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F-117A Nighthawk Maintenance

The F-117A program demonstrated that a stealth aircraft can be designed for reliability and maintainability. The aircraft maintenance statistics were comparable to other tactical fighters of similar complexity. Logistically supported by Sacramento Air Logistics Center, McClellan AFB, Calif., the F-117A was kept at the forefront of technology through a planned weapon system improvement program located at USAF Plant 42 at Palmdale, Calif. The F-117A Combined Test Force is a diverse organization that includes military members, government civilians and various contractors who work together to test the latest F-117 improvements. The test force works out of U.S. Air Force Plant 42 in Palmdale, Calif, just south of Edwards. As a reflection of the Nighthawk itself, the F-117A Combined Test Force maintained a stealthy profile when it first began testing the revolutionary plane.

Air Combat Command's 1996 Senior Noncommissioned Officer of the Year was Master Sgt. Richard Acevedo. An 18-year veteran, Acevedo was the resource advisor for the 49th Maintenance Squadron, Holloman AFB, NM. Acevedo contributed to a 60 percent increase in the F-117A mission capable rate over the previous two years and reduced F-117A flight control computer testing and repair cycle time from 40 to three hours. He also managed the squadron's 517 Government American Express accounts and funds for 44 temporary duty assignments. His efforts with the Aerospace Guidance and Metrology Center provided advanced training to Holloman members on Inertial Navigation System (INS) test station maintenance, saving the wing $123,300. He personally supervised dual-intensity modification on 26 F-117A display indicators with new checkout procedures, completing critical mission-essential time-change directives two months ahead of schedule.

In an effort to improve the combat effectiveness of the stealth fighter, test experts from the F-117 Combined Test Force at Air Force Plant 42 in Palmdale, Calif., worked to expand what it brought to the fight. On April 2 2002, developmental test experts in Palmdale teamed up with their operational counterparts from Holloman Air Force Base, N.M., to complete the second phase of a demonstration project designed to provide the F-117 and its pilots with the ability to receive and transmit mission and target data in real-time from the air. Phase one tests, completed in October of 1998, allowed a pilot to receive live-threat information and manually replan a mission from the cockpit. The second phase completed the test cycle by demonstrating the transmission of real-time mission and target data out of the cockpit and into the hands of command and control forces on the ground.

Until this testing, the potential time-critical combat capabilities of the F-117 had not been explored. The target data technology works by allowing the aircraft to receive and transmit tactical information on targets or pop-up threats via satellite communication. The fighter's ability to send and receive text and images enhances its combat flexibility yet does not compromise its stealth configuration.

The fleet of F-117As has been refurbished, including removing the aging thin films and coatings and replacing them with a special radar-absorbent paint that was easier and less expensive to apply and maintain. During manufacture, the thin films and coatings of radar-absorbent materials were painstakingly applied to each F-117A to ensure that no defects existed. Any slight deviation from the Nighthawk's exacting surface specifications -- even an air bubble or a screw not tightened exactly to specifications -- could result in a blip on an enemy's radar screen. The new painting process was no less exacting.

Nighthawks were large aircraft -- 65 feet long with a 43-foot wing span -- and each F-117Awas slightly different from the others. The Nighthawk's angularity and the need to keep the paint spray nozzles at exactingly precise distances from the aircraft's surface at all times require both accuracy and adaptability to adjust for variabilities from one aircraft to another. Maintenance downtime for the F-117As needs to be minimized so that each fighter was available for military operations as soon as possible.

The first Nighthawk to be refurbished with the new coating was done manually by five painters and a masking crew, and took 4 and a half days. A Sandia National Laboratories development team created the system concept, identified the needed hardware, wrote the custom software that operates the system, and integrated the system's commercial and noncommercial components as part of a 3-year development project.

The first challenge in designing the automated painting system was to find a robot or robots big enough to reach all of the plane's surfaces. To keep costs down, the design team used commercially available equipment as much as possible. The Sandia painting system features three commercial robotic arms used in U.S. auto factories called the Motoman P8. Two of the arms were mounted on 30-foot-long rails. Each 10,000-lb robot-and-rail system was mounted on a specially designed air lift so that two people can move its base to desired locations around the aircraft. A paint nozzle at the end of each of the robotic arms was connected via tubes and wiring to an oversized stainless steel paint can. The coating-delivery system -- the paint nozzles, tubes, pumps, and cans --was also a Sandia creation. One robot-rail combo paints the Nighthawk's top surfaces; the second paints the bottom surfaces. Cameras and other sensors help a nearby computer plan and guide the robots' every move. This merging of commercial hardware with Sandia-designed custom hardware and software exemplifies Sandia's unique system integration capabilities. The third floor-mounted, stationary robot was for painting the Nighthawk's removable parts, such as weapon bay doors and rudders.

