David C. Isby details the F-15E and the upgrade programmes destined for America’s tactical bomber
MILITARY
The two-seat McDonnell- Douglas F-15E Strike Eagle was the first air-to-ground version of the F-15, originally designed in the late 1960s. One official description of the F-15E lists the aircraft as a twin engine, tandem seat, fixed wing, all weather, multi-role fighter aircraft equipped with a fully missionised cockpit and a multimode air intercept and air-to-ground radar, giving the aircrew the capability to employ air-to-air and air-to ground munitions, a 20mm cannon, and countermeasures for evading enemy fire.
The F-15E entered service almost 30 years ago, in 1988. It will remain operational to 2035-2045 and beyond, with the decision on its replacement still in the future. Upgraded international versions of the F-15E will be coming off the Boeing production line in St. Louis, Missouri for years to come, with Qatar’s order for 72 F-15QAs, announced in November 2016, making it a future major two-seat F-15 operator. Recent years have seen the US Air Force both make extensive use of the F-15E in combat and invest in a series of upgrades intended to assure it will be able to operate with enhanced capabilities.
Combat Experience
F-15Es went back to Libya on February 19, 2016. They had flown a long way from their base at RAF Lakenheath to attack a Daesh terrorist training camp near Sabratha. The strike, carried out in conjunction with unmanned air vehicle (UAV) participation, was the first F-15E strike on targets in Libya since Operation Odyssey Dawn in 2011. Lakenheath-based F-15Es, forwarddeployed to Aviano in Italy, had played a major role in coalition air operations over Libya. They lost an F-15E to mechanical failure, on March 22, 2011, with its crew picked up by a US Marine Corps MV-22B Osprey tiltrotor.
Libya is unlikely to be the last stop in the combat career of the F-15E that started with Operation Desert Storm in 1991, striking targets in Iraq and occupied Kuwait. Since then, US Air Force F-15Es have played a major role over Bosnia, Kosovo, Iraq, Afghanistan and Syria. F-15Es operating from Camp Lemmonier in Djibouti have reportedly flown combat missions against targets in Yemen and Somalia. In January 2015, the US Air Force announced F-15Es had flown 37% of its 9,600 sorties, up to that time, against targets in Syria and Iraq as part of Operation Inherent Resolve (OIR). In March 2017, unidentified US aircraft, likely to have been F-15Es, joined UAVs in attacking Al Qaedaassociated targets in Yemen.
The F-15E earned the name Mudhen because, unlike earlier Eagles, it was an air-toground design and therefore moves mud when its bombs are dropped, and looks a little like a hen bird when fully loaded. But the reduction in the size of the US Air Force’s fighter force means that F-15Es have to be capable of multiple missions. Before 2001, F-15E units did not devote much attention to the close air support (CAS) mission. This soon changed. Many of the 20,000 US Air Force CAS sorties flown annually in Afghanistan at the height of the US commitment there were conducted by F-15Es. In 2016, Air Combat Command (ACC) announced it would elevate CAS to be the “primary mission tasking” for some F-15E squadrons.
General James Holmes, now commander of ACC, described flying CAS missions in F-15Es in Afghanistan for the Senate Armed Services Committee on March 19, 2015. “As a wing commander at Bagram, during our year there, I flew the F-15E completely in a CAS role. I flew 83 combat missions. I employed 20 weapons. We made modifications to that airplane, starting about seven or eight years ago. We added an advanced targeting pod so that you can see things from altitude and distance that you could only see with your eyes if you were closer. We added radios to the airplane, ones the [Fairchild] A-10 [Thunderbolt II attack aircraft] has, so pilots can talk directly to a ground commander. I could talk to a battalion commander and his TACP [Tactical Air Control Party] on one radio; to the JTAC [Joint Terminal Attack Controller] on the ground on another radio; and to the command and control authority on a third radio. I had a range of weapons that allowed me to do almost everything. There were certainly situations where if I was without a JTAC on the ground and I was caught with troops up very close to me that, if I were the guy on the ground, I’d prefer to have the A-10. But there are certainly situations where if I got into trouble and the closest airplane to help me was 300 miles away then I’d like to have that F-15E come in to get to me.”
