Cover: Applying Best Practices to Military Commercial-Derivative Aircraft Engine Sustainment

Applying Best Practices to Military Commercial-Derivative Aircraft Engine Sustainment

Assessment of Using Parts Manufacturer Approval (PMA) Parts and Designated Engineering Representative (DER) Repairs

Published Sep 19, 2016

by Mary E. Chenoweth, Michael Boito, Shawn McKay, Rianne Laureijs


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Research Questions

  1. To what extent do military and commercial engines within the same families of engines share common parts?
  2. What are the potential savings for the Department of Defense of using estimate savings of greater use of Parts Manufacturer Approval (PMA) parts and designated engineering representative (DER) repairs?
  3. What processes do the Air Force and commercial airlines use to approve alternate sources of suppliers and repairs?
  4. What real and perceived risks are associated with greater use of PMA parts and DER repairs?

Parts Manufacturer Approval (PMA) parts and designated engineering representative (DER) repairs are parts and repairs that are provided by third-party companies and certified by the Federal Aviation Administration to be airworthy and interchangeable with original equipment manufacturer (OEM) parts or repairs. Currently, all major U.S. carriers use PMA parts and DER repairs in their own fleets so they can introduce competition, save costs, and maintain a more robust supply chain of parts and repairs. The Department of Defense (DoD) is interested in increasing its use of similar kinds of alternate parts and repairs.

This report assesses the feasibility and extent to which DoD might decrease its aircraft operating and support costs without a loss of safety or reliability through the increase in the use of non-OEM parts and repairs. The authors performed case studies on two engines used by the Air Force and the Navy; conducted a literature review; interviewed subject matter experts, engineers, and contracting personnel; and mined PMA and DoD data to analyze parts commonality among DoD engines. The authors find substantial evidence of cost savings where the Air Force and Navy have used PMA parts and DER repairs; however, they also find large differences in how, and how aggressively, the military services pursue the use of these practices in comparison with commercial airlines. The authors offer recommendations on how DoD and the services can revise their processes to realize greater benefits from PMA parts and DER repairs.

Key Findings

The Potential for Savings from Parts Manufacturer Approval (PMA) Parts and Designated Engineering Representative (DER) Repairs

  • For the commercial-derivative case-study engines analyzed (the CF6-50 and CFM56-2), the authors found a large number of parts that could be suitable from PMA suppliers and DER repairs.
  • Engine overhaul costs for the CF6-50 engine have been reduced by 20–25 percent through the use of PMA parts and DER repairs. PMA parts and DER repairs have been used only occasionally for the CFM56-2, but when they have been, there have been significant savings as a percentage of the original part or repair.

Comparing Air Force and Commercial Source Approval Processes

  • Commercial airlines solicit the supply base in a cooperative fashion — for example, share usage and part failure data with potential suppliers — whereas such cooperative relationships are rare or absent in the Air Force.
  • Commercial airlines consider Federal Aviation Administration (FAA) certification of PMA parts and DER repairs to be important, whereas Air Force reviewers tend to discount FAA certification as being relevant only to commercial usage.
  • Commercial airlines supplement FAA certification with their own engineering capability to assess PMA parts and DER repairs, whereas the Air Force does not devote the same level of engineering capability to such assessment.

Real and Perceived Risks of Greater Use of PMA Parts and DER Repairs

  • One persistent perceived risk is that PMA parts are more likely to fail. Commercial carriers manage this concern by retaining a robust engineering capability to evaluate the approval and use of third-party parts.
  • A second risk is the response of original equipment manufacturers (OEMs) to non-OEM vendors and operators who use non-OEM parts and repairs.
  • A third perceived risk is that the FAA's certification of FMA parts and DER repairs is not valid in military usage. The authors did not find sufficient evidence to support this concern.


  • Monitor engine operating and support costs, trends, and metrics over time and benchmark the trends against commercial experience. Make the information available to personnel involved in engine supply chain management, program management, and engineering. Make the responsibility for achieving cost savings part of the responsibility of all involved with engines, including engineering staff.
  • Invest roughly $1.2 million annually for propulsion engineers with commercial experience who understand part design and function and can analyze parts for their material composition and manufacturing processes. Dedicate this expertise to assessing potential PMA parts and DER repairs.
  • Establish a process whereby parts or repairs identified during the source approval process could be installed and monitored on a limited number of engines, as is done by U.S. airlines.
  • Initiate a pilot program to invite DER engineers to observe engine maintenance processes at organic depots and recommend alternatives based on commercial practices. Include as part of this pilot the outsourcing of engineering expertise to help identify prospective candidate parts for potential use of DER repairs.
  • Establish an integrated process team aimed at analyzing cradle-to-grave processes that would be affected if PMA parts, DER repairs, and used commercial parts were used more regularly in legacy commercial-derivative weapon systems.

The research described in this report was sponsored by the Office of the Under Secretary of Defense, Acquisition, Technology, and Logistics and conducted within the Acquisition and Technology Policy Center of the RAND National Defense Research Institute, a federally funded research and development center sponsored by the Office of the Secretary of Defense, the Joint Staff, the Unified Combatant Commands, the Navy, the Marine Corps, the defense agencies, and the defense Intelligence Community.

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