John Denker wrote: > On 12/31/2008 10:29 AM, I wrote >> Standard dogma in IFR training is that the VOR CDI indicates >> two degrees per dot, while the LOC CDI indicates half a degree >> per dot. These numbers are quite believable. Good practice >> is to check them as part of the 30-day IFR receiver check. >> > > Important clarification: The VOR numbers are quite believable, > and are checked monthly. However..... > > The LOC numbers are only a rough rule of thumb. According to > the AIM, the localizer beam is supposed to be designed to be > 700 ft wide at the threshold. That's ±350 feet if you prefer > to think of it that way. > > That means that as the runway length varies from (say) 6000 ft > to 15000 ft, the CDI sensitivity varies from more than 0.6 > degrees per dot to less than 0.3 degrees per dot. (I hear > rumors that it is artificially pegged at a minimum of 0.3 > and a maximum of 0.6, overriding the 700 ft rule, but don't > quote me on that.) > > The 0.5 degree dogma will get you in the ballpark, but > that's all. >
I've observed this variation in sensitivity in practical operations. We can get away with using the 0.5 degree rule, but I'd prefer us to perform the divide-and-constrain that John describes. If you want more detail than the handwave that the AIM contains, go read the FAA technical manual on how to design and deploy LOC antenna arrays ... ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
