This article originally appeared in the April 2006 issue of "Arms" magazine. In this reprint, the content has been re-improved and edited, and some illustrations have been added and organized to share with fellow readers. Personally, I think "Arms" magazine is a professional and objective military magazine, and I recommend continuing to subscribe to it to enrich your own military knowledge. Reprinting some of the older articles on it is mainly to allow readers to examine past things and opinions from another unique perspective.
Previous Dilemma
In the 1960s, the United States faced such a severe reality: as modern large-scale integrated weapons systems became increasingly complex, battlefield maintenance and support conditions became relatively poor, resulting in an alarming increase in maintenance and support costs, a continuous decline in combat readiness rates, and maintenance and support work becoming increasingly difficult.
Take the F-15A, the first third-generation fighter aircraft equipped by the U.S. Air Force at that time, as an example. In 1975, the full mission rate was only 40%, and by 1982 it only increased to 68%. On average, only 9% of the aircraft were able to operate continuously, and the fleet was in maintenance, awaiting repair, or waiting for parts approximately 50% of the time. Poor maintenance support also leads to frequent flight accidents. From 1963 to 1978, 3,824 flight accidents occurred for the active fighter of the US Air Force alone, an average of 255 per year.
On the other side of the Iron Curtain , although there is a certain gap in performance among the huge Soviet-made aircraft fleet, the simple system structure of the MiG-21 and MiG-23 fleets, lower airport conditions and fuel label requirements make Soviet military maintenance and support work relatively easy. If a full-scale war breaks out, a large number of MiG fighters taking off from simple field airports will undoubtedly exhaust the F-15s that can only be invested in batches and in small quantities due to low combat readiness rates, eventually causing the United States to lose air superiority .
The simple, sturdy and easy-to-maintain Soviet fighter jets are more suitable for modern warfare than the expensive and delicate American fighter jets.
Measures - Integrated Support Project
Faced with the unoptimistic military aircraft maintenance and support situation, the U.S. Department of Defense has gradually established the Integrated Support Project (ILS) [Note 1] since the mid-1960s, and it has been used as a necessary technical and management activity for the military in the process of purchasing new equipment. It mainly consists of two stages (development stage and use stage).
[Note 1] Comprehensive support engineering: refers to the management and technical activities that, in order to achieve the goal of combat readiness integrity, comprehensively consider support issues in product design to improve its supportability, determine the best support requirements, reasonably purchase support resources, and provide the required support at the lowest life cycle cost during the use phase.
In the development stage, the US military mainly focuses on improving the supportability of the aircraft, that is, through the design of reliability, maintainability [Note 2] and self-protection [Note 3]. In 1987, the U.S. Air Force took improving combat effectiveness as the central goal in the R&M2000 plan, and proposed that aircraft support performance is crucial to the unit's combat capabilities, readiness, and sustained combat effectiveness.
[Note 2] Maintainability: In the 4th Middle East War in 1973, about 77% of the tanks of the Israeli army lost their combat effectiveness in the first 18 hours, but they successfully implemented battlefield maintenance of tank weapons. In less than 24 hours, 80% of the battle-damaged tanks regained their combat effectiveness, and some even returned to the battlefield 4 to 5 times. This shows the importance of battlefield repair. At present, due to the low survivability of aircraft and the increase in enemy lethality, the combat damage rate of aircraft has greatly increased. It is difficult to repair in time just by improving the troops' emergency repair capabilities. Therefore, the aircraft is first required to have good maintainability. The U.S. Air Force requires that 80% of battle-damaged aircraft can be repaired in the field and repaired to a state that can perform certain tasks within 24 hours.
[Note 3] Self-preservation: Future wars will be fought in great depth, with no obvious distinction between front and rear. In order to avoid the airport being attacked and the aircraft being unable to take off or being destroyed, it is required that the aircraft can be dispersed to field airports with poor support conditions as the smallest independent combat unit for mobile operations, and be able to provide various energy sources required for takeoff and takeoff line maintenance without relying on takeoff line support equipment. This ability is called self-preservation.
