Instrument approach peculiarities

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I've been working towards my instrument rating, and have been doing a lot of flight-sim practice at home flying approaches and such. I came across this one, and was wondering if anyone could explain something unusual about it.

The approach is the NDB 1 approach at Orange Municipal (ORE). Here's the most current link to the plate that I could find, apologies if the link dies.

Notice the "BESAC FIX MINIMUMS". BESAC fix appears to be the intersection of the NDB final approach bearing and the Gardner 272 radial. However, the minimums state that, for BESAC minimums, "DUAL VOR RECEIVERS REQUIRED." I cannot find anything in the approach that would require dual VOR receivers. BESAC is identified using the Gardner VOR, as is the missed approach and the IAF.

Can anybody explain why one would need dual VOR receivers in order to identify BESAC?

-- Joshua Levinson, August 25, 2012


I've emailed the contact folks in the back of the chart book to ask questions like this and they typically respond "Yes, that's a mistake and we will fix it."

I can't see why a second VOR receiver would be required. Arguably you could have one turned to the 257 radial for the final approach fix and then the second one set up for 272 so identify the intermediate fix. Maybe there is a doctrine that the FAA does not want you fiddling with the CDI once inside the final approach fix?

-- Philip Greenspun, August 27, 2012

Sounds good. I emailed them about this one as well, and got a similar response. On the one hand, I'm glad they're quick about reviewing and correcting it, on the other, I hope they're better about double checking obstruction clearance than they are navigation equipment requirements...

-- Joshua Levinson, August 29, 2012

I looked at this approach and I believe that the the missed approach point is determined by time here, not by a radial from the VOR. Radial 292 from GDM points to the NDB, not the missed approach point, and is a feeder route (from GDM to the NDB then to KELPE, which is the IAF).

It is clearer on the Jeppesen version of the chart, where you can clearly see the difference between the missed approach point and the NDB in the profile view. Jeppesen also gives the times for various approach speeds from KELPE to the MAP.

So, I think Phil is right that the FAA doesn't want you to change the setting on the VOR during the final approach, so one VOR is supposed to be set to R-257 (for KELPE) and one to R-272 (for BESAC). Both VORs are tuned to the GDM. That is why two VORs are required. Also, this argument makes sense only if the VOR is not also required to locate the MAP (otherwise, they would have to say 3 VORs required!).

I also wanted to say that the types of questions you are thinking about is an excellent way to learn for your instrument rating. I did the same tyype of thing. The better instructors enjoy discussing these points even if they get a bit academic.

The only thing I would caution is where you said you hope the FAA did a better job checking these approaches than drawing them or something like that. The FAA carefully flight checks each approach on a scheduled basis, and, in my experience, the approaches are carefully designed to suit a wide variety of aircraft. I know you were joking, but accidents in IFR flying are almost always due to pilot mistakes, not mistakes by the FAA. One of the major lessons I have learned from flying is humility, and I encourage a tone of respect for FAA and ATC. They have helped me out more than once. Again, I know you were joking, and I am just passing on my opinion.


-- Todd Ramming, September 5, 2012


I don't think the problem can be fiddling with a CDI inside of a FAF. Lots of approaches have stepdown fixes after the FAF that are tuned to the same VOR whose crossing- adial that is used to define the FAF. The Hanscom LOC 29 approach does the same for LICPI.

To confirm, I emailed the FAA and they confirmed that the requirement was a mistake, and that they're removing it. A single VOR receiver is all that is required.

-- Joshua Levinson, September 5, 2012

Hi Joshua,

I will take a look at the approach you mentioned. I was not able to find any statement in the FAA publications about changing the VOR radial at or past the FAF. I was just pointing out that the MAP is not determiend by the VOR radial, but by time. You can let me know if you agree.

Also, I enjoy reading and discussing these types of a points because it keeps us all sharper.

Finally, I hope my comment about the FAA came across in the spirit I meant it. I wasn't trying to be critical. I think your questions and replies are thoughful and helpful.


-- Todd Ramming, September 5, 2012


I do indeed disagree. There is no timing table listed on the NACO plate, since the MAP is the NDB. It doesn't look like there should be any reason to time this approach at all.

The two radials from GDM are used to identify the FAF and the stepdown fix only. Crossing the FAF radial, you'd spin the CDI to the stepdown radial, and descend to the stepdown altitude. Crossing the stepdown radial, you'd descend to the MDA. Crossing the NDB, you'd initiate the missed approach.

I realize your point about the FAA, but I also should be clear that I was only half-joking. I know the FAA and ATC are there to help, but they are not perfect. "Trust but verify" and all that. This particular incident comes to mind. I know it's a rare case that involved a number of combining factors, but just like a pilot error, any one link in the chain, including pilot verification, would have prevented what was very lucky not to be a fatal accident.


-- Joshua Levinson, September 5, 2012