Airframe Upgrades
While the US Air Force took delivery of its last F-15E in 2003, its 74% mission capable rate in 2017 is about the same as the less-complex single-seat General Dynamics F-16C. Originally designed for a life of 8,000 flight hours, most operational F-15Es have now logged over 10,000. But the US Air Force has determined it will get 30,000 hours out of its F-15Es, according to a statement made by US Air Force Deputy Chief of Staff, Lt Gen John Cooper in Washington on February 2, 2017.
This extended service life comes from a US Air Force initiative for all aircraft types dubbed ASIP or Aircraft Structural Integrity Program. Boeing has conducted full-scale fatigue test certification to extend the F-15E’s airframe life to 32,000 hours. While the F-15E may need new longerons – if not new wings – to meet this objective, the current Program Depot Maintenance (PDM) schedule includes complete wing overhauls. The F-15E’s wing – internally redesigned to carry heavy bomb loads compared to the F-15C and F-15D – has proven to be robust in service. In addition to depot maintenance, 122 F-15s received a complete rewire at the Warner Robins Air Logistics Complex, Robins, Georgia between 2009 and 2014.
Since an F-15C suffered inflight structural failure over Missouri on November 2, 2007, and because of the type’s projected service life, structural integrity of F-15E airframes is closely monitored. A flaw in the sill longeron of the F-15E’s canopy has been detected, which if left unchecked could have caused catastrophic failure under high-g conditions. A fleet-wide inspection led to repairs on 32 F-15Es.
In 2016, flight-testing of the F-15 Wheels and Brakes System Improvement Program was completed at Edwards Air Force Base, California: the effort is intended to increase brake performance and service life to 1,400 landings between brake changes.
New Radar
Speaking at the Air Force Association Air and Space Conference and Technology Exposition in Washington, DC, last September, the then commander of Air Combat Command General Hawk Carlisle said the F-15E needs an AESA (active electronically scanned array) radar. “The AESA radar will be implemented through the F-15 RMP [Radar Modernisation Program] as well as a digital radar warning receiver that works with the AESA radar, and new ECM [electronic countermeasures] with an ability to conduct EA [electronic attack] and EW [electronic warfare].”
By 2021, all F-15Es will be retrofitted with the Raytheon APG-82(V)1 AESA radar under the RMP.
The RMP replaces the F-15E’s legacy APG-70 mechanically scanned radar with an AESA system designated the APG-82(V)1. The RMP is designed to retain functionality of the legacy radar system while providing expanded mission employment capabilities to include:
• Near simultaneous interleaving of selected air-to-air and air-to-ground functions;
• Enhanced air-to-air and air-to-ground combat identification capabilities. Its synthetic aperture radar (SAR) mode creates high-resolution ground maps from long range;
• Longer range air-to-air target detection and enhanced track capabilities;
• Longer range and higher resolution air-to-ground radar mapping; and
• Improved ground moving target track capability.
The RMP upgrade is also intended to address legacy F-15E radar system suitability shortfalls including poor reliability, parts obsolescence and high sustainment costs.
The RMP APG-82(V)1 design leverages capabilities from currently fielded AESA radar systems. The APG-82(V)1 antenna and power supply are currently in use on the F-15C APG-63(V)3, and the radar receiver/exciter and common integrated sensor processor are based on the F/A-18 Super Hornet APG-79 AESA radar system.
Other hardware and software modifications include a more powerful environmental control system, updates to the aircraft operational fiight programme and electronic warfare software, a new radio frequency tuneable filter, and aircraft modifications to include a new wideband radome and wiring changes.
The Radar Modernization Program came into being in October 2008 when the US Air Force awarded Boeing a $238 million system development and demonstration (SDD) contract to modernise the F-15E Strike Eagle’s radar system.
Twenty-six months later, an F-15E fitted with an APG-82(V)1 radar flew for the first time from Eglin Air Force Base, Florida on January 18, 2011. Following the successful functional check flight and completion of a flight test readiness review, the F-15E, assigned to Air Force Materiel Command’s 40th Flight Test Squadron, started an aggressive 14-month, 110-sortie developmental flight test programme at Eglin.
