Well… Now that I have my first own aircraft I also am making new experiences. This one I probably don’t need to make very often.
With a safety pilot I was flying today from EGBJ to EGTK and back. On both ILS approaches the glideslope worked fine initially. The check altitudes were all right. But once we were visual with the runway and the PAPIs we saw 4 reds while the glideslope indicator showed no deviation at all.
Anyone has any idea what that might be?
After we returned to EBGJ we used an ILS simulator and a brief test did not turn anything up.
Ooops! That one is disturbing. Let RGV check the whole system again! I have never seen that …
Was the Papi damaged by a storm maybe?
Anyone has any idea what that might be?
Anything conducting in the critical area of the ILS (where the ground reflection lies)?
Propeller modulation? What RPM did you use, how many blades does your prop have (3?) and where is your GS antenna located? And did you do the ground test with the engine running or not?
We do have a guy here who tests ILS installations, right? Who was that?
They used the ILS simulator but the avionics guy was not available today. I guess I will end up in Straubing for this.
The aircraft has a 3 blade prop. The engine was NOT running during the ground test.
I’m trying to learn where the GS antenna on the airframe is located.
Ok, so 1800 RPM could be critical. Next time you do a ground check, put the GS transmitter at least 10m in front of the aircraft, run the engine, and vary RPM between say 1700 and 2400 RPM and check whether the GS needle is affected.
Thank you. That’s an interesting thought. I will try to perform this experiment.
You learn all kinds of interesting stuff on this forum!
In case Stephan manages to reproduce this issue on the ground with the engine running, what would be the fix? Move the antenna?
In my case it was moving the antenna from above the front seat row to above the rudder (i.e. move it as far away from the propeller as possible)
As a calibration pilot this is rather disturbing. Your profile indicates that your the lucky owner of a Cirrus which should be bulletproof as far as instrumentation is concerned. If you are not getting a flag your receiver is obtaining a signal which is powerful enough to be interpreted – the strength of the signal clearly improves as you get closer to the runway. I suspect you have a problem with one of the 90/150hz filters on the UHF element of your navbox.
Prop mod – unlikely.
Antenna location – unlikely.
Loose wire outside of the navbox – unlikely.
Take it to RGV (or whoever you use) and get a full diagnosis.
