Noah

Noah

Well Known Member
Is a VOR receiver check required to legally fly an ILS under IFR?

The question is whether an ILS is part of "the VOR system of radio navigation" per 14 CFR § 91.171, VOR equipment check for IFR operations:

(a) No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft—
(2) Has been operationally checked within the preceding 30 days, and was found to be within the limits of the permissible indicated bearing error set forth in paragraph (b) or (c) of this section.

Let's say a pilot has a GNS430W with a NAV (VOR/ILS) receiver, but he almost never does the VOR check since he never uses VOR - only GPS - except he DOES use the nav receiver when flying an ILS approach.

Is "Johnny Hypothetical" operating legally?
 
Aren't you testing the accuracy of your aircraft's equipment? Not only from a legal stand point, but I'd want to make 100% certain that the plane's equipment works before flying 200' AGL in cloud.

I've heard that an ILS can often be quite a bit out of alignment when they check the calibration. Combine that with a receiver that hasn't been checked recently and is slightly out of limits. Johnny Hypothetical is a bit tired and has to pee, ATC is rushing him because of that Air Force jet behind him. He gets to half scale on the localizer, maybe a little low on the glide slope....accumulative errors might just ruin his day.
 
Great question,
I would be in favor with Johnny, but like wise, There is probably another regulation that spits out the requirement.
Like you
It is not spelled out in Part 91 about flying IFR Using GPS as your only method of navigating utilizing GPS approaches but I understand that even if you had IRU's for navigation you still have to have a VOR in order to fly IFR
Smilin' Jack
 
It is possible to wire and configure a 430W such that you do not have VOR (and therefore cannot execute any check) but still have LOC and GS.

My system is that way today. No VOR. Honestly had not thought about the VOR check.
 
No, you do not need it to for ILS.. LOC/ILS is not same as VOR.. even in old analog days, it uses slightly different circuitry. Remember how on ILS, you didn't need to set course.. needle centers anyways.. obviously not the case with VOR navigation...


PS. Bill, what do you mean you don't have VOR? How did you manage to configure your system not have it? :) aside, as good as it is, GPS can fail or signal can be lost.. intentionally eliminating a means of navigation doesn't sound productive..
 
My first thought was "Duh" of course you do. Then like Radomir I remembered the GS is different and the LOC is different than a VOR. I don't know that a pilot can check a ILS for calibration other than flying it and verifing visually.
Or the always identifing the morse code which I do on every ILS approach.
 
No check needed for localizer or glide slope. The method of de-coding is completely different than VOR signals.
The reason for the rule is that earlier OBS decoding circuits used RC phase shifting circuits which could drift as the components aged. Newer radios like the SL30 use digital phase locked loops which do not have this problem. If you read the SL30 manual, it says, in so many words, "yea, you still need the 30 day check even though there is no way this radio will ever lose accuracy".

With a G430 if you only wire the 430 analog out signals to a CDI you will see localizer and GS information, but no VOR data unless you also have and connect OBS data.

No, a VOR is not required for IFR. You must have "suitable" equipment. What that means is sort of stated, in a maze of words, in CFR 14 Part 1 but only for RNAV (including GPS). There used to be a few routes in Alaska that could be flown ifr with nothing but an ADF!
 
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Hey Radomir,
Bob T describes it right. One can use the analog outputs (there are about a dozen wires) from the 430 to drive an indicator (in my case the GRT EFIS) for LOC and GS. It works fine.

If I want VOR functionality, I need to supply OBS dial data from the GRT to the 430. That requires a separate ARINC module for my older GRT screens. Since I was pinched for cash at that point of the build, I decided to skip it. I am considering putting it in......if I get one of them there round tuits...:)

The comment about 2nd nav source is certainly valid. I have not completely attained the designed configuration of my panel. It included an SL30, not the SL40 I have installed. That gives separate nav source in a completely different box. I don't like all my eggs in the 430 basket either, even if the VOR was hooked up.
 
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I had to look up "analog" in the dictionary :) Thanks for clarifying the setup.. The ARINC module is really worth it, not just for this but works great when driving a capable autopilot too..
 
MarkW said:
I don't know that a pilot can check a ILS for calibration other than flying it and verifing visually.
Or the always identifing the morse code which I do on every ILS approach.
Click to expand...

My VOR/GS/LOC ramp test set can test calibration of the ILS and VOR, and yes centering and deflection can drift out of calibration for ILS signals.
 
