Downloaded from https://www.everyspec.com ADS-79D-HDBK (Copies of this document are available online at http://www.armyproperty.com/tm/TB%2043-0211 or 505 E. Huron Street, Suite 202; Ann Arbor, MI 48104 2011 Crystal Drive, Suite 400; Arlington, VA 22202 DUNS Number: 829504880 / CAGE Code: 5BMR7 (703) 269-0013 / (734) 585-5061) (Copies of these documents are available from sources as noted.) H.3 GENERAL GUIDANCE. H.3.1 Background Maintenance processes are currently focused on diagnosing failure of electronic components.
The Army is utilizes a two level maintenance process, field maintenance which consists of aviation unit maintenance (AVUM) and aviation intermediate maintenance (AVIM), and sustainment maintenance (Depot). Typically, unit level maintenance is performed while electronic systems are still installed on the aircraft via primary test equipment built into the electronic systems. Maintenance technicians use the built-in test (BIT) and built-in test equipment (BITE) to verify that systems are operating properly while they are in the helicopters. Pilots also use the equipment to verify system readiness before and during combat missions.
The repair capability at the unit level is normally limited to minor troubleshooting, removal and replacement of parts and components, and daily servicing. The AVIM refers to maintenance that must be done in a repair shop. If a system defect is identified and cannot be repaired at the unit level, the faulty component is removed and sent to the intermediate level repair shop. Various terms are used to refer to an item that is removed and replaced and include Line Replaceable Unit (LRU) and Weapon Replaceable Assembly (WRA). The repair shop has more sophisticated test equipment that can diagnose faults at a more detailed component level.
Intermediate maintenance provides backup support for the unit level maintenance as well as an expanded capability to perform diagnostic troubleshooting, tear-down analysis and repair, and limited rebuilding of components, to include engines. Doctrinally, repairs of aircraft and components completed by the intermediate maintenance unit are usually returned to the owner. Faulty components that cannot be repaired at the intermediate level repair shop are shipped to a remotely located depot. The depot level refers to maintenance that is beyond the capability of the AVUM/AVIM and is performed at a central facility located farther away from tactical units.
During the conceptual and early design phase a failure rate prediction is a method that is applicable mostly, to estimate equipment and system failure rate. Following models for predicting the failure rate of items are given (in MIL-STD-217F):
- Failure rate prediction at reference conditions (parts count method) - Failure rate prediction at operating conditions (parts stress method) 137 TECHNICAL MANUALS TM 1-1520-248-T Operational Checks And Maintenance Action Precise Symptoms (Maps) Diagrams Aviation Unit and Intermediate Maintenance Manual for Army OH-58D Helicopters TM 1-1520-248-MTF Maintenance Test Flight Army OH-58D Helicopter BOOKS Vachtsevanos, George and Frank Lewis, Intelligent Fault Diagnosis and Prognosis for Engineering Michael Roemer, Andrew Hess, Biqing Wu, Systems, Wiley, September 2006. Pecht, Michael. Prognostics and Health Management of Electronics, Wiley, September 2008.