U.S. Department of the Interior, National Park Service
IV. APPLYING THE NATIONAL REGISTER CRITERIA TO HISTORIC AVIATION PROPERTIES
THE NATIONAL REGISTER CRITERIA FOR EVALUATION
The four National Register Criteria represent different types of values embodied in districts, sites, buildings, structures, and objects.
Associative value/Event-Criterion A: Properties that are associated with events that have made a significant contribution to the broad patterns of our history.
Associative value/Person-Criterion B: Properties that are associated with the lives of persons significant in our past.
Design or Construction value-Criterion C: Properties that embody the distinctive characteristics of a type, period, or method of construction, or that represent the work of a master, or that possess high artistic values, or that represent a significant and distinguishable entity whose components may lack individual distinction.
Information value-Criterion D: Properties that have yielded, or may be likely to yield, information important in prehistory or history.
A property can qualify for listing in the National Register under one or more of the criteria. For a complete listing of the Criteria for Evaluation refer to the National Register Bulletin: How to Apply the National Register Criteria for Evaluation.
Properties can be eligible for the National Register if they are associated with an event or events that have made a significant contribution to the broad patterns of our history. The property may be associated with a specific event marking an important moment in American prehistory or history, or it may represent a pattern of events or a historic trend that made a significant contribution to the development of a community, a State, or the nation. To meet this criterion, a historic property needs (1) to have existed at the time of the important event and (2) be associated in a significant way with the event.
Aviation properties may be associated with a wide variety of events. Some examples are the origins of manned flight, the development of air power for military purposes, the transportation of airmail, commercial airline development, exploration by air, aerial photography and mapping, aviation employment during the Great Depression, air power during war, scientific and engineering research activities, transoceanic flying, air races, and America's "romance" with aviation.
Several examples are already listed in the National Register. Hangar One at the Los Angeles International Airport was a stop on the courses of the National Air Races in 1933 and 1936. Isley Field, on Saipan Island in the North Mariana Islands, is listed in the National Register because the American conquest of Saipan in 1944 marked the breaking of the inner line of Japanese World War II defenses in the Pacific, and allowed Isley Field to become a base for U.S. B-29 bombers for long-range bombing of the Japanese homeland through the end of the war. The Secretary of the Interior designated the field as part of the National Historic Landmark on Saipan.
A historic property may be significant in State or local history. Felts Field in Spokane, Washington is a historic district locally significant for its association with the development of early aviation in eastern, inland Washington. The district contains six buildings contributing to the historic significance of the airfield-three hangars, a passenger terminal, a National Guard headquarters building, and a storage building; and two historic structures-a clock tower and a memorial.
Under this criterion, an aircraft might be eligible for listing in the National Register if it had a significant role in an important event (for example, a battle) or pattern of events (for example, early airmail carriers). The Pilgrim 100B Aircraft, manufactured in 1931, is listed in the National Register under Criterion A for its historic association with the development of air commerce and transportation in Alaska.
CRITERION B-SIGNIFICANT PERSON(S)
Under Criterion B, a property can be eligible for the National Register if it is associated with the lives of persons significant in our past. The person must be important as an individual and within a historic context, not simply representative of a group or class. The individual's association with the historic property should be compared with that person's association with other properties in order to determine relative importance of the property in question. Properties associated with living persons usually are not eligible for inclusion in the National Register. Architects, artisans, artists, and engineers are often represented in the National Register by their works, which are eligible under Criterion C. Their homes, workshops, or studios, however, can be eligible under Criterion B, because these usually are the properties with which they are most personally associated.
Individuals significant in the history of aviation may be pilots, technical representatives, engineers, industrialists, airline executives, military officers or the rank and file, airport managers, or government officials. After World War I, Maj. Gen. William "Billy" Mitchell advocated a strong air force, even in peacetime, for the defense of the United States. His house in Virginia is a National Historic Landmark. The Ford Airport Hangar in Lansing, Michigan, is listed in the National Register in part for its association with Henry Ford, who built it in 1926 as part of the airline system he was developing. The hangar is also significant under Criterion A for its association with the early development of commercial aviation.
The College Park Airport in Maryland similarly derives some of its historic significance from association with important people. There in 1909 aviation pioneer Wilbur Wright taught military personnel, including Frank P. Lahm and Benjamin Foulois, how to fly. The airport was the first training site for military fliers in this country and was listed in the National Register under Criteria A and B. Benjamin Foulois once commanded the U.S. Air Service station at Henry Post Air Field in Oklahoma. This fact provides that historic site with a strong association with an important person.
Aircraft can be listed under Criterion B if they are associated with a significant aspect of an important person's life. The Hughes Flying Boat Hercules, popularly known as the "Spruce Goose," is listed under Criterion B for it association with the life of noted aviator Howard Hughes. In addition, the Hercules is significant for its engineering design and construction technique. The aircraft is located in Long Beach, California, the site of its successful air tests in 1947.
For additional guidance refer to National Register Bulletin: Guidelines for Evaluating and Documenting Properties Associated with Significant Persons.