Thanks for the responses guys, much appreciated. Makes sense that the ILS circuitry is different from the VOR, did not know that. Since VOR frequencies and ILS frequencies are pretty darn close together, I figured it was all one Nav receiver that needed to be calibrated. Good stuff to know.
 
My M.O.S.

Noah, avionics theory and repair was my MOS at Ft. Gordon, Ga. in the '60's.

The VOR system uses two 30 hertz signals that shift phase by one degree for each degree around the VOR antenna and your receiver compares this phase relationship to determine your VOR radials, essentially.

By contrast, the ILS signal consists of a 90 hertz and 150 hertz, a.m. signal, side by side, transmitted by highly directional antennae, near the approach threshold of the runway you're approaching. The amplitude of each signal is compared and gives you your lateral guidance.

For the glideslope portion, it also uses the 90/150 hertz signals, but one on top of the other, but the carrier frequency is around 300 megahertz, while the LOC signal is in the 100 Mhz range, so the two don't interfere with each other....and it's angled up around 3 deg, sometimes more, for obstacle clearance....two completely different internal circuits in the receiver for processing. The signal arrangement drawing is usually found in the Airman's Information manual, for the details.

The glideslope receiver used to be a separate, remote unit and the LOC and GS signals are always paired and when you select an ILS frequency in the 108.5 (odd) frequency range, your GS receiver is also automatically tuned to the proper, matching frequency. VOR signals are even decimal freq's, e.g. 108.4, .6 and so on...while the ILS/LOC freq's are odd decimals.

Best,
 
Pierre, you do your instructors a solid by pulling that info out of your skull, what, ten years down the line? :)

Thanks for that, it was a topic of discussion on a recent flight with a retired physics professor (more difficult to intellectually satisfy than a typical passenger), and that fills the gaps in my knowledge nicely.
 
Awesome thread. I really love stuff like this. Three thoughts immediately come to mind:

  1. It seems most ILS approaches I've seen also make use of a VOR -- such as a cross-radial to identify a fix on the approach, or to fly the missed approach procedure. So you're really limiting yourself if you have a VOR receiver and don't keep up with the 30-day check.
  2. Despite the fact that localizer reception works differently than VOR reception, I wouldn't put it past the FAA bureaucrats or a judge nailing a pilot anyway for violating the letter of the regulation. 14 CFR 91.171 applies to "the VOR system of radio navigation." A "system" is "a set of connected parts forming a complex whole." One could argue that the VOR receiver (even the one built-in to the panel-mounted GPS) is a part of "the VOR system." It's a stretch when you're just using it to track a localizer, and I'd really hope one wouldn't get nailed given how the localizer works. Has anyone seen an FAA Letter of Interpretation on this question? (Don't ask them for one if not!) I just called AOPA's Pilot Info. Center to see if they know of one, but the hold times are long right now, and I've got an airplane to build. :)
  3. A 30-day check is so easy -- you can even do it while settled in cruise flight with nothing else to do and it costs nothing but a minute of your time. Just do it (and log it) and don't worry about it! (Do it before 30 days is up or while using something other than VOR for your primary navigation of course.)
 
M.O.S. = "Military Occupational Specialty" in case anybody was wondering.

This forum needs a "Like" button!
 
Small correction: The localizer antenna is at the departure end, not the approach end, of the runway.

More info than you really wanted to know: The reference 30 Hz signal is FM modulated onto a sub-carrier just below 10 KHz. The variable 30 Hz signal comes from (electronically, these days) rotating a directional antenna 30 times a second, to AM modulate the signal you receive. The antenna points to magnetic north at the same time the FM subcarrier is at a modulation peak. This is so different than the "compare which audio signal is stronger" method used to decode the localizer and GS that I cannot imagine any FAA guy trying to make a case against using the ILS without a VOR check. They are completely different sections within the receiver. And the only way to check the localizer section is airborne, or at a shop.

Usefulness of VOR?: I think a lot of people who are not keeping up with the 30 day requirement are using approved GPS to find all those cross fixes, feeder routes, missed approach procedures, etc., so they don't miss it on an ILS. I cannot recall the last time I used a VOR outside of practice.

Keeping 30 day current: For pilots like myself who only have 1 VOR it's not quite so easy. I don't have access to a VOT nor a ground check point. So I'm left with an airborne check with an identified landmark, which is a bit of a hassle. What I really do is use the GPS to do a cross check when I'm not busy but strictly speaking (and there is a reason for this) this is not one of the approved methods.
 
catmandu said:
Pierre, you do your instructors a solid by pulling that info out of your skull, what, ten years down the line? :)

.
Click to expand...

