As aircraft design and manufacturing evolved, the  development of lightweight metals and the demand for  increased production moved the industry away from aircraft  constructed entirely of wood. Some general aviation aircraft  were produced with wood spars and wings, but today only a  limited number of wood aircraft are produced. Most of those  are built by their owners for education or recreation and not  for production. In the late 1930s, the British airplane company DeHavilland  designed and developed a bomber named the Mosquito.  Well into the late 1940s, DeHavilland produced more than  7,700 airplanes made of spruce, birch plywood, and balsa  wood.  [Figure 6-1] During the early part of WWII, the U.S. government put  out a contract to build three flying boats. Hughes Aircraft  ultimately won the contract with the mandate to use only  materials not critical to the war, such as aluminum and steel.  Hughes designed the aircraft to be constructed out of wood. Quite a number of airplanes in which wood was used as  the primary structural material still exist and are operating,  including certificated aircraft that were constructed during  the 1930s and later. With the proper maintenance and  repair procedures, these older aircraft can be maintained  in an airworthy condition and kept operational for many  years. After many delays and loss of government funding, Howard  Hughes continued construction, using his own money and  completing one aircraft. On November 2, 1947, during taxi  tests in the harbor at Long Beach, California, Hughes piloted  the Spruce Goose for over a mile at an altitude of 70 feet,  proving it could fly.  The information presented in this chapter is general in  nature and should not be regarded as a substitute for  specific instructions contained in the aircraft manufacturer’s  maintenance and repair manuals. Methods of construction  vary greatly with different types of aircraft, as do the various  repair and maintenance procedures required to keep them  airworthy.  When specific manufacturer’s manuals and instructions are  not available, the Federal Aviation Administration (FAA)  Advisory Circular (AC) 43.13-1, Acceptable Methods,  Techniques, and Practices—Aircraft Inspection and Repair,  can be used as reference for inspections and repairs. The AC  details in the first paragraph, Purpose, the criteria necessary  for its use. In part, it stipulates that the use of the AC is  acceptable to the FAA for the inspection and minor repair  of nonpressurized areas of civil aircraft.  It also specifies that the repairs identified in the AC may  also be used as a basis for FAA approval of major repairs  when listed in block 8 of FAA Form 337, Major Repair and  Alteration, when:  Certificated mechanics that have the experience of working  on wooden aircraft are becoming rare. Title 14 of the Code  of Federal Regulations (14 CFR) part 65 states in part that a  certificated mechanic may not perform any work for which  he or she is rated unless he or she has performed the work  concerned at an earlier date. This means that if an individual  does not have the previous aviation woodworking experience  This was the largest seaplane and the largest wooden aircraft  ever constructed. Its empty weight was 300,000 pounds with  a maximum takeoff weight of 400,000 pounds. The entire  airframe, surface structures, and flaps were composed of  laminated wood with fabric covered primary control surfaces.  It was powered by eight Pratt & Whitney R-4360 radial  engines, each producing 3,000 horsepower.  [Figure 6-2] Wood Aircraft Construction and Repairs 6-2 1.  The user has determined that it is appropriate to the  product being repaired; 2. It is directly applicable to the repair being made; and  3. It is not contrary to manufacturer’s data.  Figure 6-2.  Hughes Flying Boat, H-4 Hercules named the Spruce  Goose. Figure 6-1.  British DeHavilland Mosquito bomber.