More than a decade after the concept was first considered, the first aerial-refuelling tanker based on an Airbus aircraft is in flight testing, writes Graham Warwick. As tests of the first A310 Multi-Role Tanker Transport (MRTT) gather pace, EADS is finalising the first orders for a follow-on A330-based tanker: the aircraft the European company plans to offer the US Air Force.

With six A310s to be converted to tanker/transports for the German and Canadian armed forces, five A330 MRTTs to be produced for the Royal Australian Air Force and a mix of around 16 new and used A330s selected to meet the UK Ministry of Defence's Future Strategic Tanker Aircraft (FSTA) requirement, Airbus has taken an early lead over Boeing in the next-generation tanker market.

The lead could switch overnight if the USAF's stalled lease/purchase deal for 100 Boeing KC-767A tankers is approved, but EADS is increasingly confident it will be invited to compete for future US tanker contracts, taking the potential world market from 110 aircraft to 550. That confidence was boosted by the recent wins over the 767 tanker in Australia and the UK.

Much has changed since the USAF rejected EADS's KC-330 tanker in 2001, citing the European company's lack of relevant experience. The first A310 converted to MRTT configuration, with two underwing hose-and-drogue pods, was rolled out by EADS last year and entered flight testing in March. In January, the EADS-led AirTanker team was selected for final negotiation of the 27-year, £13 billion ($23 billion) FSTA private-finance initiative programme. In April, Australia announced a $1.4 billion deal to acquire five A330 MRTTs, the first Airbus tanker/transports to be equipped with a refuelling boom - the key to competing for any future USAF contract.

Six A310-300s are being converted to MRTT configuration by EADS Elbe Flugzeugwerke in Dresden and Lufthansa Technik in Hamburg - four for the German air force and two for the Canadian Forces. The aircraft has two Flight Refuelling Mk32B-900 pods under the outboard wing sections, each with a 23m (75ft) hose and 1,500 litres/min fuel transfer capability. The pods are fed from the centre wing tank by new fuel lines and hydraulic transfer pumps. Four auxiliary tanks are installed in the lower cargo hold, each holding 5,700kg (12,500lb) of extra fuel. Five such tanks can be fitted in the A310 MRTT, for a total fuel capacity of almost 77,500kg.

Air-to-air refuelling is monitored from an operator station installed behind the cockpit, using infrared floodlighting and cameras mounted in the wing/fuselage fairing. Night-vision-compatible external lighting is installed. As a transport, the A310 MRTT can carry 214 troops, or 54 passengers and 12 cargo pallets.

The first German A310 MRTT was due for delivery this month, but by early May EADS had completed only a handful of the planned 40-45 test flights - around 15 of which will involve refuelling Panavia Tornados. Canada is due to receive its first aircraft in August, after which refuelling tests with the Boeing CF-18 are planned.

EADS says its experience with the A310 MRTT is directly transferable to the A330. The version planned for the FSTA programme - assuming talks on the complex deal are successful - uses the same 900-series underwing pods, with 27m hoses, while some of the UK's aircraft will also be equipped as three-point tankers with a 2,270 litre/min Flight Refuelling Mk40 hose-drum unit in the lower aft fuselage. The twin-engined A330 and four-engined A340 share the same wing, allowing the pods to be mounted on the existing hardpoints for the outer engines.

Due for delivery from 2007, ahead of arrival of the first FSTA A330s, Australia's aircraft will be the first MRTTs to have a refuelling boom as well as underwing pods. Under company-funded development by EADS Casa, the fly-by-wire boom is the last piece in the Airbus tanker puzzle. Qualification flight-testing on an A310 demonstrator is set for late next year, followed by certification on the A330.

Designed for operation at altitudes up to 35,000ft (10,700m) and airspeeds between 180kt (335km/h) and 325kt, the boom can transfer more than 4,500 litres/min. Boom extension, retraction and flight control are via dual-redundant electromechanical actuators. The fly-by-wire system provides automatic load alleviation.

The A330 tanker will normally be flown by a pilot, co-pilot and mission controller, but the dual-redundant boom operation console allows for a fourth occupant to take over during training and refuelling missions. The operators share a centre-console pitch-roll sidestick, and monitor and control the boom via an enhanced-vision system that combines visual and infrared sensors, with a rangefinder and flight-director symbology on stereoscopic displays.

A full-scale test rig is being readied at EADS Casa's Getafe, Madrid plant, with ground testing of a prototype boom system set to begin in November. The rig includes all boom hardware, including fuel system, flight controls, operator console and enhanced-vision system. Manufacture of the installation kit is set to begin in September, with conversion of the A310-300 to begin in January. Flight testing is planned to run from September to December 2005.

All of the A330 MRTT's 111,000kg of fuel is contained in the existing wing tanks, leaving the lower hold for cargo. As a transport, the aircraft can carry up to 380 passengers, or 70 stretchers. Maximum zero-fuel and take-off weights for the commercial passenger and military tanker variants are identical, as is the basic payload/range performance, says EADS.

The European manufacturer believes the development risk in the A330 MRTT is low because both the hose-and-drogue and boom refuelling systems will be flight tested and qualified first on the A310. "Even though real flight testing of the A330 with pods has not been performed," says EADS, flight testing on the German A310 MRTT, windtunnel testing on an A330 model, and proximity flight tests with an A330 and fighters "have given us enough confidence in the solution".

Source: Flight International