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F/A-18 Hornet Service Life

Since its US Navy fleet introduction in 1983, the F/A-18 Hornet has defined the role of the modern carrier-based, multi-mission, fighter/ attack aircraft. The Navy is in the process of transitioning older models of the Hornet to the F/A-18 E/F Super Hornet, while the Marine Corps has chosen to extend the service life of the F/A-18 A, C, and D models.

When the F/A-18 was first introduced, it quickly gained a reputation for reliability and ease of maintenance. As of July 2012, almost 30 years later, 76 percent of Marine Hornets are beyond their original design service life of 6,000 flight hours, and like any other aging platform, require a significant amount of extra work to maintain combat serviceability.

With at least another decade of service required from Marine Hornets, it is not enough to simply continue flying; it is imperative to maintain a common capability baseline that ensures that Marine Hornets remain both available and combat effective. The stated program goal is to enable 150 Marine Corps aircraft to operate to 10,000 flight hours. With the Marine Corps planning to operate the F/A-18 A, C, and D aircraft to at least 2024 to 2026, careful planning and execution of airframe inspections, repairs, and modifications will be critical to maintaining airworthiness, operational availability, and combat readiness.

As the F/A-18 A-D inventory continues to fly past the original design service life, fleet operators need a structured approach to airframe inspection, repair, and maintenance. The F/A-18C program has four life-limiting criteria: flight hours, wing root fatigue life expended (WR FLE), catapults and traps, and landings. The PM manages to all of these criteria to maximize the lifetime of the aircraft fleet, but flight hours and WR FLE are the two primary life-limiting factors that result in lost aircraft. The service life of the F/A-18C is 8,000 flight hours. It cannot be assumed that each aircraft will reach 8,000 hours due to WR FLE limits.

The F/A-18C program has four life-limiting criteria: flight hours, wing root fatigue life expended (WR FLE), catapults and traps, and landings. The PM manages to all of these criteria to maximize the lifetime of the aircraft fleet, but flight hours and WR FLE are the two primary life-limiting factors that result in lost aircraft. The service life of the F/A-18C was 8,000 flight hours. The WR FLE is a measurement of the impact of flight activities on the main structural components of the aircraft and has a limit of 1.0, or 100%. The F/A-18 PMO has evaluated the impact of wartime on aircraft and discovered that while utilization (flight hours) increased, WR FLE does not always increase based on how the aircraft are flying and used in combat (i.e., straight missions, without aggressive maneuvers). On the other hand, training missions (peacetime use) can result in aggressive maneuvers and have a greater impact on WR FLE.

Engineering analysis and testing of the F/A-18 program have resulted in revised service life estimates, from 6,000 flight hours to 8,000 flight hours for the A/C models, and another change is possible to 8,000 or 10,000 flight hours for the E/F models. These changes are based on the amount of fatigue life that is remaining on the aircraft at the time of inspection. Initial flight hour projections were made based on the engineering assessment (expressed in terms of hours) of when the aircraft would reach a fatigue life expended of 100%. Initial analysis resulted in an estimate of 6,000 flight hours. However, due to Navy aircraft mission management and maintenance, the fatigue life expended is less than originally planned at the current level of flight hours consumed, and this is leading to additional flight hours or service life for the program. For example, the F/A-18 aircraft does not carry missiles on the wing tips unless it is critical for carrying out mission requirements. This action has resulted in a decrease in the total amount of wing fold fatigue life expended for the aircraft, which in turn, enables the aircraft to realize more flight hours than initial planned estimates. Engineering analysis and testing of the F/A-18 program have resulted in revised service life estimates, from 6,000 flight hours to 8,000 flight hours for the A/C models, and another change is possible to 8,000 or 10,000 flight hours for the E/F models. These changes are based on the amount of fatigue life that is remaining on the aircraft at the time of inspection.

The good news is that, despite the high airframe time, global structural fatigue issues appear to be manageable, with most structural damage discovered on teardown being related to other factors such as mechanical wear, heat damage, and various forms of corrosion. The bad news is that every airframe requires some level of repair, creating a new and variable demand for a large number of airframe components that were never intended to be replaced.

There are three major factors that limit the service life of the fleet: structural fatigue, challenges in obtaining system support and the weakening comparative capabilities of the Hornets in relation to the development in the security environment. When the Hornet fleet was procured the projected lifespan of each individual aircraft was 30 years. This has been the guiding principle in acquiring upgrades as well as in planning the use and support of the fleet.

