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Was wondering whether someone could help me understand how to perform a visual approach (not using the VOR) specifically if I look at RWY 35L at LFLL. Airport elevation is 821 ft.

It's a 3° GS approach if you look at charts for the LSE VOR. Therefore I was thinking why would the 3x rule not work for visual approach landing?

I mean charts say that I should be at 2740 ft at 8 DME, 2420 ft at 7 DME, 2100 ft at 6 DME, 1790 ft at 5 DME, 1470 ft at 5 DME.

These do not seem to align to ×3 rule which we could use to see if we're on profile when we start our descent.

If I use this rule I should be at 1800 ft at 6 DME, 1500ft at 5 DME and 1200 ft at 4DME correct? What am I missing here?

Flying at S spoed so rate of descent should equate to roughly a 3° descent if I use a vertical speed of GSx5.

What is the technique then for a visual approach if we can't use that x3 rule?

The VOR seems not be be offset and is situated near TDZE it seems so was wondering why we can't use x3 rule?

enter image description here

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  • $\begingroup$ Your difference at 5 dme is just 30 feet! $\endgroup$ Sep 3, 2023 at 0:04
  • $\begingroup$ I've added what I believe is the approach plate referenced in your question. If this is incorrect, please feel free to delete the image of the VOR Rwy 35L approach. It's possible that more people will review your question with the addition of the approach plate you have referenced. $\endgroup$
    – user22445
    Sep 3, 2023 at 3:48
  • $\begingroup$ The runway end is 2.1 DME from the VOR. Are you taking that into your equation? $\endgroup$
    – Timbo
    Sep 3, 2023 at 5:10
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    $\begingroup$ I do not intend to answer, but your question may be similar in some ways to the question I asked: aviation.stackexchange.com/q/97583/65367 $\endgroup$
    – pilot162
    Sep 3, 2023 at 6:00
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    $\begingroup$ Why do you care about the vertical profile of the VOR approach if you intend to fly a visual approach? $\endgroup$ Sep 3, 2023 at 7:19

2 Answers 2

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What is the technique then for a visual approach if we can't use that x3 rule?

To be blunt, look out the window.

Nothing says you can't use the x3 rule, and nothing says you can't occasionally reference the stepdown altitudes in a published instrument approach procedure. (they aren't that different - 30' at 5 miles is insignificant...) Neither is a bad idea, but there is no requirement to hit any altitudes so you shouldn't fixate on either one.

ICAO:

An approach by an IFR flight when either part or all of an instrument approach procedure is not completed and the approach is executed in visual reference to terrain.

FAA:

A visual approach is an ATC authorization for an aircraft on an IFR flight plan to proceed visually and clear of clouds to the airport of intended landing. A visual approach is not a standard instrument approach procedure and has no missed approach segment.

While you remain on an IFR clearance, you should fly the approach as if you were VFR.

So again, look out the window - and make sure your approach path is clear of terrain, clouds, and the descent angle is appropriate.

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  • $\begingroup$ Agree with the sentiment, but for the sake of completeness the FAA definition of a visual approach probably doesn't carry a lot of weight in Lyon, France. The FAA's definition is similar to ICAO's definition — An approach by an IFR flight when either part or all of an instrument approach procedure is not completed and the approach is executed in visual reference to terrain — and the crux of the matter, "visual reference," is found in both definitions. $\endgroup$
    – randomhead
    Sep 3, 2023 at 20:55
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    $\begingroup$ @randomhead, good point. To be honest I didn't look at the approach plate for location. The definitions are similar enough, but I added the ICAO in the interest of being thorough and complete. Thanks. $\endgroup$ Sep 3, 2023 at 23:01
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You can use the X3 rule (very close to it). Your calculation appears to be incorrect.

My answer assumes that you are interested in why, when making a visual approach and descent while following the X3 "rule-of-thumb" descent (3 nm of travel for every 1000 feet of descent) the altitudes beginning from 8 DME (LSE VOR) to the runway threshold do not correspond to your calculations:

If I use this rule I should be at 1800 ft at 6 DME, 1500ft at 5 DME and 1200 ft at 4DME correct? What am I missing here?).

