THE DEVELOPMENT OF AIRCRAFT COMBAT SURVIVABILITY AS A DESIGN DISCIPLINE OVER THE PAST HALF CENTURY

By: Robert E. Ball, Mark Couch, and Christopher Adams

A BRIEF INTRODUCTION TO THE BASICS OF ACS

The term “aircraft combat survivability” (ACS) is defined in The Fundamentals of Aircraft Combat Survivability Analysis and Design, Second Edition as “the capability of an aircraft to avoid or withstand a man-made hostile environment” [1]. This definition forms the basis for the ACS design discipline.

“To avoid” means to avoid being detected, tracked, engaged, and physically “hit” by one or more of the damage (causing) mechanism(s) carried or generated by a threat weapon or warhead, such as a gun-fired ballistic armor-piercing projectile with incendiaries (AP-I) and the blast and fragments generated by the detonation of a high-explosive (HE-frag) warhead. The inability of an aircraft to avoid the hostile environment is referred to as the aircraft’s susceptibility. Aircraft susceptibility can be measured by the probability that the aircraft is hit by one or more damage mechanisms, PH. Avoiding the hostile environment (i.e., reducing the aircraft’s susceptibility) can be achieved using the six susceptibility reduction concepts:

  • Threat Warning.
  • Noise Jamming & Deceiving.
  • Signature Reduction.
  • Expendables.
  • Threat Suppression.
  • Weapons & Tactics, Flight Performance, and Crew Training & Proficiency.

“To withstand” means the aircraft continues to function at some useful or acceptable level after any unavoidable hits by the enemy’s damage mechanisms. The inability of an aircraft to withstand the hostile environment is referred to as the aircraft’s vulnerability.  Aircraft vulnerability can be measured by the probability that the aircraft is killed given a hit, PK|H. Withstanding the hostile environment (i.e., reducing the aircraft’s vulnerability) can be achieved using the six vulnerability reduction concepts:

  • Component Redundancy With Separation.
  • Component Location.
  • Passive Damage Suppression.
  • Active Damage Suppression.
  • Component Shielding.
  • Component Elimination or Replacement.

An aircraft that is unable to both avoid and withstand one or more damage mechanism hits is said to be killed, and the product PH•PK/H = PK is a measure of its killability. The probability an aircraft survives the man-made hostile environment is PS, the complement of PK. Thus, PS = 1-PK.

There are two primary categories of an aircraft’s inability to withstand hits (i.e., its inability to continue to function at a usable or acceptable level): an aircraft attrition kill and an
aircraft mission kill.  An aircraft suffers an attrition kill if it loses one or more flight-essential functions (lift, thrust, control, and structural integrity) due to combat damage (i.e., we say the aircraft was totally unable, or failed, to withstand the hit[s]). An aircraft suffers a mission kill if it loses one or more mission-essential functions due to combat damage (i.e., we say the aircraft was partially able to withstand the hits[s]). Mission kills include mission abort, forced landing, etc.

Any particular characteristic of the aircraft, specific piece of equipment, design technique, armament, or tactic that reduces either the susceptibility or the vulnerability of the aircraft has the potential for increasing an aircraft’s survivability and is referred to as a survivability enhancement feature. Table 1 lists some of the many, varied design features and operational tactics and techniques that can contribute to an aircraft’s combat survivability. Each of these features is an example of 1 of the 12 susceptibility and vulnerability reduction concepts listed previously.

The two goals of the ACS discipline are (1) the early identification and successful incorporation of those specific survivability enhancement features that will increase the combat cost effectiveness of the aircraft as a weapon system; and (2) in those situations where the damage will eventually lead to an aircraft attrition kill, the ability of the survivability enhancement features to allow a graceful degradation of the system capabilities, giving the crew a chance to depart the aircraft over friendly territory.

Of particular interest here is the development of ACS as a design discipline for aircraft that has taken place over the past 50 years. In general, design disciplines for the individual aircraft systems or capabilities, such as structures, fuel, propulsion, flight controls, aerodynamics, power train, and rotor blades—and now combat survivability—have a terminology, a methodology for assessing or quantify- ing the important capability metrics (e.g. measures of performance [MOPs]), a design technology for achieving the desired capabilities (e.g., key performance parameters [KPPs]), a set of user requirements that can be validated by testing, a place in the acquisition process, and an infrastructure that includes educational opportunities in the discipline.

The ACS design discipline must also be broad in concept and coverage, and it must be an integral part of systems engineering (SE) for military aircraft because it can have a major impact on all of the other aircraft design disci- plines (e.g., rugged structures; explosion-proof and leak-proof fuel tanks and lines; stealthy propulsion; redundant and separated self-repairing flight controls; highly maneuverable, agile, and stealthy aerodynamic shapes; and rugged rotor blades, drive shafts, and run-dry gear boxes), as well as on the operational tactics of military aircraft.

