By Bjorn Fehrm
23 March 2016, ©. Leeham Co: Airbus is showing a select group of airlines a stretched version of the A350-1000. The idea is to get enough feedback from potential customers so that a decision to go ahead or not can be made during the summer. Airbus COO customers, John Leahy, told LNC at the ISTAT conference earlier this month that an announcement could be made at the Farnborough Air Show in July. Other sources say it might take longer.
We have covered the possibility to extend the A350-1000 to a longer 400 seater version in several articles over the years. The key question for Airbus is how large is the market for a dual aisle twin with 400 seats and has Boeing already covered a large part of that market with its 777-9?
What has changed now it that the A350-1000 is taking form on the Airbus Toulouse Final Assembly Lone (FAL) and Airbus can now see that the A350-1000 will hit its performance and weight numbers. Airbus also has a lot of learning from the A350-900 which makes it confident that an A350-1000 stretch can be made with rather small changes.
A key feature of the A350-1000 is that it’s very close in capacity to the Boeing 777-300ER, yet is considerable lighter. This gives the A350-1000 a distinctive performance advantage. Part of this is that the A350-1000 is made with more modern construction techniques and is equipped with a more modern engine, but a contributing factor is also that the fuselage meets the capacity requirements with only four door pairs.
The fifth door pair on the 777-300ER takes away passenger capacity and it also increases the aircraft’s empty weight. The present capacity of the A350-1000 is around 360 seats in a two class cabin. It would be possible to stretch that to 400 seats, still in a two class cabin, without forcing an additional door pair or additional emergency exits.
Over the years we have called a stretched A350-1000 the A350-1100. Leahy has said that it’s not a favoured name for the proposals that Airbus is right now presenting to airlines. We therefore call the proposed aircraft configuration the “A350 stretch.” Staying with four door pairs, the total length of the aircraft can only be stretched with around 4m before the distance between exit doors go beyond the allowed 60 feet. As no additional safety exits will be necessary, such an extension will increase the aircraft’s capacity to around 400 seats.
Leahy has said that the favoured engine alternative is a stretched variant of the A350-1000 engine Rolls-Royce TWB 97k. There has been information in media describing the Max Take Off Weight (MTOW) of the variant as going from 308t to 319t. When we feed our proprietary aircraft model with these data, we can see that it’s possible to make an A350 Stretch to 76 meters, which would only require 2-3klbf extra thrust from the engines. Such a thrust increase is available in the Trent XWB 97k. The core was resized in the upgrade from 93 to 97klbf. A 3% thrust stretch is therefore fully possible.
We can also see that the variant would still be very weight-competitive against the 777-9, having an empty weight of some 25t less. With a modest increase in empty weight and an equally modest increase in MTOW, the A350-1000 wing would need no changes. Wingloading goes from a moderate 670kg/m2 to just above 680kg/m2, well below the wingloading of the 777-300ER of 760kg/m2 and close to the wingloading of the 777-9 at 660kg/m2.
One can further assume that Rolls-Royce can offer slightly better specific fuel consumption for a Trent XWB with an EIS of around 2020. Airbus might also gain aerodynamically from having done extensive testing on the A350-900 and -1000 by then. When we feed our model with all this data, we get a range of the stretched A350-1000 which is within 200nm of the range of the A350-1000.
The base design of the A350-1000, which use rather modest values for wing and span loading, makes a stretch variant possible that keeps the range in the same bracket as the A350-900 and -1000 with a lowly 11t increase of the aircraft’s MTOW. Such a weight stretch is within the margins of components like landing gear, aircraft structure and engines, enabling a low cost upgrade project.
Airbus has the gradually gained the knowledge around the A350 platform that makes a stretch of the A350-1000 possible without major changes to the aircraft. By staying within the exit limits of four door pairs (max capacity 440 seats), a capacity increase of 40 seats is possible with minimal changes to other parts of the aircraft.
This would enable a 400 seat aircraft which has a 7,600nm range with a MTOW which is below 320t. This is a full 32t less than a competing Boeing 777-9 that has only a marginally higher passenger capacity. The lower take-off and empty weight would give an A350-1000 stretch around 10% lower trip costs and around 5% lower seat mile costs.