David C Isby reviews the US Air Force fleet of McDonnell Douglas F-15 Eagles
US Air Force F-15C Eagles have been, for decades, undefeated champions in air-to-air combat. They have accounted for 38 victories - the vast majority of aircraft shot down by US aircraft since the end of the Cold War - without suffering losses in return. Currently, the US Air Force operates 212 single-seat F-15Cs and 24 two-seat F-15Ds, which, along with its fleet of Lockheed Martin F-22 Raptors, remain the only American air superiority aircraft flown by pilots trained in the art of air-to-air engagement.
Still at the edge
“From an operational perspective … the F-15 has been an absolutely spectacular airplane, a great airplane. The same airplane I flew in 1989 is still flying today. When I flew it in 2001, it had 7,000 [flight] hours. We extended it and keep extending it,” said Lieutenant General Mark Newland, air force deputy chief of staff for operations, at a briefing in Washington on April 12, 2017. But the average age of the F-15 fleet is now 33 years, and the 1970s design makes its potentially vulnerable to new-technology advanced threats.
F-15C and F-15Ds equip three active-duty squadrons – one based in the UK and two in Okinawa - and five Air National Guard squadrons all based on the periphery of the continental United States. While the Air National Guard squadrons frequently deploy overseas, their primary mission since the Cold War has been homeland air defence. While this originally meant intercepting Soviet long-range bombers and offcourse airliners, the mission has taken on additional importance since the terrorist attacks of September 11, 2001. They must now also be able to defeat low-flying cruise missiles and unmanned air vehicles.
Today, F-15s are still at the sharp end of airpower, most recently providing fighter cover for the US-UK-French strike against Syria on 13-14 April 2018. Each of the two strike waves was protected by a flight of four F-15Cs from the 493rd Fighter Squadron forward deployed to Vaiano Air Base, Italy from RAF Lakenheath, England for the operation.
Throughout the years of Operation Inherent Resolve, operating over Syria and Iraq, F-15s, supplemented by F-22s, have provided much of the coalition’s air-to-air capability; as have F-15Es Strike Eagles, when one of the latter shot down an armed Iranian-made Shaheed 129 drone over Syria on June 20, 2017.
When not deployed to fly air policing missions in Iceland, Bulgaria, Romania and Lithuania on NATO’s eastern frontier, the squadrons’ experience in alert duty and intercepting potential threats proved valuable.
As the Lockheed Martin F-35A Lightning II continues to equip fighter squadrons in the 388th Fighter Wing at Hill Air Force Base, Utah, the first US Air Force combatcoded wing, F-15s are training with them to create and hone tactics that will enable both types to be more effective when flying together.
Speaking to media at RAF Lakenheath during the first European F-35A deployment by the 388th in April 2017, Lt Col Scott Taylor, an F-15C pilot and the 493rd Fighter Squadron’s director of operations discussed his unit’s first opportunity to train with F-35As. He said: “The sensor fusion capability of the F-35A provides [F-15s] unprecedented situational awareness, which is invaluable when you’re fighting against a high-end threat. The key is, it allows us to make quicker, more accurate decisions on targets.”
The Air Force is funding upgrades for its F-15 fleet throughout the current Future Years Defense Plan (FYDP). A plan that includes the budget for FY2019 and FY2020, and planned spending for the subsequent four years. How many F-15 aircraft will receive each upgrade – those that receive the full set are referred to as Golden Eagles – will depend on the Air Force’s upcoming decision on how long the aircraft will remain in service.
The most significant upgrade involves installation of the Raytheon APG-63(V)3 active electronically scanned array (AESA) radar system on 179 aircraft, of which more than 125 had been fitted by the early part of the year.
In addition to a new radar, Eagles will be fitted with a new mission systems computer dubbed ADCP II or advanced display core processor II running the latest Suite 9 software to introduce a range of enhanced capabilities most significantly Boeing’s Eagle Passive- Active Warning and Survivability System or EPAWSS. Suite 9 software enables integration of any threat detected by EPAWSS with the overall battle space’s picture displayed in the cockpit. Designed by BAE Systems, the electronic warfare capabilities of the EPAWSS includes threat detection, active jamming, and decoy, chaff and flare dispensation capabilities.
Following its critical design review in February 2017, the EPAWSS is undergoing labbased testing; flight-testing on F-15Cs and F-15Es will start before the end of this year. Retrofits are planned take place in the early 2020s, and while the current Air Force plan is to fit the system on its F-15Cs, any change to retire all or part of the fleet would increase the per-aircraft cost.