THE MOTIVATION FOR ESTABLISHING ACS AS A DESIGN DISCIPLINE

Military aircraft have been shot at; hit; and downed, lost, or killed ever since they were first used in combat in the early 1900s. As a consequence of the loss of hundreds of thousands of military aircraft in combat (nearly 50,000 U.S./UK fighters and bombers were lost in combat in Europe in World War II)—not to mention the accompanying death, injury, or incarceration of their crews—many actions, both operational and design, have been taken over the past 100+ years to enhance the combat survivability of military aircraft to the increasingly effective man-made threats, starting with the early ground and airborne guns and progressing to the modern ground and airborne guns and guided missiles.

From the beginning of the 20th century up to, and particularly including, the Southeast Asia (SEA) conflict (1964– 1973), most military aircraft were not required to have much in the way of survivability in their original design.Furthermore, any design and operational actions taken to enhance an aircraft’s survivability were mostly a reaction to an empirically discovered aircraft killability in combat.

The quickest remedy was often to try new tactics, including mission and force package changes, that reduced the susceptibility of the participating offensive aircraft. These changes included flying higher to avoid the enemy’s air defense weapons; employing metal chaff to create detection and tracking problems for radar-directed weapons; employing on-board threat warning and noise- jamming and deceiving electronic equipment (known as aircraft survivability equipment [ASE]); and adding fighter escorts, electronic countermeasures (ECM) aircraft, flak suppression aircraft, and search and rescue aircraft to the mission package.

Unfortunately, these actions often resulted in fewer offensive aircraft available to accomplish a given mission (such as bombing a bridge), as well as possibly reduced effectiveness of the weapons used (such as bombing the bridge from high altitude using dumb bombs). Furthermore, these operational actions were not always successful in preventing aircraft losses. (Perhaps the most successful action taken to enhance aircraft survivability in the SEA conflict was the later introduction of smart [precision-guided] weapons, which could be launched from a distance and guided to the target.)

The other survivability enhancement option was to reduce the vulnerability of the recently discovered killable aircraft [2]. This option usually took longer to achieve and could result in a less-than-optimum enhancement of survivability, as well as degradations in other important operational capabilities of military aircraft (e.g., reduction in aircraft payload, range, speed, and maneuverability due to added weight) and an increase in the aircraft’s initial and operational costs and downtime.

This problem of not designing for ACS from the beginning of any aircraft program peaked before the SEA conflict when the goal was to develop fast, high-flying fixed-wing aircraft with long-range air-to-air and air-to- surface weapons (possibly nuclear) and helicopters that would be mostly operating (it was assumed) in safe skies. Simply put, most of the aircraft used in SEA were never designed to survive in the man-made hostile environment in which they were eventually assigned to operate.

This lack of available ACS-designed aircraft in SEA resulted—according to the most recent combat loss data—in the loss of approximately 4,100 U.S. aircraft (2,052 fixed-wing and 2,066 rotary-wing) due to hostile combat action from all three U.S. military departments over 10 years. (An additional 4,300 aircraft [1,117 fixed- wing and 3,193 rotary-wing] were lost to nonhostile action [i.e. mishaps]— many of which occurred while intentionally flying to avoid enemy detection in a hostile environment, such as low-level flights and night- time flights without night vision devices [3].) This long-term neglect, inadequate consideration, and/or simple omission of the importance of ACS in the design and operation of military aircraft had to be changed.

MAJOR ACTIONS IN THE ACS DESIGN DISCIPLINE DEVELOPMENT

Perhaps the first public recommendation that U.S. military aircraft must be designed—from the beginning—for combat survivability was a 1969 paper by Dale Atkinson, Paul Blatt, Levelle Mahood, and Don Voyls titled “Design of Fighter Aircraft for Combat Survivability” [4]. In 1967, a forensic team from Wright-Patterson AFB, led by Dale, went to SEA to find out why the Air Force was losing so many of its fighter aircraft to the relatively primitive air defenses used by North Vietnam. The team discovered that the aircraft being used in SEA were both susceptible (because of the missions flown and the tactics being used) and vulnerable (because the aircraft were not designed to with- stand hits by gun-fired ballistic projectiles and the HE warhead blast and fragments they encountered while on these missions).

The results of the team’s study were summarized as follows (in the paper’s abstract) [4]:

Aircraft survivability must be considered during preliminary design and during every succeeding phase of airplane subsystem and airframe construction. To enhance survivability a minimization of vulnerability of critical systems and components must be designed and engineered into the aircraft system.  Some areas wherein design application can reduce vulnerability of aircraft are crew protection as well as structural and fuel system components. Experience in Southeast Asia indicates that many aircraft losses occur due to vulnerability of flight control systems to ground fire.  This paper reviews in detail design parameters for hydraulic logic isolation elements, emergency flight control techniques, less flammable fluids, and integrated actuator packages which, together with redundancy and dispersion techniques, will increase the survivability potential of flight control systems. In conclusion, a systematic design procedure must be developed for all critical systems in the aircraft to assure that survivability is given prime consideration during the complete design cycle. [Bold added for emphasis.]

