The other day I was practicing an ILS approach on runway 07 and to my surprise, the EHSI (Sandel 3308) showed the localizer coming from the left, instead of straight ahead.
Do you have any idea on how can this happen? The dots on the bottom correctly show me centered on the localizer and those on the right side slightly below glideslope, however the whole image is somehow rotated, showing the localizer coming from 038 instead of 070.
Is it possible I somehow fiddled with other avionics equipment causing this behavior?
Hello
Of course I think you are on the right RWY/ right frequency and no on a crossing RWY and his own ILS …
I don’t heard about trouble shooting like this with SANDEL
So it looks like wrong D Bar indication by false ILS due to an airplanes or a véhicule out of the mandatory holding point ( and outside TWR hours and no information about that) or an occasional disturbance by a relief element or airplane flying in the vicinity.
Did you proceed a missed approach (of course if you were IMC) and report for another approach ?
Good to know !
Seems like an instrument glitch with the llz.
. Do you mean slightly below or 2 dots below glideslope?
The picture all looks to me as an aircraft that has the course bar mis set to 038 but with the aircraft on the LOC and heading towards the runway, had the auto slew failed or been manually disconnected in error ?
Absolutely. Course set to 038, runway 07. For an ILS, the needle position does not change when the course pointer moves (other than for a VOR). So if you turned the course pointer to 338 in that case, the needle would run left to right, but still be centered.
So the real question is – why was the course pointer at 038? And why was that not picked up on the base leg of the approach?Maybe the wrong knob was twisted on the turn onto final?
On the Sandel EHSIs (I have two of the SN3500) the course pointer has to be set to the bearing of the localiser. If it is slightly off it doesn’t matter but if it is off by more than 90 degrees then the EHSI will show “BC” (back course) and will suppress the glideslope indicator.
Well, after countless hours of debugging this, finally the mistery is solved.
It seems there was a known issue with the WAAS capable navigators from Garmin. As I recently upgraded to an IFD540 which emulates the GNS530W behavior, here’s what happens:
AFFECTED PRODUCTS
All GNS 400W/500W products installed with a Sandel SN3308 EHSI
ISSUE
The Sandel model SN3308 EHSI has a feature called AUTO SLEW. When this feature is enabled and GPS is the selected navigation source, the SN3308 will automatically rotate the course pointer to the desired course sent by the 400W/500W Series unit. When the SN3308 is given a new course from the GPS, it slews to the new commanded course.
When NAV (VLOC) is the selected navigation source for the SN3308, course selection is always manual. If the navigation source is switched from GPS to NAV (VLOC) before the SN3308 has completed slewing to the new course, the course pointer will stop and may indicate a heading that will not intercept the desired course. Setting the ILS CDI CAPTURE to ‘Auto’ on the CDI/ALARMS AUX page causes the Garmin 400W/500w navigation system to automatically change to VLOC as the navigation source when
using GPS navigation to intercept an ILS or localizer approach.
RESOLUTION
The Pilot should always verify the selected course on the SN3308 after any change to the navigation source (GPS-VLOC/NAV).
Setting the ILS CDI CAPTURE to ‘Manual’ on the CDI/ALARMS AUX page of the Garmin 400W/500W unit is recommended to disable the automatic switching of the navigation source (as when the ILS CDI CAPTURE setting is ‘Auto’).
I hope this info helps someone that may find himself in the same situation…