The Sandia team developed a unique feedback, path-planning system that adjusts for variabilities from aircraft to aircraft. Path planning was the fruit of Sandia's years of research in "geometric reasoning," which was developed using DOE Defense Programs and Lab-Directed research funding. Geometric reasoning gives robots the capability to automatically determine the movements needed to carry out the task, even if the workpiece varies from piece to piece, as do the F-117As. A pair of stereovision cameras mounted at the end of the robotic arms locate "landmarks" on an F-117A corresponding to vertices where a Nighthawk's angular facets meet. Based on this feedback about the unique geometry of each plane and information about the robot's reach, joint limits, characteristics of the painting process and other factors, the software automatically generates a path for the robot to follow as it paints. The system also ensures that the robotic arms don't violate a 6-inch buffer zone around the fighter. The motion-planning software was what allowed Sandia to rapidly and inexpensively develop robot systems for small-lot production operations like painting a limited number of aircraft.

To design the system, Sandia used a 3-D computer model of the F-117A provided by Lockheed Martin. Models permit the team to use Sandia's geometric reasoning software to perform a "reachability analysis" of the F-117A, which helped determine where the system's two robot-and-rail systems would have to be repositioned on the hangar floor to reach the entire aircraft.

Before painting began and each time a robot-and-rail system was moved during painting, the computer vision system automatically registered reference points corresponding to three jack stands the Nighthawk was placed on inside the hangar. It then measures the precise locations of the two robot-and-rail systems with respect to the aircraft. With almost human-like agility, the rail-mounted robotic arms move with seven degrees of freedom. Six of those are the three spatial dimensions (x, y, and z) plus roll, pitch, and yaw, which was normal for many manufacturing-type robots. The seventh degree of freedom gives the robot the ability to maintain a fixed x, y, z, roll, pitch, and yaw position from multiple poses. This was like having an "extra elbow" to reach around things that are in the way. It also gives a large range of motion along the 30-foot rail required to coat a large aircraft.

The system was delivered to Lockheed Martin's Advanced Development Projects group, better known as the "Skunk Works," in September 1998. Members of the Sandia team helped install and acceptance-test the system during the following five months. Safety precautions were incorporated into the system and personnel were trained in robot awareness. In terms of size and level of complexity, this was the largest intelligent system Sandia has ever delivered to an outside customer.

Whereas the first aircraft was refurbished using five painters and a masking crew taking four and a half days, the first robotically painted aircraft at the Skunk Works took only three days with a smaller crew. Once it was in a production mode, the system would provide considerable cost and time savings to the Air Force. The new system also improved the final finish quality and reduce maintenance costs by minimizing the amount of time spent painting and reworking each aircraft. Signature testing was performed on the robot-sprayed aircraft and the results were significantly better than expected.

The Air Force, on 30 September 1998, awarded Lockheed Martin Skunk Works (LMSW) a sole source, Total System Performance Responsibility (TSPR) depot-level acquisition and sustainment weapon system support contract for the F-117 Stealth Fighter that provides stable logistics support into the next decade. This contract, beginning 1 October 98, continues the logistics support necessary to fulfill the weapon system mission, ensure combat capability and provide services presently performed by LMSW, breakout contractors and the System Program Office (SPO). This contract includes all support functions with the exception of Intermediate and Organizational maintenance.

The original concept for F-117 was for a Contractor Logistics Supported weapons system with a small SPO to oversee necessary government functions. Accomplishment of Program Management Responsibility Transfer (PMRT), in October 1989, moved the SPO from Wright-Patterson to the Sacramento Air Logistics command (SM-ALC). The ALC began the process of breaking out subcontractors and increasing technical oversight, generating considerable duplication of effort. All hardware, item management and distribution functions transferred to Sacramento creating a "third leg" in the weapon system support pipeline. SPO size ultimately increased to 226 providing sustaining management and contractor oversight.

LMSW provided 75% of the core sustaining for the F-117. All technical support was conducted under the annual sustaining contract and individual upgrade programs. LMSW also operates the modification/depot line at Site 7, AF Plant 42. These core capabilities provide a solid foundation for effectively increasing the LMSW Program Management role. TSPR expands LMSW responsibilities in the areas of system engineering, material management, subcontractor management, system & subsystem support, direct support to the user and AF reporting requirements. The majority of tasks scheduled to transition from the SPO were items already performed at LMSW. Government responsibilities would continue to include program direction, requirement determination, contract management, business/financial execution, product/service acceptance and security. The SPO size was targeted to reach 55 people by the end of FY99 with a goal of 20 by FY01 as LMSW demonstrates support capability. The TSPR contract would return the F-117 to the original concept -- Contractor Logistics Support with LMSW as the prime system integrator and a small SPO providing oversight capacity.

F-117 TSPR offered an incentive package to assure performance while encouraging the contractor to reduce costs. The contract would have a 3% Award Fee provision for subjective evaluation of technical, management, subcontracting and customer satisfaction. Grading was based on input from all aspects of the government including the SPO, ACC, the 49th Fighter Wing (FW) at Holloman AFB, DLA and DCMC. A 7% Incentive Fee provision based on seven performance metrics would track Non-Mission Capable Supply, MICAP rates, Readiness Spares Provisioning (RSP) Kit fill rates, Depot Quality, Depot Delivery, Delinquent Deficiency Reports and Weapons System Trainer Availability. All items were tracked by the 49th FW and SPO and were considered the most important indicators of program support. Finally, TSPR provides for 50/50 cost share between the government and LMSW on any under run with no ceiling. A minimum performance of 50% on metrics was necessary to receive any additional fee. Overruns were also shared 50/50 to the maximum of the Award and Incentive fees combined.