Since the implementation of R&M2000 in the United States, remarkable results have been achieved.For example, the Navy adopted a phased incentive approach (a total of US$8 million) in the development and improvement process of the F/A-18's F-404 engine, so that the reliability and maintainability are better than the specified values at each measurement point. The F-100 series engines used by the F-15 that had constant problems in the past adopted new technologies such as "long-life core engine", digital electronic control, improved gear pumps and engine diagnostic devices. By the time of the F100-PW-220, the design life had reached 4,300 cycles. Equivalent to a 7-year service life, the failure rate is reduced to 0.2~1 times/1000 flight hours, and the return rate is reduced to 0.3 times/1000 flight hours (in the 1960s and 1970s, flight accidents caused by engine failures in U.S. Air Force fighter jets accounted for more than 60% of the total accidents).
Cross-sectional view of the F-100 jet engine used by the F-15 "Eagle" fighter jet
In the "Desert Storm" operation in 1991, the F-15 dispatched more than 2,200 sorties, with a mission executability rate as high as 96%. The entire U.S. Air Force dispatched a total of 65,000 aircraft sorties during Operation Desert Storm, with an average mission availability rate of 92%.
The maintenance and support capabilities of military aircraft during the use phase of the US military have the following measurement indicators-executable mission rate, missed flight rate, maintenance man-hours, repair rate, and spare parts supply.
The aircraft mission executable rate is the main indicator of maintenance support capabilities. It refers to the number of aircraft that can perform the original combat mission as a percentage of the total number of aircraft. In the past 10 years, as the U.S. Air Force has continuously replenished new advanced aircraft and increased its spare parts budget, the mission executability rate of aircraft (including fighters, tankers, and bombers ) has skyrocketed, and finally stabilized at around 80%. Especially in the 1991 Gulf War, the aircraft mission executability rate was as high as 91%.
The F-16 fighter engine was re-equipped. The maintenance pilots used a wheeled platform to stuff the entire engine into the tail of the aircraft, and then fixed the details.
The missed flight rate refers to the percentage of aircraft flights that return due to Category III or Category II malfunctions to the total number of flights. Category III faults must be eliminated before takeoff is allowed, while Category II faults (i.e. non-serious faults) are still allowed to take off again until they are finally eliminated. In recent years, the misflight rate of U.S. Air Force aircraft has continued to decline. The main reason is that new aircraft have been added, and aging aircraft that are difficult to maintain (such as F-111) have also been modified for reliability and maintainability. The Air Force believes that an effective way to solve the maintenance problem of aging aircraft is to modify the aircraft.
Maintenance man-hours refer to the maintenance time required for an aircraft per flight hour. The U.S. Air Force's average maintenance hours per aircraft has decreased significantly in recent years due to the implementation of aircraft reliability and maintainability modifications.
Repair refers to removing relevant parts from a temporarily grounded aircraft and installing them on another aircraft to keep the latter in good condition. Repair rate refers to the percentage of aircraft that are repaired per 1,000 flight hours to the total number of aircraft. Usually, the patchwork repair method is expensive and significantly increases the maintenance workload. In the 1970s and early 1980s, the U.S. Air Force had a serious repair problem. For example, the omission of initial spare parts in the F-15 acquisition plan caused the repair rate of the F-15 to be as high as 56.5% in 1980, shortly after it was equipped with the army. The repair rate of U.S. Air Force aircraft has dropped significantly in recent years.
U.S. Air Force ground crews are performing maintenance on the F-15 "Eagle" fighter jets. The use of various advanced instruments has greatly reduced human errors.