Some context for the team’s call for development of a systematic design procedure for aircraft survivability is appropriate here. Around 1970, the discipline now known as ACS (or simply survivability) was then known as nonnuclear survivability/vulnerability (or simply S/V) [5]. The definition of survivability at that time was “the capability of an aircraft to avoid and/or withstand a man-made hostile environment without sustaining an impairment of its ability to accomplish its designated mission.”

Likewise, susceptibility was defined as “the combined characteristics of all the factors that determine the probability of hit of an aircraft component, subsystem, or system by a given threat mechanism.” Threat mechanisms were defined as “mechanisms, embodied in or employed as a threat, which are designed to damage (i.e., to degrade the functioning of or to destroy) a target component or the target itself.” Vulnerability was defined as “the characteristics of a system that cause it to suffer a finite level of degradation in performing its mission as a result of having been subjected to a certain level of threat mechanisms in a man-made hostile environment.”

Apparently, there was no definition at the time for susceptibility reduction, but the definition of vulnerability reduction was “any technique that enhances the aircraft design in a manner that reduces the aircraft’s susceptibility to damage when subjected to threat mechanisms.”

In the early 1970s, the aircraft nonnuclear survivability/vulnerability discipline had a terminology that was acknowledged to be inconsistent among the Services; the capability metrics and associated assessment methodology were in their infancy as the digital computer came on the scene; both the design technology for enhancing survivability and the user demands (both informal and formal) for incorporating survivability enhancement features on existing aircraft were beginning to grow as the SEA losses grew; and testing in combat was pretty much the norm. Also, the survivability/vulnerability infrastructure at the time was relatively small, and there was no opportunity for an education in how to design more survivable aircraft.

To rectify this unacceptable situation, numerous major actions initiated by the Department of Defense (DoD) and the Services over the following five decades have moved ACS from a commonly held attitude of “Yes, ACS is an important aircraft capability; but payload, range, cost, etc., are more important” to “ACS is an extremely important aircraft capability—perhaps one of the most important—and it must be considered from the beginning to the end of any aircraft acquisition program.”

The following subsections provide a brief description (in rough chronological order) of some of the most important actions that have contributed to the establishment of ACS as a design discipline, as called for by the Atkinson team in 1969. Note that this list of actions is far from complete, and the authors thank the many individuals (both named and unnamed) throughout the DoD, aircraft industry, and acquisition communities who have contributed to the growth of ACS during the last five decades.

1971 – Establishment of the JTCG/AS and JASP

One of the most important actions taken by the DoD near the end of the SEA conflict to improve combat survivability—and thus prevent unacceptable losses in future conflicts—was the establishment of the Joint Technical Coordinating Group on Aircraft Survivability (JTCG/AS) by the Joint Aeronautical Commanders Group in 1971. The proposal to establish the JTCG/AS came from the Survivability Task Force created earlier in 1969 by Dr. Joe Sperazza, Chairman of the existing Joint Technical Coordinating Group on Munitions Effectiveness (JTCG/ME).

One of the major (Atkinson-proposed) goals of the newly formed JTCG/AS was to establish survivability as a formal design discipline. The rationale for this goal was based upon the belief that when survivability becomes an established design discipline for military aircraft, designing for survivability will be a major consideration in the design and SE processes, starting from the initial concept of the aircraft to the final design (and not as an afterthought when the bad news starts to show up after the shooting begins).

Two of the early actions taken by the JTCG/AS consisted of (1) three biennial survivability symposia held at the Naval Postgraduate School (NPS) starting in 1974, followed by cosponsored symposia with the American Defense Preparedness Association (ADPA), which later became the National Defense Industrial Association (NDIA); and (2) the start of the JTCG/AS quarterly newsletter in 1977. The newsletter mailing list grew from approximately 400 in the early days to approximately 10,000. (Note that this newsletter was eventually replaced by the current Aircraft Survivability journal, and the JTCG/AS became the current Joint Aircraft Survivability Program [JASP] in 2003.)

Early 1970s – The Birth of Stealth Aircraft

Another crucial action taken at this time as a result of the heavy losses in SEA (and the prospect of flying over a hostile Soviet Union some day in the future) was the decision that susceptibility reduction, in the form of significantly reduced aircraft signatures, required a serious, long-term commitment, extending throughout the lifetime of an aircraft. Because an aircraft’s signatures are strongly dependent upon many factors that are set early in the aircraft’s design (e.g., external shape, surface materials, tolerances, size and placement of engines, etc.), nearly all of the important capabilities of a military aircraft are impacted when signature reduction is the design driver.  Consequently, a new and prominent design discipline in ACS, as proposed by the JTCG/AS, was needed to properly account for all aspects of this new driving capability, which was called stealth.