Properties can be eligible for the National Register if they embody the distinctive characteristics of type, period, or method of construction; or that represent the work of a master; or that possess high artistic value; or that represent a significant and distinguishable entity whose components may lack individual distinction.
Distinctive Characteristics. Aircraft and air-related facilities can be eligible if they embody the distinctive characteristics of a type, period, or method of construction important in aviation history. An aircraft can be eligible if it is a good representative of an important type (military, commercial, civilian), or if it represents a significant development in aircraft technology, or if it represents a significant doctrinal development, like an organization's response to changing technology or tactics. The 1905 Wright Flyer III, located in Dayton, Ohio, was designated a National Historic Landmark for its significance in engineering history as the first airplane capable of sustained and controlled flight and suitable for practical application. It was with this airplane that Orville and Wilbur Wright perfected the technique of flying and designed a powered airplane completely controlled by the pilot.
Air-related buildings, districts, structures, and objects may also be significant under this section of the criterion. Hangar One at Los Angeles International Airport represents an important style of architecture-Spanish Colonial Revival. In contrast, the Bryce Canyon Airport Hangar in Utah illustrates vernacular construction in the use of sawn-log and corrugated-tin features. The Marine Air Terminal at La Guardia Airport in New York is an example of Art Deco architecture of the late 1930s, as well as a tangible reminder of the era of clipper ships and early transoceanic air service. The decorative interior design is also Art Deco. All three buildings are listed in the National Register. Built in 1929, the Goodyear Airdock in Akron, Ohio, is where the Goodyear Zeppelin Corporation developed and constructed dirigibles, including the Akron and Macon. The airdock's shape (semi-paraboloid), size (1,175 feet long by 325 feet wide by 211 feet high), and structural system (no interior supports) are architecturally significant. In a final example, the Unitary Plan Wind Tunnel at Ames Research Center in California represents the continual development of superior technical aeronautical research facilities after the end of the Second World War and is a National Historic Landmark.
The Work of a Master refers to the technical or aesthetic achievements of an architect, engineer, or craftsman. African American architect Clarence Wesley Wigington designed the Holman Field Administration Building in St. Paul, Minnesota. Wigington's significance as an important architect gives that building an association with a local master, an association recognized through listing in the National Register. Internationally known architect Albert Kahn designed the Ford Airport Hangar at Lansing Municipal Airport in Lansing, Illinois. He applied his famous "factory-type" style to provide natural light and structural strength to the building. The work of a master may also apply to aircraft, particularly owner/designer-built models and small production runs of light planes built by craftsmen.
High Artistic Value concerns the expression of aesthetic ideals or preferences and applies to aesthetic achievement. Inside the Marine Air Terminal at La Guardia Airport in New York City is the mural "Flight," by James Brooks, which adds artistic value to the building.
A Significant and Distinguishable Entity Whose Components May Lack Individual Distinction refers to historic districts. Cheyenne, Wyoming, was once an air transportation center. Surviving properties include a Boeing/United Airlines building, a hangar, and a fountain, constructed between 1929 and 1934. The famous Boeing 247B airplane appears in the detail on the fountain, built in 1934 as a memorial to aviation. The properties might not qualify individually for the National Register, but together they signify the importance of Cheyenne as a transportation center in the days before high-altitude flying made such remote centers obsolete. Similarly, the Bowman Field Historic District in Louisville, Kentucky, consists of three adjacent buildings constructed in the late 1920s and 1930s. The administration building, Curtiss Flying Service hangar, and Army Air Corps hangar together reflect the early days of aviation in that locale.
CRITERION D-INFORMATION POTENTIAL
Properties can be eligible for the National Register if they have yielded, or may be likely to yield, information important in prehistory or history. The property must be known to contain information that would be important to our understanding of history or prehistory. Archeological sites and districts can qualify under this criterion, including sites and districts studied by historical archeologists and industrial archeologists. Buildings, structures, and objects might also qualify under Criterion D. It is necessary to demonstrate (1) the importance of the information within an appropriate historic or archeological context, (2) the connection between the important information and the specific property, and (3) the presence of adequate data in the property. According to the National Register, a property with information potential is a geographic location having important historical or archeological information. The information may be literally buried under ground, submerged under water, or scattered across the surface.
An aviation property is significant under Criterion D if that property has yielded or is likely to yield information important to history, such as the physical characteristics of an aircraft that provide information about the craft's construction, use, or operation. Aviation wrecks and ruins of aviation facilities might qualify for listing in the National Register under Criterion D. Also, a rare aircraft for which inadequate or no documentation has survived might also be considered.
The B-24D on an Aleutian island in Alaska is an example of an aviation property that qualified for the National Register under Criterion D for its information potential. All the pieces are "in the area," according to the nomination form. The aircraft is the oldest known surviving D model. It participated in the Aleutian Campaign of the World War II, and it is the only B-24D in Alaska. A combat veteran, the plane crash-landed in bad weather upon return from a weather observation mission. The historical context of the plane includes the war and military aircraft in general, and more particularly the history of Alaska as a United States territory and the history of Alaskan aviation. The geographical context or setting is the area in which the plane saw combat and where it crashed. The information potential includes construction features of the early B-24Ds that differ from later planes due to modifications introduced after this plane, the nineteenth 24D, was produced. The crashed plane also illustrates skillful emergency landing.
