MIL-HDBK-17-3F Volume 3,Chapter 8 Supportability the first,is that edges of doors or panels can erode if they are exposed to the air stream.This erosion can be attributed to improper design or installation/fit-up.On the other hand,metal structures in contact or in the vicinity of these composite parts may show corrosion damage due to: Inappropriate choice of aluminum alloy Damaged corrosion sealant of metal parts during assembly or at splices Insufficient sealant and/or lack of glass fabric isolation plies at the interfaces of spars,ribs and fit- tings Assessing operator experience with composite structure is,taken as a whole,an extremely difficult task.A survey of operators provides responses depending on the composite application ranging from horror stories for thin skinned sandwich structures,to outstanding success for thick skinned sandwich or solid laminate primary structures.Some of the facts and data that are available are the detailed reports that were received from the operators on parts involved in the NASA-sponsored Advanced Composites Energy Efficiency(ACEE)program,which supported the design and fabrication of composite parts such as the B727-200 elevators and the B737 spoilers and horizontal stabilizers.Five shipsets of B727 eleva- tors have accumulated more than 331,000 hrs.and 189,000 cycles;108 B737 spoilers have accumulated more than 2,888,000 hrs.and 3,781,000 cycles.Five shipsets of B737 horizontal stabilizers,which incor- porated laminate torque boxes and sandwich ribs,had amassed over 133,500 flight hours and 130,000 landings as of May.1995.The service exposure data collected for these parts have not indicated any durability or corrosion problems.One B737-200 aircraft with the ACEE stabilizers was removed from ser- vice after 19,295 flight cycles and 17,302 flight hours,and one stabilizer was acquired by Boeing for a detailed tear-down inspection.The stabilizer was found to be in excellent condition with no fatigue dam- age,and the only corrosion discovered was some minor pitting found in some fastener holes of the alu- minum trailing edge fittings.This was determined to be due to a fastener sealing practice which has since been obsoleted.Several repairs have been satisfactorily performed on the 727 elevators and remaining 737 horizontal stabilizers which are still in service. The in-service success of these ACEE components is in part due to the integrated teams which de- veloped them.The teams for both the B727 sandwich elevators and the B737 stiffened-skin configured horizontal stabilizers considered maintainability during the developmental programs.They devised repair and inspection schemes,and for each component,Maintenance Planning Manuals were compiled and released as part of the NASA contractual obligation.The airlines,United for the ten B727 elevators,and Delta and Mark Air for the five shipsets of B737 stabilizers,were in essence part of the teams who planned these documents.As mentioned above,both of these components have been damaged and repaired using the repair schemes designed for them.In all of the instances,the repairs were satisfacto- rily performed in-place on the aircraft. An in-service evaluation,launched in 1980,with twenty-two airbrakes/spoilers(14 fabricated with car- bon-epoxy tape,and 8 fabricated from carbon-epoxy fabric)installed on Air France A300 aircraft,is still going on.Non-destructive inspections(visual and ultrasonic)are performed on aircraft and in the labora- tory during the service life.Thirteen airbrakes are still on aircraft,and seven have been withdrawn from service for testing to assess stiffness and residual strength.As of November,1995,these components had accumulated 405,698 flight hours and 236,588 flight cycles.The component with the most time in service had accumulated 32,069 flight hours and 16,802 flight cycles.Bolted repairs(metal patches for temporary,and composite precured patches for permanent repairs)were designed.Two components have been repaired with blind fasteners to arrest manufacturing produced disbonds between the skins and ribs.Some minor corrosion pitting was found on the aluminum(7075)spar at the central fitting splice due to the protect scheme having been damaged and not restored during assembly.A modification of the trailing edge was implemented early in the program;the rubber one being replaced by a solid carbon one. As an example of successful thicker solid laminate structure,the ATR 72 outer wing box has accumu- lated 1,429,539 flight cycles and 1,163,333 flight hours since entering into service in 1989.The aircraft with the most time service has accumulated 23,343 flight cycles and 14,988 flight hours.Service experi- ence has been very good with only one accidental damage being reported:an aircraft crashed into a han- gar door at a speed of 15 miles/hr(25 km/hr).The composite outer wing box was repaired using bolted 8-3MIL-HDBK-17-3F Volume 3, Chapter 