The Airbus A321XLR jet will be subject to special conditions imposed by the European Union Aviation Safety Agency (EASA). The stipulations from EASA pertain to the inclusion of a Rear Centre Tank (RCT), a feature central to the aircraft’s “Xtra Long Range”.
The inclusion of an RCT within the fuselage is integral to Airbus’ highly anticipated aircraft. The XLR possesses a further range than other single-aisle aircraft, reaching up to 4700 NM. Most importantly, the expanded range on XLR offers travel routes that are unavailable to its competitors.
But the placement of fuel storage within the fuselage volume is also central to EASA’s concerns over the aircraft’s safety. Fuel tank storage on jet aircraft is generally located within the wings. Airbus intends to store fuel within the aircraft’s body to increase its overall fuel capacity – a feature crucial for the A321XLR’s extended range.
In a consultation paper, first reported by Flightglobal, EASA commented that
“The integration of a fuselage integral fuel tank located behind the wheel bay, under the passenger cabin, brings additional risks (explosion, penetration by fire, vapor migration, etc) if it is exposed to an external fire”.
EASA also warned that passengers situated above the RCT would experience a ‘cold feet’ effect. This would be caused by fuel in the tank reaching low temperatures when the plane hits high altitudes.
The European safety agency stipulated that Airbus must equip the A321XLR with fire-resistant insulation pads located above the RCT to ensure burn-through protection. This would increase the burn time of the RCT and increase the period for passengers to disembark in case of an accident.
But Airbus has already stated that this modification won’t be possible due to a lack of space in the fuselage. The manufacturer state that the protection on the aircraft’s cabin floor cannot be significant as they are unable to place insulation panels alongside the decompression panels in the aircraft’s body.
Boeing has further compounded this through concerns put forward to EASA regarding the XLR’s. In comments to EASA, the U.S aircraft manufacturer commented on the redundancy of the RCT, citing risks these tanks face when exposed to fire. Boeing speculated that if a fire were to reach the fuel tank, there could be a lack of protection to prevent this from spreading.
Mildred Troegeler, Director of Global Regulatory Strategy at Boeing, also stated that,
“The inclusion of an auxiliary fuel tank integral to the fuselage presents many potential hazards, particularly the protection against structural disruption due to an otherwise survivable off-runway or landing gear failure event.”
An Airbus spokesperson commented that,
“Public consultation is part-and-parcel of an aircraft development programme” and further stated that Airbus are “working hand in hand with the airworthiness authorities to fulfil all requirements for type certification”.
The RCT debate
Often ACJs are fitted with additional centre tanks to increase operational range. So, why are there concerns for the RCT on the A321XLR? The answer is simple – as there is less room needed for passengers/cargo, there’s nothing forcing engineers to make the same space compromises for passenger jets.
The benefits of an additional centre fuel tank are clear. The improved fuel capacity increases an aircraft’s range for both average and low payloads. This, in turn, ensures more operational flexibility, which should benefit airlines and passengers. The RCT in the A321XLR is there for precisely this purpose.
Outside of concerns over their fire resistance, the primary risk for the RCT on the A321XLR is damage that could occur if the fuel tank is compromised. This could happen in events such as heavy landings. In this case, damage like this is unavoidable if G loads are exceeded. But under normal circumstances, this is highly unlikely.
Airbus doesn’t release specific structural load limits for their airframes, so it’s difficult to judge the capacity for the XLR. Additionally, the function of weight, VS at touchdown and G limit, also plays a factor in landings.
Boeing’s interjections on the viability of A321XLR aren’t wholly unusual either. It is not uncommon for different manufacturers to share expertise, especially if this helps avert any possible risk.
Long-range upgrades to the a320neo family
Of course, the most significant talking point over the AXLR surrounds the addition of the RCT. This is significant to the 15% additional reach upgrade over its older brother, the currently in-service A321LR “Long Range”. On the XLR, the two added rear fuel tanks of the LR are now permanently replaced by the inclusion of RCT. There is also the possibility for the installation of a forward centre tank to increase fuel capacity even further.
Yet, the single-aisle jet is also receiving upgrades in other vital areas. The A321XLR will have an adapted trailing-edge system with a new single-slotted inboard flap design. This will be significant in upgrading both weight and drag from the A321neo. The flap system upgrades will enable surfaces to be changed to intermediate positions and increase low-speed performance.
Moreover, the XLR will also feature upgrades to its landing gear. This will include modified wheels and brakes to ensure better take-off speeds whilst reserving the A321neo’s engine thrust values. Airbus has also promised “larger capacities for the aircraft’s water and waste tanks”.
But the comfort of XLR will be on the minds of frequent-flyers and cabin crew. The extended range will be useful in reducing costs and improving convenience. But lengthy journeys in a single-aisle plane will remain uncomfortable for passengers and crew alike.
Airbus has previously stated that the A320 series has one of the widest fuselages for narrow-body aircraft. The manufacturer has also said of the XLR, that
“passengers will experience widebody-type comfort with the optimised Airspace cabin – which already is in service with the A350 XWB and A330neo widebody aircraft.”
Despite their assurances, like with all single-aisle jets, travellers will be unable to stretch out or walk around as they would on larger aircraft. This may be integral to the success or failure of Airbus’ new model.
Commercial production of XLR continues regardless, with it still expected to enter airline service in 2023, despite complications of the COVID-19 pandemic. With 450 orders already made by operators, customers will soon be able to experience the aircraft for themselves.
Words by Jonathan Ritchie