For additional guidance refer to National Register Bulletin: Guidelines for Evaluating and Registering Historical Archeological Sites and Districts.
Certain kinds of property are not usually considered for listing in the National Register:
C-Birthplaces and graves
G-Properties that have achieved significance within the past fifty years
A property thus might meet one or more of the National Register
criteria and still not be eligible for listing unless special requirements are met. These special requirements are called Criteria Considerations and labeled A-G.
Of particular relevance to aviation properties are Criteria Considerations B, E, F, and G. Consideration B (moved properties) applies because airplanes are mobile. Consideration E (reconstructed properties) would apply if too much original materials have been replaced. Consideration F (commemorative properties) applies if the property commemorating some aspect of aviation history has its own exceptional significance. Consideration G (properties that have achieved significance within the past fifty years) is particularly relevant because half of aviation's history occurred within the past fifty years. Other Criteria Considerations may also be applicable to a particular property.
CRITERIA CONSIDERATION A-RELIGIOUS PROPERTIES
A historic aviation property owned by a religious institution or used for religious purposes will be eligible if it derives its primary significance from architectural, engineering, or artistic distinction (Criteria C) or historical importance (Criteria A or B). Religious properties must be judged solely in secular terms. Given the use of airplanes to support missionary and other religious work, Criteria Consideration A may apply to a variety of aviation properties owned by religious institutions yet significant in secular terms (for example, the economic or social impact of an air field upon a rural locale).
CRITERIA CONSIDERATION B-MOVED PROPERTIES
A moved property can be eligible if it is significant primarily for its architectural or engineering value or if it is the surviving property most importantly associated with a historic person or event. In general, the National Register discourages moving historic properties because a property derives historical significance from its location and setting. Moving a historic building or other historic property is acceptable when there is no feasible alternative for preservation. But for the moved property to qualify for the National Register, the new location must be historically appropriate. Often moving a historic property lessens that property's integrity to such a degree that it no longer qualifies for listing in the National Register.
Building 105 of the Boeing Airplane Company has been accepted by the National Register despite having been moved from its original location. The Port of Seattle acquired and redeveloped the original site. That redevelopment threatened the building with destruction, so the building was moved nearby. The building remained in an industrial and aviation setting, but out of harm's way. The National Register approved the move when it accepted the building for listing. Similarly, the National Register recognized the need to move the 1938 Rogers-Post monument in Alaska because it was sinking at the original site. The Naval Arctic Research Laboratory moved the monument to higher ground 95 feet away.
Aircraft, like ships, are transportation vehicles designed to move during operation. Because aircraft are designed to be moved, they do not need to meet Criteria Consideration B (and the consideration should not be checked on the National Register registration form).
See above for the related issues of integrity of location and setting for aircraft, and artificial collections of aircraft.
CRITERIA CONSIDERATION C- BIRTHPLACES OR GRAVES
A birthplace or grave of a person associated with the history of aviation is eligible if that person is of outstanding importance and if there is no other appropriate site or building directly associated with the person's productive life.
CRITERIA CONSIDERATION D- CEMETERIES
To be eligible, a cemetery must derive its primary importance from graves of persons of transcendent importance, from age, from distinctive design features, or from association with historic events. Aviation-related graves, for example, may be found in war cemeteries that might merit National Register listing.
CRITERIA CONSIDERATION E- RECONSTRUCTED PROPERTIES
A reconstructed property must meet three requirements to be eligible for the National Register. One, the property is reconstructed accurately in a suitable environment. Two, the property is presented in a dignified manner as part of a restoration master plan. Three, no other building or structure with the same associations has survived. Accurate reconstruction implies sound historical or archeological data, appropriate materials, and adequate documentation. A suitable environment refers to both the physical context and the interpretative scheme.
Individual reconstructed aircraft are not eligible for the National Register because they are not authentic historic resources. A reconstructed airplane is a modern aircraft which reproduces the exact form or detail of a vanished aircraft as it appeared at a specific period of time. After the passage of fifty years, a replica aircraft might attain significance in its own right as a product of one generation's perception of aviation history.
In rare instances, replica aircraft can be a contributing component of a National Register property if:
1) the reconstruction is based on scholarly analysis or graphic, written, and archeological sources; 2) the aircraft's construction is accurately executed, using appropriate period materials and construction techniques; 3) the reconstruction is presented in a historically appropriate manner as part of a restoration master plan; 4) no other aircraft with the same association has survived. Being part of a restoration master plan means that the reconstruction is an essential component in a group of historic properties which together constitute a historic district. The reconstruction must be part of an overall restoration master plan for the entire district. For example, a reconstructed aircraft may be eligible as part of a restoration master plan for an early 20th century airport historic district, which includes historic properties, such as hangars, terminal building, tower, etc. In this case, the reconstructed aircraft may be essential to convey the aviation significance of the district.
