The informal survey results suggest that in principle flight inspection should be feasible even in COVID-19 times, possibly with some restrictions requiring prioritization/rearranging of schedule as discussed above.
As a result, periodicity of flight inspection should not be affected substantially, and it should be possible to limit any potential deviations from the nominal intervals to within the time window of extension mentioned in Doc 8071, 1.15.15 (see Excerpts from the Manual on Testing of Radio Navigation Aids (Doc 8071)). While Doc 8071 makes no recommendations on the length of such time windows, the extension window needs to be a reasonable fraction of the nominal interval. For example, some States use a maximum delay of 1 month for nominal inspection periodicities of 6 months.
In cases in which nominal periodicity cannot be maintained and the appropriate extension time window is exceeded (e.g. because of initial set-up issues with cross-border operations, as discussed above), Doc 8071, 1.15.15 offers a choice of actions that may be considered:
allowing for further extension time, after engineering evaluation and/or ground maintenance reinforcement;
downgrading of ILS (Category III down to Category I or II); and
temporarily removing the navigation aid from service.
In choosing among those actions, the responsible entities should take into account the exceptionality of the current situation, in which aviation has suffered an unprecedented setback and is facing what can be expected to be a very difficult recovery phase. In this context, the navigation infrastructure must remain operational both to support the reduced level of traffic during containment measures (including flights meeting critical pandemic-related needs, such as delivery of medical supplies) and to facilitate the resumption of regular flight operations. Therefore, in cases where timely flight inspection cannot be ensured, the preferred method for maintaining safe signals in space is to either take advantage of the (short) periodicity extension window, or, if a longer extension is required, to grant an extension of periodicity intervals in line with the principles described in Doc 8071. Furthermore, in cases where flight inspection operations were suspended and periodicity intervals extended, careful planning should ensure that navigation aid availability of service can be ensured to support the recovery.
At the same time, no compromise on operational safety due to non-standard performance of navigation aids should be accepted. Instead, potential extensions of nominal inspection intervals should be considered only in the presence of appropriate mitigations maintaining nominal safety levels. To this end, the provisions of Doc 8071, 1.15 should be taken into account.
Doc 8071, 1.15.2 recognizes that the suggested periodicities are given as general guidance and may be modified based on the manufacturer's recommendation or operational experience. Subsequent sections (1.15.4 – 1.15.6) discuss the factors influencing the inspection intervals, including reliability and stability of operation of the equipment, extent of ground monitoring, degree of correlation between ground and flight measurements, changes in the operating environment, manufacturer recommendations, and quality of maintenance. In many cases, modern ground facilities using current technology provide highly stable and reliable signals. A point of particular practical interest in the current context is given in 1.15.6 with the observation that equipment reliability may be adversely affected by too frequently scheduled major maintenance activities, which should therefore be limited to essential needs if extended periodicity is desired.
Further sections of Doc 8071, (1.15.7 – 1.15.8 and 1.15.10- 1.15.14) discuss the type of technical analysis that would need to be performed to extend nominal ground and flight inspection periodicities in a normal situation. While performing such detailed analysis may be impractical in a pandemic situation, it should be noted that the most important item to ensure safe facility performance is the verification of the proper functioning of executive monitor shutdown capabilities. Special attention should also be given to site safeguarding, especially if aircraft or other large equipment is being parked near a navigation aid.
While the guidance in Doc 8071 does not explicitly address the current situation, it does indicate that, in situations in which maintaining nominal flight inspection periodicity is effectively impossible, case-by-case extensions can legitimately be considered on an exceptional basis when the relevant enabling factors are present. In other words, in the unprecedented situation now being faced by aviation, a reliable system running in a stable configuration with a history of nominal performance, undergoing regular ground checks consistent with manufacturer recommendations which indicate normal functioning, and in the absence of anomaly reports, should normally qualify for an extension of the periodicity interval.
Special considerations apply to the specific case of Category III ILS. Because of the particularly demanding requirements, rigorous testing is essential. For that reason, during the current pandemic several States are prioritizing flight inspection of Category III ILS. Should it nevertheless occur that flight inspection intervals for a Category III ILS are significantly exceeded, as mentioned above a potential option would be downgrading of the facility from Category III to Category II or Category I.
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