Longest Straight In Approach from IAF

NealRomeoGolf

NealRomeoGolf

Final Approach
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As I am studying for my instrument rating I have been studying the approaches to my home airport. On the RNAV (GPS) approach it puts you on a 14.1 nm straight in final. That seems really long. Anyone seen longer straight ins from an IAF?
 
Missoula has an ILS with a FAF that’s ~16nm from the runway, IIRC. Lots of terrain out there!
 
Its RNAV/GPS who cares if it is 5 miles or 50, you aren't timing it anyway.
 
Clip4 said:
If your VOR received accuracy is >2.3 degrees and Vis is 1 mile you may fly by this airport.
You have decreasing accuracy as you fly from the VOR.
https://aeronav.faa.gov/d-tpp/1904/06189VA.PDF
https://aeronav.faa.gov/d-tpp/1904/05763V27.PDF
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25.8 on the VOR-A. That’s the record so far for straight in from IAF. I’m getting 2.3 puts you .989 off to the side. A lot of VOR stuff is based on +/- 4.5 degrees error. I don’t know for sure on this final approach course. @aterpster ???
 
luvflyin said:
25.8 on the VOR-A. That’s the record so far for straight in from IAF. I’m getting 2.3 puts you .989 off to the side. A lot of VOR stuff is based on +/- 4.5 degrees error. I don’t know for sure on this final approach course. @aterpster ???
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Both of those finals are less than 5 miles in length. As far as the distance from the VOR is concerned, the final segment's MAP cannot be more than 30 miles from the VOR. It is sufficiently wide to protect from obstacles, but presents the problem of sighting the airport with max error and minimum visibility. Not nearly as bad as NDB, though.
 
You are right. I was thinking about the OP in pretty general terms. The straight-in segment starts at NRMAH. The approach starts over 40 miles from the airport, which is still an impressive amount of airspace for an ILS.
 
In CLT they'll put you on a 30-40 mile final. Join in LNAV, switch to green needles once closer.
 
My own necro thread. As I was planning for my long IFR cross country I found a VOR approach in my state that is straight in 26.4 nm. I'm glad I have a GPS.

upload_2021-4-24_7-39-17.png
 
NealRomeoGolf said:
My own necro thread. As I was planning for my long IFR cross country I found a VOR approach in my state that is straight in 26.4 nm. I'm glad I have a GPS.

View attachment 95797
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Normal +/- VOR tolerances could put you a couple miles one side or the other at the MAP. Visibility minimum is 1 mile. The MDA, if you have DME, is 80 feet lower than RNAV LNAV. I guess there’s a reason but I can’t see it. Are going to fly it?
 
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luvflyin said:
Normal +/- VOR tolerances could put you a couple miles one side or the other at the MAP. Visibility minimum is 1 mile. The MDA, if you have DME, is 80 feet lower than RNAV LNAV. I guess there’s a reason but I can’t see it. Are going to fly it?
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For the cross country? No. I don't have this airport in my logbook and could do it. Less than an hour away....and then half an hour on the approach. :D
 
That's neat. I wouldn't have guessed DNV lined up with KTIP. Funny they used RBS for the FAF when CMI is so close. Maybe it's too close? Or maybe the hospital blocks it at that altitude.
 
Jim K said:
That's neat. I wouldn't have guessed DNV lined up with KTIP. Funny they used RBS for the FAF when CMI is so close. Maybe it's too close? Or maybe the hospital blocks it at that altitude.
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RBS and CMI are only a half mile difference to TIP and RBS probably has a better angle being a little further east than CMI.
 
This thread illustrates the problem with linking to approach plates without posting the names of the approaches and airports (or alternatively, uploading the PDFs). There are several broken links, and no way to figure out which approaches are being referred to.
 
NealRomeoGolf said:
RBS and CMI are only a half mile difference to TIP and RBS probably has a better angle being a little further east than CMI.
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Yup. Using CMI would have made what's called the 'fix displacement error' a little bigger. Doubt if it would have affected minimums but it's possible.
 