See the Integrity section below for related issues of evaluating an aircraft's integrity of materials and the nature of aircraft maintenance.
CRITERIA CONSIDERATION F- COMMEMORATIVE PROPERTIES
A commemorative property can be eligible if design, age, tradition, or symbolic value has invested it with its own exceptional significance. The National Register has recognized the exceptional significance of commemorative properties related to aviation.
The Wright Brothers National Memorial shaft, for example, is a granite, triangular obelisk atop Kill Devil Hill in North Carolina. Completed in 1932, it commemorates "the conquest of the air by the brothers Wilbur and Orville Wright" on what were shifting sand dunes at the time of the first flights in 1903. The sandy soil is now stabilized, and building developments block the view to the beach, but a grass field and this memorial shaft commemorate the historic place where the Wrights flew. The shaft's design is also significant. On the sides of the obelisk are outspread wings in bas-relief to give the impression of flight.
For another example, two monuments near Barrow, Alaska, commemorate the humorist Will Rogers and pilot Wiley Post who died there in an airplane crash in August of 1935. The wreckage of the hybrid Lockheed Orion-Explorer, a low-wing plane equipped with pontoons for Alaskan flying, was removed. The first monument was built in 1938 with funds raised through public subscription. It consists of poured cement, local aggregate rock, and beach boulders. Its dedication attracted national attention. In 1953 a private individual built the second monument, a rectangular obelisk of poured concrete in four blocks of diminishing size. Both are listed in the National Register for their symbolic value in memorializing Rogers and Post.
CRITERIA CONSIDERATION G- PROPERTIES THAT HAVE ACHIEVED SIGNIFICANCE WITHIN THE PAST FIFTY YEARS
Such properties are eligible only if they are of exceptional importance. The fifty-year requirement allows sufficient time to elapse to develop historical perspective, guards against listing properties of passing interest, and ensures that the National Register is a list of historic places.
Given that airplanes and the infrastructure of aviation (like navigation aids and hangars) were not designed or constructed for fifty years of operation, Criteria Consideration G deserves special attention. Other aviation properties, like wartime training fields and temporary buildings, similarly were never intended to last fifty years. Without identification and preservation of some of these properties before they reach the age of fifty years, the properties will not survive to reach fifty years of age.
The National Park Service has recognized and addressed this fifty-year challenge in regard to the space program. In the early 1980s the National Park Service surveyed sites associated with the early space program. In 1984 the Park Service completed a study of the theme "man in space" and identified properties associated with the space program for National Historic Landmark status and thus also listing in the National Register. President John F. Kennedy extended the man-in-space program to man-on-the-moon with his 1961 announcement "that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth." The young National Aeronautics and Space Administration (successor of the National Advisory Committee on Aeronautics) constructed and converted facilities for the space program. These facilities, which are significant to the nation's space program and its successful Project Apollo, are less than fifty years old.
Many space facilities of exceptional importance are National Historic Landmarks listed in the National Register of Historic Places. In Hampton City, Virginia, there are several landmarks of the space program-the Lunar Landing Research Facility, the rendezvous docking simulator, the Saturn V dynamic test stand, and the Saturn V launch vehicle. Other space-age landmarks listed in the National Register include the Space Environment Simulation Laboratory in Houston, Texas; a twenty-five-foot space simulator in Pasadena, California; and the neutral buoyancy space simulator in Huntsville, Alabama.
The National Park Service has determined that the main terminal building at the Dulles Airport outside of Washington, a building designed by architect Eero Saarinen, is eligible for listing in the National Register because of the building's exceptional architectural importance and despite the fact that the building was not yet fifty years old at the time it was evaluated.
The end of the Cold War, and the subsequent closing of many Cold War facilities, means that Cold War properties present challenges to preservationists and other cultural resource managers. Through the Legacy Resource Management Program, the Department of Defense sponsored many studies of Cold War cultural resources. Cold War properties-including aviation properties-may be candidates for the National Register under this "exceptional importance" rule; the exceptional importance is in addition to meeting National Register Criteria in general. The phrase "exceptional importance" may be applied to the extraordinary importance of an event or to an entire category of resources so fragile that survivors of any age are unusual. Exceptional importance does not require that the property be of national significance. It is a measure of the property's importance within the appropriate historic context, whether the scale of the context is local, state, or national.
The retirement and replacement of aircraft by airlines raise preservation issues concerning obsolete jet liners that are less than fifty years old. Similarly, the replacement of private and sport aircraft with newer, higher-technology models poses questions now about the preservation of aircraft less than fifty years old. Some of these aircraft may qualify for National Register listing.
Refer to National Register Bulletin: Guidelines for Evaluating and Nominating Properties That Have Achieved Significance Within the Last Fifty Years for further guidance on this topic.
