Military


F-16 Fighting Falcon

Service Life

The F-16 fleet consists of several different configurations that were acquired in a long and successful evolutionary program. The Air Force has invested billions over the years to upgrade capabilities, engines, and structural enhancements needed to achieve its original life expectancy of 8,000 hours. Significant unknowns exist about extending the life beyond 8,000 hours should that be necessary. The oldest F-16s are to be retired by 2010, and the Air Force has halted modifications and funding for these aircraft.

As of 2007 the Air Force was not currently purchasing any new F-16's, but the contractor was still producing them for foreign sale. The production is slated to continue past 2009 to accommodate recent sales. If the Air Force were to buy new aircraft, officials estimated that it would cost $380 million for development and about $50 million per aircraft procured.

In April 1990, the Secretary of Defense announced that a review of the Air Force's Advanced Tactical Fighter (ATF) program had found that the ATF is needed to replace the F-16 for the air superiority mission, but its production could be delayed because of changed world conditions and the possibility of a longer F-16 service life. The review showed that ATF production could be delayed because of a reduced conventional threat in Europe and indications that the life of the F-16 airframe could be extended beyond the year 2000. The Secretary directed that the initial production of the ATF be delayed from fiscal year 1994 to 1996.

The US Air Force's Multi-Role Fighter (MRF) program began in 1991 as a relatively low-cost F-16 replacement. Similar in size to the F-16, the MRF was to have been a single-seat / single-engine aircraft, with a unit flyaway cost in the range of $35 to $50 million. A formal program start was expected around 1994. The MRF was expected to replace a large number of F-16s reaching the end of service life. The MRF might also have replaced Air Force A-10s and Navy F/A-18C/Ds. However, the post-Cold War defense drawdown made the F-16 service life situation considerably less critical. A reduction in the total number of U.S. Air Force fighter wings meant that the existing aircraft would not be replaced one-for-one. Furthermore, F-16 aircraft flying hours were reduced, allowing F-16s to remain in service longer than originally projected. In August 1992, the MRF program was effectively put on hold.

The readiness of America's Armed Forces generally deteriorated throughout the 1990s. During this time, combat readiness of the Air Force fighter aircraft declined in varying degrees. One indicator of aircraft combat readiness, the mission capable (MC) rate, is used to identify the percentage of aircraft able to perform their primary wartime missions. The not mission capable (NMC) rate shows the converse. From fiscal year (FY) 1991 through fall 2001, the aggregate Air Force aircraft total not mission capable rate for maintenance (TNMCM) for all aircraft steadily increased from 7.6 percent to 18.1 percent while total not mission capable rate for supply (TNMCS) increased from 5.5 percent in FY86 to 13.4 percent in FY01.

The F-16 "sustainment crisis" in the late 1990s resulted from an inadequate life-cycle sustainment strategy, which negatively affected aircraft readiness. Preliminary analysis obtained from AFLMA's TNMCM study of the F-16 block 42 aircraft revealed the total man-hours expended on TCTOs increased 120 percent from FY95 to FY99 and the man-hours per TCTO event increased 69 percent, indicating TCTOs may be becoming more manpower intensive and technically challenging. The analysis also indicated that low manning and fewer experienced technicians contributed to increases in man-hours required to complete them.

As a system's cumulative operating time increases, the probability of its failure tends to increase, decreasing the system's potential reliability. Reliability also decreases when the conditions under which the system was designed to operate change. Many of these aircraft are at critical points in their life cycles. For example, by 2001 many F-16s had reached 2,400 hours flying time, a significant point in an 8,000-hour service life. As these aircraft age and operating conditions changed, the reliability of systems and components decreases, and failures occur more often, which increased maintenance costs. Increased failures affect aircraft maintainability, requiring more maintenance and often increasing repair times when more hard breaks occur. In the case of the F-16, operational usage had been more severe than design usage (eight times more), resulting in the acceleration of its airframe service life at a rate that may not let it reach its expected overall service life.

The mission-capable rate for Air Force Reserve F-16s increased from 69.7% in fiscal 2001 to 76.3% during the first three months of fiscal 2002, despite Operation Noble Eagle flight activity.