Such is the need to field the APG-82 on the F-15E, the Air Force also fitted an APG-82 to another F-15E assigned to Air Combat Command’s operational test organisation, the 53rd Wing, so some early operational testing could run concurrently with the developmental test effort.
According to the FY2014 Annual Report by the Director, Operational Test and Evaluation (DOT&E) released in January 2015, the Air Force Operational Test and Evaluation Center (AFOTEC) conducted APG-82 Initial Operational Test and Evaluation (IOT&E) from March to September 2013 to assess the system’s operational effectiveness, operational suitability, and mission capability.
The APG-82 IOT&E included 85 sorties and 175 hours of dedicated flight testing in which AFOTEC evaluated the F-15E fitted with the APG-82 in an operationally representative cross-section of counter air and counter land operations employing both live and simulated air-to-air and air-to-ground weapons in realistic tactical scenarios.
Assessment
DOT&E assesses the F-15E RMP:
• As operationally effective and operating modes and pilot-vehicle interfaces are functionally equivalent with those of the legacy APG-70 radar system.
• Provides significantly improved capability in the air-to-air operational environment compared to that of the legacy APG-70 radar system.
• Demonstrated comparable air-to-ground radar performance compared with that of the legacy system and improvements in target location accuracy.
• Software stability did not meet the Air Force Mean Time Between Software Anomaly (MTBSA) criteria of 30 hours during IOT&E. However, post-IOT&E flight testing of a subsequent radar software version corrected the single anomaly that resulted in six of 12 observed software stability events encountered in IOT&E.
• Hardware operational reliability and maintainability support F-15E operational availability requirements. However, limited flight hours and the low failure rate observed throughout the evaluation period precluded DOT&E’s ability to confirm, with confidence, that the APG-82(V)1 hardware reliability, maintenance man-hours per flight hour, mean repair time, and built-in test fault diagnostics requirements were met. Therefore, additional monitoring of system suitability will be required in order to fully assess system performance in these areas. At the conclusion of the IOT&E, there were unresolved RMP system support and deployable shortfalls which included:
• The Air Force currently lacks a long-term programmatic solution for providing ground-cooling carts to service the APG- 82(V)1 at operational unit locations.
• The Gore® communications cables that connect the radar common integrated signal processor to the receiver/exciter cannot be functionally checked with the Joint Services Electronic Combat Systems Tester.
• The Air Force has yet to define the readiness spares package provisioning necessary to determine the number of 463L pallets and Gore® communications cables needed to support the deployment of APG-82-equipped operational F-15E squadrons.
DOT&E Recommendations
As of January 2015 the Air Force was addressing APG-82 software stability issues previously identified in the FY2012 and FY2013 Annual Reports.
Recommendations made to the Air Force in the FY2014 report:
• Correct the anomalies identified in IOT&E that resulted in software reliability events to ensure F-15E APG-82 software stability meets Air Force requirements.
• Provide a long-term solution for APG-82 ground cooling carts, Gore® communications cable spares posture and ground test set compatibility, and readiness spares package provisioning and deployment pallet posture, in order for the F-15E APG-82 system to be fully supportable and deployable.
• Continue to monitor installed system reliability, availability, and maintainability metrics to confirm, with confidence, that APG-82(V)1 hardware reliability, maintenance man-hours per flight hour, mean repair time, and built-in test fault diagnostics performance meet the Air Force requirements.
Prior to the January 2015 release of its FY2014 Annual Report, in March 2014, DOT&E published a classified report on the operational effectiveness, suitability, and mission capability of the F-15E RMP system upon completion of the IOT&E data analysis. That same month, the F-15E APG-82 entered full-rate production.
Operational Fielding
On July 16, 2014, the Air Force announced the first F-15E fitted with an APG-82(V)1 radar, had flown 11 flight hours. The aircraft and aircrew were assigned to the 389th Fighter Squadron, part of the 366th Fighter Wing based at Mountain Home Air Force Base, Idaho.
Under supervision of Boeing representatives, the aircraft was modified by Air Force personnel at Mountain Home and took nearly three months to complete and was finished in June. Modification of the 366th Fighter Wing’s 45-plus F-15E fleet was expected to be completed this year.