The early U.S. stealth, or low observables, program was developed by the Defense Advanced Research Projects Agency and demonstrated via the Have Blue program. This program produced the world’s first practical combat stealth aircraft, leveraging new design concepts, new radar cross section prediction tools, new materials, and eventually new tactics. It also led directly to the Air Force’s procurement of the state-of-the-art F-117 stealth fighter [6].

The decision to rely on full-blown, all-in stealth as the primary survivability design feature for certain types of high-risk aircraft (and a major feature for other, less exposed aircraft) carried with it the risk that our enemies, if  they knew that we were engaged in the development of stealth aircraft, would attempt to learn about the specific stealth technology we were using and would (1) develop sensors and weapons that could defeat our stealth advantage, and/or (2) embark on their own stealth aircraft development programs using our advanced technology. The solution to this problem consisted of the imposition of a level of security from the beginning of the program that was unprec- edented in military aircraft acquisition programs.

Unfortunately, the movement of everything related to the development of stealth aircraft into a “black” world significantly complicated the development of ACS as a design discipline, particularly the signature reduction aspect of susceptibility reduction.  Whereas spreading the word about how to do ACS was essential to developing ACS as a design discipline, spreading any word about stealth aircraft was strictly forbidden. The world of vulnerability reduction was also classified, but at a much lower level, so it did not pose the same problem.

1972–1973 – Designing New Post-SEA Aircraft for Reduced Vulnerability

An unprecedented action taken by the Army near the end of the SEA conflict to reduce helicopter vulnerability was the ground-breaking requirement that the latest Army helicopters in development, the UH-60A Black Hawk and the AH-64A Apache, be designed to withstand a single hit by a particular ballistic projectile anywhere on the helicopter by flying for 30 minutes after the hit. This requirement eliminated the single-hit “cheap kills” by small-caliber projectiles that were seen in SEA. (Note that the single-hit requirement, in effect, built in a capability to withstand multi-hits.) The Air Force’s A-10A Thunderbolt II and the Navy’s F/A-18A Hornet, which were also initiated near the end of the SEA conflict, were also designed with vulnerability reduction as a major consideration, particularly the now- famous A-10 Warthog. The Navy’s F/A-18A also included some design features intended to reduce susceptibility.

1976–1982 – Post-SEA Military Policies for ACS

There was a flurry of official documents issued after the SEA conflict involving first nonnuclear S/V and later survivability. Although the fundamental objective of the three Services during this time was to require a thorough and systematic survivability program be incorporated in current and future U.S. airborne weapons systems, each Service had its own policies, procedures, and organizations.

The Army had Army Materiel Development and Readiness Command Regulation 70-3, “Survivability,” in 1976 [7]; and the Navy had Naval Material (NAVMAT) Instruction 3900.16, “Combat Survivability of Naval Weapon Systems,” in 1979 [8]. This instruction was the result of the 1974 policy memorandum by ADM I. C. Kidd, Chief of Naval Material, who said [9]:

Survivability should be treated as follows during the weapon system acquisition process. (1) Threat analysis should be conducted and firm survivability objectives established during the conceptual phase of the acquisition process. (2) It is essential that both survivability requirements and measurement and validation criteria be specified upon entry into full scale development; these requirements must be included in the contract. (3) The request for authorization to proceed into production must specify the survivability requirements to be imposed and the means for measuring their attainment. (4) Weapon systems should be tested against expected threat weapons wherever practical. I expect each of you to ensure that survivability is fully considered in development proposals and that they are properly reflected in contracts.

In addition, Air Force Regulation 80-38, “Management of the Air Force Systems Survivability Program” (1982), stated that survivability must be considered in developing the requirements for, and the trade-offs leading to, the  basic design of an Air Force system [10]. To achieve acceptable survivability with the minimum impact on the performance of each system, survivability must be “balanced” with the other performance parameters of the system.

1977 – Development of the First ACS Academic Course at NPS

In general, all aircraft design disciplines (such as structures, fuel systems, flight controls, et al.) have academic engineering courses available in that discipline. Prior to 1977, however, there was no similar academic course available anywhere that taught all aspects of ACS as an engineering design discipline. No one had ever learned in school how to design a military aircraft to make it more survivable in combat.  Consequently, to assist in the establishment of ACS as a design discipline that was similar to the other aircraft design disciplines, the development of a brand new academic course in the fundamentals of ACS was essential.

In the mid-1970s, Dr. Robert E. Ball, an Associate Professor originally hired by NPS in 1967 to teach aircraft structures, was being funded by the JTCG/ AS to develop a computer program to predict the structural response of a B-1 aircraft wing fuel tank to the impact of  a ballistic projectile.  Because Bob was working closely with the JTCG/ AS, he knew of the stated goal of establishing ACS as a design discipline, and he believed NPS was the perfect place to provide specialized educa- tional training to support that goal.