EVALUATING THE INTEGRITY OF HISTORIC AVIATION PROPERTIES
In addition to being significant under the National Register Criteria, properties must retain integrity to be listed. Integrity is the ability of a property to convey its significance. The National Register recognizes seven aspects or qualities that, in various combinations, define integrity. To retain historic integrity a property will always possess several, and usually most, of the aspects. The retention of specific aspects of integrity is paramount for a property to convey its significance. Determining which of the aspects are most important to a particular property requires knowing why, where, and when the property is significant.
The basic guidance for evaluating the integrity of historic properties if found in National Register Bulletin: How to Apply the National Register Criteria for Evaluation. The following sections supplement that bulletin with an emphasis on evaluating the integrity of historic aircraft.
SEVEN ASPECTS OF INTEGRITY:
Location is the place where the historic property was constructed or the place where the historic event occurred.
Setting is the physical environment of a historic property. Whereas location refers to the specific place where a property was built or an event occurred, setting refers to the character of the place where the property is found. It involves how, not just where, the property is situated and its relationship to its surroundings.
The relationship between a property and its location is often important to understanding why the property was created or why something happened. The actual location of a historic property, complemented by its setting, is particularly important in recapturing the sense of historic events and persons. Except in rare cases, the relationship between a property and its historic associations is destroyed if the property is moved. (See Criteria Consideration B above for the conditions under which a historic aviation property which has been moved is eligible.)
The National Register recognizes, however, that some types of resources were designed to be moved. Ships, railroad cars, trolleys, and airplanes are property types that were constructed to be mobile; their significance is inherent in their ability to move. In many instances, they are today not located in the place where they were constructed or where the historic event(s) with which they are associated occurred. These properties may still be able to convey their importance despite not being at their original location. Thus it is not required that movable objects be at their original location in order to retain integrity.
What is required of these movable properties, in order to be eligible, is that the structure (as the National Register categorizes ships, railroad cars, trolleys, and aircraft) must have an appropriate setting. This requirement applies both to historic aircraft which are still being flown and those which are not.
Aircraft located in museums directly raise the issue of appropriateness of location and setting. The National Register generally excludes museum objects from being listed. It would not be practical or useful to list in the National Register the many millions of museum objects which might be found significant under the criteria. Museum objects do not have integrity of location or setting under the National Register criteria because museums are not the location or setting in which aircraft achieved significance.
How does this policy relate to aircraft? In short, aircraft which have been removed from an aviation setting and are now museum objects, in the traditional sense, generally will not qualify for the National Register. National Register status for museum objects is redundant since the objectives of recognition and preservation are inherent in the museum mission. For example, the airplanes maintained and displayed at the Smithsonian Institution's National Air and Space Museum on the Mall in Washington, D.C., while historically significant, would not meet the National Register criteria because they do not meet the requirement for setting. This in no way detracts from the extraordinary importance of the Wright brothers' or Charles Lindbergh's aircraft, or the many others, maintained in this facility.
This general policy would not, however, disqualify an aircraft simply because it is part of a collection. The deciding factor will be appropriateness of setting. If an aircraft is part of a collection and: (a) is important under the National Register criteria, (b) retains integrity of materials, design, workmanship, feeling and association; and (c) is in a setting which is appropriate to an aircraft and allows it to convey its significance as an aircraft, then it will be eligible. An example of an appropriate setting would be an air-related facility where the aircraft is maintained. A historic SBD Dauntless dive bomber parked on an aircraft parking ramp, or inside of a hangar, at a naval aviation station would meet the requirement of integrity of setting, as would a historic DC-3 maintained in a hangar at a municipal airport. Aircraft kept within modern buildings constructed to house a collection could qualify if the building itself were in an appropriate setting. For example, if a period aircraft is situated within a modern building designed to store and display the aircraft, and the building is located near the runways at an airport, it might qualify. As with all other National Register property types, the aircraft must be judged on an individual basis to determine if it is significant and retains integrity.
A question to consider is does the aircraft have to be located at a facility where it was historically associated to qualify? The short answer is NO. It is not required that period aircraft be located at an airfield where historically they were based. Nor would we expect, for example, to find a WWII carrier based airplane still located on a ship floating off of an island in the Pacific. The general requirement, then, is that historic aircraft must be located in an appropriate setting, such as an air-related facility.
Materials are the physical elements that were combined or deposited during a particular period of time and in a particular pattern or configuration to form a historic property.
A property must retain the key materials dating from its period of its significance. If the property has been rehabilitated, the historic materials and significant features must have been preserved. The property must also be an actual historic resource, not a recreation; a recent structure fabricated to look historic is not eligible. Likewise, a property whose historic features and materials have been lost and then reconstructed is usually not eligible. (See Criteria Consideration E on page 33 for the conditions under which a reconstructed property can be eligible.)
An aircraft's integrity of materials cannot be evaluated without an understanding of the nature of aircraft maintenance, and the periodic replacement of parts. With this understanding one can identify the essential components of an aircraft which must be retained for the aircraft to be considered historic. The following discussion of aircraft maintenance focuses on military aircraft, but the general principles are broadly applicable to all aircraft.