In the late 1990s, the Air Force Reserve Component [ARC] recognized there was no follow-on replacement for the F-16 and reduced the annual flying-hour program in ANG and AFRC squadrons to 210 airframe hours per year. This number is a generalization with some fighter squadrons flying more to support spinup training and actual overseas AEF deployment rotations of Northern and Southern Watch. However, in 2002 and 2003, the aircraft were flown an average 300 hours per aircraft, way beyond their programmed 210 flying hours used in support of contingencies at home and abroad. Fiscal year (FY) 2002 saw ANG and AFRC aircraft heavily taxed in support of Operation Noble Eagle. Combat air patrol flying conditions were favorable to slow the effect of upper and wing-support bulkhead cracking caused by excessive wing root bending movement. FY03 saw continued support for Operation Enduring Freedom (Afghanistan) and excessive use of F-16C aircraft supporting Operation Iraqi Freedom. These contingencies resulted in additional stress on the bulkheads and airframes alike. This was caused by excessive munition loads and heavy landings to deliver the payload during combat in support of close air support and air interdiction missions.

Simple calculation of 210 airframe and flying hours per year would mean the fleet would be able to support missions for another 19 years. At 300 airframe and flying hours, that number is reduced to 13 years or a 32- percent reduction. These numbers are actual flight hours. To receive a true meaning of the impact on the airframe, one needs to calculate using equivalent flight hours. Equivalent flight hours are the actual accounting of structural degradation that is determined from damage index data stored in the individual aircraft-tracking database, which is part of the aircraft structural integrity program.

The Falcon Up Structural Improvement Program program incorporates several major structural modifications into one overall program, affecting all USAF F-16s. Falcon Up will allow Block 25/30/32 aircraft to meet a 6000 hour service life, and allow Block 40/42 aircraft to meet an 8000 hour service life. Falcon UP and the Falcon STAR programs include numerous depot level structural modifications required to extend the service life of all F-16 aircraft to 8,000 hours. The F-16 CUPID program brought older F-16s (Blocks 25-32) new life by adding night vision equipment, enhanced avionics, and the ability to carry an infrared targeting pod and laser-guided munitions. Ultimately, CUPID-modified aircraft will have the capability to carry JDAM and other GPS-guided munitions. A small decrease in Ogden Air Logistics Center (OO-ALC) capacity in the outyears is due to the completion of the F-16 Falcon-up Program and to a decrease in the F-16 Service Life Improvement Program (SLIP) quantity.

In view of the challenges inherent in operating F-16s to 8,000 flight hours, together with the moderate risk involved in JSF integration, the Department established a program to earmark by FY 2000 some 200 older, Block 15 F-16 fighter aircraft in inactive storage for potential reactivation. The purpose of this program was to provide a basis for constituting two combat wings more quickly than would be possible through new production. This force could offset aircraft withdrawn for unanticipated structural repairs or compensate for delays in the JSF program. Reactivating older F-16s was not a preferred course of action, but represented a relatively low-cost hedge against such occurrences.

One analysis in 2002 estimated that by fiscal year 2008, the Air Force would have a 108-fighter deficit based on a 20 Fighter Wing Equivalent requirement, with that number growing to 311 by fiscal year 2021. These numbers were based on the today's programmed F-16 attrition rate of 3.6%, an estimated 8,000-hour F-16 service life, and fielding of the Joint Strike Fighter beginning in fiscal year 2009.

Even relatively "young" aircraft like the F-16 (average age 9 years in 1998) are affected by age: skin corrosion, bulkhead cracks and landing gear wear are common. The F-16 Service Life Extension Program (SLEP) extends the F-16A/B service life to 8,000 hours at a cost of $703K per aircraft in Fiscal Year 98. The F-16 Pre-Block 40 aircraft were developing structural cracks that must be repaired. As of 1999 an estimated 152 aircraft could be grounded due to structural cracks within the next two years. The Air Force's fiscal year 1999 appropriations included $15 million to define a service life extension program and capability enhancement package for F-16- aircraft. But the Air Force did not plan to define this life extension program or the capability enhancement package. The F-16 Service Life Extension Program was completed in FY 2003.

FALCON STAR (Structural Augmentation Roadmap)

FALCON STAR (Structural Augmentation Roadmap) is an effort to modify the airframe to allow the F-16 to reach the original 8,000 hours estimated for its flight life. The roughly $1 billion program is the result of more than four years of design and planning and ensures the F-16's original service life while allowing for an operational capability beyond the year 2020. Falcon STAR will allow the aircraft to remain in service through 2025. The first F-16 fighter jet to be a part of Falcon STAR, was handed off in February 2004 to members of the 148th Fighter Wing, Minnesota Air National Guard. The planning for the Falcon STAR program began in 1999. Aircraft modifications will continue through 2014, the majority of which will be performed at Hill AFB. By program's end, more than American 1,200 F-16s will have been modified including active-duty, Air National Guard and Air Force Reserve aircraft. As of 2005 a total of more than 2,000 aircraft were to be modified by 2014. Participants in the program include the Air Force and air forces in Belgium, Denmark, the Netherlands, Norway, Portugal, Israel, Greece, Singapore, Thailand and Bahrain. On average, it takes 175 days to modify an aircraft with the Falcon STAR kit.

