Airbus will begin delivery of A350-900s incorporating a "wing-twist" aerodynamic improvement in July when it hands over Iberia's first aircraft of the type.
The wing twist was originally introduced on the A350-1000 and will become standard on all A350s.
Iberia is due to receive its first A350-900 next month
Another -1000 improvement – the replacement of titanium passenger-door surrounds with carbonfibre – is being incorporated into all A350s from the first ultra-long-range -900ULR (MSN216). This aircraft, which made its first flight on 23 April, also features the wing twist and is due for delivery to launch customer Singapore Airlines in the second half of 2018.
"These are natural evolutions of a product... Continuous improvement is an Airbus tradition," says A350 marketing director Francois Obe.
"What we are doing is taking the lessons from the -1000 and reverting them to the -900. Any innovations on the -1000 are reverted to the -900 so we have a true family."
Obe says the carbonfibre surrounds are lighter and that the change simplifies the production process.
The ULR incorporates a series of changes to provide additional range including increased operating weights and fuel capacity, along with weight savings. The maximum take-off weight rises to 280t (616,700lb) from the previous highest value of 275t. This increases range by around 1,600nm (3,000km) to 9,700nm.
There are no additional fuel tanks, but Obe explains that Airbus is using part of the existing centre tank's "empty space" to increase capacity. This enables the ULR's centre-tank capacity to be raised by around 24,000l over the -900's 140,450l to 165,000l.
This is even more than the capacity of the -1000 (158,791l), with Obe explaining that "there's fuel in the -1000 [centre tank] that we are not using".