Additionally, you are using the profile descent information (highlighted in yellow on the approach plate in your question) from the Lyon, France VOR Rwy 35L approach.

If you use the "Continuous Descent Final Approach" (CDFA) glide path shown on the approach plate it equates to a 3 degree descent angle, which is about 320 ft/nm (similar to the 3X rule-of-thumb).


If you begin at the published threshold crossing height (TCH) of 59 ft. and add that to the runway 35L threshold elevation of 814 ft. (noted from the ILS Rwy 35L approach plate and not using the "airport elevation" of 821 ft. published on the VOR approach) you get an MSL TCH of 873 ft. Then, if you work backwards starting at the threshold (2.1 DME), with a 3 degree glide slope, the result is very similar to what is published and highlighted in yellow on the profile view of the VOR approach plate from your question. Perhaps, as @Timbo suggested in a comment below your question, you did not consider that the runway end is 2.1 DME from the VOR.

Anyway, my calculations, assuming I correctly understand specifically what your question is asking are shown/illustrated below.

(Ref: the VOR rwy 35L profile view LSE DME distance/altitude chart referenced in your question):

enter image description here



enter image description here

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  • $\begingroup$ Yes you understood my question. What I wantzd to know if how would you fly that visual approach if you had clearance to do that. My thought was to use the 3x rule to be abke to get to touchdown safely but you are also right, I didn't see that VOR was 2.1 NM further away. Sorry I'm not a pilot. Can you detail your calculation? I'm assuming if I'm visual, I'd use the touchpoint as reference and start my 3° descent to ensure I'm on ground at touchzone, therefore would ignore VOR distance of 2.1 NM? $\endgroup$
    – R O
    Sep 4, 2023 at 9:20
  • $\begingroup$ My thinking would be that if I'm visual, at 6.7 NM from TDZE ( corresponds to 8.8 DME VOR), I'd need to be at 2010 ft if I use x3 rule, plus TCH 59ft + Airport elevation 821 ft which would be 2890 ft, this is where I' d descend a 3° path, is.'t that correct? $\endgroup$
    – R O
    Sep 4, 2023 at 12:31
  • $\begingroup$ Sorry I understand your calculation but what I'm struggling to understand is this. From chart, FAF is 8.8 NM from TDZE which is at 2.1 NM. This means that distance between FAF and TDZE is (8.8-2.1)= 6.7 NM. Then if I use x3 rule, I should be at (6.7x3)= 2010 ft + 873 ft= 2883 ft is that correct? Then since it's a CDFA, I can say that at 5NM tp TDZE, I need to be at (2883/6.7)×5=2151 ft. What would be wrong here? Again, this situation is in case I get authorized for a visual approach, no FCOM procedure, instrument failure...wouldn'tthat be the quickest way to know whether I'm on a 3°descent? $\endgroup$
    – R O
    Sep 5, 2023 at 8:54
  • $\begingroup$ @RO X3 rule is 3 nm of travel for every 1000 ft. of descent (or 330 ft of descent for every nm traveled). A 3 degree GS is about 320 ft. descent for every nm traveled. So, I used almost the X3 rule, but instead of using 330 ft of descent for every nm traveled, I used 320 ft. of descent. There are 6.7 nm from 8.8 dme to 2.1 dme (total of 6.7 nm traveled descending on a 3 degree GS). 6.7 nm X 320 ft/nm = 2144 ft total descent. Each 1000 ft of descent = 3.2 nm traveled. To be continued in the comment below: $\endgroup$
    – user22445
    Sep 5, 2023 at 15:40
  • $\begingroup$ @RO So, 2144 ft to descend over 6.7 nm = 320 ft/nm. Start at 873 ft and add 288 ft (.9 X 320) this equals 1161 ft at 3nm, add 320 ft to 1161 which equals 1481 ft., and so on up to 8 nm (reference the LSE DME/ALTITUDE chart highlighted in yellow in my answer from the approach chart). Those altitudes are very close to the X3 rule (330 ft/nm) but I used a 3 degree GS (about 320 ft/nm, which is very close to what the chart - highlighted in yellow - shows). I think you are misapplying the X3 rule-of-thumb. $\endgroup$
    – user22445
    Sep 5, 2023 at 15:46

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