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IAPs with IAF not a facility

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IAPs with IAF not a facility

Old 3rd Jul 2007, 19:57
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IAPs with IAF not a facility

I have come across a number of instrument approach procedures where the IAF is not a beacon but a specified radial/DME from a VOR or even an NDB. For those of you with RNAV, FMS etc this isn't a problem, but for the basic requirements of flying it using just the raw data from the facilities, how would it be possible unless you were flying along the outbound radial from the beacon?
NS
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Old 3rd Jul 2007, 20:31
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If there's a procedure path to get the IF/IAF, follow it...

If there's a holding pattern on it... do the entry required coming off from the outbound.

If there aren't any of the above, (and no terrain concerns), go outbound and then do a "reversal"... teardrop, 45deg procedure turn or the 80/260... do this at a certain point after you pass the fix...

Get someone licensed to tell you since I don't have one!
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Old 3rd Jul 2007, 21:56
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How about some examples?

The IAF/IF's may be part of the enroute structure or an arrival.
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Old 3rd Jul 2007, 22:39
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DME arcs have an infinite number of IAFs ..... I guess
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Old 3rd Jul 2007, 23:40
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If the IAF is on a radial, do a point to point navex to join the radial outside the IAF distance (so you cross it at less than 30, of course).

If the IAF is on an arc (and no, reynolds1, there aren't inifinite IAFs on an arc), join the defining radial outside the arc short of the IAF, then join the arc and fly around it to fly thru the IAF.

If you are not comfortable with the above, track straight to the fix and do a sector entry, which of course will require some type of point to point nav if the holding pattern is not overhead an aid!
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Old 4th Jul 2007, 02:44
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for the basic requirements of flying it using just the raw data from the facilities, how would it be possible unless you were flying along the outbound radial from the beacon?
Commonly known as "point to point" navigation. While it's more easily pictured when you have an RMI or HSI instead of just a CDI, you can sketch it on your note sheet. Reference the NavAid in the center. Plot where you are (radial/DME). Plot where you want to go. Estimate the heading. Refine every few minutes as needed.

It works as well in an A-4 Skyhawk as a C172 Skyhawk!
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Old 4th Jul 2007, 11:22
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Commonly known as "point to point" navigation
Or, in ICAO Doc 8168 terms, "dead reckoning". If we are talking about instrument approaches designed to international standards, then that dead reckoning segment - i.e. the arrival segment, prior to the Initial Approach Fix - must be shown, e.g. as a Direct Arrival procedure. Otherwise, as you say Intruder, you just have to guess!

To see what I'm talking about take a look at the Dinard ADIDI VOR DME 17 procedure at:

http://www.sia.aviation-civile.gouv....D%202.LFRD.pdf

How does one find ADIDI or DIRGO? There is no procedure for how to get to either. Clearly the two IAFs are designed to give traffic from the north a shortened procedure so they don't have to go all the way to the DIN then out again, but if you're supposed to get there by flying a radial off something else, or a DME arc outside of either ADIDI or DIRGO followed by a turn at a lead radial, shouldn't that be shown?
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Old 4th Jul 2007, 12:25
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I must be missing something here, but that looks to me like one of the simplest approaches I could fly?

MSA 2000', IAF 4000' on a radial from the approach VOR. Actually I cannot see why you cannot join the proc neared to Adidi at 3000'. What have I missed?
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Old 4th Jul 2007, 12:36
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Yes, simple if you're already on that radial, but if not, you're using dead reckoning to find the IAF. And yes I agree, the purpose of DIRGO isn't obvious - you could simply join the DIN 178 a bit further out than 8.2d at 3000ft and go directly into the final approach.
NS
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Old 4th Jul 2007, 13:32
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dead reck for ifr??????