NealRomeoGolf said:
RBS and CMI are only a half mile difference to TIP and RBS probably has a better angle being a little further east than CMI.
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Ahh...I didn't look (obviously).
 
KIAH has a couple of LOC/ILS apr's. Most have multiple IAF's, some out to almost 30 NM.
 
M19 (Newport, AR) VOR RWY 18 has the MAP 29.8 DME from the VOR. Since 30 nm away from the facility is the limit for a VOR approach (without waivers), that's about the longest you'll see. I'd really like to find one further away though.

upload_2021-4-25_9-41-10.png

luvflyin said:
25.8 on the VOR-A. That’s the record so far for straight in from IAF. I’m getting 2.3 puts you .989 off to the side. A lot of VOR stuff is based on +/- 4.5 degrees error. I don’t know for sure on this final approach course. @aterpster ???
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The "half-width" (from centerline to the edge) of the primary area evaluated for obstacle clearance on a VOR final is 0.05D + 1, where D is the distance from the VOR. So for the M19 example, that's 2.49 nm either side of centerline, or 4.98 nm total width. There is an additional "secondary area" outside of that, but the obstacle clearance there gradually tapers to zero. Whether you can see the airport from there or not, or can land from there, is a separate issue, and that's why missed approaches are important to brief!

Palmpilot said:
This thread illustrates the problem with linking to approach plates without posting the names of the approaches and airports (or alternatively, uploading the PDFs). There are several broken links, and no way to figure out which approaches are being referred to.
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I agree. However, it is not technically correct to say there's "no" way, it's just a little complicated. There is a standard naming convention used when the FAA publishes the digital files. For example, one of the procedures linked above is:

https://aeronav.faa.gov/d-tpp/1904/00166IL27L.PDF

From the file name, this means that it is at the airport identified by "Approach and Landing number" 00166 and is the ILS OR LOC RWY 27L (IL27L). The leading zeros are dropped, so we just need to figure out what airport AL-166 is. Each airport has a unique AL number, and it is shown at the top of every approach chart. I do not know if there is a listing of all the AL numbers available on the internet or not. However, a Google search for "AL-166 airport" shows it's O'Hare, ORD. And they do have an ILS OR LOC RWY 27L with a very long straight-in.
 
RussR said:
...From the file name, this means that it is at the airport identified by "Approach and Landing number" 00166 and is the ILS OR LOC RWY 27L (IL27L). The leading zeros are dropped, so we just need to figure out what airport AL-166 is. Each airport has a unique AL number, and it is shown at the top of every approach chart. I do not know if there is a listing of all the AL numbers available on the internet or not. However, a Google search for "AL-166 airport" shows it's O'Hare, ORD. And they do have an ILS OR LOC RWY 27L with a very long straight-in.
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Good info, but I tried that with the links in post #5 and couldn't identify the airport.
 
Palmpilot said:
Good info, but I tried that with the links in post #5 and couldn't identify the airport.
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Found out it works better if you put the "AL-xxxx" in quotes. So I googled for ("AL-5763" airport) and it is 1G5. AL-6189 is I22.

But I would classify this way of lookup as more of a "hack", and not to replace good posting etiquette of including the airport ID and procedure name.
 
RussR said:
Found out it works better if you put the "AL-xxxx" in quotes. So I googled for ("AL-5763" airport) and it is 1G5. AL-6189 is I22.

But I would classify this way of lookup as more of a "hack", and not to replace good posting etiquette of including the airport ID and procedure name.
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OK, that works. It would still save time if people would at least post the name or ID of the airport along with the link.
 
