DME ARC

Ian_J

Ian_J

Hubschrauber Flieger
Staff member
Okay, thanks to Surreal's Instrument Oral post, I've been searching for the answer to this question all day.

I'll preface this with I'm a DME retard, because we don't have them in the Army, and I've been exposed to DME exactly once in my airplane life.

The question: Can you join a DME arc anywhere on the arc, or just at the IAF?

I've searched the IPH, IFH, and the AIM with no results.

My guess is, the answer is pretty dang obvious and I've simply read over it a zillion times.
 
meritflyer said:
No, you can not. The was the subject of a 1994 LOI from the FAA.

The DME arc must be initiated at the IAF.
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1994 LOI said:
You also ask whether a Distance Measuring Equipment (DME) arc initial approach segment can be substituted for a published IAF along any portion of the published arc. A DME arc cannot be substituted for a published IAF along a portion of the published arc. If a feeder route to an IAF is part of the published approach procedure, it is considered a mandatory part of the approach.
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clear as mud
 
Thanks, guys.

Out of curiosity, where does it say that, except when being radar vectored, one must proceed to an IAF?
 
Ian J said:
Thanks, guys.

Out of curiosity, where does it say that, except when being radar vectored, one must proceed to an IAF?
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I think it's the same rule that says,

==============================
Unless otherwise authorized by the Administrator, when an instrument letdown to a civil airport is necessary, each person operating an aircraft, except a military aircraft of the United States, shall use a standard instrument approach procedure prescribed for the airport in part 97 of this chapter. 91.175(a)
==============================

I think that's part of the reason the FAA Legal opinions talk about mandatory parts on an approach.
 
mojo6911 said:
I don't have a lot of instrument experience, but aren't you cleared to the IAF from the enroute phase, from ATC?
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Not necessarily, although that happens quite commonly, it isn't the ONLY way for it to happen. It's also probably not the most common thing that happens.

Frequently, you will just get vectors to final, especially in larger cities. In that case, you may not get cleared, or even fly to, the IAF AT ALL. Approach control's vectors align you on final and you'll typically pass the FAF, but you might not pass the IAF.

Another way to not get clearance to the IAF during the enroute segment would be if you were already cleared to teh IAF right from takeoff. So, for example, you could put the IAF as the last point in your route of flight before the destination, and then be "cleared as filed". In that case, you would have gotten your clearance to the IAF from a ground controller. You would still need separate clearance for the approach itself, but not to just go to the IAF.
 
fish314 said:
Not necessarily, although that happens quite commonly, it isn't the ONLY way for it to happen. It's also probably not the most common thing that happens.

Frequently, you will just get vectors to final, especially in larger cities. In that case, you may not get cleared, or even fly to, the IAF AT ALL. Approach control's vectors align you on final and you'll typically pass the FAF, but you might not pass the IAF.
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Well, the OP asked in his second question if you aren't being radar vectored. Everytime that I have not been radar vectored, I have been cleared to the IAF.

fish314 said:
Another way to not get clearance to the IAF during the enroute segment would be if you were already cleared to teh IAF right from takeoff. So, for example, you could put the IAF as the last point in your route of flight before the destination, and then be "cleared as filed". In that case, you would have gotten your clearance to the IAF from a ground controller. You would still need separate clearance for the approach itself, but not to just go to the IAF.
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Even so, you are still going to the IAF first.
 
If you fly the entire published approach, it will always begin at an initial approach fix (IAF). Often, approach control will direct you to intercept a segment of an approach without going to the IAF. You may hear: "Cessna 101 turn right 170 to intercept the 10 DME arc, cleared VOR DME 12 approach, descend and maintain 3000. Contact tower 118.2 established inbound." On a 170 heading you can descend to 3000' now and join the DME arc; however, you may not descend below 3000 feet until you are established on a published segment of the approach and, that segment calls for, or allows a lower altitude. If you can see the airport, you could also request from approach control a visual approach (still an IFR approach) and land visually. Once cleared for a visual approach, you are not bound by any speeds or altitudes other than to remain in protected airspace and obey any published airspeed limits, or as otherwise directed by ATC.

So to answer your question: If ATC clears you for the approach and does not clear you to intercept the arc elsewhere, you must begin the approach at the appropriate IAF for your arrival. As you probably know, there may be more than one IAF for any given approach depending on where you are arriving from.
 
Ian J said:
Thanks, guys.

