KSNA LOC BC RWY 01L

[iomagico]

I was working on back course approaches (full procedure) and thinking on the best way to solve one rude intercept.
If you take off from KSNA 01L direct to SLI VOR should approach SLI with a HDG around 280° inbound SLI and after have to fly the SLI 133R outbound to proceed to LOC BC RWY 01L full procedure approach.
The question is: is it convenient/legal to cross SLI and then right turn to intercept 133R outbound as I did ?
If it is not, what's the best way to manage that?
Thanks in advance

Angelo

[Mark Hargrove]

Angelo,

Since no one who actually knows what they're doing has replied, I'll go ahead and take a stab at this

First and foremost, I'm not sure what context you're operating in when you ask if the course reversal you're executing at SLI is "legal" -- but I think the answer is "no, it's not".

• If you're there after a missed approach, you're in the holding pattern and waiting for radar vectors to proceed with whatever you're going to do next.
• If you're there as the terminal fix from your 'enroute' routing, then you're almost certainly arriving there from the north or east -- if you were arriving from the south you'd have been vectored to MINOE. Even if it's the terminal enroute fix from a northern or eastern origin, you're going to have to be vectored to MINOE after SLI(see the next bullet).
• If you're there because your departure clearance took you there, then I don't know what the heck is going on, because SLI is neither an IAF for the LOC BC Rwy 01L approach, nor is it the start of a feeder route to the IAF. MINOE is the one and only IAF that I can find on the plate, and there are no feeder routes.

What's particularly interesting to me about the overall approach is that I cannot actually see any way (other than vectors from ATC) to get to the IAF! None of the depicted radials from SLI, LAX, or ELB are flyable, yet the "full approach" starts at MINOE.

I hope somebody jumps in here with an explanation!

-M.

[Keith Smith]

Angelo,

There are many cases were flying approaches offline can cause more harm than good. This may well be one of them

As always, there are two flavors of an approach, you can be vectored to final, or you might fly the full approach from an IAF (or less commonly, from a feeder route).

Mark has nailed just about all of it, in my opinion.

Angelo, you said:

If you take off from KSNA 01L direct to SLI VOR should approach SLI with a HDG around 280° inbound SLI and after have to fly the SLI 133R outbound to proceed to LOC BC RWY 01L full procedure approach.

There's no reason you should be heading to SLI after taking off from 1L, no should you really be taking off from rwy 1L at SNA If you WERE, for some reason, heading to SLI, or were at SLI (as Mark eludes to above), then there is NO way to fly the approach from SLI....period. By that, I mean, you will not receive an approach clearance where the last fix on your cleared route is SLI.

Now, if you happen to be around SLI, then a few things can happen regarding your approach clearance:
1) FULL APPROACH: if you're RNAV equipped, "cleared direct MINOE, cross MINOE at 3000, cleared LOC BC RWY 1L approach," or
2) FULL APPROACH: if you're not RNAV equipped, "fly hdg xxx, intercept the LAX 123 radial to MINOE, cross MINOE at 3000, cleared LOC BC RWY 1L approach"
3) FULL APPROACH: if you're not RNAV equipped, "fly hdg xxx, intercept the localizer backcourse outbound to MINOE, cross MINOE at 3000, cleared LOC BC RWY 1L approach"
4) VECTORS TO FINAL: "fly hdg xxx, vectors LOC BC RWY 1L final approach course..." (this will be followed by a series of vectors).

You will not, however, fly the approach by yourself from SLI because SLI is not an IAF or feeder for the approach.

[iomagico]

Thanks Mark and thanks Keith for your explanations, I really appreciated and learning a lot, as usual.

But my post wasn't about the specific KSNA LOC BC procedure.
I would like to focus on how manage rude intercepts.
So I try to put the question in a different way.

Sometimes (flying IFR on pilotedge and offline too) we have to manage rude intercepts (angles < 90 degrees or around 90 degrees between inbound and outbound radials) for example around a VOR.
So I think we have 3 different scenarios:
1 - start turning a couple of miles before the VOR;
2 - crossing the VOR and then turning with a greater angle to join the course;
3 - crossing the VOR and after a couple of miles turning 360 degrees or more to cross again the VOR on the correct course.

Maybe the rule is that we have ALWAYS cross the fix and the option 1 is not correct.

About LOC BC RWY 1L now it's clear how to correctly fly the full procedure (thanks again Mark and Keith).

Sorry again for my previous post in which it was't clear what I was asking for.

[Peter Grey]

This is from a post I made a while ago answering a similar question, but if you are math inclined the intercept can be done mathematically. Out of the 3 choices you make generally number 1 is the correct answer (see AIM figure 5-3-1). Number 2 can be the correct answer if and only if (iff anyone?) the procedure states you must fly over the point.

To determine how far before the VOR to do the turn, you can use these rules of thumb:

For a 90 degree turn, lead your turn by .5% of your ground speed. For example if your ground speed is 100 knots, you should lead a 90 degree turn by .5 NM, note this is the DME where you should be established in the turn, not starting it, start it a tenth or 2 early. If you do not have ground speed you can estimate it (as long as its within 20 knots it won't affect the formula too much).

For a 60 degree turn, lead your turn by 90% of the value for a 90 degree turn (unless your going fast this isn't worth the extra calculation, just use the 90 degree number)

For a 45 degree turn, lead your turn by 70% of the value for a 90 degree turn.

For a 30 degree turn, lead your turn by 50% of the value for a 90 degree turn.

For turns beyond 90 degrees you can do the lead as 2 separate leads added together (1 for 90 and 1 for the remainder). Note the further away you get from 90 degrees the less this works.

[iomagico]

Thanks Peter for your precious info.
Never thought that AIM can even helps with this kind of question: definitely it's a terrific resource.

I like the math method too, it's really useful, specially with GA planes.
At higher altitudes we have to take care of vertical distance from plane and transmit station and higher aicrafts speed.
Will try to apply this equation to the next fly.