While the Joint Strike Fighter programme may soon be under way, an ageing inventory of US frontline combat aircraft still needs to be maintained

Relief at long last is in sight for the US Air Force's hard-pressed tactical aircraft fleet. The Lockheed Martin/Boeing F-22 Raptor has received initial production approval and, with the conclusion of the concept demonstration phase, the Joint Strike Fighter (JSF) is expected to move to full-scale development. But there still remains the formidable financial challenge of keeping the incumbent inventory of ageing Boeing F-15 Eagles, Fairchild OA/A-10 Thunderbolts and Lockheed Martin F-16s flying for years to come.

The task faced by USAF Air Combat Command (ACC) is twofold: ensuring that fighters, which by any previous measure would now be due for retirement, keep flying for another 20 or more years while maintaining their combat relevance. The dilemma for budget planners is to find the necessary resources to upgrade not just USAF assets, but those of the US Navy and Marine Corps, without dipping into the $258-338 billion the Congressional Budget Office estimates will be needed by 2026 to buy more than 3,700 Boeing F/A-18E/Fs, F-22s and JSFs.

In the absence of a significant recapitalisation, or a reduction in the USAF's force structure of 20 tactical fighter wings by the pending Quadrennial Defence Review (QDR), the ACC risks running short of more than 1,100 aircraft by the time the JSF reaches initial operational capability in September 2011.

"We're going to look at the results of the QDR and how JSF source selection goes and balance our risks and affordability to bridge the gap," says Gen Daniel Leaf, USAF director of operational requirements.

The backbone of the legacy inventory comprises approximately 1,300 Block 25/30/40/50 F-16C/Ds which now average 12 years old. Even older are the USAF's 400 F-15C/D Eagles and 366 A-10 Thunderbolts, with an average age of 17 years and 20 years, respectively. Based on the F-22 purchase being pared back to just 295 fighters and a maximum JSF output of 196 aircraft per year for all services, planners envisage running on 179 F-15Cs and a "significant number of F-16s" to at least the year 2020, while the A-10 fleet is expected to remain active until 2028.

Death spiral

Without funding, however, many will not last the decade and have already entered what the USAF Aeronautical System Center's new ageing aircraft system programme office (SPO) is terming the "death spiral". SPO commander Col Rosanne Bailey explains: "As systems get older, maintenance requirements tend to increase. As this increases, the need to replace broken parts also goes up, as well as maintenance hours per flying hour and stress on maintainers. Finally, aircraft availability goes down and the fixed cost per flying hour goes up."

While it has been apparent to most within the air force that the average age of aircraft was climbing as the procurement of new aircraft diminished throughout the 1990s, a healthy post-Cold War inventory of spares and surplus aircraft meant the full extent of the problems did not become apparent for some time. With fewer aircraft having to fly longer hours in support of operations such as Kosovo and Northern and Southern Watch over Iraq, the parts bubble burst and mission capable rates went into a nose dive. The problem has been further exacerbated by a contracting industrial base, which in some instances has meant the original manufacturer no longer exists.

One of the ageing aircraft SPO's main tasks is to combat the rising cost of aircraft overhaul and support, which is estimated to rise by 3% to 7% a year, through identifying a common set of solutions for upgrading or extending the life of different types of aircraft. "Cross-cutting" upgrades include adopting a standard cockpit display ideology for not just different fighter types, but also bombers and transport aircraft. Other examples include working with the Air Force Research Laboratory (AFRL) to field a common low observable verification system for different stealth aircraft and a mobile automated scanner that employs eddy-current technology to inspect for corrosion without removing skin panels.

With aircraft flying longer than ever before, previously unknown problems are starting to emerge such as ageing aircraft wiring. Given the drawn-out procurement planned for 1,763 new JSFs, the average age of the USAF's tactical fighter fleet will still be hovering around 16 years in 2025, some five years higher than the historical average. Consequently, another key objective for the SPO, according to Bailey, "is to prevent us getting into this situation again by developing tools to predict what's going to break out of those things that have never broken before".

Hand in hand with the job of extending a fighter's airframe and engine life is the need to modernise its systems. In the decade since the first F-16 Block 50 fighter was delivered, the single monolithic threat posed by the former Warsaw Pact has given way to a multitude of different potential adversaries. At the same time, air warfighting has been technologically transformed by the advent of stealth technology, the revolution in precision guided munitions (PGMs) beyond visual range (BVR) combat and the emergence of network-centric warfare.