Bob’s students in 1977 were military aviators, including a number who had flown in combat. Many of his students after graduation would go to work in (and possibly lead) numerous engineering offices involved in the development of Navy aircraft.  Thus, a graduate-level education in ACS would turn out to be highly beneficial to both them and the Navy. It didn’t take much persuasion to convince Dale Atkinson (then at the Naval Air Systems Command [NAVAIR]) and the JTCG/AS leadership to fund Bob to develop such a program at NPS. The first ACS course was offered in the fall of 1977 to 26 students, and it continues today, with two offerings annually. A similar course was established at the Air Force Institute of Technology (AFIT) for Air Force and Navy resident students in 2014. (For more information on ACS education and the educators, see the article in the spring 2018 issue of Aircraft Survivability [11].)

1978 – Development of the First ACS Short Course

In the spring of 1978, shortly after the first NPS ACS academic course, the JTCG/AS sponsored the first ACS short course. It was held in a packed auditorium at the NAVAIR Headquarters in Washington, DC. Dale and Bob had strongly believed that if ACS was ever going to become a formal design discipline, many others involved with (or influencing) the design of military aircraft should have the opportunity for an education in the ACS fundamentals. So Dale asked John Morrow (from the Naval Weapons Center, China Lake) and Bob to work with him to develop an ACS short course based upon Bob’s NPS course. The first short course was well received, and a second one was held at NPS a few months later, followed by at least one per year for most of the next 40 years at NPS and other important ACS locations.

1981 – Publication of DoD MIL-STD-2069 and Other MIL-STDs and MIL-HDBKs

As a result of a major focus by the JTCG/AS on developing ACS as a design discipline, several DoD military standards and handbooks were developed by the group over the first decade. For example, the JTCG/AS sponsored the development of DoD MIL-STD-2089 (“Survivability Terms and Definitions”) in 1981, which tackled the challenging problem of getting a uniform agreement on a consistent terminology for all organizations involved [12]. (Note the change of title from the earlier survivability/ vulnerability to survivability. The old S/V was being replaced by survivability during this time frame.)

Another major 1981 DoD document, MIL-STD-2069 (“Requirements for Aircraft Nonnuclear Survivability Program”), also contributed to ACS design discipline development by requiring a standardized systems approach to designing for ACS [13]. This DoD document, which replaced the earlier individual Service requirements documents, provided the requirements and guidelines for establishing and conducting aircraft survivability programs while maintaining the flexibility required by acquisition program managers in the development  of  a  survivability program compatible with the needs of the procuring Service and the scope of the acquisition program. It also required the weapon system contractor to have a survivability program, a survivability organization, a program plan, program reviews, and specific program tasks—including a mission- threat analysis; Failure Mode, Effects, and Criticality Analysis (FMECA); aircraft  susceptibility,  vulnerability, and survivability assessments; survivability enhancement trade-off studies; and combat damage repair assessment.

The popular four-volume DoD MIL- HDBK-336 (“Survivability, Aircraft, Nonnuclear”) and two-volume “Countermeasures Handbook for Aircraft Survivability” were also developed by the JTCG/AS during this time [14, 15].

1984 and 1987 – The JLF Program and Live Fire Test Law

The Joint Live Fire (JLF) Program was chartered in 1984 by the Office of the Under Secretary of Defense, Director Defense Test, and Evaluation, due to concerns regarding (1) the vulnerability of current U.S. military aircraft and ground vehicles to foreign weapons and (2) the lethality of current U.S. weapons against foreign targets.  JLF’s initial aircraft program consisted of firing live threat-representative rounds at frontline U.S. aircraft, including the F-15, F-16, F/A-18, A-6E/F, AV-8B, UH-60, and AH-64. The JTCG/AS was responsible for oversight of the vulnerability testing.

To address the perceived inadequacy of the (then) current platform vulnerability and weapon lethality testing, the Live Fire Test Law was passed by the U.S. Congress in FY87. It consisted of an amendment to Title 10, Code, which added Section 2366 (“Major Systems and Munitions Programs: Survivability and Lethality Testing; Operational Testing”). The law requires that the Secretary of Defense conduct realistic survivability and lethality testing on covered weapons systems before they proceed beyond low-rate initial production (LRIP). Covered systems include new, major acquisitions, or any product improvement that significantly affects vulnerability or lethality.

According to the law, realistic survivability testing means testing for the vulnerability of the system in combat by firing munitions likely to be encountered in combat (or munitions with a capability similar to such munitions) at the system configured for combat, with the primary emphasis on testing vulnerability with respect to potential user casualties and taking into equal consideration the susceptibility to attack and combat performance of the system. (The DoD term for such testing is “full-up, system-level testing.”) The law states that this testing shall be carried out sufficiently early in the development phase of the system to allow any demonstrated design deficiency to be corrected in the design before proceeding beyond LRIP.