Falcon STAR is a US Air Force-managed structural modification program for the F-16 that addresses service-life deficiencies for the Air Force. Falcon STAR modifications are applied to existing aircraft and added to all new F-16's to compensate for aircraft stress increased usage rates and heavier gross weights cause. Each aircraft, which uses an array of weaponry from GPS guided bombs to radar-guided air-to-air missiles, has a current [2007] maximum operational weight of approximately 39,000 pounds; the old, designed weight for the F-16 was only 22,500 pounds. Originally designed primarily for air-to-air missions, in practice it has mainly been used for air-to-ground operations.

Due to increased workload and weight that exceed the original specifications of the aircraft, the F-16 must be structurally modified to compensate for the increases. A number of common avionics and capabilities upgrades are necessary to provide increased processor speed and memories, color displays, and incorporate the Joint Helmet Mounted Cueing System. The F110 engine service life extension program addresses safety, reliability and maintainability concerns and new engines for the Block 42 aircraft will provide needed thrust improvements.

Under the Falcon STAR program, maintainers replace or repair known life-limited structures to avoid the onset of widespread fatigue damage. This is done to maintain flight safety, enhance aircraft availability and extend the life of affected components. Before Falcon STAR, some aircraft exhibited fatigue damage as early as 3,500 hours, he said. Once modified, the aircraft will meet its designed service life of 8,000 flight hours. The entire program involves modifying 13 different structural components, including wing fittings, and reworking skin areas. F-16 system program office experts at the Ogden Air Logistics Center manage the Falcon STAR program. Somewhere between 40 and 100 iterations of the kit are expected. The kit configuration is constantly changing because of the different aircraft configurations.

By 2007 the F-16C/D fleet was in the midst of standardizing capabilities through the Common Configuration Implementation Program. This modification program is a combination of several upgrades to F-16 avionics that enable integration of advancedprecision weapons, Link-16 communications, improved situational awareness, and off-bore sight cueing of sensors and weapons. It provides for a new modular mission computer, color displays, advanced interrogator/transponder (Block SO/52only), Link-16 communication capability, and the joint helmet-mounted cueing system. It also enables the Block 40/42 aircraft to use the same operational flight program (OFP) software as the block SO/52 aircraft, which will reduce the sustainment cost of future OFPs. The FY08 PB requests $72.6M in FY08 to continue the modification of Block 40 aircraft. Block 50 modifications are complete.

Without improvements, as of 2007 it was estimated that almost 90 percent of the fleet would exceed design limits on engines by 2010. High usage, increased stresses, and more weight than planned threatened to cut life expectancy in half. Significant unknowns exist about extending the life beyond 8,000 hours should that be necessary. If it became necessary to enable the newest F-16 aircraft to reach a 10,000 flying hour life, a program official estimated in 2007 an additional cost of $2.2 billion for structural enhancements. The program office also identified another $3.2 billion in unfunded requirements, including radar upgrades to aircraft capable of suppressing enemy air defenses.

Service Life Extension Program (SLEP)

By 2011 the US Air Force was considering a Service Life Extension Program (SLEP) to the newest Block 40/50 F-16s, with a 12,000-hr. goal per airframe. Modern combat aircraft were designed on what is termed a “damage-tolerance design philosophy” which trades performance of an aircraft for its durability to maintain an adequate airframe lifespan. This allows designers to use structures that last only as long as they need to which determines design life. Following a monitoring program of the fleet, the Air Force concluded that the F-16s were flying 15-20% “less hard” than anticipated, not flying to maximum limits of such elements as speed or g-forces. In the decade after 9/11, the F-16s had been used to support ground forces or fly patrol in permissive airspace, missions that did not require the stressful maneuvers of dogfighting. This led the Air Force to calculate "equivalent flying hours" for F-16 airframes to estimate the projected life, reflecting the lighter use of the fleet. This alone adds several years of life to each aircraft.