Continual challenge

The threat is not just in the air but in the continued evolution of surface-to-air missile (SAM) systems and hybrid developments that are continually challenging the defence suppression. This has been compounded by the fielding of new more capable surface-to-air missiles. In places like Kosovo this has forced the USAF to adopt new tactics, such as precision air-to-surface strikes from medium altitudes and above, but for which aircraft like the relatively slow-flying A-10 were never designed.

While the expanded use of stealth will have to await fielding of the F-22 and JSF, there is already in the development pipeline a range of new systems and weapons that will help the legacy fleet hold the line in the interim. These include the Joint Helmet Mounted Cueing System (JHMCS), Fighter Data Link (FDL) the newly selected Lockheed Martin Sniper XR Advanced Targeting Pod (ATP), the Raytheon AIM-9X high off-boresight air-to-air missile and the new J-series of GPS-guided weapons such as the Boeing GBU-31 Joint Direct Attack Munition (JDAM) and Raytheon AGM-154 Joint Stand-off Weapon (JSOW).

There are also a number of equally critical upgrades that remain underfunded. These include $452 million for the F-16C/D Falcon Star structural life extension. There is a mid-life update for the F-16 engines, which in some cases have already exceeded 12,000 total accumulated cycles (TAC) and are well beyond the original design life. The A-10 needs a more powerful replacement turbofan, while the F-15E will require a new active electronically scanned array (AESA) radar.

"Balancing the money is really difficult," concedes Leaf. "The ACC and air staff are putting an extraordinary effort into balancing capability and risk for legacy aircraft with what is affordable. We have had to make some very tough decisions and there are things we're not doing that we would like to do."

Precision engagement

The A-10 is an aircraft that has refused to die despite repeated attempts to park the fleet in the desert. Designed originally as a Cold War tank-buster, the Thunderbolt is a low-level attack fighter with a powerful, multi-barrel cannon which has won strong support from the US Army. The aircraft proved a valuable asset in the 1991 Gulf War, but over Kosovo the rules of engagement specified medium-altitude operations and PGMs and in such an environment the A-10 has a number of shortcomings.

A lack of medium-altitude target identification, datalink for secure communications or PGMs other than the Raytheon AGM-65 Maverick, means the A-10 either misses targets it cannot see at medium altitude or has to descend to within the threat envelope of man-portable air defence systems (MANPADS). "Precision engagement is part and parcel of getting into the fight these days. The key endeavour is to keep the A-10's loiter and payload capability and modernise the aircraft to where it can operate, survive and contribute to the joint fight with precision capability," says Leaf.

The A-10 has received few modifications since the late 1970s and the manufacturer, Fairchild, no longer exists. The move towards "total system performance responsibility contracting" and the lack of an integrating contractor has resulted in fractured upgrade acquisition. The solution was to give Lockheed Martin Systems Integration-Owego (LMSI-Owego) a nine-year "Prime Team" contract. Northrop Grumman is responsible for the aircraft structural integrity programme (ASIP).

LMSI-Owego "is developing the modernisation package, sustainment planning, software block upgrades and the avionics roadmap", as well acting as systems integrator for these plans, says Bill Paradies, Lockheed Martin Prime Team programme manager. Northrop Grumman's ASIP work is not part of LMSI-Owego's prime contract, but the two will work closely together on implementation, adds Paradies. The wing centre-section and outer panels are being strengthened under the Hog Up programme.

To keep the A-10 combat effective, a series of separate improvement plans, including a digital stores management system (DSMS), situation awareness datalink (SADL) and 1760 weapons databus were drawn up. The DSMS and SADL required changes to the cockpit, incorporating electronic displays for the first time. These will both now be 130 x 130mm (5 x 5in) displays rather than a 130 x 180mm DSMS unit and a 100 x 100mm SADL screen. Missing, however, was funding for a targeting pod, incorporating JDAM and the Lockheed Martin WCMD PGMs and a DC electrical power upgrade.

All these modifications, funded and unfunded, have been wrapped into a single Precision Engagement programme, which will cost $150 million less than doing the six separately, says Paradies. This is the result of one level of engineering design, one set of development and operational flight tests, one release of new technical orders and a single aircraft maintenance input incorporating all the upgrades. Low rate initial production of upgrade kits is due to start in 2004, and full rate production starts the following year.

The choice of targeting pod hinges on extra funds to acquire new Sniper ATPs or equipping the aircraft with existing, but upgraded, Lockheed Martin LANTIRN pods. Paradies says there are discussions about further upgrades including: the head-up display, which is "old and has limitations"; a digital map; advanced infrared countermeasures; and improvements for the combat search and rescue mission. A more important need is a new engine, with ACC now writing an operational requirements document.