THE NATURE OF AIRCRAFT MAINTENANCE
An aircraft is a complex, relatively fragile machine, intended to operate in an environment inherently unforgiving of failures of judgment or material. The design of aircraft has evolved with a tendency to incorporate redundant critical components and rigid schedules of inspections. These designed inspection requirements include the periodic, programmed, replacement of system components. For instance, a "time change item" is a part that is to be changed after the accumulation of a specified number of operational hours or cycles. An example of a time change item is an oil filter. Regardless of the apparent condition of the item, at the end of its specified operational time the item is removed and replaced. Depending on the type of item, it might be refurbished and installed in another aircraft. Aircraft engines are good examples of system components that are removed, inspected, refurbished, and reinstalled on an operational time basis. After a number of operating hours specified by the manufacturer, an aircraft engine is removed and thoroughly inspected and refurbished. The U.S. Army's aircraft that circled the globe in 1924, the "World Cruisers," used Liberty engines, which were replaced after every fifty hours of operation. In the case of a modern F-15, some items are changed based on the number of times the pilot cycles the throttle.
The modern military fighter aircraft undergoes an inspection of its airframe and systems prior to the first flight of the day (pre-flight inspection). A less detailed inspection is performed after every flight (thru-flight inspection), and after the last flight of the day, another detailed inspection is performed, (post-flight inspection), and is usually even more thorough than the pre-flight. If the aircraft operated in an unusual altitude or high-g condition special inspections are performed. In addition to these daily inspections the aircraft is subject to "periodic, phase inspections." The periodic inspection, like time change item replacement, is based on the number of hours the aircraft has flown. Most modern aircraft operate under a periodic cycle of in-depth inspections that vary in degree, depending on where they are in the cycle. For instance, after two hundred hours an aircraft might enter its Number 1 phase inspection; after another two hundred hours it enters a slightly more in-depth Number 2 phase. After a further two hundred hours it enters the most detailed Number 3 phase inspection, after which it starts the cycle all over again. Each of these periodic or phase inspections removes panels and parts to thoroughly inspect the aircraft for wear or damage. These inspections can take from two to six weeks to complete. This entire system of preventive maintenance is aimed at preventing or fixing problems before they ground the aircraft or endanger the aircrew.
The Bureau of Aeronautics Manual for 1945 states that periodic inspections will be performed as specified in the specific aircraft's technical manual and:
The following factors shall determine when an aircraft is to be overhauled:
(1) The current condition of the aircraft and its component parts;
(2) The number of months that the aircraft has been in an operating status since its last overhaul or since commissioning;
(3) The number of operating hours since its last overhaul or since commissioning; and
(4) The service to which the aircraft has been subject.
In addition, the manual provides that the aircraft will undergo daily inspections, 30-hour inspections, and 6-week inspections.
These systems of inspection contribute to the relatively frequent replacement of parts. When F-111A, number 67-087, goes into the phase dock for inspection and has both engines changed, a refurbished wing sweep mechanism installed, repacked main gear struts installed, and its primary hydraulic reservoir replaced, it leaves the phase dock as F-111A number 67-087. In fact, even if the wings are removed and replaced along with numerous skin panels and the radar nose cone, it is still aircraft 67-087.
As is the case with most artifacts, frequent hard use over a long period of time equates to frequent repair or replacement of component parts. Aircraft are designed for the frequent removal and replacement of parts. Close examination of the skin of modern and historic aircraft will reveal that many skin panels have quick release latches or easily removed fasteners to allow access to the interior of the fuselage. Many aircraft have quick access panels, whose sole reason for existence is to allow quick inspection of some interior section or component. Even the terminology of hardware indicates the replaceable nature of components; modern "black boxes" are often "LRUs" (Line Replaceable Units). Electrical instruments in historic and modern aircraft are connected to the power system through "Quick Disconnects" or "Cannon Plugs." To remove the engine of a P-80 or T-33 jet aircraft, the after portion of the fuselage (the empennage) is removed. The P-80/T-33 empennage is attached to the rest of the fuselage with only three bolts. The J-33 engine of the T-33 is mounted inside the fuselage with three bolts. An F-111A main gear tire is held to the strut axle with one nut. These examples indicate the "Remove and Replace" nature of many aircraft components.
Aircraft are also subject to continual modification in their service lives. As operational experience is gained, changes are made to the original design. If these changes become substantial the design may be identified with a new model designation thus the existence of both F6F-3 Hellcat and F6F-5 Hellcat aircraft designations. Throughout their service life aircraft are continually being updated. A F4-E Phantom that participated in action over Vietnam and continued its career for ten or twenty years afterwards will have features incorporated that did not exist during its time of war service. How does this impact integrity of design and materials?
