The UK Government recently awarded a £131.5m contract to Raytheon UK to upgrade the RAF’s Sentinel surveillance aircraft. BILL READ FRAeS reports from Broughton to learn more about the upgrade and its implications for the future of the Sentinel fleet.

At the end of October, it was announced that the RAF had awarded Raytheon a £131m contract to continue support services for the Sentinel battlefield and ground surveillance aircraft programme. Under the new Integrated Sentinel Support Solution contract, Raytheon will continue to manage the design, configuration management, modification and support aspects of the Sentinel at its facility in Broughton in Wales. AEROSPACE visited Raytheon UK Airbourne Solutions in Broughton, where the second Sentinel was in the middle of a heavy overhaul, to ask what this contract might mean for the longer-term future of the Sentinel fleet.


Guarding the skies

Radar SAR image from a Royal Air Force Sentinel R1 from RAF Waddington showing floods surrounding a railway line in Oxford in February 2014 (Crown copyright)

The Sentinel is based on a modified Bombardier Global Express business jet powered by two Rolls-Royce BR700s. the first prototype aircraft flew in August 2001. The first production Sentinel R1 made its maiden flight in May 2004, after which the aircraft entered operational service with RAF V (Army Co-operation) Squadron based at RAF Waddington and flew its first operational sortie in Afghanistan in February 2009. There are currently five Sentinels in operation - the first of which was modified in Greenville, Texas and other four at Broughton.

The aircraft operates at altitudes of 40,000ft or above to conduct strategic reconnaissance and provide military commanders with a high-resolution view of a large battlefield area. Crew comprises a pilot, a co-pilot, an Airborne Mission Commander (AMC) and two image analysts. Missions can last up to nine hours.

The Sentinel uses AESA (active electronically scanned array) technology and is equipped with a Raytheon Systems/BAE Systems dual-mode synthetic aperture radar / moving target indication (SAR/MTI) radar known as Sentinel Dual Mode Radar Sensor (DMRS). It. The cockpit has a centrally housed, pull-down screen capable of displaying a moving map, Link 16 datalink information. The aircraft is also equipped with a defensive aids subsystem (DASS) data comprising a towed radar decoy, missile approach warning system and chaff and flare dispensers which can be operated in automatic, semi-automatic or manual mode.

Sentinels have been used in campaigns in Afghanistan, Libya and Mali and is currently operating in Syria and Iraq. In addition to military applications, the aircraft’s capability has also been used for humanitarian and disaster relief missions, including mapping and scaling the floods that hit Southern England in 2014.


Heavy maintenance

Raytheon is currently working refurbishing Sentinel 691, the second aircraft in the fleet.

Because the Sentinels have now been in RAF service for over ten years, the aircraft are in need of an upgrade. The contract to refurbish the aircraft has been awarded to Raytheon UK which ‎has been supporting the Sentinel since 2007. Raytheon is currently working on the second airframe up to the end of this year and will move onto the third in January. “We currently have a contract up to the fourth aircraft with an option for the fifth,” said Roland Howell, Raytheon’s UK Head of Airborne Solutions.

When seen in October the second Sentinel was little more than a basic airframe with no engines, undercarriage or interior fittings. “What we’re doing here is a ten-year ‘HC’ check,” explained Roger Shone, GM of Raytheon Broughton. “HC is basically an airframe inspection but, to get to the airframe. you need to strip everything out. There are a number of other Global Express 5000 business jets currently going through HCs as well but, because the Sentinel has been missionised, it’s no longer a basic model and there’s a lot more work to it. A corporate Global Express needs around three to four months to be refurbished but we need more time than that. We’ve got to take out all the mission equipment, the racks and the panelling, after which we go in there and inspect areas of the aircraft that haven’t been looked at since it was built. If we find issues, whether they’re electrical, connective or a bit of corrosion, then we go in and fix them.”


The Sentinel includes a number of missionised modifications not found on the original Global Express 5000.

“Because we don’t always know what we might find, it’s quite a dynamic programme,” he adds. “We have an integrated master schedule to make sure that we can manage and fix them any problems that might arise. On top of that, the aircraft comes in with a tech log listing additional issues which need to be sorted. We work closely with the project team (PT) on what we do, including timescales and costs. If it’s a basic green aircraft issue, we go straight to Bombardier, if it’s an area that we’ve modified, we bring in the original equipment manufacturer (OEM). We may ask the PT whether to replace parts and buy new ones or we can defer issues until later if it will affect delivery times. We have our own design authority for Sentinel but we work closely with Bombardier and have agreements in place to make sure what we do is airworthy. In the past, if there was a particular issue, Bombardier has supplied us with engineers for one or two weeks. We also talk to engineers at RAF Waddington to come up with solutions which we then discuss with the customer to give it the go ahead.”

The aircraft’s radar system is also being refurbished. “The main work on refurbishing the radar is being done here on site,” said Roger Shone. “Sometimes we also bring in our radar trained field service representative (FSR) engineers from RAF Waddington who have a better skill set. The radar has some maintenance checks that we do some here and some can be done at Waddington.”

“We’re now completed what we call the virgin work and were about go into refit where we start to build the aircraft back up. The aircraft is now essentially like a new green airframe and what we’ll do now is to start putting all the pieces back together. When we’ve done that, we’ll link in the mission systems and test them, after which we’ll fly it to RAF Waddington where they’ll do some more tests over two more weeks. RAF Waddington will add some more capability equipment and then the aircraft is flight mission capable.”


