F-15 Eagle
Service Life
Designed in the 1960s and built in the 1970s, the F-15A - D aircraft has now been in service for over twenty years. While the Eagle's aerodynamics and maneuverability are still on a par with newer aircraft, quantum leaps in integrated circuit technology have made the original F-15 avionics suite obsolete. The objective of the Multi-Stage Improvement Program (MSIP) was to set the Eagle in step with today's vastly improved information processing systems. Some F-15C/D aircraft (tail numbers 84-001 and higher) came off the assembly line with MSIP in place. All F-15A/B/C/D aircraft produced before 84-001 will receive the MSIP retrofit at the F-15 depot. Improvements incorporated via MSIP vary between F-15A/B and F-15C/D aircraft; the C/D MSIP has been completed. However, all air-to-air Eagles gain improved radar, central computer, weapons and fire control, and threat warning systems.
The purpose of the F-15 Multi-stage Improvement Program (MSIP) was to provide maximum air superiority in a dense hostile environment in the late 1990s and beyond. All total, 427 Eagles received the new avionics upgrades. Along with later model production aircraft, these retrofitted aircraft would provide the Combat Air Forces (CAF) with a total MSIP fleet of 526 aircraft. The MSIP upgraded the capabilities of the F-15 aircraft to included a MIL-STD-1760 aircraft/weapons standard electrical interface bus to provide the digital technology needed to support new and modern weapon systems like AMRAAM. The upgrade also incorporated a MIL-STD-1553 digital command/response time division data bus that would enable onboard systems to communicate and to work with each other. A new central computer with significantly improved processing speed and memory capacity upgraded the F-15 from 70s to 90s technology, adding capacity needed to support new radar and other systems. The original Eagle had less computer capacity than a 1990s car. Some of the work prefaced the addition of the Joint Tactical Information Distribution System, adding space, power, and cooling that would allow the new avionics to run in the harsh environments in which the Eagle operates. The new programmable armament control set (PACS) with a multi-purpose color display (MPCD) for expanded weapons control, monitoring, and release capabilities featured a modern touch screen that allowed the pilot to talk to his weapons. A data transfer module (DTM) set provided pre-programmed information that customized the jet to fly the route the pilot had planned using mission planning computers.
An upgrade to the APG-63 Radar for multiple target detection, improved electronic counter-countermeasures (ECCM) characteristics, and non-cooperative target recognition capability enabled the pilot to identify and target enemy aircraft before he was detected or before the enemy could employ his weapons. An upgrade of the advanced medium range air-to-air missile (AMRAAM), that carried up to eight missiles, represented an improvement that complimented the combat-proven AIM-7 Sparrow by giving the pilot capability to engage multiple targets to launch and leave, targeting and destroying enemy fighters before they could pose a threat. The upgraded Radar Warning Receiver (RWR) and an enhanced internal countermeasures set (ICS) on F-15C/D models improved threat detection and self-protection radar jamming capability that allowed pilots to react to threat and to maneuver to break the lock of enemy missiles.
F–15 combat capabilities can be improved substantially with upgraded radars, jammers, and helmet mounted targeting systems. The most cost effective upgrade may be a new datalink which allows aircraft to share target information. Air Force testimony to the House Appropriations Defense Committee in 1999 described the so-called "Link 16" datalink as "the most significant increase in fighter avionics since the introduction of the on-board radar." Tests with this $200,000 per aircraft upgrade to the F–15 demonstrated a five-fold increase in air combat kill ratios.
The 830th Aircraft Sustainment Group of the 330th Aircraft Sustainment Wing at Warner Robins Air Logistics Center serves as the single focal point for cradle-to-grave sustainment management for the F-15 aircraft to sustain mission effectiveness throughout the system’s life cycle. Responsible for all sustainment activities required to ensure F-15 aircraft availability is adequate for the weapon system to fulfill its assigned missions. Primary activities include engineering,worldwide logistics,weapon system readiness, and wartime sustainability support. Manages aircraft overhaul, modernization and modification programs, and unscheduled depot level maintenance repair for the F-15 aircraft to include foreign military sales.
The F-15 initial operational requirement was for a service life of 4,000 hours. Testing completed in 1973 demonstrated that the F-15 could sustain 16,000 hours of flight. Subsequently operational use was more severely stressful than the original design specification. With an average usage of 270 aircraft flight hours per year, by the early 1990s the F-15C fleet was approaching its service-design-life limit of 4,000 flight hours. Following successful airframe structural testing, the F-15C was extended to an 8,000-hour service life limit. An 8,000-hour service limit provides current levels of F-15Cs through 2010. The F-22 program was initially justified on the basis of an 8,000 flight hour life projection for the F-15. This was consistent with the projected lifespan of the most severely stressed F-15Cs, which by the turn of the century had averaged 85% of flight hours in stressful air-to-air missions, versus the 48% in the original design specification.