The Hornet fleets completed and ongoing structural repair projects are optimised to serve the planned use profile. The ongoing structural modification program in Finland was designed on the grounds of a study carried out from 2002 to 2009. Following the structural repairs, on the basis of information received from the international F/A-18 user community and damage inspections, additional structural life-limiting aspects were identified. The most critical points as regards the implementation of repairs were included in the program in 2014. The structural repair program for the entire fleet would be completed by the end of 2016.

To extend the lifespan of the Hornet fleet new, augmenting structural modifications would have to be implemented. The extent of needed structural repairs depends on any possible new damage detected, airframe-specific flight hours and the stress caused by flight loads.

System support for the Hornet fleet consists of spares and Line Replacement Units (LRUs), component repair and overhaul, and software support. The technical obsolescence of components and their reduced obtainability create challenges for repair and maintenance, which can, however, be managed. The Hornet contains in all 46 equipment-specific software-driven systems. Eight of them require software updates throughout the service life of the aircraft. The costs of software support keep rising as the other user countries keep phasing out their fleets and, hence, no longer participate in sharing the costs.

The service-life-associated plans of the United States, the main user country of the F/A-18A-D, significantly impact the obtainability of system support. The United States Navy is the most important user of the aircraft type and, according to the present plans, the USN will decommission its F/A-18 C/D models by 2025. The United States Marine Corps will continue using the aircraft until the end of 2031. The USMC and Switzerland are upgrading their mission computers so as to be comparable with those in the F/A-18 Super Hornets.

Upgrading the mission computer is a long and expensive project. Australia will phase out its F/A-18 A/B aircraft in 2022 and Canada in 2025. In the early 2020s Finland will be solely responsible for the software development of the present mission computer, as a result of which the costs of software updates and support will grow exponentially.

Extending the lifespan of the F/A-18 Hornet into the 2030s, counter to present plans, would translate into added expenses in life-cycle management and increase the cost risks of system support. The relative capabilities of the Hornet fleet will degrade in the 2020s and the most significant degradation falls on its interdiction capability. Extending its structural life and implementing a new, sizeable mid-life upgrade would make it possible to delay the decision to replace the capabilities by five years, at most. The extra costs incurred by service life extension consist of structural repairs, system support and capability upgrades.

Boeing is having ongoing dialogue with U.S. Navy officials to offer a holistic solution to help solve their inventory management issues. The company is working to help accelerate the SLEP program to help provide continual maintenance and extend the life of the Super Hornet fleet. The Navy plans to extend the Super Hornets life from its 6,000 hour design limit to 9,000 hours but still faces significant strike fighter inventory issues even with this life extension.

Chief of Naval Operations Adm. Jonathan Greenert told reporters in March 2015 after a Senate hearing that there was a shortfall of about three squadrons, or 36 planes, due to legacy Hornets burning through their service life faster than anticipated. He said maintenance depot workers wouldnt know until summer 2015 whether a plan to extend the F/A-18A-Ds service life from 6,000 flight hours to 9,000 would work.

The F/A-18E/Fs have flown approximately thirty-five percent of the total flight hours available at the 6,000 hour limit and this will not be adequate to meet operational commitments out to 2035. As a result, the three-phased F/A-18E/F Service Life Assessment Program (SLAP) commenced in 2008 will last through 2018. Its goal is to analyze fleet actual usage versus structural test data to identify the feasibility of extending F/A-18E/F service life from 6,000 flight hours to 9,000 flight hours via a follow on Service Life Extension Program (SLEP). The Fiscal Year 2015 Presidents Budget includes a request for $13.8 million in RDT&E and an additional $74.3 million throughout the FYDP, to support the F/A-18E/F SLAP requirement.

One of the F/A-18E/F SLAP goals is to define the necessary inspections and modifications required to achieve 9,000 flight hours. Current SLAP methods would allow feasibility studies to assess an F/A-18E/F service life to 12,000 flight hours. Other SLAP goals relate to increasing total landings, arrested landings and catapults beyond currently defined life limits. Phase A, which developed methodologies to be used in assessing airframe, flight controls, and subsystems, is complete. Phase B constitutes a majority of the SLAP analysis activities and as analysis is completed will feed into SLEP extension activities. The F/A-18A-D SLAP showed that the airframe can fly to 10,000 hours with a combination of modifications and inspections to maintain airworthiness.

By 2015 Boeing was preparing to undertake an F/A-18E/F Service Life Extension Program [SLEP] to extend the aircrafts usability from 6,000 flight hours to 9,000 hours. The first Super Hornet to reach 6,000h was inducted for overhaul in 2015, while the lives of legacy Hornet types were already being extended out to 10,000 hours.



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