Flight inspection is the means by which the performance of a navigation aid is measured to ensure that it is meeting the requirements of the operational procedures based upon it. It can involve laboratory-type measurements in an environment which is generally unstable and sometimes hostile. The first requirement is the position of the aircraft fixed to an accuracy commensurate with that implied by the operational specification of the navigational aid. A range of techniques for position fixing has been developed over the years. Where possible the technique should just meet the ‘one order better than’ criteria. The use of systems with accuracies significantly better will usually result in financial or logistic penalties.