USAF and Air National Guard pilots are pushing strongly for more power to improve the A-10's medium-altitude and single-engine climb performance in hot and high conditions, so reducing the time the aircraft is exposed to MANPADS following a dive attack. While there is a strong case for improved performance and safety, the General Electric TF34 does not suffer from the same repair and maintainability issues as the F100 or F110. Replacing or uprating the engine is likely to depend on finding a creative funding method, such as power-by-the-hour arrangements.

Proposed solutions include re-engining the aircraft with either a derated GE CF34-8C or smaller -3B, an uprated Rolls-Royce AE3007L, or a Pratt & Whitney Canada PW308 or PW800. The alternative is to upgrade the TF34, but none of these options appear to have won over the USAF.

"Right now we have not found an affordable option. There are a lot of engines out there but they are either all too expensive, or if they are affordable they don't deliver a significant enough improvement in performance to be worth it," says Leaf.

Eagle enhancements

The F-15 Eagle has been in continuous USAF operation since 1974 and with no replacement for the two-seat F-15E Strike Eagle version in sight, the type is to remain in front-line service for another 30 years. The older F-15C/D air superiority fighter was due to have been replaced by the F-22 from late 2005, but successive cuts in the planned procurement of Raptors will require that the Eagle soldiers on for several years to come.

"We see them staying all through not just this decade but the next decade in limited numbers. But you're going to have to have the F-22 as the enabler and there will almost certainly be an evolution in specific roles. Right now, the F-15's role is to be 'first in to cleanse the skies', but it's not going to do that once we get the F-22, especially on day one of war with advanced threats," says Leaf.

There is already a series of enhancements funded for the F-15C/D and F-15E, along with a lengthy wish-list of additional mid-life updates (MLU) for the latter variant that are now the subject of talks between Boeing and USAF and targeted for inclusion in the 2004 budget. Where possible, the ACC is driving for commonality between the two Eagle derivatives, particularly in the area of core software.

Link 16 FDL is now in the process of being fitted to the F-15C/D, along with the 100 remaining earlier A/B fighters, and this will be extended to the F-15E, opening up access to offboard data from airborne early warning and ground surveillance platforms. Other common retrofit items include the instrument landing system and the replacement of honeycomb in the wingtips and vertical stabiliser leading edges with Gridlock structure. "The problem with honeycomb is that water is getting in, freezing and rupturing," says Mike Ridnouer, Boeing F-15 new business development.

While post-Cold War spending cuts curtailed ACC's original planned buy of 392F-15Es, US Congressional budget supplements have helped sustain limited output. Boeing is building 10 more fighters, which will boost the USAF total buy to 227. They incorporate several improvements, which in time will be backfitted to the entire Strike Eagle fleet, including a programmable armament control system and software for the carriage of J-series PGMs.

The aircraft will feature two 130 x 130mm and five 150 x 150mm liquid crystal displays (LCD) as a drop-in replacement for earlier CRTs. The LCDs are colour capable if the USAF chooses to upgrade its monochrome display drivers. The aircraft will also receive a new LCD engine display, which like the larger multi-purpose displays, will become the preferred spare for the existing fleet. The F-15C is already equipped with two new displays as part of an earlier multi-stage improvement programme.

South Korean contest

Boeing's hope of keeping the F-15 line active beyond 2004 rests on winning the South Korean F-X competition. Its proposed F-15K offering includes an improved BAE Systems ALR-56C(V)1 radar warning receiver (RWR) and Northrop Grumman ALQ-135M jammer. "If we win in Korea, I think the air force would like the possibility of leveraging that technology for its own use on at least the F-15C through to E fleet," says Ridnouer.

At the heart of any F-15E MLU is the potential for an AESA replacement for the Raytheon APG-70 radar in 2008-10. The F-15C fleet is already being partially re-equipped with improved APG-63(V)1 radars, which feature ground moving target track, sea surface search and enhanced resolution mapping, while another 18 Elmendorf AFB, Alaska-based Eagles have been fitted with the APG-63(V)2 featuring an AESA antenna. Other AESA options could include fitting a version of the F-22's Northrop Grumman APG-77 or the next generation JSF radar.