Full-scale fatigue testing between 1988 and 1994 ended with a demonstration of over 7,600 flight hours for the most severely used aircraft, and in excess of 12,000 hours on the remainder of the fleet. A 10,000-hour service limit would provide F-15Cs to 2020, while a 12,000-hour service life extends the F-15Cs to the year 2030. The APG-63 radar, F100-PW-100 engines, and structure upgrades would be mandatory. The USAF cannot expect to fly the F-15C to 2014, or beyond, without replacing these subsystems. The total cost of the three retrofits would be under $3 billion. The upgrades would dramatically reduce the 18 percent breakrate prevalent in the mid-1990s, and extend the F-15C service life well beyond 2014.
By 2005 the F-15 Sustaining Engineering and Supply Chain Management efforts were being seriously impacted by continuing platform service life extensions. This necessitated a proactive engineering response to Diminishing Manufacturing Sources and Material Shortages (DMSMS) management. DMSMS is a condition brought about when the last known manufacturer announces the intention to discontinue production of an item or group of items still required by DoD activities for systems support. In FY 2006 the Aging Aircraft program established enabling avionics capabilities that can be affordably inserted into the legacy force structure, facilitating a force multiplier combat capability across diverse platforms. It worked to develop an affordable F-15 Heads Up Display (HUD) cathode ray tube (CRT) replacement item that can be transparently inserted into fielded assets as part of the normal repair cycle. Planned CRT advancements will eliminate an inherent F-15 failure mode, increasing the incurred CRT mean time between failure rate from under 400 hours to over 3,000 hours, and will be transferable to alternate platforms experiencing marginal HUD CRT reliability performance.
The F-15 was reportedly [Flight International, February 14, 2006] cleared for 18,000 flight hours [this must reference the F-15E]. As of 2006 the Air Force planned to upgrade and maintain around 170 F-15s through 2025. Planned improvements included the installation of a new active electronically scanned array (AESA) radar, which was expected to enter competition early in FY07, as well as integrating a new digital radar-warning receiver. The Air National Guard was upgrading 48 F-15C fighters between 2006 and 2012 with a new AESA radar, the Raytheon APG-63(V)3.
On 02 November 2007 an F-15C mishap resulted in the loss of the aircraft. The Accident Investigation Board found defects which indicated potential structural damage in the rest of the fleet. A failure of the upper right longeron, a critical support structure in the F-15C Eagle, caused the crash of a Missouri Air National Guard F-15C, four miles south-southeast of Boss, Missouri. The initial findings of the Accident Investigation Board, while at the mishap site Nov. 27, indicate the fleet of F-15s A-D might not be airworthy after a metallurgical analysis of the mishap aircraft. The findings focus specifically on the upper longerons, major structural components of the aircraft, which are located near the canopy of the aircraft and run along the side of the aircraft lengthwise.
The discovery of more structural damage in the F-15s prompted a 03 December 2007 stand-down order from Air Combat Command Commander Gen. John Corley. The stand-down does not impact the operational status of the F-15 E Strike Eagle. Maintainers performed methodical and time-intensive inspections on all F-15 Eagle A, B, C and D model aircraft, which revealed more cracks in the aircraft longerons. Maintainers at Langley initially found no cracks or evidence of fatigue in F-15 longerons; however, throughout the Air Force, maintainers had found cracks in the upper longerons of eight F-15s (as of 10 December 2007). Four of these aircraft were assigned to the Air National Guard's 173rd Fighter Wing, Kingsley Field, Ore.; two were assigned to the 18th Wing, Kadena Air Base, Japan; another was assigned to the 325th Fighter Wing, Tyndall AFB, Fla.; and one assigned to the ANG 131st Fighter Wing, St. Louis, Mo.
Every aircraft underwent all previously published time compliance technical order inspections. However, the cleared aircraft did not immediately return to flight. Technical experts at Warner Robins Air Logistics Center, Ga., developed new inspection techniques based on findings in parts of the mishap aircraft. These inspections were performed as soon as the new TCTO [time compliance technical order] was available for the affected F-15s. As part of the previous TCTO, maintenance crews around the Air Force stripped paint and performed non-destructive inspections in the F-15's upper longeron just aft of the canopies. Inspections are more than just a visual check. After the paint is stripped and bare metal is exposed, Airmen from the non-destructive inspection shop apply chemicals that reveal cracks under a black light. Other inspections in hard-to-see areas are done with a borescope - a tool that uses a tiny camera and fits in tight areas.
According to the Air Combat Command Accident Investigation Board report [released 10 January 2008], a technical analysis of the recovered F-15C wreckage determined that the longeron didn't meet blueprint specifications. This defect led to a series of fatigue cracks in the right upper longeron. These cracks expanded under life cycle stress, causing the longeron to fail, which initiated a catastrophic failure of the remaining support structures and led to the aircraft breaking apart in flight. The one longeron, already not up to design specifications, cracked apart under the stress of a 7G turn, the colonel said. This led to the other longerons failing as well, which then caused the cockpit to separate from the rest of the fuselage. The pilot was able to eject, but suffered a broken arm when the canopy snapped off.
Air Combat Command officials cleared a portion of its F-15 A through D models to begin flying on 09 January 2008. As of that date, the Air Force had approved 60 percent of F-15 A through D models to return to service with no flight restrictions.
The F-15E structure is rated at 16,000 flight hours, double the lifetime of earlier F-15s.
