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Software that is used in airborne systems, especially those systems that require certification by the Federal Aviation Administration (FAA), is developed in accordance with DO-178B. The development and verification objectives imposed by DO-178B depend on the criticality level of the software. The cost of development, and especially of verification, is significantly higher each step the criticality is increased. Developers want to produce software to the lowest criticality level possible, consistent with a safety analysis, to keep development costs down. It may be desirable to increase the design assurance level of software without incurring the full cost of verification at the next higher criticality level. This paper presents a method of locating undetected software defects, that could cause a hazardous condition, in software that has been verified to DO-178B level D criticality. Locating and removing such defects has the effect of increasing the design assurance level of the software, at about 10% of the cost of a full verification to level C.