Air Combat Command’s 53rd Wing is currently flight-testing the Legion pod, an infrared search and tracking system that provides long-range detection and tracking of airborne threats; a process that started at Eglin Air Force Base, Florida in 2014. The Legion pod’s primary sensor is the Lockheed Martin IRST21 long-wave infrared system, as used in the ASG-34 pod that is currently carried by US Navy F/A-18 Super Hornets.
The Legion pod will give the F-15 an enhanced air-to-air detection capability against low observable targets while allowing missile shots without the need to use the radar system. Equipped with an integral datalink, the system uses open architecture to enable installation of a multitude of sensor options on the flight line as required for each mission scenario such as a pylon-mounted fibre-optic towed decoy. A production order is expected before the end of 2018.
The Air National Guard now operates more F-15C-equipped squadrons than its active-duty counterpart. Consequently, the Air National Guard Bureau is also funding upgrades to its Eagles, one of which is the F-15 Persistent Air Dominance Enabler programme or PADE valued at $441 million. One component of the PADE programme is a conformal fuel tank (CFT) system produced by Israeli Aircraft Industries. Traditionally, the US Air Force has primarily relied on underwing drop tanks as part of its Eagle fuel system, except for F-15Cs and F-15Ds assigned to the 57th Fighter Interceptor Squadron based at Naval Air Station Keflavik, Iceland between July 1985 and late 1995.
The latest CFTs are similar to those that will be used on Boeing’s Block III F/A-18 Super Hornet, carry 12,000lb (5,500kg) of fuel, in addition to the 13,000lb (5,900kg) internal fuel load.
The PADE programme will also provide each of the Air National Guard’s 105 combatcoded F-15Cs with additional weapon stations mounted directly to the CFTs or multi-rail missile launchers carried on the underwing hard points previously used for external drop tanks thereby increasing the number of air-toair missiles, multi-spectral pods or electronic warfare and infrared countermeasures carried.
An F-15C assigned to the Louisiana Air National Guard’s 159th Fighter Wing was the first aircraft to be fly fitted with the latest CFTs on a test and evaluation flight in February 2018. The PADE programme will procure one set of CFTs for each of the Air National Guard’s 105 combat-coded F-15Cs.
US Pacific Command has an urgent operational requirement for a fourth-to-fifth generation communication link to enable F-15Cs or F-15Ds to share data with fifthgeneration F-22 Raptors and F-35 Lightning IIs. The solution? Boeing’s Talon HATE pod developed by its Phantom Works division.
Mounted on a F-15C, a Talon HATE pod receives data from Link 16 and the Common Data Link protocol systems and transmits the fused data via the wideband global satellite communication system. Talon HATE has already taken part in Exercise Red Flag and Northern Edge in the hands of Air Combat Command’s operational test organisation, the 53rd Wing.
The upgrades listed for the F-15C have largely been made possible because the same systems are also required for the Air Force’s two-seat F-15E Strike Eagle (which will be in service until the 2040s) and international F-15 users (which may be flying even longer than that).
Despite the current plans, the US Air Force has been reluctant to invest in F-15C upgrades beyond FY2020 - which raises questions about the type’s likely future, and no commitment has been made to either upgrade or retire.
Lieutenant General Jerry Horn, deputy chief of staff for plans and requirements, told the Senate Armed Services Committee on April 18, “The study is still ongoing. … There’s nothing off the table”.
An uncertain future
The F-15C may be undefeated in air-to-air combat, but its future has been in question since November 2007, when F-15C assigned to the Missouri Air National Guard’s 131st Fighter Wing suffered an in-flight structural failure of a fuselage longeron during air combat manoeuvring. The pilot ejected as the Eagle disintegrated. A fleet-wide grounding followed, followed by structural fixes. But problems have remained. A Lakenheath-based Eagle was lost due to manufacturing defects in the nose assembly. In April 2018, all 30 F-15C and F-15D Eagles assigned to Oregon Air National Guard’s 173rd Fighter Wing were grounded for inspection.
All F-15s built prior to the F-15E (which introduced a redesigned, reinforced, structure) were designed for 9,000 flight hours of airframe life. In August 2016, the Air Force awarded Boeing a five-year contract for static fatigue testing on two F-15C airframes to determine the type’s likely service life. Current Air Force planning sees a final decision on the future of the F-15C and F-15D Eagles to be taken when the study is complete.
But the Air Force may look to an alternative before the fatigue testing is finished. Retaining the F-15C and F-15D fleet in service beyond the mid-2020s – possibly into the 2040s – will require structural upgrading as part of a service life extension programme (SLEP). This could mean rebuilding the centre fuselage section and possibly re-winging. The peraircraft cost, depending on the extent of the work required and the number of aircraft to be upgraded, has been estimated by Air Combat Command at $30-40 million per aircraft if the most expensive upgrades are required; the cost values in current-year dollars.