Commenting on the new radar’s lower maintenance footprint, an avionics manager assigned to the 366th Fighter Wing said: “The old [APG-70] radar system is hydraulic, has moving parts and requires three maintainers to perform repairs after every 30 flight hours. The new radar system is a beam scan, doesn’t have any moving parts and is projected to only require one maintainer to perform repairs after more than 2,000 flight hours.”
Over on the East coast at Seymour Johnson Air Force Base, North Carolina, home of the 4th Fighter Wing, the largest Strike Eagle unit in the Air Force, received its first aircraft upgraded to RMP standard in 2016. Equipped with 90-plus aircraft, the fleet is expected to take between seven and nine years to upgrade.
In November 2016, Boeing announced the APG-82(V)1 will equip new-production F-15QAs.
New Sub-systems
In addition to the AESA radar, other system upgrades are also being integrated on the F-15E to provide a networked tactics capability.
The BAE Systems’ Eagle Passive/Active Warning and Survivability System (EPAWSS), will replace the ALQ-135 jammer and other internal electronic warfare systems.
EPAWSS is an open architecture electronic warfare system that integrates the BAE Systems ALQ-239 Digital Electronic Warfare System (DEWS) with passive sensors and cockpit displays, on-board jammers and ALE-47 chaff and flare dispensers. A follow-on increment will add the ALE-55 towed jammer decoy system.
Two F-15E Strike Eagles leave the KC-135 Stratotanker after receiving fuel over Iraq during a mission in support of Operation Inherent Resolve. SSgt Douglas Ellis/ US Air Force
EPAWSS will give the F-15E a precise geolocation capability to enable the use of advanced datalinks – also planned for the F-15E – for precision networked targeting without requiring radar emissions, a capability already demonstrated by US Navy F/A-18F Super Hornets.
In 2015, the EPAWSS entered the engineering and manufacturing development (EMD) phase which is scheduled to run until 2020.
In early November 2016, the US Air Force awarded Boeing a $478 million contract for the EPAWSS EMD phase, which includes integration on the aircraft and with its onboard systems.
Upon conclusion of the EMD phase, the EPAWSS will be ready to enter production, along with the associated Suite 9 software.
Eight F-15s will have the EPAWSS fitted for its flight test programme which is currently expected to start in 2018.
As of late March 2017, the Air Force plan involves upgrading all operational F-15C and F-15D Eagles and F-15E Strike Eagles with the EPAWSS at a cost in excess of $7.5 billion for over 400 aircraft.
Boeing selected Lockheed Martin Missiles and Fire Control to develop a long-wave, high-resolution pod-mounted infrared search and track (IRST) system for the F-15. Lockheed Martin’s solution is based on its IRST21 sensor, processing and networking technologies and called the Legion IRST.
Lockheed Martin says the Legion IRST is a multi-function sensor system that supports collaborative targeting operations in radardenied environments providing aircrew with high-fidelity detection and tracking of air-to-air targets. The system designed for the F-15E can be housed in a standard 16-inch diameter pod carried on one of the under-fuselage stations or mounted in a larger pod similar to that used for the Talon Hate communications system, and carried on the centreline station.
Components include an advanced processor, the infrared search and track sensor and a real-time video streaming two-way datalink so troops can see what the pilot sees. The F-15E’s pod configuration will be fully integrated with the aircraft’s sensor suite (the APG-82 AESA radar and the EPAWSS) and linked directly to the system’s communication suite. This level of integration provides a multi-spectral target acquisition capability so if the radar detects a potential target, the pilot can automatically point the IRST to provide identification.
The Legion system integrated on the F-15E will also take advantage of the pod’s ability to house additional systems and feature the enhanced sensors used in the latest Sniper targeting pod dubbed the Sniper ATP-SE or Sniper Advanced Targeting Pod – Sensor Enhancement. The company says the ATP-SE allows aircrew to detect, identify, automatically track and laser designate small tactical targets at long ranges, supporting employment of all laser- and GPS-guided weapons against multiple fixed and moving targets.
F-15C and F-15D Eagles will be the first types to use the Legion pod for the air-to-air role, followed by the F-15E for air-to-ground and air-to-air roles.