GE is looking to take advantage of an extended F-15E production run for South Korea to finally equip the fighter with its F110-129 engine, which is already qualified on the Strike Eagle but was never ordered by the USAF as a result of its curtailed buy. The company is also targeting the 130 Seymour Johnson AFB and Mountain Home AFB-based F-15Es powered by the lower thrust P&W F100-220 engine, which could then be "flowed down" to re-engine older F100-100-powered F-16s, instead of buying -220E upgrade kits, says Mark Miller, GE's F110 programme manager.

Operational flexibility

Under current plans, the F-16 will make up more than half the US Air Force's fighter fleet until at least 2015. While the USAF wants 50-100 new F-16Cs to fill out its 10 aerospace expeditionary forces, the bulk of the fleet will be Block 40 and Block 50 aircraft delivered between 1984 and 1997, augmented by earlier Block 25/30 aircraft operated by the reserve forces.

The air force has several programmes under way to extend the life and improve the capability of its F-16Cs, as well as to increase commonality between the different blocks to provide greater operational flexibility. Currently, only Block 40 F-16s can carry the LANTIRN targeting pod used for precision strike while only Block 50s, newer but fewer in number, can carry the HARM targeting system (HTS) pod required for defence suppression missions.

Under the Common Configuration Implementation Programme (CCIP), 650 Block 40s and 50s will be upgraded to a standard enabling all aircraft to carry either the LANTIRN or HTS, says Bob Keighery, Lockheed Martin director, domestic F-16 business development. Under the Combat Upgrade Plan Integration Details (CUPID) programme, 620 Block 25/30s are already being equipped to improve interoperability with active air force F-16Cs.

Beginning with the Block 50s, the CCIP will install colour displays, JHMCS helmet display, Link 16 datalink, advanced identification friend-or-foe (AIFF) interrogator/transponder and modular mission computer. Two aircraft modified to test the upgrade are scheduled to fly later this year, says Irma Sippel, Lockheed Martin deputy director, USAF F-16 programmes.

Induction of Block 50s for upgrade at Ogden Air Logistics Center, Hill AFB, Utah, begins this month. Around 250 aircraft are to be upgraded by 2005, Sippel says. The timeline for upgrade of Block 40s under the CCIP is "in limbo". But 400 aircraft are likely to be modified from 2007. The upgrades are similar, although the AIFF is on the unfunded list for the Block 40.

The CUPID upgrade is fully funded, and scheduled for completion in mid-2003. The programme brings Air Force Reserve and Air National Guard Block 25/30s close to Block 50 standard. Elements include an embedded GPS-satellite/inertial-navigation system, SADL datalink, night-vision cockpit and a countermeasures management system.

Towed decoy

Other upgrades include the RaytheonALE-50 towed decoy and Northrop Grumman Litening II targeting pod, while future updates - some unfunded - will add colour displays, the JHMCS and Raytheon AIM-9X air-to-air missile.

With F-16s bearing the brunt of USAF operations in the Balkans and over Iraq, aircraft are falling short of their projected lifetimes. This has resulted in the Falcon Star structural upgrade programme, intended to restore all F-16s to their originally planned 8,000h lives. Block 25/30s will require less work than early F-16A/Bs, while upgrades needed by Block 40/50s will be "minimal", according to George Washabaugh, Lockheed Martin Falcon Star programme director.

Work involves strengthening bulkheads and other structures - "just the hot spots", he says - without tearing down the aircraft. Proof kits will be delivered in late 2002/early 2003, with the structural improvements scheduled for completion, incrementally, by fiscal year 2010, according to the F-16 SPO.

The F-16s' engines are also ageing. Designed for 8,000 TACs, the P&W F100 and GE F110 will be approaching 12,000 cycles by 2005 and will exceed 16,000 TACs if the F-16 stays in the active inventory until 2024 as planned. Older engines are falling short of their target 1,000h "on wing", typically achieving 250-350h. GE is hoping for a F110 MLU beginning in 2005. The company is also looking for funds to fit a low-observable ejector nozzle, also beginning in 2005. The nozzle has fewer parts, runs cooler and will last 4,000h, compared with 400-500h today.

F-16C production for the USAF resumes next year, with 10 aircraft procured with fiscal year 2000 funding, followed by four FY2001 aircraft, the last of which will be built to CCIP standard. Procurement of "eight to ten" aircraft a year is planned to restart in FY2004, says Keighery, with the eventual number of new-build aircraft still undetermined.

For in-service aircraft, ACC has a "laundry list" for unfunded future upgrades it wants to keep its F-16s operationally relevant. These range from the Northrop Grumman APG-68(V)9 radar, with synthetic-aperture radar capability, to the higher thrust/longer life F110-132 engine.

Source: Flight International