Although modified slightly since its passage, the Live Fire Test Law has proven to be both enduring and flexible, permitting test realism to be balanced against cost and practicality. Most importantly, the law has had a significant positive impact on the development of ACS as a design discipline because it has ensured that program managers are giving a sizable amount of motivation, attention, and resources to design a survivable aircraft because they know it will be tested.

1985 – Publication of the First ACS Textbook

As the NPS ACS course notes grew in size and improved in content, the decision was made to publish a formalized textbook on the subject.  This text, titled The Fundamentals of Aircraft Combat Survivability Analysis and Design, published by the American Institute of Aeronautics and Astronautics (AIAA) in 1985, was the first book to cover all aspects of ACS as a design discipline. From the Preface [16]:

The U.S. Eighth Air Force, operating over Germany in daylight and without fighter escort, suffered a 24% attrition rate in October 1943 in raids against the ball bearing factories in Schweinfurt. This heavy loss of aircraft led to the termination of the Air Force’s daytime unescorted, deep penetrations into Germany.

During the Korean War, U.S. Air Force B-29s suffered a 20% loss rate during a series of daylight missions, causing the Bomber Command to cancel the daylight raids and operate only at night.

The heavy losses of Israeli A-4 aircraft on the first day of the Yom Kippur War in 1973 resulted in cancellation of the close air support missions over the Golan Heights. When the ground situation absolutely required resumption of the close air missions, the tactics were changed so that the A-4s operated at the outer fringes of the battle zone and were not faced with the intense Syrian air defenses.

All of the above examples, both strategic and tactical, illustrate the overwhelming requirement for the consideration of survivability in the design and utilization of military aircraft. As a result of this requirement, a technology for enhancing survivability and a methodology for assessing survivability has evolved over the past 70 years. However, because the importance of survivability is sometimes either forgotten or neglected in the design and development of military aircraft during periods of peace, aircraft designers, program managers, and operators must be reminded that survivability considerations must be neither overlooked nor ignored. They need to be informed about the current technology for increasing survivability and about the methodology for assessing the payoffs and the penalties associated with survivability enhancement features. This text is devoted to that end.

Approximately 10,000 copies of the 400-page book were sold in 5 printings between 1985 and 2003.

1985 and 2014 – Establishment of SURVIAC and DSIAC

A major part of the ACS infrastructure created by Dale Atkinson while he was the JTCG/AS Chairman was the establishment of the Survivability/ Vulnerability Information Analysis Center (SURVIAC) in 1985. SURVIAC, which was operated by Booz Allen Hamilton, was designed to be a dedicated center of excellence, providing a centralized information and analytical resource for all aspects of nonnuclear survivability, lethality, and munitions effectiveness. After serving nearly 30 years in this role, SURVIAC and its responsibilities were integrated into the Defense Systems Information Analysis Center (DSIAC) in 2014. Operated by the SURVICE Engineering Company under the sponsorship of the Defense Technical Information Center, DSIAC consolidates the activities of multiple DoD Information Analysis Centers, focusing on S/V, advanced materials, autonomous systems, directed energy, energetics, military sensing, non-lethal weapons, reliability/maintainability, and weapon systems.

1988 and 1989 – Establishment of the NDIA CSD and AIAA STC

The establishment of the National Defense Industrial Association’s (NDIA) Combat Survivability Division (CSD) by RADM Robert Gormley in 1988, as well as the establishment of the AIAA’s Survivability Technical Committee (STC) by Professor Ball in 1989, added to the ACS infrastructure by providing an open-communication link between the industrial companies that design and build military aircraft.  The NDIA CSD holds an annual Aircraft Survivability Symposium at NPS, and the AIAA STC holds annual meetings at one of the principle AIAA meetings.

1991 – DoD Directive 5000.2

The February 1991 version of DoD Directive 5000.2 included survivability as a “critical system characteristic”— that is, a characteristic of the system that has a critical role in the successful operation of the proposed system as it functions in its operational environment. The directive went on to say [17]:

The survivability of all systems that must perform critical functions in a man-made hostile environment shall be an essential consideration during the acquisition life cycle of all programs, to include developmental and nondevelopmental programs.  Survivability from all threats found in the various levels of conflict shall be considered. This includes conventional; electronic; initial nuclear weapon effects; nuclear, biological and chemical contamination (NBCC); advanced threats, such as high-power microwave, kinetic energy weapons, and directed energy weapons; and terrorism or sabotage.

(Note: This DoD guidance on survivability is now contained in DoD Instruction 5000.02 and the Defense Acquisition  Guidebook.)

1996 – Survivability Included as One of the Four Program Pillars of the F-35

By 1996, ACS had advanced in importance from the old attitude of “nice to have, but…” to the very top level of aircraft attributes. One notable example of this advancement was the inclusion of survivability in the four stated program pillars for the state-of-the-art Joint Strike Fighter (JSF)/F-35 program—namely, afford- able, lethal, survivable, and supportable. With inclusion such as this in major high-visibility programs, it was clear that survivability had secured a permanent position as a formal design discipline in military aircraft development and acquisition.