Extensive flight hours and stressing mission profiles resulted in the need for the FalconStar structural modification to the F-16. This upgrade program, scheduled in 2011 to complete in FY14, replaces known life-limited structural components and maintains the original design airframe life of 8,000 flight hours. Structural upgrades in the F-16 SLEP include rework and replacement to extend airframe structural service life by 25% (6-8 years). In other inspections, maintainers found bulkhead cracks in approximately 67 percent (428 of 642) of Block 40/52 F-16 aircraft. As of early 2011 about 285 aircraft had been repaired and 83 aircraft had the bulkheads replaced. An additional 54 aircraft continued to fly with increased inspections to measure crack growth.

Similar to the F-15, the Air Force started conducting a full-scale durability test for the F-16 in FY11 to enable F-16 Block 40-52 airworthiness certification to be extended from the current 9,000 actual flight hours to 11,000 plus actual flight hours. The FY12 budget request added $15M in FY12 to begin design and development of structural and avionics capability modifications for the Block 40-52 fleet to be responsive to the Air Force’s total fighter requirement. This funding was in addition to the $10.6M requested to continue the full scale durability test. There is $108 million in the 2012 budget; however, the total program is 300 aircraft. The total SLEP with structural modifications of 300 aircraft plus an avionics modification would be roughly $9.4 million per aircraft.

By 2012 the F-16 SLEP was slated to include up to 350 of the newest F-16s — Block 40 and newer — and was larger in scope than a structural SLEP considered in 2010. This new program, estimated to cost $2.8 billion, will include an active, electronically scanned array [AESA] radar. Modeling and simulation data available suggest the service could extend its life to 10,000-12,000 hours.

Most F-16 pilots accumulate about 3,500 flying hours in the course of a career. The F-16C model has undergone a service life extension program (SLEP), raising its lifetime hours to 8,000; however, by 2012 the average F-16C already had nearly 5,500 hours. Some observers believe that the SLEP added a maximum of 10 more years to the airframe, which would imply an annual flight rate of 250 hours per year. As of 2011, the Air National Guard stated that the F-16C required 20.6 Flying Hours / Crew / Month [nearly 250 hours/year], but it had funded 18.6 Flying Hours / Crew / Month [nearly 225 hours/year]. The F-16D required 10.3 Flying Hours / Crew / Month [nearly 125 hours/year], but it had funded 9.0 Flying Hours / Crew / Month [nearly 110 hours/year].

Continuation Training [CT] is how pilots train for combat during peacetime to produce combat mission ready (CMR) pilots. The fighter aviation community has encountered training gaps that have stemmed from a systematic reduction in the average pilot’s flying hours coincident with massive increases in aviation technology complexity. One way to stretch that life is to rely more on simulation and less on live flying. That way pilots can accumulate hours on the fleet of airplanes at a slower rate.

The Air Force uses Aircrew Position Indicator (API) to differentiate between pilots who are fully ready for war and pilots that need additional training before deploying for combat. API-1 pilots are at the highest state of readiness. These pilots fly enough sorties to maintain Combat Mission Ready (CMR) status. CMR means “maintain[ing] proficiency and qualification in all core missions of the flying unit to which they are assigned or attached”. If the squadron were to deploy to a combat zone, the API-6 pilots must be able to reach combat readiness with 30 days of increased training. API-8 pilots are usually staff officers who are required to maintain flying currency for job related duties.

Studies have indicated that flying 13 sorties permonth would do away with the need for a squadron pre-combat spin-up program. The squadron would be ready to deploy to a combat location immediately. Given an average average sortie duration (ASD) of 1.2 hours, the total number of flying hours for the year would be 187 hours. In 1999 the 31st FW out of Aviano Italy utilization rate was 550 hrs/aircraft, when the wing was deployed for over 50% of the time in direct support of Operation ALLIED FORCE.

After September 11th, the average sortie durations (ASDs) for ANG fighter wings changed much more than the ASD for active duty fighter wings during this time period. The ASD suddenly increased while at the same time, the active duty fighter wing’s ASD stayed mostly stagnant. There are inherent differences between ANG and active duty fighter wings. Active duty fighter wings fly almost four times as many hours as ANG fighter wings. There is a higher number of block 50’s in active duty fighter wings and a higher number of block 30’s in an ANG fighter wing. As of 2004 the average ANG fighter wing had 52% Block 30s and no Block 50s whereas the average active duty fighter wing had 25% Block 50s and 10% Block 30s.



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