The F-15E’s existing mission computers are being replaced with new high-speed examples called ADCP IIs or Advanced Display Core Processor II.
The ADCP II enables integration and critical processing capacity for systems such as the APG-82 radar, EPAWSS, Legion IRST, and future software suite upgrades. Each ADCP II is linked to the sub-systems via gigabit ethernet and fibre channel connections, and provides better stability and additional tolerance to faults.
Air Force Materiel Command’s 40th Flight Test Squadron first flew the ADCP II and its associated Suite 8E upgraded software on an F-15E at Eglin Air Force Base, Florida on July 8, 2016.
Other upgrades for the F-15E include a digital video recorder and Mode 5 identification friend or foe (IFF) transponder.
Current programmes are not necessarily the last word in F-15E upgrades. Boeing has offered its Eagle 2040C upgrade to the US Air Force and international operators boasting longer range with conformal fuel tanks, increased payload (potentially increasing the AIM-120 AMRAAM load-out from eight to 16 missiles) and weapon adaptability.
The 2040C upgrade was primarily intended for F-15C and F-15D Eagles, many of the components are applicable to F-15Es and export variants of the Strike Eagle.
In addition to Eagle 2040C, Boeing has developed a range of upgrades including an improved cockpit design with large area displays developed for the Advanced Super Hornet project. Low-observable technology offered to the Republic of Korea for the proposed F-15SK could be made available to other allies. That all said, the US Air Force does not currently have a programme to fund any such technologies for upgrading the F-15E.
New Weapons
Boeing’s adverse weather, autonomous GBU- 39/B Small Diameter Bomb I (SDB I) glide weapon currently provides the F-15E with a stand-off precision attack capability. The F-15E can carry up to 36 GBU-39s (four per bomb rack unit) enabling the aircraft to strike multiple targets in a single sortie. However, the Mudhen’s stand-off strike capability is to be further improved with the release to service of the Raytheon GBU-53/B SDB II - a joint US Air Force-US Navy programme. Equipped with a terminal seeker with three modes of operation, millimetre wave radar to detect and track targets through weather, imaging infrared for enhanced target discrimination, and semi-active laser to enable the weapon to track an airborne laser designator or one on the ground, and extendable wings, the SDB II precision-guided glide weapon can attack moving targets at extended ranges - a capability currently unavailable to the US Air Force throughout its extensive arsenal of GPS/INS-guided weapons.
The SDB II underwent live-fire testing with an F-15E in July 2016, yet the weapon’s required assets available (RAA) for the F-15E – a critical precursor to achieve initial operational capability (IOC) which was originally scheduled for July 2017 – has slipped to January 2018. Under the current plan, the SDB II will complete its operational testing in 2020. Hardware and software upgrades for the SDB II, including anti-jam technologies, are being developed and will be introduced post-IOC.
In practice, it’s feasible for a single F-15E to carry 40 GBU-53s (four per BRU) on ten BRU-61/A pneumatic multi-carriage bomb rack units, though this is an unlikely load-out.
While there has not been an announcement about integrating the BAE Systems Advanced Precision Kill Weapon System (APKWS) on the F-15E, its ability to provide semi-active laser (SAL) accuracy from medium altitude, while minimising the risk of collateral damage, would be a useful weapon for close air support missions.
Originally introduced on helicopters and operational on US Air Force F-16s, Lt Gen Holmes likes the 2.75-inch (70mm) APKWS: “It’s a point-and-shoot weapon with a similar [kinetic] capability to the A-10’s GAU-8 gun and you can hang it on an F-16, or an F-15E.”
An F-15E pilot can use the Vision Systems International’s Joint Helmet Mounted Cueing System (JHMCS) to cue weapons and sensors against either airborne or ground targets. The JHMCS comprises a modified HGU-55/P helmet incorporating a visor-projected headup- display (HUD). The helmet’s HUD projects target symbology and aircraft performance information on to the visor allowing the pilot to keep eyes on target. F-15E pilots first used JHMCS in combat over Afghanistan in 2010, but JHMCS is currently only available to the pilot and not the weapon system officer in the aft cockpit. Once the Suite 7 OFP software upgrade is introduced to the F-15E weapon system, weapon system officers will then have JHMCS capability.