2003 – Publication of the Second Edition of the Ball ACS Textbook

After 15 years of adding new ACS content; improving existing content; and adding learning objectives, many more notes and references, and a long list of questions, it became time to publish a new, much more extensive edition of the ACS fundamentals textbook. Among other things, the revised text strongly encouraged the continued development of ACS as a formal, unified design discipline across the community. From the text’s Prologue [1]:

To accomplish the goal of designing the right amount of combat survivability into military aircraft early in the life of the aircraft, all of the contributors to survivability, such as the tactics developers, signature specialists, electronic combat old crows, and the vulnerability assessment/reduction engineers, should be gathered together into a common survivability discipline. The people who work the engineering issues of combat survivability should be called survivability engineers, and the discipline should be treated as a unified discipline in the system engineering process, in the same manner as the traditional disciplines of structures, flight controls, aerodynamics, and propulsion are treated.

FY05 – The Statutory Requirement for Force Protection and Survivability KPPs

Section 141 of the National Defense Authorization Act of Fiscal Year 2005 (also known as Public Law 108-375) requires in part that KPPs for force protection and (vehicle or system) survivability be included as part of the documenting system requirements for any manned system that “is expected to be deployed in an asymmetric threat environment.” Although the term “asymmetric threat” was not formally defined, it is a threat that permits an enemy to attack a superior force, usually by easy-to-use, inexpensive means and irregular tactics, to achieve political, economic, or military (tactical and strategic) gains. The most commonly employed threats against aircraft in recent conflicts that meet these criteria are small arms, machine guns, rocket-propelled grenades, and man-portable air defense systems.

In the Joint Requirements Oversight Council memorandum on implementation of this law, Gen. Peter Pace summarized the meanings of force protection and survivability attributes. Force protection attributes are those that contribute to the protection of personnel, while survivability attributes are those that contribute to the survivability of the manned systems. In other words, force protection is concerned about designing the aircraft to protect all of the occupants in the aircraft, not just the critical operating crew, whereas survivability is concerned about the survival of the aircraft itself. This law implies that in addition to the traditional approach used in the second edition of the Ball ACS textbook,” in which the focus is on the survivability of the aircraft, we should also be concerned about the separate, but related, capability of protecting the on-board force.

2018 – The Current Role of ACS in the SE and T&E of Military Aircraft

Chapter 3 of the Defense Acquisition University’s on-line Defense Acquisition Guidebook defines “systems engineering” as follows [18]:

SE solves systems acquisition problems using a multi-disciplined approach. The Systems Engineer should possess the skills, instincts and critical thinking ability to identify and focus efforts on the activities needed to enhance the overall system  effectiveness, suitability, survivability and sustainability. [Bold added for emphasis.]

In other words, ACS is one of the four primary capabilities of a military system, and therefore the system engineer should know understand, and apply the fundamentals of ACS.

Similarly, DoD Instruction 5000.02 states [19]:

The fundamental purpose of test and evaluation (T&E) is to enable the DoD to acquire systems that work. To that end, T&E provides engineers and decision-makers with knowledge to assist in managing risks, to measure technical progress, and to characterize operational effectiveness, suitability, and survivability. [Bold added for emphasis.] [Note that T&E does test and evaluate sustainability.]

LEARNING ABOUT THE ACS DESIGN DISCIPLINE TODAY

Today, there are several opportunities available to DoD and military aviation personnel for an education in the ACS design discipline. As mentioned, NPS has been teaching ACS since 1977, and AFIT has been teaching a similar course to Air Force and Navy resident students since 2004. Additionally, off-campus educational opportunities include the annual JASP-sponsored ACS short course taught at various locations.  The short course is intended for DoD and contractor personnel who work in aircraft survivability fields; however, the course also benefits personnel working the program management and acquisition of DoD aircraft. The most recent new educational opportunity in combat survivability is the AIAA STC 8-hour classified short course “Aerospace Survivability,” which was offered for the first time during the AIAA Defense Forum at Johns Hopkins University in May 2018.

SUMMARY AND CONCLUSIONS

As ACS approaches a half century of development as a formal design discipline, it is clear that it has been firmly established and now holds a prominent place in the acquisition and SE processes. As with other aircraft design disciplines, ACS has a relatively standardized terminology, a methodology for quantifying the important capability metrics, a design technology for achieving the desired survivability capabilities, a set of user requirements that can/must be validated by testing, and a strong infrastructure that includes educational opportunities in the discipline. Additionally, ACS is one of the four major SE activities, consisting of overall system effectiveness, suitability, survivability, and sustainability.

As for the next half century, the ACS discipline must continue to evolve to address the ever-emerging new and different threats. In addition, to keep the discipline relevant, timely, and essential, new educational materials and instruction will need to be developed to cover topics such as advanced anti-air weapons (including improved guns and guided missiles), as well as new weapons with different damage mechanisms (such as lasers and cyber attacks) and the new topics of cyber survivability, aircraft recover- ability, and force protection.

