MIL-HDBK-1530B(USAF)
APPENDIX A
Force inventory. If the certification basis is considered adequate, then the compliance with the U.S. Air Force structural performance requirements for the candidate air vehicle is evaluated. This effort should examine the differences between the structural design criteria of the candidate air vehicle and the U.S. Air Force structural design criteria. Each aspect of the criteria that affects the vibration, acoustic, flutter, load, strength, fatigue, and
damage tolerance capability of the air vehicle should be examined. For example, the candidate air vehicle may have been designed to a limit load factor of 3.5, while the U.S. Air Force operations dictate the need for a limit load
factor of 4.5. This indicates a deficiency in strength and possibly in durability and damage tolerance capability. An incompatibility in the velocity/altitude boundary requirements may indicate a deficiency in the flutter margins. If
the structural performance requirements for the air vehicle are not compatible with the design of the candidate air vehicle, then the air vehicle is subjected to a technical assessment. If it is compatible, then the candidate air vehicle is assessed against the service life goals, missions, and usage desired. If the candidate air vehicle is not compatible with the desired service goals, missions, and usage, then it goes to the technical assessment. If it is compatible, then the candidate air vehicle service history is examined. For this task, the maintenance program for the candidate air vehicle and its operational history would be assessed. Also, it should be determined if it has adequate past and continuing operational experience to ensure that any potential economic issue with the air vehicle has been revealed and that any potential safety issue will be revealed before it occurs on a USAF air vehicle. If there is adequate service history, then the air vehicle should be expected to meet the structural requirements, and the evaluation
would be complete. If it is judged that there is not an adequate service history, then it should be subjected to a technical assessment.
A.1.4 Additional analyses. If the air vehicle cannot meet the requirements from A.1.2, then suitable additional analyses should be performed in an in-house technical assessment to ensure that any potential economic or safety problem is revealed. In many cases, FAR Part 25 air vehicles have been subjected to a damage tolerance assessment as part of the FAA requirements for a Supplementary Structural Inspection Document (SSID). In these cases, this damage tolerance assessment can be modified by the contractor to evaluate the impact of usage changes. The in- house assessment should be based on information from the contractor. Typically, this information is more easily obtained during on-site visits to the contractor facility. This information should include information on design configuration and design usage, loads, stresses, tests, corrosion protection systems, and service experience.
A.1.5 Risk assessment. If the in-house assessment of the candidate air vehicle shows it can meet the desired objectives, then that information is given to the Program Manager. In the event the in-house assessment reveals the candidate air vehicle has significant deficiencies or an inadequate database exists, then the results are submitted to the Program Manager with an assessment of the associated risks so that a decision can be made to either reject the candidate air vehicle or define further efforts.
A.1.6 New or modified structure. The engineering and manufacturing structural development and qualification guidance in this document are appropriate for new or extensively-modified structure. This describes the level of effort, design analyses, and testing required regardless of who certifies the new or modified structure.
An in-house structural assessment of the magnitude of the structural modification can be conducted to clarify further the required level of design effort, analyses, and testing.
A.1.7 Airframe condition. Particularly difficult structural integrity problems often accompany the procurement of aging, off-the-shelf aircraft. There are many used aircraft in the marketplace which may be
purchased far below the price of a new, off-the-shelf air vehicle. The reasons for the low price on these aircraft may be that they have flown beyond their design service goal, they have corrosion problems, they have widespread fatigue problems, they have numerous repairs (many of which are not damage tolerant), or any combination of these reasons. That is, they generally possess all of the ingredients to be classified as aging aircraft. Unfortunately, many of these problems can be hidden from view and the aircraft may appear to be airworthy. Experience has shown that significant problems do exist and the cost of refurbishing these aircraft is considerably above original expectations.
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