Out of curiosity, where does it say that, except when being radar vectored, one must proceed to an IAF?
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Think of it this way - If you are cleared to do anything by ATC, it has to be defined in some fashion. An IFR approach is defined by a beginning point (IAF). So, if we are cleared for an approach, we are expected (and it would make sense), to proceed to it's point of origin unless directed otherwise.
 
mojo6911 said:
Well, the OP asked in his second question if you aren't being radar vectored. Everytime that I have not been radar vectored, I have been cleared to the IAF.



Even so, you are still going to the IAF first.
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Ahhhh.... I think I misunderstood what you were asking, then. I thought you were asking if you were always cleared to the IAF "from the enroute phase, by ATC". So I was trying to show examples where you wouldn't be cleared to the IAF "from the enroute phase". Being vectored is one example, but just being cleared there right from takeoff through clearance delivery is another.

Seems like what you were REALLY asking is whether you had to commence an approach at a published IAF. For this question, I honestly don't know the answer for sure, but I think it's probably "usually, but not ALWAYS". I'm imagining a procedure like an Arc to radial with a depicted holding pattern over the FAF (but in this example the FAF isn't also a procedure turn fix). In such a scenario you could be cleared to hold as published, and after being established in holding you could be subsequently cleared the approach. In this type of scenario, you wouldn't be starting from an IAF.

This avoids the basic thrust of the thread, though... I don't know whether it's legal or not to intercept a DME arc type approach at a radial other than the one which defines the IAF. I've asked for, and been cleared, exactly this sort of a procedure before.... but I don't know if it was legal or not.
 
Full interpretation attached:
==============================

Mr. Tom Young, Chairman
Charting and Instrument Procedures Committee
Air Line Pilots Association
535 Herndon Parkway
Herndon, VA 22070

Dear Mr. Young:

This is a clarification of our response to your letter of August 23, 1993. In that letter you requested an interpretation of Section 91.175 of the Federal Aviation Regulation (FAR) (14 CFR Section 91.175). You address the necessity of executing a complete Standard Instrument Approach Procedure (SIAP) in a non-radar environment while operating under Instrument Flight Rules (IFR). Our response assumes that each of the specific scenarios you pose speaks to a flight conducted under IFR in a non-radar environment.

Section 91.175(a) provides that unless otherwise authorized by the Administrator, when an instrument letdown to a civil airport is necessary, each person operating an aircraft, except a military aircraft of the United States, shall use a standard instrument approach procedure prescribed for the airport in Part 97.

First you ask whether an arriving aircraft must begin the SIAP at a published Initial Approach Fix (IAF). A pilot must begin a SIAP at the IAF as defined in Part 97. Descent gradients, communication, and obstruction clearance, as set forth in the U.S. Standard for Terminal Instrument Approach Procedures (TERPs), cannot be assured if the entire procedure is not flown.

You also ask whether a Distance Measuring Equipment (DME) arc initial approach segment can be substituted for a published IAF along any portion of the published arc. A DME arc cannot be substituted for a published IAF along a portion of the published arc. If a feeder route to an IAF is part of the published approach procedure, it is considered a mandatory part of the approach.

Finally, you ask whether a course reversal segment is optional "when one of the conditions of FAR section 91.175(j) is not present."

Section 91.175(j) states that in the case of a radar vector to a final approach course or fix, a timed approach from a holding fix, or an approach for which the procedures specifies "no procedure turn," no pilot may make a procedure turn unless cleared to do so by ATC. Section 97.3(p) defines a procedure turn, in part, as a maneuver prescribed when it is necessary to reverse direction to establish the aircraft on a intermediate or final approach course. A SIAP may or may not prescribe a procedure turn based on the application of certain criteria contained in the TERPs. However, if a SIAP does contain a procedure turn and ATC has cleared a pilot to execute the SIAP, the pilot must make the procedure turn when one of the conditions of Section 91.175(j) is not present.

If you have any questions regarding this matter, please contact Patricia R. Lane, Manager, Airspace and Air Traffic Law Branch, at (202) 267-3491.

