As part of future activities associated with implementation of a 1,000-foot vertical separation standard above flight level 290, it will be necessary to verify that altimetry system performance previously observed to be unacceptable is brought into compliance with requirements. Some of this unacceptable performance was observed to be characteristic of all aircraft of a given type, while other substandard performance was associated with only a few airframes of an otherwise acceptable aircraft type. Certification of aircraft for operation in airspace above flight level 290 may require that decisions about acceptable altimetry performance be based on the testing of only a few airframes of a given aircraft type after retrofit. Performance requirements and standards, however, have been developed for the aggregate performance of airspace users.This paper reviews the process of developing individual standards for airframes from group requirements. It points out the need for both engineering principles and statistical analysis to produce a usable certification and operational approval methodology.