8 Supportability 8-3 the first, is that edges of doors or panels can erode if they are exposed to the air stream. This erosion can be attributed to improper design or installation/fit-up. On the other hand, metal structures in contact or in the vicinity of these composite parts may show corrosion damage due to: • Inappropriate choice of aluminum alloy • Damaged corrosion sealant of metal parts during assembly or at splices • Insufficient sealant and/or lack of glass fabric isolation plies at the interfaces of spars, ribs and fit￾tings Assessing operator experience with composite structure is, taken as a whole, an extremely difficult task. A survey of operators provides responses depending on the composite application ranging from horror stories for thin skinned sandwich structures, to outstanding success for thick skinned sandwich or solid laminate primary structures. Some of the facts and data that are available are the detailed reports that were received from the operators on parts involved in the NASA-sponsored Advanced Composites Energy Efficiency (ACEE) program, which supported the design and fabrication of composite parts such as the B727-200 elevators and the B737 spoilers and horizontal stabilizers. Five shipsets of B727 eleva￾tors have accumulated more than 331,000 hrs. and 189,000 cycles; 108 B737 spoilers have accumulated more than 2,888,000 hrs. and 3,781,000 cycles. Five shipsets of B737 horizontal stabilizers, which incor￾porated laminate torque boxes and sandwich ribs, had amassed over 133,500 flight hours and 130,000 landings as of May, 1995. The service exposure data collected for these parts have not indicated any durability or corrosion problems. One B737-200 aircraft with the ACEE stabilizers was removed from ser￾vice after 19,295 flight cycles and 17,302 flight hours, and one stabilizer was acquired by Boeing for a detailed tear-down inspection. The stabilizer was found to be in excellent condition with no fatigue dam￾age, and the only corrosion discovered was some minor pitting found in some fastener holes of the alu￾minum trailing edge fittings. This was determined to be due to a fastener sealing practice which has since been obsoleted. Several repairs have been satisfactorily performed on the 727 elevators and remaining 737 horizontal stabilizers which are still in service. The in-service success of these ACEE components is in part due to the integrated teams which de￾veloped them. The teams for both the B727 sandwich elevators and the B737 stiffened-skin configured horizontal stabilizers considered maintainability during the developmental programs. They devised repair and inspection schemes, and for each component, Maintenance Planning Manuals were compiled and released as part of the NASA contractual obligation. The airlines, United for the ten B727 elevators, and Delta and Mark Air for the five shipsets of B737 stabilizers, were in essence part of the teams who planned these documents. As mentioned above, both of these components have been damaged and repaired using the repair schemes designed for them. In all of the instances, the repairs were satisfacto￾rily performed in-place on the aircraft. An in-service evaluation, launched in 1980, with twenty-two airbrakes/spoilers (14 fabricated with car￾bon-epoxy tape, and 8 fabricated from carbon-epoxy fabric) installed on Air France A300 aircraft, is still going on. Non-destructive inspections (visual and ultrasonic) are performed on aircraft and in the labora￾tory during the service life. Thirteen airbrakes are still on aircraft, and seven have been withdrawn from service for testing to assess stiffness and residual strength. As of November, 1995, these components had accumulated 405,698 flight hours and 236,588 flight cycles. The component with the most time in service had accumulated 32,069 flight hours and 16,802 flight cycles. Bolted repairs (metal patches for temporary, and composite precured patches for permanent repairs) were designed. Two components have been repaired with blind fasteners to arrest manufacturing produced disbonds between the skins and ribs. Some minor corrosion pitting was found on the aluminum (7075) spar at the central fitting splice due to the protect scheme having been damaged and not restored during assembly. A modification of the trailing edge was implemented early in the program; the rubber one being replaced by a solid carbon one. As an example of successful thicker solid laminate structure, the ATR 72 outer wing box has accumu￾lated 1,429,539 flight cycles and 1,163,333 flight hours since entering into service in 1989. The aircraft with the most time service has accumulated 23,343 flight cycles and 14,988 flight hours. Service experi￾ence has been very good with only one accidental damage being reported; an aircraft crashed into a han￾gar door at a speed of 15 miles/hr (25 km/hr). The composite outer wing box was repaired using bolted