well i dont think you can fly DR on a IMC flight.
you fly to the fix (in this case the IAF) in 3 ways direct following the navaid (VOR, NDB whatever), radar vectored or following a STAR.
for example the last post contained a VOR approach, so you fly to the VOR as per filed or with the altitude given by the controller then when you are intercepting the IAF you are in the published portion of the IAP and you can start descending as per proc.
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Old 4th Jul 2007, 13:36
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To see what I'm talking about take a look at the Dinard ADIDI VOR DME 17 procedure
You can't look at that IAF in isolation though. Look at the arrivals. The standard STAR from the north is (JSY) MINQI DIN, but "sur instruction" you follow the 190 radial from JSY to DIRGO, then track 178 (DIN 358 radial) to ADIDI whence you commence the approach. With conventional nav kit, that is the only circumstance in which you should be using ADIDI as the IAF.
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Old 4th Jul 2007, 14:10
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Call me old-fashioned, but above MSA with a VOR radial display and DME? Why on earth do I need a 'prescribed track'?

Like Intruder says - what are the 'yoof' of today being fed on? No wonder they get lost when the coloured writing on the screen goes out.
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Old 4th Jul 2007, 14:12
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Ah yes I see now - my lack of familiarity with the layout of the French AIP, they put SIDs/STARs in a different section from the procedures charts.
NS
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Old 4th Jul 2007, 14:27
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...follow the 190 radial from JSY to DIRGO, then track 178 (DIN 358 radial) to ADIDI whence you commence the approach. With conventional nav kit, that is the only circumstance in which you should be using ADIDI as the IAF.
Yes, but...

In the above case, ADIDI serves as a FAF, not an IAF.

The racetrack reversal at ADIDI may be used for beginning the approach at the DIN VOR.

Overfly ADIDI Northbound, it's an IAF.

Following completion of the racetrack and inbound toward the runway, ADIDI becomes a FAF.

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Old 4th Jul 2007, 14:52
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Why would anyone want to use that when there's a perfectly good standard reversal procedure from overhead the DIN to only 10.2d before turning in to the FAF?
NS
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Old 4th Jul 2007, 14:58
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Good point -- the base turn procedure would be more efficient, but ATC may have a tactical requirment to park you in the racetrack hold at ADIDI.
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Old 4th Jul 2007, 17:07
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In the above case, ADIDI serves as a FAF, not an IAF.
Yes, my mistake. DIRGO is the IAF, ADIDI is the FAF. Doesn't change the point though.
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Old 4th Jul 2007, 19:14
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AFAIK, there is nothing wrong with flying "Direct" to a fix defined as a Radial/DME from a VOR. I was taught that 32 years ago in Navy flight training, and have used it ever since. While RNAV makes it easier, it can be done with reasonable accuracy with VOR/DME and an RMI (better if you can sketch it on the crosswind calculator screen of your whiz-wheel) or HSI. It is a lot tougher with a CDI, but can be done with the pencil and plastic/paper method...

What am I missing here? Is there some regulation somewhere that prohibits such navigation? Is point-to-point navigation not taught any more?!?
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Old 4th Jul 2007, 20:00
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Intruder - we seem to be very much on the same frequency? What appears to be missing is the 'Where am I now' and 'Where am I going' element of flying which I predicted years ago would fade away with the advent of the glass cockpit. Maybe we 'trads' should just give in and plug in a 'direct to' in the FMC and declare a Mayday if it stops working? As I said in #12 - "No wonder they get lost when the coloured writing on the screen goes out."

I had the 'misfortune', a couple of years ago, to fly with an 'empty' FMC database for a while with a few F/Os - and most of them did not have a clue.
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Old 5th Jul 2007, 01:10
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Doesn't change the point though.
Indeed not.

Your point about examining arrivals and airways was right on the mark.

The sole reason for picking the nit was to provide some context or "big picture" on how IAPs are constructed.

While it shouldn't be necessary for a pilot to be a procedures designer, an awareness of the segments of an approach sometimes helps answer questions about IFR navigation --e.g., when is it OK to fly straight-in, when is it necessary to fly a course reversal pattern, etc.

Best,

Z

Last edited by Zeffy; 5th Jul 2007 at 01:36.
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