The F-15E in a Fifth- Generation World
When Air Combat Command’s 388th Fighter Wing based at Hill Air Force Base, Utah deployed seven Lockheed Martin F-35A Lightning IIs to Mountain Home Air Force Base for an operational evaluation in June 2016, they suffered no losses in air-to-air engagements. Their adversaries were F-15Es assigned to the resident 366th Fighter Wing.
The ongoing challenge for Air Combat Command is how F-15Es can carry out missions if opposed by hostile fifth generation fighters while both benefitting from, and providing additional capability to US and allied fifth-generation F-35s and the F-22s. To meet the challenge, the US Air Force is expanding the F-15E’s capability for networked tactics. Today, F-15Es fight as part of a network, linked to troops using the ROVER (Remotely Operated Video Enhanced Receiver) or to UAVs. The latter is a scenario in which the weapon systems officer can watch a live video feed fed from a UAV before coming in range of the target.
One of the most important future upgrades for the F-15E will be a capability to enable network connectivity with fifth-generation fighters without compromising the latter’s stealth capabilities. Networked tactics make it possible for F-15s to “light up” using their radars to detect targets on the ground (or in the air) and ensure the data created is available to fifth-generation fighters for increased situational awareness but without the need for F-22 and/or F-35 pilots to activate their own radars.
Gaining mutual advantage from fifth-generation stealth aircraft has required Air Combat Command to develop a pod-based system called Talon Hate which functions like a miniaturised version of the Air Force’s Battlefield Air Communications Node (BACN). Talon Hate acts as translator between an F-15’s Link 16 datalink and an F-22’s stealthy in-flight datalink. The Talon Hate system was originally scheduled to achieve initial operational capability in 2015 with four pods, but only entered operational test in early 2016. F-15C Eagles tasked with air-to-air missions will likely be the first aircraft to use Talon Hate. Last year, the then commander of Air Combat Command, General Hawk Carlisle said Air Combat Command needed the system yesterday. “The Talon Hate pod is a programme of record and is being tested. With software programmable radios, we are looking to transition between waveforms and determining what kind of antennas and apertures allow us to do multi-capability,” he said.
Upgrading and expanding the F-15E’s Link 16 datalink communications capability will include F-35s and, after upgrade, F-22s. Hawk Carlisle said: “Link 16 is going to be around for a while. It has got to be part of the solution to the Air Combat Command objective of creating and operating an aerial layered network with the Navy.” This will be achieved with the Link 16 Imagery Processing System [LIPS], which will give the F-15E cockpit the ability to receive, control and display geo-registered imagery accompanied by precise and reliable GPS coordinates enhancing the F-15E’s capability to detect and strike time critical targets. An F-15E will receive and transmit geo-registered imagery using Tactical Targeting Network Technology (TTNT), also known as the Multifunction Information Distribution System-Joint Tactical Radio System Increment 2: a four-channel radio system with Link 16, tactical air navigation capabilities, Link 16 Enhanced Throughput and a wideband Link 16 transceiver.
TTNT-enabled capabilities have been repeatedly demonstrated by the US Navy as part of its Naval Integrated Fire Control- Counter Air (NIFC-CA) network. NIFC-CA is being developed to link aircraft, sensors and warships together, to extend the range of weapons and allow over-the-horizon engagements, integrating multiple systems, airborne and on the ground, into a single kill chain.
Director of Air Warfare in the office of the Chief of Naval Operations, Rear Admiral Michael Manazir, wants TTNT-enabled F-15Es to link into the NIFC-CA network. “Ideally, when flying with a blue aircraft, I want to be able to connect with them. Same as talking with somebody on a radio…you talk on a secure frequency. Now, I want to be able to share actual information across our machines with them,” he said.
Buying new aircraft rather than upgrading older ones is usually the preferred option for the US Air Force. But at present, the current programme of record for 1,763 F-35As does not include replacing the F-15E. Similarly, air forces flying export variants of the F-15E are planning to keep them well into the future, some are also going to be flying the F-35A. Current upgrade programmes will enable the F-15E to carry out its mission even in a future air environment potentially dominated by fifth-generation fighters.
