A reduced level of service invoked by equipment outage or malfunction, staff shortage or procedures becoming inadequate as a knock-on effect of one or several deficient system elements.
Degraded modes of operation are defined to occur when staff continue to maintain levels of service when elements of the underlying technical infrastructure are unavailable. Degraded modes of operation occur when members of staff find ways of working around failures in the underlying technical infrastructure. They should not jeopardise safety given that they are subject to appropriate levels of risk assessment. Degraded modes describe failures that stop short of the loss of an air traffic control facility such as an area control centre (ACC), however, they may be precursors to contingencies if further failures occur. For 'emergency', 'degraded' and 'service continuity modes of operation', it is important to conduct both a safety assessment and a security risk assessment. The aim is to ensure that the planned contingency measures meet safety and security requirements set at the policy step.
One critical element that should not be under estimated is the role and ability of engineering and technical support to support the contingency strategy and resulting measures. Appendix G of the EUROCONTROL "Guidelines for Contingency Planning for Air Navigation Services Guidelines" addresses systems engineering perspective of contingency strategies. This provides additional guidance on this important aspect of contingency planning. Similarly, it is important to consider the ways in which external resources can be secured, for instance, from sub-contractors and other maintenance organisations both during degraded modes of operation, as service providers work to rectify a potential problem, and after any contingency has been declared.