I was just wondering if anyone here has encountered significant tangible errors regarding certain conventional navigation systems as we read in the books.

Polarization error - regarding the VOR, NDB, and LOC has anyone here seen any significant effects while using these systems with high angles of bank and/or pitch? If so, what were the effects?

Propeller modulation error - regarding the VOR, has anyone here seen the effects of this error? If so what were the effects and what was the RPM range?

FM interference - regarding the LOC (and perhaps the VOR as well), has anyone seen this interference from commercial broadcast stations? I recall some time ago there was a mandate in Europe to install FM immune receivers....I don't believe your typical bendix/king nav radio in the US is FM immune but I could be wrong.

Quadrantal error - regarding the NDB, has anyone seen the effects of this error, and if so what are they?

 

Yes - sometimes on what seems like daily basis
I'm beginning to wonder how we ever got around before I saw the man behind the curtain!
Recent experience:
RF near Arlington, Lubbock, and Amarillo, TX though it was not affecting the LOC as a user had complained.
VORTAC modulation on an intersection they are trying to establish off of EMP.
Only seen one VP fail so far on a LOC, but have heard of it from others.
We might see some prop mod problem during a GCP inspection, but can usually work that out with a reposition obviously

This can all be consider job security though
It does make me feel good though about the overall quality of our system and the tight tolerances to which it is maintained.

USMCFLYR

 

Thanks for the response USMCFLYR, but I have to say I have a hard time understanding what you're saying.

Could you define the acronyms EMP, VP, and GCP.

When you refer to RF in Arlington, Lubbock, and Amarillo....are you just talking about general RF interference or something specific?

 

EMP is the ID for the Emporia VORTAC
VP is vertical polarization with regards to a localizer.
GCP is a Ground Receiver Checkpoint

Pilots had made complaints of LOC deviations in the cases of the approaches I mentioned. We didn't find anything in Lubbock or Amarillo. Arlington had some Spanish radio station interference but it was not affecting the LOC performance.

USMCFLYR

 

I fly quite a bit near Arlington.....how was the Spanish radio station interfering with the signal, was it heard along with the identification for the LOC?

When you say, "VORTAC modulation on an intersection they are trying to establish off of EMP." What modulation are you referring to?

When you say, "Only seen one VP fail so far on a LOC, but have heard of it from others." I thought at first you were saying "vertical path" as in glideslope. How can you have vertical polarization "fail" on a LOC? As I understand, the LOC transmits a horizontally polarized signal.

Thanks

 

KGYB. yes - radio on the LOC freq. They said that it was swinging the needle, but there wasn't any effect with the course guidance. You'll notice the restriction on the LOC course in the AF/D? If you are coming at the LOC course from the east (or are holding in that area) you can expect some interference. Just did another RFI today around Wichita KS. 107.3 KTHL 'The Brew' bleeding over onto ZKC's 102.2 freq. Good music btw.

The modulation of the VOR and TCN signals. There are numerous tolerances that must be applied to the signals both inside and outside (as was the case with this extended service volume request) the standard service volumes.

VP. That is the name of the check conducted on the LOC signal prior to the FAF. You are correct - the signal is transmitted in the horizontal plane (thus the horizontally mounted receiver on the aircraft). We bank the aircraft left and right (how much depends on what we are inspecting) to see if the antennas detect any VERTICALLY polarized energy which should not be there. If there is an amount of vertically polarized energy that is beyond the tolerance then the LOC VP fails.

USMCFLYR

 

I see......so you do flight inspection work??

I did see the note in the A/FD for KGKY "LOC unusable beyond 15 degrees right of course." Makes sense seeing as you have all those tall noisy radio towers in Cedar Hill just east of the LOC course.

You referred to a GCP in one of your earlier posts which reminds me of another nagging question I have.....what a VOT looks like. I have noticed that at all airports that are listed as having a ground or airborne VOT station there is a strange structure, with four tall pillars that have antennas forming a square around a small building in the middle....is this the VOT? I had always thought that a VOT would be a small conspicuous item like marker beacons are.

Thanks for all the great answers!

 

PSP VORTAC is notorious for being unrelieble below 15k between the 40 and 20 DME.

 

Fly -

Here are the restrictions listed for PSP:
03/25/92 VTAC unusable 135° - 215° byd 20 NM blo 10200'
03/25/92 VTAC unusable 215° - 270° byd 15 NM blo 12800'
03/25/92 VTAC unusable 278° - 320° byd 25 NM blo 13000'
03/25/92 VTAC unusable 320° - 090° byd 15 NM blo 7300'

Quite a few but not as many I have seen.

MoZak - A VOT is no different than a VOR except that it transmits the same signal - omnidirectional. You tune in the frequency and select either 360 or 180 and hopefully your needle will center. A GCP is different than a VOT in that it is a checkpoint established either on the ground or airborne (ACP) with a radial/distance (and a geographical location if airborne) for you to test your aircraft if a VOT is not available. What you are describing actually sounds like more of a comm relay/facility - but it is hard to tell unless you have a picture.

USMCFLYR