Although the above aircraft may have been updated, it is still the same aircraft that flew in Vietnam. If possible, changes that were incorporated over time should be identified in documenting an aircraft for National Register nomination. This does not mean that every minor detail, such as an "O-ring" seal change or every wire bundle support bracket modification, needs to be documented. What it does mean is that if the landing gear struts were significantly modified, that change should be documented, since it may reflect important developments in the use of the aircraft. If all of the wire bundle support brackets were modified because of a vibration problem, that too might warrant discussion. It should be kept in mind that an aircraft is a piece of complex technology. No matter what criterion for nomination is used, the technical aspects of the aircraft's history will remain important. For military aircraft this is relatively easy to discern; when significant modification has occurred the military usually redesignates the aircraft. For instance, when F-111A 67-041 was modified to test the F-111's potential for electronic jamming it was redesignated EF-111 A, number 67-041.
So, when does an aircraft stop being the "original?" As long as an aircraft retains the majority of its original structural members, it should be considered the authentic aircraft. Spars, stringers, longerons and other structural parts are not usually changed in an aircraft's existence. Some repair work may be done that replaces ribs or stringer sections but never comprehensively. Most commercial and military operators will not invest the money required to comprehensively replace major structural members to re-establish an air-worthy aircraft. Private flying enthusiasts may be willing to make that investment. Thus, the aircraft records should be examined to identify the depth of any restoration work accomplished outside of the aircraft's military operational life.
As discussed above, aircraft by their nature undergo constant changes of system parts throughout their service lives. Engines, pumps, actuators, radios, etc., are all periodically replaced based on time in operation and condition. For an aircraft at an underwater crash site, the site is a physical record of the time of the crash. An aircraft that continued to fly beyond its historic period must be examined to establish that it is still indeed the historic aircraft. Research into the design history of a given aircraft type is essential to verification of design integrity and identification of features that must be present to qualify as a specific aircraft type. Those features and system parts, so identified, should be authentic to the historic operational period. Refurbished contemporary parts were historically used in the aircraft maintenance cycle, and are, therefore, appropriate, as is replacement in kind as part of routine maintenance.
THE ESSENTIAL TEST FOR INTEGRITY OF MATERIALS
Aircraft structures such as ribs, frames, longerons, stringers, spars, skin panels, etc., are not readily removed and replaced in the life of an aircraft, and these must be considered the key materials of an aircraft. Although it is possible that a given aircraft may have seen some of these things replaced, it is likely only a small percentage. If an aircraft is de-paneled, and all of the structural members (ribs, spars, stringers, etc.,) are replaced, and the skin panels or fabric is replaced, it is no longer the original aircraft but a replica. If the structural members are replaced and the original skin and components are reinstalled, the aircraft retains a minimal integrity of materials and would not normally be considered a candidate for the National Register. Aircraft that are reconstructed from parts in a crash site debris field do not have integrity of materials. However, an aircraft crash site that does not contain all of the aircraft parts (a debris field) may still have integrity as an archeological site.
Other components, such as systems parts (fuel system, hydraulic system, power plant, flight control system, etc.) are more readily changed. Engines, pumps, actuators, reservoirs, cables, etc., are all likely to have been repeatedly changed if an aircraft had a long operational life. Integrity of materials therefore should be interpreted in this light, i.e., contemporary replacement parts would be acceptable versus original parts; if possible verify the historical replacement of the part versus a modern reconstruction.
Some materials are obviously inappropriate for a given aircraft. It would be inappropriate to use aluminum ailerons on an aircraft that historically had fabric-covered ailerons. In the same light, a World War II aircraft with an engine that was not available during the 1940s would not be a candidate for the National Register if it is being submitted for association with World War II. An SBD Dauntless dive bomber has been recovered from Lake Michigan by the National Museum of Naval Aviation. This SBD-2, Bureau Number 2106, a U.S. Navy Dauntless dive bomber, saw action with the U.S. Marine Corps, Scout-Bomber Squadron VMSB-241 at the Battle of Midway in World War II. The aircraft was damaged and returned to the U.S. for training use. On June 11, 1943, this SBD-2 crashed into Lake Michigan (the pilot survived). SBD-2, number 2106 most likely does not have the Wright R-1820-32 engine in it that it had at Midway, but it should have an R-1820-32 engine and it should be the R-1820-32 engine that was installed in it when recovered from Lake Michigan. In other words, in the course of normal flight and maintenance, the engine on 2106 may have been changed numerous times, but its design required a Wright R-1820-32 engine and that is the engine type that should be on the aircraft.
Aircraft recovered from under-water, especially from salt water, require conservation treatment to stabilize and preserve them for the future. If this conservation process repairs or replaces portions of the aircraft, the treatment may affect the aircraft's eligibility for the National Register. The question is one of degree. Those conservation methods and treatments required to preserve an aircraft are not likely to jeopardize an aircraft's eligibility. Cosmetic changes or additions to the recovered property are inappropriate unless the intent is to return the aircraft to its configuration immediately before the crash. In other words, if a historic aircraft is recovered and is found to be missing its canopy and wing flaps as a result of its underwater environment, replacement of those parts with contemporary or clearly identified modern replicas is appropriate and should not jeopardize the historic integrity of the aircraft. However, the ideal is to conserve the aircraft as an archeological artifact, and therefore, minimum cosmetic actions should be employed.