The supply of spare parts is sufficient, and the mission executability rate of the aircraft is high. In 1993, the US Air Force's allocation of repairable spare parts was basically consistent with the demand, but the allocation of consumable spare parts only reached 78% of the demand. However, with the downsizing of the Air Force, the remaining aircraft can be used as repair aircraft, thus easing the contradiction in the supply of spare parts.
In the 1980s, the U.S. Department of Defense established a "Requirements Management Committee" composed of acquisition and maintenance personnel to organizationally solve the problem of integrated use and maintenance. When the Air Force was also implementing the R&M2000 plan, it merged the Air Force Logistics Command (AFLC) and the Air Force Systems Command (AFSC) into the new Air Force Equipment Command, with the purpose of strengthening the comprehensive management of weapons and equipment systems.
A new maintenance system
The maintenance and support costs of modern weapons and equipment after they are put into service account for a large share of the full life cycle costs of weapons. Since 1960, the U.S. Department of Defense has entrusted its Logistics Management Institute to conduct full life cycle cost research. According to the requirements of the Logistics Management Institute, the Air Force logistics department should try to save expenses as much as possible during non-war periods, among which rear-level repairs have the greatest potential for savings.
Therefore, the Air Force is introducing a competition mechanism for rear-level repairs, including competition between rear-level repair bases and the private industry sector, as well as competition between different rear-level repair bases, so as to improve efficiency and save costs. Another way to save money in logistics is to save the cost of spare parts, such as purchasing spare parts with higher reliability and better maintainability.
U.S. Air Force ground crews are checking the mounted items on the F-16 "Fighting Falcon" fighter jet to ensure flight safety.
The implementation of two-level maintenance (forward level and rear level) is the biggest change in the US Air Force's maintenance system. Compared with the original three-level maintenance (primary, intermediate and advanced), the two-level maintenance can save personnel costs and improve the squadron's rapid deployment capability. Taking engines and onboard electronic equipment as an example, implementing two-level maintenance is expected to save hundreds of millions of dollars every year. After the implementation of two-level maintenance, the original intermediate-level maintenance tasks were shared by the rear level of the army. Due to the implementation of two-level maintenance, the wing's maintenance personnel has been greatly reduced, which is conducive to the rapid deployment of emergency forces overseas.
In the previous three-level maintenance system, about 70% of field replaceable parts were repaired in intermediate repair workshops. After the third-level maintenance is transformed into two-level maintenance, continuing to maintain the normal turnover of repair spare parts has become a new problem that logistics personnel need to seriously solve. To be on the safe side, the Air Force conducted a two-level maintenance pilot in 1991. The pilot majors focus on engines and airborne electronic equipment, because these two majors used to be the main body of intermediate maintenance work. As a pilot unit, Hill Air Force Base has undertaken the intermediate maintenance tasks of F-16, and 10 nearby combat units have sent faulty parts for repair according to the new maintenance system.
A Minnesota Air National Guard Maintenance Squadron engine maintenance technician works on an F-16 Block 50 jet engine.
Two-level maintenance pilot has found an effective way to improve maintenance efficiency. The pilot unit's repair flow time (that is, removing the faulty parts from the aircraft, repairing them at the logistics center and then reinstalling them on the aircraft) has dropped from 45 days in the past to 7.5 days now. In other words, the availability of spare parts can be greatly improved without increasing the cost of spare parts. In addition, the air force wing has converted from a single aircraft type to a mixed aircraft type, which poses new challenges to logistics support. In a mixed wing, maintenance can no longer be divided according to aircraft types. Maintenance personnel must learn to solve technical problems in the maintenance of multiple aircraft types.
Maintenance and support requirements for fourth-generation fighters
This article mainly takes the use and maintenance support requirements and expectations of the F/A-22 fighter jet and the F-35 Joint Strike Fighter (JSF) that will be in service after 2010 as examples to illustrate the development trends of future US Air Force aircraft use and maintenance support, which mainly focus on complete aircraft, engines and electronic equipment.
