and not compromise our ability to ramp up later on," says Brousse.
"This shows the care we're taking for the industrial maturity."
Airbus is already producing its current A320 family at 42 aircraft per month, a rate it achieved in October 2012. But concerns over the supply chain's ability to feed the assembly lines have led the airframer to resist temptations to push the output further, and it has settled on maintaining rate 42 through the three-year A320neo transition period.
Brousse says the company has visited automotive plants to analyse industrial production cut-over processes, and to apply similar best practice to the Airbus switch.
He says the principles of pre-series development are being applied to the air inlet on CFM engines, to examine the effects on "takt time" - the measurement of assembly line production time against demand, which serves to gauge the smoothness of output. Airbus will apply a series of stress tests to reduce takt time.
The schedule indicates a production rate of three A320neos per month by the end of 2015, rising to 16 per month during the next year, with a corresponding fall in production of the baseline A320.
Airbus has required the A320neo to meet the conditions of various maturity gates before being permitted to enter the next development stage. The latest, MG7, marks the end of the design phase. "We have passed all the gates without any delay," says Brousse. "The level of quality when gates were passed was very high."
With the A320neo scheduled to enter the final assembly line in the first quarter of 2014, manufacturing of components for the first aircraft is already under way - for several months in the case of the longer-lead items.
Among components already being produced are the pre-cooler - forming part of the bleed-air system, and already on the test bench at supplier Liebherr-Aerospace - as well as bleed pressure relief valves.
United Technologies has produced the fan cowl and air inlet structures for the first PW1100G powerplant, while some electronic systems, including the fire-detection unit from Meggitt, have also been built.
"We will be doing a lot in terms of readiness of the industrial system, and not neglect all the enablers that allow smooth entry into service," says Brousse.
Both engines are "on track", he says, with the PW1100G entering the flight-test phase following completion of ground testing at West Palm Beach in April. Pratt & Whitney says the first engine's performance has so far exceeded pre-test forecasts.
CFM International will produce its first Leap-1A engine to test later this year, while flight testing will begin in 2014.
Owing to the larger engines, the A320's pylons are being reinforced - the primary change to the type's basic structure - and Airbus has been conducting laboratory and flight tests of pylon components.
First metal was cut for the pylons, sections for which have already been flown on an A380 testbed
"It's a similar design to the [pylon] we have on the A380 today," says Brousse, although some of the secondary structure differs.
The flight testing has involved using one of the A380 testbeds, MSN4, to assess the design for the A320neo's aft pylon fairing, which is situated close to the nozzle.
"We chose the most demanding environment, the A380," says Brousse, referring to the exposure of the fairing during tests.
The A320neo's engines will operate at higher temperatures. Brousse says that the fairing is designed to be "optimised in terms of weight while showing the required strength to meet the new, demanding temperature environment".
Airbus is following a minimum-change policy for the aircraft, to minimise the spares investment and ensure A320 cockpit crews can transfer easily to the new twinjet under the same type rating.
Demand for the A320neo and the rapid transition schedule mean slots for the baseline A320 have rapidly diminished.
At the end of April, the A320-family backlog stood at 3,927 aircraft, of which 2,125 were for the re-engined version, according to the airframer's order data.
That left a baseline A320 backlog of 1,802 aircraft. Airbus's transition schedule indicates 1,875 available production slots for A320s until the airframer starts building A320neos exclusively - a surplus of only 73.
However, Airbus parent EADS maintains it is not organising a clearance sale and insists it will stay "rational" on pricing. By the end of April, Airbus had secured 763 gross orders for the A320 since the A320neo's launch at the beginning of December 2010.
Entry into service of the A320neo in the fourth quarter of 2015 will be followed by that of the A319neo in mid-2016 and, at the end of that year, the A321neo.
Airbus is developing a new fuselage door configuration for the A321neo, which will enable customers to raise occupancy beyond the 220-seat limitation of the regular A321. "We see trends in the market that have pushed us to increase that," says A320-family marketing head Frank Vermeire.
The modifications include changes to the second pair of doors forward of the wing, fitting of an overwing exit, and a four-frame shift rearwards of the doors immediately aft of the wing.
Airbus says the use of flexible cabin and lavatory layouts can increase accommodation by 11 seats, to 231, while the installation of a space-saving rear galley enables a high-density single-class configuration of 236 seats.
For the two-class version the second forward doors could be de-activated, typically providing room for another four seats. "This would give us a much longer forward section in the cabin," says Vermeire. "[We] take out the cross-aisle and have a smooth configuration all the way through."
All A320neos will be fitted with the newly-developed sharklet wing-tip as standard. Following certification of the modified tips towards the end of last year, Airbus has started delivering A320s with the sharklets.
All A320neos will be fitted with the newly development sharklet wing-tip as standard
JetBlue Airways, which co-operated with Airbus to perform experimental flights during development, has also carried out initial sharklet retrofits on aircraft whose wings had already been reinforced during production to accept the new tips.
Several carriers have put sharklet-equipped A320s into service, including China Eastern Airlines which accepted, in mid-May, the first such aircraft to be produced at Airbus's local assembly line in Tianjin.
Airbus is also looking at developing a retrofit option for aircraft assembled and delivered without the reinforced wing.