Radar requirements for SRA/SRE
Can anybody tell me what the actual radar requirements are in order to carry out an SRA/SRE approach.
It has long been folklore within the Mil that SRA/SRE can only be carried out using primary radar i.e. Watchman, which rotates at 15rpm. As the Mil does not go in for piggy backed SSR, if the Watchman is off the SSR should still be available from a different site but this usually rotates at 8rpm. This has always been considered as not good enough for the purposes of SRA approaches.
As most civil airports do use piggy backed primary/SSR, if the primary is off but the SSR on, are SRE approaches allowed.
Finally, my understanding of Mode S (SSR) is that it does not rely on the challenge/respond method but rather the ac just transmits at the maximum rate it can all the time. Therefore if you have a triangulated set of receivers that can receive this level of information and display it, will this mean that SRA/SRE approaches can be carried out without ever having primary radar at all. Thereby chipping away at the requirement for primary and potentially saving money.