F-117 TSPR was identified as a pilot program for the Air Force and DoD. This small fleet of 52 aircraft, located at a single operating location at Holloman AFB, offered a unique opportunity for the Air Force and LMSW to continue the F-117's excellent program health. Timing for this transition was optimum due to the BRAC decision to close McClellan AFB, current location of the F-117 SPO. LMSW, as system integrator, would compensate for anticipated SPO program experience loss and complement a significantly downsized SPO with resident expertise. TSPR represents a departure from "business as usual" as it allows LMSW the flexibility required to manage sustaining funds, as appropriate, over the eight years of the contract with no degradation of the total program support posture. The contract makes LMSW accountable for complete weapons system support. TSPR challenges the company to provide support to the 49th FW that was "equal to or better than" current levels while reducing Total Ownership Cost to the US Air Force.

The F-117 program was the Air Force's most complete application of Acquisition Reform initiatives and was successfully operated with reduced government oversight. The program was implemented with a significantly reduced Air Force support capitol investment. The commitment of the Air Force to a long-term supplier relationship has allowed for optimal contractor investment.

The Advanced Composites Program Office (ACO) at Hill AFB led an in-house effort to reduce cost of ownership of F-117A composite structures. As a high-usage trailing-edge component, the 20D82 was required to endure high temperatures from the engine exhaust. Problems with this component included short service-life, high cost, poor fit, large part-to-part variances, and lack of repair procedures. The latter forced the Air Force to replace the component at a cost of $46,400 per item until effective field and depot level repair procedures were developed by the ACO, working with the F-117A System Program Manager (SPM) and SM-ALC/TIM composite manufacturing personnel. Each component repair costs approximately $4,200. After providing a repair, the team set out to totally redesign the troublesome component. They were able to simplify the design, increase service temperature capability, maintain low observable requirements, and reduce the assembly part count from fifteen to six. The cost of the redesigned component was half of the original cost for twice the capability.

The Single Configuration Fleet (SCF) program was intended to reduce the total ownership costs of the F-117 by standardizing the fleet to a single optimized spray/sheet coating and edge configuration. The Single Configuration Fleet modification consolidates the existing seven different F-117 radar-absorbing material configurations into one optimized for maintainability and deployability. This would reduce LO maintenance requirements and take advantage of state-of-the-art robotic technology. The F-117's low-observable features have always been costly and difficult to maintain because of the various radar-absorbing material configurations. To correct this, the Single Configuration Fleet modification consolidates the existing seven different radar-absorbing material configurations into one optimized for maintainability and deployability.

The modification, entailing stripping and re-coating the entire F-117 fleet, replaces the sheet-coated RAM on the wings, rudders and fuselage and uses a precise robotic process to apply a RAM coating to almost 75 percent of the airframe, he said. These areas which were never accessed for maintenance would require virtually no future RAM repairs. Areas that were frequently accessed would have removable RAM sheets applied to the maintenance panels. The new spray-coated RAM was much more durable than previous versions of sheet-coating. This would result in the new (Single Configuration Fleet) aircraft requiring fewer RAM repairs. The optimized configuration provides maintainers easy access to maintenance panels while eliminating the need to repair infrequently accessed areas.

The biggest advantages of the new standardized configuration, for maintainers and the Air Force, would be common repair procedures and materials for all F-117s. With so many configurations, there were numerous repair procedures and materials. Maintainers must keep track of which procedures and materials belong to which aircraft. Maintaining the aircraft would be much easier once the entire fleet undergoes its modification. The Air Force should also see a 50 percent reduction in the size of our technical order -- the manual airmen must follow step-by-step when working on aircraft maintenance.

The new modification also would greatly reduce the amount of hardware and other supplies that units would need when they deploy to forward locations. The Air Force would be able to phase out a number of materials leading to further cost savings in the logistics and materiel management. Based on flight test results and an initial operational evaluation, the new SCF configuration would reduce maintenance manhours per flying hour due to (RAM) maintenance by over 50 percent. Since low observability was the primary maintenance driver for the F-117, the SCF improvements indirectly improved sortie generation capability. Additionally, once SCF is implemented in the entire F-117 fleet, the annual consumable material costs would be reduced from the current level of $14.5 million to approximately $6.9 million.

The modification was implemented on a five-year schedule as the F-117s were rotated through the contractor depot at Palmdale, CA. To make best use of this time, the Air Force was also implementing numerous other F-117 modifications and repairs. The entire process takes approximately five months for each aircraft. The first completed production aircraft to undergo the modification was delivered to Holloman in April 2000. Holloman was the only base in the Air Force that flies the F-117.



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