Design is the combination of elements that create the form, plan, space, structure, and style of a property. In evaluating integrity of design you might ask, does a building still retain the design qualities of its architect? Does an airplane reflect the design of its type; or the design of a special purpose of historic importance? Does a radio range beacon contain the features characteristic of its design? Have changes over time altered the design associated with the historical significance of the particular property?
Aircraft by their nature undergo constant changes of system parts throughout their service lives; engines, pumps, actuators, radios, etc., are all periodically changed. Research into the history of a given aircraft design series is essential to verification of design integrity and identification of features which must be present to qualify as a specific aircraft type.
Determination of integrity of design, therefore, requires a knowledge of designation attributes. An F4F Wildcat can be distinguished from an F6F Hellcat fairly easily even though both have a similar silhouette. If the main landing gear resembles a trapeze extending from the underside of the fuselage, just forward and below of the windscreen, then it is an F4F. If the main landing gear is comprised of two individual gears, each a single strut extending from under each wing, then the aircraft is an F6F.
However, an F4F-3 is not as easily distinguished from an F4F-4. The F4F-3 Wildcat had four .50 caliber machine guns, two in each wing, and lacked a folding wing feature. An F4F-4 had folding wings and six, .50 caliber machine guns. An F4F billed as a F4F-4 model that has non-folding wings should be suspect. Within any given design series there may be numerous modifications and models. The changes that distinguish one model from another may or may not be readily discernible, thus sound research is required.
Workmanship is the physical evidence of the crafts of a particular culture or people during any given period of history or prehistory. It is the evidence of artisans' labor and skill in constructing or altering a building, structure, object, or site. Workmanship can apply to the property as a whole or to its individual components. Workmanship is important, because it can furnish evidence of the technology of a craft, illustrate the aesthetic principles of a historic or prehistoric period, and reveal individual, local, regional, or national applications of both technological practices and aesthetic principles.
Aircraft can exhibit examples of distinguished workmanship. Production methods can reflect workmanship as evidenced in the transition from shop to line production during the wars and how prewar and wartime aircraft differ, even for the same model. Distinctive aircraft markings such as nose art should be considered examples of workmanship. Other field modifications should fall under this category. An F4F squadron stationed on aircraft carrier CV-6 in 1942, installed steel boiler plate to protect its pilots in a time prior to factory installation of aircraft armor plate on F4Fs. This modification is an example of field response to an immediate need. As such, it is also an example of workmanship. Whether the boiler plates were bolted in or welded, and the workmanship of the machinist's holes or the cut edges of the plate and weld seam are indications of the quality of the welder's workmanship.
Another example is the engine bolts on SBD-2 bureau number 2106, the aircraft discussed earlier. Critical attachment bolts in various parts of an aircraft have holes drilled in the bolt-head faces through which pass steel safety, or locking wire. The wire is intended to keep the bolts from backing out, much like cotter keys are used to keep nuts from loosening. The appropriate way to attach safety wire is to loop it through a series of bolts, with the tension pulling on the bolt head in a clockwise, tightening direction. The safety wire on the engine case bolts of SBD-2, 2106, is pulling in a counter-clockwise direction. Either the case bolts are a non-standard type or the safety wire is installed incorrectly. If incorrectly installed, this poor workmanship is an indication of aircraft maintenance ability both at the Naval Air Station that the aircraft was assigned to and where the engine was assembled.
Workmanship may be particularly evident in airplanes built before WW II. During that period, light airplanes had numerous hand-crafted parts. Many aspects of the airplanes' construction, such as ribstitching, propeller carving, the placement of reinforcing tape, or the doped finish, can be evidence of high-quality or poor workmanship. These features should be noted and evaluated.
Feeling is a property's expression of the aesthetic or historic sense of a particular period of time. It results from the presence of physical features that, taken together, convey the property's historic character.
Association is the direct link between an important historic event or person and a historic property. A property retains association if it is the place where the event or activity occurred and is sufficiently intact to convey that relationship to an observer. Like feeling, association requires the presence of physical features that convey a property's historic character. This is a self-explanatory requirement; the aircraft either is directly associated with an historic event or person or it is not.
In conclusion, old airplanes often require restoration. As noted by the Paul E. Garber Preservation, Restoration, and Storage Facility of the National Air and Space Museum: "Many [aircraft] have been left to the ravages of weather, and airplanes are not built to last in adverse conditions. Their materials-light metal alloys, wood, fabric, rubber, and plastic-are not selected for durability but for maximum strength and minimum weight. Wood rots, cloth decomposes and tears, rubber hardens and crumbles, and metals succumb to corrosion." In addition to weather, aircraft suffer accidents, salvage and souvenir hunters, parts cannibalization, wear and tear of normal operation, the replacement and modification of components as routine maintenance of operational aircraft, as well as damage from moisture, light, fungus, and rodents. These factors affect an aircraft's integrity, and each aircraft must be evaluated individually to determine if it retains the essential features necessary to retain historic integrity.
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