Learning by experience 

Raytheon has used its experience from the first Sentinel refurbishment to reduce the time needed for subsequent overhauls.

Raytheon’s experience with refurbishing the first Sentinel has enabled to accelerate the schedule for the second aircraft and will complete the programme ever faster for the third and fourth. “We’ve taken advantage of the learning we’ve achieved over past few years and doing things more efficiently in terms of structure and manning,” explained Roland Howell. “Roger’s team have applied a great deal of effort working with the customer in terms of Six Sigma working techniques.”

“The first Sentinel was here for 12 months,” said Roger Shone. “This second one will be with us for eight months and, for the third, we’ve come up with six month schedule, which is likely to become the base line for the remaining two. There are still some challenges working with MoD, the project team and the airworthiness authorities but we think we can achieve it. When we took the first Sentinel to bits, we didn’t find anything unusual or unexpected. We learned a lot from the process and we’ve now got a good idea of the type of parts we need to order which helps reduce the schedule. When we did the first HC, we learned what materials and components we needed to replace and in what order. So, when we came to the second aircraft, we were able to reduce lead times by ordering the components in advance, so when we took a panel off we’d have to so we already have the parts available. This has often been a challenge, as third party suppliers all have different delivery times and like to have as much notice as possible.

Shone admitted that one problem had been that of obsolescence. “Everything goes obsolescent eventually,” he admitted. “Vendors go out of business or cease to supply or support components, sub-assemblies, or cards within line-replaceable units (LRUs). We have to look at new ways to ensure that redesign is achieved which may include solutions that might not have previously been economic.”


On-going process

The third, fourth (and possibly the fifth) Sentinels will be refurbished in a different hangar at Broughton.

At present, the second Sentinel is on schedule to be delivered on 30 January 2017. Work on upgrading the third aircraft will begin immediately afterwards but in a refurbished hangar located across the Broughton airfield within the Airbus UK site. “Raytheon is looking to further invest in this region and, with the support of the Welsh government, have invested in a new hangar at our Broughton facility to ensure that we can continue to deliver design-to-flight-trials capability for improved operational availability,” said Raytheon UK’s Business Development Executive, John Craib, “With this investment, the company will be able to manage export work and optimise Sentinel support, reducing the time and costs involved in HC deep maintenance checks.”


Radar upgrades

Upgrades could help keep the Sentinel watching. (MoD) 

Raytheon is hoping that it may be awarded an additional MoD contract to upgrade the Sentinel’s ASTOR (Airborne StandOff Radar) and has prepared plans in case this contract be forthcoming. “Part of the programme includes radar redesign, obsolescence redesign and sat com activity,” said Roland Howell. “We’ve done a range of minor modifications on an ongoing basis and we anticipate some further upgrade activity which will be planned taking into account maintenance, modification and flight test activities.”

According to Raytheon UK’s Airborne Solutions Design Support Services (DSS), the radar upgrades would involve replacing the earlier core mission system servers, workstations and mission software with new hardware. The upgrade will reduce the size, weight and power consumption of the system while enhancing image processing power and throughput. The ASTOR mission software would also be upgraded so that it is compatible with new MMS hardware.


Uncertain future

Who is watching over the watcher?

The long-term future of the Sentinel fleet has been uncertain since the UK Government’s 2010 SDSR (Strategic Defence and Security Review) called for the Sentinel fleet to be retired in 2015 after British forces had pulled out of Iraq. However, this deadline has been granted a number of extensions. However, the 2016 SDSR extended the service time of Sentinel to 2021 as part of a wider intelligence, surveillance, target acquisition and reconnaissance (ISTAR) plan, which plans to keep the Shadow intelligence platform in operation up to 2030 and the Sentry AEW and Rivet Joint signals intelligence aircraft to 2035.

This year’s Farnborough Air Show saw an impassioned plea from RAF’s ISTAR Force commander, Air Commodore Dean Andrew, encouraging the Government not to reduce the size of the Sentinel fleet which were in high demand for different missions. Four of the aircraft are now expected to remain in service until at least 2021.The fifth Sentinel R1 was due to be retired this October but this date has now been put back until March next year.


Government plans?

UK Minister for Defence Procurement Harriet Baldwin gave no clear signals over the Sentinel’s long-term future.

So, given that the UK government has now contracted Raytheon to upgrade at least four out of the five Sentinels for further service, what are its plans for the long-term future of the fleet? This question was put to Harriet Baldwin - Minister for Defence Procurement who came to Broughton to announce the awarding of the £131.5m contract. Unfortunately, when asked whether the fifth aircraft would remain in the fleet beyond March or if the Sentinel fleet would remain in service after 2021, her answers were far from clear. “We are always in the process of evaluating our choices and opportunities across our whole portfolio of ISTAR and C4I (command, control, communications, computers and intelligence) assets", she said. Beyond that, she refused to be drawn, saying only that: “SDSR sets out very clearly the strategic framework. Today is a strong announcement announcing the extension of the platform.”

While admitting that there was no decision as to the future of Sentinel beyond 2021, Roger Shone was still hopeful about its future. “However,” he added. “Because of the performance of the platform and the capability it provides, we fully expect that it will survive beyond that date.”

Bill Read
22 November 2016