Date: 06 Apr 99 11:46:18 From: Ralf Sipple <firstname.lastname@example.org> Organization: Sipple Aviation & Engineering References: 1
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Paul MacDougall <email@example.com> wrote: > just wondering if anyone is familiar with the inner workings of the ILS > system and how it integrates with the FMC....ie if you dial in the correct > localizer frequency but mis-set the front course setting how does the system > work or not work... does it matter if you mis-set it only 10 degrees verses > 80 degrees....my AOM is not very helpful and I know this system has screwed > a few people... sorry, don't know, but I have a similar question: Today I was flying an ATR72. We were cleared ~30 nm from FCO to intercept the localizer 16L and as the the indication this far far out is often somewhat inreliable I decided to follow the extended centerline with LNAV. I monitored the ILS indication on the captain's CRT (in the ATR you have either RNAV or conventional NAV indication, but not both) and confirmed by that that I was precisely on LOC and GS. Closer to the field I switched my display to L/V (conventional NAV). This caused the LNAV mode to go off, the AP was in basic lateral mode (maintain bank). I armed APP. The course selector was set 50 deg off to the right fron the correct course (162deg). As I was already precisely on LOC and GS they both captured immediately. But then the unexpected happened: The A/C banked sharply to the right (the direction the course selector was pointing to) and came off the LOC to the right. I then turned the course selector to the correct approach course and the AP re-intercepted the LOC. It appeared to me that the AP used the set course as an initial value for a heading which may be appropiate to follow the LOC (in this case it wasn't). I once discussed a maater with a B737 captain. He said that his company rules called for flying an approach with the ND in APP mode. He said he likes to keep the ND in MAP mode to improve situational awareness. The reason for the rule to have APP mode displayed is that he couldn't see the course dialed in MAP mode. However, the deviation signal from the localizer (opposed to VOR) is completely indepent fom the selected course. Has anyone tried similar things? How does your plane behave? Viele Gruesse, Ralf -- Ralf Sipple | Fax +49-711-7777206 | firstname.lastname@example.org D-70794 Filderstadt| Anrufbeantw. +49-711-7777208| pgp key on request!