RussR said:
M19 (Newport, AR) VOR RWY 18 has the MAP 29.8 DME from the VOR. Since 30 nm away from the facility is the limit for a VOR approach (without waivers), that's about the longest you'll see. I'd really like to find one further away though.
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Has a waiver ever been provided to have the beginning or end of a VOR final approach segment more than 30 miles from the facility? If so, what was the equivalent level of safety? Offhand, I can't think of any because the 30 mile limit hits the FTE limits for along track error; at least that is my recollection of the geometry.

EDIT: 4.5 degrees along track error at 30 miles is 2.36 n.m. Close to the FAS primary areas. I can't think of an equivalent level of safety. It is already an issue to see the runway/airport if visibility is near minimums, much less lateral obstacle clearance.

Only NDB is worse. 4.5 and 6.7 degrees came from a 1964 FAA study of VOR system errors using radar tracking at OKC. I'm not convinced their sample was random. ICAO adopted somewhat more conservative VOR system errors for PANS-OPs. (There shouldn't be a difference.)
 
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aterpster said:
Has a waiver ever been provided to have the beginning or end of a VOR final approach segment more than 30 miles from the facility? If so, what was the equivalent level of safety?
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Not sure. No idea what the rationale would be, nor the equivalent level of safety provided. But I'd be interested to see one and research it.
 
aterpster said:
Has a waiver ever been provided to have the beginning or end of a VOR final approach segment more than 30 miles from the facility? If so, what was the equivalent level of safety? Offhand, I can't think of any because the 30 mile limit hits the FTE limits for along track error; at least that is my recollection of the geometry.

EDIT: 4.5 degrees along track error at 30 miles is 2.36 n.m. Close to the FAS primary areas. I can't think of an equivalent level of safety. It is already an issue to see the runway/airport if visibility is near minimums, much less lateral obstacle clearance.

Only NDB is worse. 4.5 and 6.7 degrees came from a 1964 FAA study of VOR system errors using radar tracking at OKC. I'm not convinced their sample was random. ICAO adopted somewhat more conservative VOR system errors for PANS-OPs. (There shouldn't be a difference.)
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FTE??
 
RussR said:
Not sure. No idea what the rationale would be, nor the equivalent level of safety provided. But I'd be interested to see one and research it.
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I suspect there isn't one out there.
 
luvflyin said:
FTE??
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TERPS:

8260.3E:

2-9-6. Intersection Fix Displacement Factors. The intersection fix displacement area is determined by the system use accuracy of the navigation fixing systems. The system use accuracy in VOR and TACAN type systems is determined by the combination of ground station error, airborne receiving system error, and flight technical error (FTE). En route VOR data have shown that VOR system use accuracy along radial courses of ± 4.5 degrees, 95 percent of occasions, is a realistic, conservative figure.

FTE is FAAese for pilot error.
 
The Salinas ILS (KSNS) literally doubles my flight time if I have to fly it. Intercept the glideslope at 5000' and take it to about sea level. IAF starts with a 22 mile ARC off the airport based VOR. Bunch of hills around there
 
TheGolfPilot said:
The Salinas ILS (KSNS) literally doubles my flight time if I have to fly it. Intercept the glideslope at 5000' and take it to about sea level
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That one is a x-country, especially if you start and SNS and go outbound for the procedure turn. And, the DME arc IAF is dangling because the airway is was on was deleted by the MON Program.
 
aterpster said:
That one is a x-country, especially if you start and SNS and go outbound for the procedure turn. And, the DME arc IAF is dangling because the airway is was on was deleted by the MON Program.
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I'm usually rolling it there from V111 and when I get there and I see the layer hasn't cleared yet my stomach drops. Not because I'm probably going to be doing an approach to near minima, but because our schedule is getting pushed back another 30 minutes. Our normal guest pickup lives in King City and usually if I even sniff fog I just send her to Paso Robles now.
 
Rex Kramer said:
First airport I thought of.

SEAVU to the end of the runway is about 47NM.
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But, that isn't the final segment. The ILS final segments at the lightening bolt (FAA charts), profile feather (Jepp).
 
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