In conclusion, Figures 1 and 2 provide a visual timeline and summary of the actions taken to establish ACS as an aircraft design discipline and their adoption into some of the major U.S. air systems.

Figure 1. Major Actions Taken to Develop ACS as a Design Discipline.

Figure 2. The Adoption of Survivability Into Modern Aircraft Development (Adapted From Figure 1.18 of Reference [1]).

ABOUT THE AUTHORS

Dr. Robert E. Ball is an NPS Distinguished Professor Emeritus who has spent more than 33 years teaching ACS, structures, and structural dynamics at NPS. He has been the principal developer and presenter of the fundamentals of ACS over the past four decades and is the author of The Fundamentals of Aircraft Combat Survivability Analysis and Design (first and second editions). In addition, his more than 55 years of experience have included serving as president of two companies (Structural Analytics, Inc., and Aerospace Educational Services, Inc.) and as a consultant to Anamet Labs, the SURVICE Engineering Company, and the Institute for Defense Analyses (IDA). Dr. Ball holds a B.S., M.S., and Ph.D. in structural engineering from Northwestern University.

Dr. Mark Couch is currently the Warfare Area Lead for Live Fire Test and Evaluation in the Operational

Evaluation Division at IDA. Prior to joining IDA in 2007, he enjoyed a 23-year Navy career flying the MH-53E helicopter. He has a Ph.D. in aeronautical and astronautical engineering from NPS and has taught numerous courses in aircraft combat survivability.

Mr. Christopher Adams is the Director of the Center for Survivability and Lethality at NPS, where he currently teaches combat survivability. He is also the former Associate Dean of the Graduate School of Engineering and Applied Sciences, and he has more than 20 years of operational flight experience in F-14s and EA-6Bs, serving multiple tours in Iraq and Afghanistan. Mr. Adams holds a B.S. in aerospace engineering from Boston University and an M.S. in aerospace engineering from NPS.

References

  1. Ball, Robert E. The Fundamentals of Aircraft Combat Survivability Analysis and Design, Second Edition. American Institute of Aeronautics and Astronautics, 2003.
  2. Legg, David. “Aircraft Survivability – The Early Years (Pre-World War I to World War I).” Aircraft Survivability, Spring 2017.
  3. Lindell, Dennis, et al. “Study on Rotorcraft Survivability.” U.S. Department of Defense, September 2009.
  4. Atkinson, Dale, Paul Blatt, Levelle Mahood, and Don Voyls. “Design of Fighter Aircraft for Combat Survivability.” SAE Technical Paper 690706,  https://doi.org/10.4271/690706, 1969.
  5. Joint Technical Coordinating Group on Aircraft Survivability. “Proposed MIL-STD- XXX, Aircraft Nonnuclear Survivability/
    Vulnerability Terms.” JTCG/AS-74-D-002, October 1976.
  6. Defense Advanced Research Projects Agency. “Breakthrough Technologies for National Security.” March 2015.
  7. U.S. Army Material Development and Readiness Command. “Survivability.” Regulation 70-3, February 1976.
  8. Chief of Naval Material. “Combat Survivability of Naval Weapon Systems.” NAVMAT Instruction 3900.16, November 1979.
    [9] Kidd, ADM I. C. Policy Memorandum. 1974.
    [10] U.S. Air Force. “Management of the Air Force Systems Survivability Programs.” Regulation 80-38, August 1982.
    [11] Ball, Robert E. “Aircraft Combat Survivability Education and Educators: A Personal Perspective Over 40 Years.” Aircraft Survivability, spring 2018.
    [12] U.S. Department of Defense. “Survivability Terms and Definitions.” MIL-STD-2089, July 1981.
    [13] U.S. Department of Defense. “Requirements for Aircraft Nonnuclear Survivability Program.” MIL-STD-2069, July 1981.
    [14] U.S. Department of Defense. “Survivability, Aircraft, Nonnuclear.” MIL-HDBK-336 (1– 4), 25 October 1982.
    [15] Joint Technical Coordinating Group on Aircraft Survivability. “Countermeasures Handbook for Aircraft Survivability.” JTCG/ AS-76-CM-001(1), vols. I and II, February 1977.
    [16] Ball, Robert E. The Fundamentals of Aircraft Combat Survivability Analysis and Design. First Edition, American Institute of Aeronautics and Astronautics, 1985.
    [17] U.S. Department of Defense. “Defense Acquisition.” DoD Directive 5000.2, Part 6, Section F, 2. Polices, 23 February 1991.
    [18] Defense Acquisition University. Defense Acquisition Guidebook. https://www.dau.mil/ tools/dag, accessed March 2018.
    [19] U.S. Department of Defense. “Operation of the Defense Acquisition System.” DoD Instruction 5000.02, Encl. 5, 26 January 2017.