According to the requirements of the Air Force's R&M2000 plan, the combat readiness rate (R&M) of the F/A-22 fighter jet is doubled compared to the aircraft in active service. Among them, the aircraft life span meets the aircraft structural integrity outline requirements of more than 8,000 hours. Since its main structural parts are replaceable, the life of the whole machine can be extended and can be used for 30 years. Its combat dispatch rate reaches 4.5 times/day, which is twice that of the active aircraft F-15; the preparation time for another dispatch is 2/3 of the F-15; the maintenance man-hours per flight hour (MMH/FH) and logistics support requirements are both half of the F-15 (F-15A is 44).
Illustration: The service of the fourth-generation fighter F-22 "Raptor" has brought more challenges to the US military's air support in terms of combat readiness rate, combat dispatch rate, maintenance man-hours per flight hour and life span.
The aircraft implements two levels of maintenance, and 26% of the structure (by weight) is made of composite material .It has a self-protection design and can maneuver at field airports; it has an auxiliary power unit , which can eliminate the need for various takeoff line energy sources during takeoff and takeoff line maintenance; it has a built-in airborne weapon bay, so it does not need a ground-mounted bomb truck; it has an onboard oxygen and nitrogen generation system, so it does not require ground oxygen and nitrogen supply trucks. The maneuverability in transition is approximately 2 times higher than that of the F-15. Combat support resources require 6.2 sorties C-141 transport aircraft airlift (18 sorties required for F-15). The service life of the
F-119 engine should meet the requirements of the Engine Structural Integrity Program (ENSIP) for 4,000 hours. Compared with the F-100 engine used in the F-15 aircraft, its air parking rate is reduced by 29%, the early replacement rate is reduced by 33%, the repair rate is reduced by 74%, and the field replaceable unit (LRU) replacement rate is reduced by 50%, on average The maintenance interval (MTBM) increased by 62%, the engine's MMH/FH decreased by 63%, the time required for engine replacement dropped by 60% (to 89 minutes), the number of engine parts was reduced by approximately 40%, and the amount of support tools and equipment was reduced by approximately 60%.
To facilitate maintenance, all accessories and external parts are located in the lower half of the engine; most parts, including the fuel pump , are LRUs; all accessories on the engine box are installed in a single layer; bolts are standard; only 6 types of wrenches are required for external maintenance; the time to replace any LRU does not exceed 20 minutes.
Due to the adoption of new technologies such as ultra-high-speed integrated circuits, almost 85% of LRUs have been reduced to field-replaceable modules (LRM). Their MTBF is generally 8,000 hours, which is four times the Air Force's requirements for standard electronic LRUs in the late 1980s, and some can even reach 20,000 hours. The MTBF of its radar (AN/APG-77) will increase by 25% compared with the current aircraft. Since maintenance personnel are equipped with computerized auxiliary maintenance equipment that can automatically diagnose faults, the MMH/FH of electronic equipment will be 90% lower than that of the F-15 aircraft. Electronic devices are fault-tolerant or self-healing due to the extensive use of universal module designs. If the module of the navigation device fails during flight, the module of the communication device can be automatically borrowed. At this time, although the tactical performance of the electronic equipment may be reduced, it can still work reliably.
The AN/APG-77 radar phased array scanning antenna equipped with the F-22 "Raptor" fighter
Current reports on the JSF fighter's support requirements are mainly qualitative. While requiring a high combat readiness rate, it also emphasizes that aircraft support costs should be low. In the contracts for its demonstration prototypes, electronic equipment, comprehensive weapons and other development projects, it is emphasized that it must be "affordable."
In order to achieve the requirements of high self-protection and good transition maneuverability, four major contractors are jointly researching "Joint Integrated Subsystem Technology (JIST)" for JSF, aiming to develop a system to replace the aircraft's power generation system, hydraulic pump and starter . The JIST system is simple and can be driven by engine bleed air, using a small combustion chamber or ground power. It significantly improves self-preservation and reliability. One of the alternatives is an all-electric aircraft, using high-voltage direct current transmission instead of hydraulic transmission, which can eliminate the guarantee problem of hydraulic system .