Boeing, however, believes that an F-15C and F-15D SLEP could be carried out for a fraction of that cost, citing a cost of about $1 million. The company has pointed to its success with the F/A-18 Hornet SLEP programme for the US Navy, US Marine Corps and international operators to demonstrate what might be achieved to extend the service life of the Eagle.
Beyond a SLEP, Boeing has proposed an extensive upgrade incorporating a wide range of technologies and capabilities developed for later versions of the Eagle and Super Hornet. Called F-15 2040C, the project offers an ability to carry up to 16 AIM-120 AMRAAM air-to-air missiles or air-to-surface standoff weapons such as the Raytheon GBU-53/B Small Diameter Bomb II with folding wing sets; being fitted with CFTs would provide extended on-station time. Consequently, F-15 2040C attracted interest from both the US Air Force and international operators.
Boeing presented 2040C as an “arsenal plane”, able to stand off and engage air or surface targets identified by fifth-generation fighters penetrating hostile airspace. All this without the F-15Cs having to expose their positions, and preventing coalition air defences in general and the size-limited F-22 force in particular, being saturated by large numbers of aircraft or cruise missiles. Despite the appeal, the 2040C upgrade currently appears unlikely to go forward unless a decision is made to invest in extending the Eagle’s service life. With Boeing’s Eagle production line at its St Louis facility scheduled to remain building new two-seat versions for Saudi Arabia, Qatar and – possibly – Israel until after 2020, the Air Force could choose from a range of options ranging from near-term retirement to extensive upgrades.
The coming decision
“The Guard loves the F-15, but the ones that sit on the ramp today are old airplanes”, said General Newland. The US Air Force has long preferred to upgrade old airplanes when it can buy new ones. Newland said there are “limits to what you can do with SLEPs. It comes down to fleet management”. His concerns also include the potential for the increasing costs of operating aging F-15C and F-15Ds. He said: “It takes a lot of money and a lot of maintenance expertise to keep these airplanes flying every day”.
The new US national defence strategy emphasized the need to be ready to match great power competitors, making the air-toair mission more important for the Air Force than it had been since the end of the Cold War. The Air Force is looking to expand its current 55 fighter squadrons flying fighters and attack aircraft to 57 over the course of the current FYDP. Retiring additional F-15Cs and F-15Ds (beyond the 31 already planned) would make it harder to achieve that goal. But in the mid-2020s, when the Air Force could have to ramp up and quickly carry out an F-15C/F-15D SLEP, it will be engulfed in the bow wave; the planned surge of Air Force procurement spending to pay for new-production F-35As, B-21 Raider stealth bombers, KC-46 Pegasus tankers and T-X trainers, not to mention other priorities.
One near-term response may be an increase in the F-35A production rate to enable it to re-equip F-15C units. Even though the F-35A is designed primarily for air-to-surface rather than air-to-air missions, the Air Force – and the Congress – may well prefer to pay for new F-35As (with a unit cost of under $100 million valued in current-year dollars) than upgrading F-15Cs and F-15Ds. General Horn said: “We are looking at the air superiority mission and what is the best way to do it. The near-term may also include F-35s going to those F-15C units for that role”.
A near-term alternative for re-equipping Air National Guard F-15C squadrons would be to use upgraded F-16Cs and F-16Ds fitted with AESA radars. “If you put an AESA radar in the front of an F-16, can it do home defence? Yes”, Newland said.
In the longer term, the Air Force envisions the ultimate F-15C replacement to be whatever emerges in response to its Penetrating Counter Air (PCA) requirement. Planned to enter service in the 2040s, PCA is not seen as a sixthgeneration fighter - though it may well lead to one being designed and built - but rather as a networked manned/unmanned capability able to gain air superiority over enemy territory in the face of the most sophisticated air and ground threats than can be anticipated. The Air Force is prioritizing investment in PCA - which it sees as necessary to retain an essential core competency - and upgrading and operating F-15Cs and F-15Ds may end up losing out in the competition for resources.
This decision will not be made by the Air Force alone. A decade ago, when there were fewer air-to-air threats on the horizon, the Department of Defense cut short F-22 procurement at 195 aircraft from a planned 750. The Air National Guard’s F-15C squadrons have already found strong defenders in the Congress. The Air Force would likely face opposition to retiring these aircraft without replacing them.
The F-15 Eagle has been an undisputed champion of air combat. But, facing increasing threats, “we have to quit thinking like the champion and start thinking like the contender”, Newland said in Washington on January 4. Whether this will mean a nearterm retirement or extended service life for the F-15C and F-15D Eagles remains to be seen.