...try 44 years ago...from around 1969 when I finished my 3 years, and by the grace of God and absent my American citizenship, missed Viet Nam, while I taught a bunch of youngsters all this, and how to fix it. We had vacuum-tube systems then but by 1968, we started seeing Collins' transistorized systems.....back when the earth was cooling:D Over the years, since leaving the Army, I did quite a bit of instruction toward PPL and some basic instrument flying. The repeated telling of VOR's systems and the ILS musta burned it in deep.

Best,
 
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Hey Bob and Pierre,

I you only had GPS... like I do with Dual Dynon Skyview's and Dual independent GPS WAAS antenna's and you do a RAIM Check of the GPS Via fltplan.com before you leave on a trip and the RAIM check is valid for your time peroid. Are you allowed to fly that IFR trip with Non Certified GPS even though they are WAAS Capable and you have all the fixes in the database which you can not change. Using the provision below under Second comment

I know you can fly IFR with only a single VOR and if that quits your in the same situation if the GPS Satellite system quits. Then we talk to the controllers and let them practice ASR approaches :)

Second. Under Experimental Aircraft there use to be a clause that if you proved the flight situation and verified and documented the proceedure you could fly under that authority without actually having an IFR certified aircraft. I believe this was called self certification.

This is not a test... I am really questioning why I need a VOR or ILS When every airport in the country now has GPS. I can not find a regulation in part 91 that states I need a VOR just the comment that I need the radio equipment for the route to be flown.

Smilin' Jack
 
Short answer: no, not allowed to operate ifr using a non- TSO'd gps as primary navigation.
Long answer:
1. FARs limit E-AB to day vfr unless approved by the administrator.
2. Nearly everyone's operating limitations have that approval but require you to follow the 91.205 equipment rules.
3. 91.205 says you must have "suitable" navigation equipment. What does that mean? Well, the FARs are silent about vors, dme's etc., so it seems you can do what you like there. BUT CFR 14 part 1 actually defines "suitable RNAV" (which includes gps) by saying it has to meet the FAA's non-regulatory guidance!
4. FAA guidance (a/c, tso, aim) is pretty clear. GPS used for ifr must meet TSO 145 or 146 to be used as a sole source nav. If it meets TSO 129 (non WAAS) then it is approved only as supplemental, meaning you need to also have and be able to use a vor.
 
Ground based NAV required

Not only that but you must be able to switch to ground based NAV enroute in case of gps failure, and although you can shoot a GPS aproach at your required alternate, that alternate must also have a ground based IAP available and you must have suitable equipment on board to use it.
Good thread!
Tim
Dues paid
 
Actually the above is true only for TSO129 equipment. For the waas, TSO 145/146 boxes, they are approved as sole source navigation and nothing else is needed. There are a number of planes flying ifr with nothing but a 145/146 gps. Whether or not you like having all your eggs in one basket is another question.
BTW, such an aircraft cannot currently be used for an ifr flight test or IPC (although I have a work-around).
 
AIM 1-1-19

(b) Aircraft using GPS (TSO*C129 (as revised) or TSO*C196 (as revised)) navigation equipment under IFR must be equipped with an approved and operational alternate means of navigation appropriate to the flight. Active monitoring of alternative navigation equipment is not required if the GPS receiver uses RAIM for integrity monitoring. Active monitoring of an alternate means of navigation is required when the RAIM capability of the GPS equipment is lost.

I been studying for the written and have been seeing this question. So I looked it up. I must be missing something but the question is:
During IFR en route and terminal operations using an approved GPS system for navigation, ground based navigational facilities...answer...must be operational along entire route.

So the 145/146 boxes are exempt from the above?

Ok, I see it further down in 1-1-19. So now, on the written do I go with the ASA answer or the correct answer!

Thanks, trying to learn something here!
Tim
 
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Smilin' Jack said:
\I you only had GPS... like I do with Dual Dynon Skyview's and Dual independent GPS WAAS antenna's\
Click to expand...

I'm not sure the Skyview antennae are WAAS antennae...

But as I understand, and I could be wrong, to file /G, you need a TSO'd GPS device. The certification covers much more than just the electronics...it involves the database, the hardware, the software, operations, and much more.
 
The Dynon is WAAS not certified but like most of the GPS systems out there and the pilots very few do the RAIM requirement. I think the future will see a great reductions in VOR and perhaps a laxing of the GPS rules for non LPV or non LNAV approach
In reality were safer with any GPS than we ever were with a sole VOR.
Smilin
 
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