In addition, an intelligent skin structure is applied to incorporate electro-optical sensors, transceivers and other units into the skin to automatically diagnose structural damage. The wing uses extensive composite materials to minimize holes, fasteners and structural elements.
At the same time, new fault diagnosis and monitoring systems are adopted. For example, Lockheed Martin is experimenting with the prediction and condition management system (AVPHM) for JSF aircraft. The system can be used to monitor, store and transmit fault prediction and diagnostic information, allowing aircraft components to be repaired based on the situation. It can provide relevant information to maintenance personnel in an appropriate manner and format and determine the aircraft's mission capabilities and required maintenance work. It can also provide pilots with aircraft status information in flight.
Ground crews are maintaining F-35 fighter jets
The United States will require the three armed forces to develop high-reliability electronic LRMs, implement single-level maintenance, and replace them if they break. Lockheed Martin and McDonnell Douglas contracted the second phase of the integrated sensor system to improve the development of universal electronic modules to improve the tactical performance and support of electronic equipment.Judging from the MTBF of the F/A-22 fighter's electronic LRM (8,000 hours) and the Air Force's expected MTBF of the fighter's electronic LRM in 2020 (20,000 hours), the MTBF of the JSF fighter's electronic LRM may reach 14,000 hours.
Ground crews from the 388th Fighter Wing and 419th Aircraft Maintenance Squadron of the U.S. Air Force maintain F-35A
Inspiration and Thoughts
U.S. Army The integrated support project (ILS) gradually improved in the 1980s is achieved through strict scientific management operation mechanisms and processes, a complete maintenance support system with the base as the core (battlefield construction base, overseas deployment base, and rear base), and regards supportability as an important part of the aircraft's comprehensive performance. It enables U.S. air power to achieve the goal of maximizing combat effectiveness on the basis of improving aircraft combat readiness.
Facing the complex and urgent surrounding situation, our military should also pay full attention to the maintenance and support of equipment while stepping up the construction of air power. Since the advanced fighters introduced and newly developed by our army are third-generation aircraft, this puts forward high requirements on the technical level and organizational management of our army's maintenance support. Therefore, we should also fully think about and learn from the US military's Integrated Support Project (ILS).
The MiG-21 fighter engine in the Soviet Air Force's spare parts library
Although the imported aircraft are designed and manufactured by foreign countries, their reliability and maintainability levels have been fixed and we cannot change them. But we can take corresponding measures to ensure the full play of its inherent combat readiness based on understanding the reliability of the aircraft. At the same time, future maintenance and repair issues should be taken into consideration during the aircraft introduction process. The technical information provided by foreign parties often does not include documents such as maintenance outlines and overhaul processes. These information are easy to obtain when purchasing aircraft, and it may be more troublesome to purchase them later. Without this information, it will cause great inconvenience to the future use and maintenance of the troops.
An image of the J-11 radar dome of a certain brigade of the Air Force Aviation Force in the Western Theater Command being opened for maintenance
In general, while our military is currently accepting a large number of new aircraft models, there are still many areas for improvement in the maintenance and support of the aircraft. A system similar to the U.S. military's Integrated Support Project (ILS) should be established as soon as possible to give full and comprehensive consideration to all aspects of the introduction, use, support, and management of aircraft models, with the central goal of improving actual combat effectiveness, and more effectively complete the tasks assigned by the people of the motherland.
A certain military region in our country has started seasonal maintenance on the H-6 aircraft. The replacement and maintenance work for this kind of large fighter aircraft is usually carried out every two years, which is very hard work.
Two operators entered the intake duct of the H66 at the same time to perform maintenance on engine-related components.
A province in southern China is carrying out maintenance work on "IDF" fighter aircraft