Sincerely,
/s/
Patricia R. Lane
for Donald P. Byrne
Assistant Chief Counsel
Regulations Division
 
calcapt said:
They can and they do.
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ATC can certainly vector you wherever they wish, and they do vector aircraft onto arcs. However, the letter of interpretation casts doubt onto the legality of that vector being counted as "vectors to final." Wally Roberts, a nationally renown expert on instrument approaches, said this about being vectored to an arc:
If the controller vectors you to the arc it becomes *marginally* legal at best, because the controller's handbook has been tightened up to pretty much limit ATC to either clearing you over an IAF or vectoring you to the final approach course in accordance to Handbook 7110.65, Para 5-9-1.
​
 
Much of the discussion / debate here seems to be JCers defending very specific scenarios. In a radar controlled ATC environment, procedures can be done legally and safely that could not be done in non radar environments. We are taking a lot of time here splitting hairs that need not be split. I think the original question was whether or not you could join a DME arc in a place other than the IAF. The absolute correct answer is "sometimes" depending where you are and the conditions that exist. The FAA letter above speaks very specifically of how things are to be done in a non radar environment. As most of us know, it is quite common for ATC to provide a vector or heading to join an approach procudure after the IAF. If every pilot in a busy and active IFR world held to the view that the approach procedure had to be shot in it's entirety, the system would jam up like rush hour in Los Angeles. It goes without saying that in a non radar environment you would need to shoot the whole procedure to guarantee terrain concerns and to arrive on short final in a configured and "safe to land" position. There has to be a place in aviation for common sense.

In the end, you are the captain of your aircraft and you must ultimately decide how you wish to fly and which procedures to employ to get the job done. Hopefully the FAA will smile on your decisions.
 
tgrayson said:
Yes. Wally's advice, however, was don't do it with an check airman or examiner on board.
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We have all seen examples of pilots/examiners that can quote page numbers and paragraphs of obscure rules and worthless information. These are typically the folks that have a hard time coping with more mundane things like snow storms, thunderstorms, emergencies and gusty crosswinds. Any reasonably intelligent check airman or FAA examiner who are worth their salt, understands the dynamic nature of what we do and doesn't create issues that need not be created. Thankfully, most fit into this category.
 
calcapt said:
We have all seen examples of pilots/examiners that can quote page numbers and paragraphs of obscure rules and worthless information. These are typically the folks that have a hard time coping with more mundane things like snow storms, thunderstorms, emergencies and gusty crosswinds. Any reasonably intelligent check airman or FAA examiner who are worth their salt, understands the dynamic nature of what we do and doesn't create issues that need not be created. Thankfully, most fit into this category.
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Maybe so, but that doesn't change the basic issue, which is that the fact that ATC has "cleared" you to do something, does not, in of itself, mean that you are LEGAL or even necessarily SAFE to do it.

A couple of examples:

"VMC climbs" for part 121 turbojets, now ok due to a change in the ops specs, but were not legal for years after Jerry Davis first published the New Standard Ops specs in the early 90s.

Frank Sinatra's mother died on a Learjet that was proceeding direct, as cleared (after they requested it) out of PSP, and flew straight into a mountain.

Cali, AA was cleared to fly "direct" to a point, but did not understand that the controller did not own terrain sep when they did that.

While you may be generally correct that it is often ok, the bottom line is that, absent a change to the rules, it is not wise to go ignoring them because you feel the "dynamic nature" makes it ok.

I know Wally personally, and I would be VERY hesitant to do something contrary to his thoughts on this. It appears, from your post, that you are not aware of who this man is?
 
I don't think I've ever started an ARC at the IAF radial. I've always been vectored to it.

"Present position, intercept the 15 DME arc, cleared for BLAH BLAH approach."
 
tgrayson said:
Full interpretation attached:
==============================
Our response assumes that each of the specific scenarios you pose speaks to a flight conducted under IFR in a non-radar environment.
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I'm just pointing this out since the discussion here seems to alternate from vectors to non-vectors. I'm not sure to what degree an opinion that starts off by saying it is addressing the rule in a non-radar environment can be used as an indicator of what is permitted when vectoring.

I tend to agree with Wally Roberts' opinion on these things as well, but he brings a strong TERPS bias to the table. And biases always have their effects on opinions. For example, I know his position (before the AIM change, anyway) on whether ATC can clear you for a straight-in approach (avoiding a depicted PT) without vectoring you was a clear "no" because, in part, ATC personnel are not versed on TERPS requirements. I never could quite understand how, assuming you were sitting on the FAF at the proper altitude, it could conceivably make any difference whether you continued straight in or made a series of turns to bring you back to the exact same place before continuing.
 
MidlifeFlyer said:
I'm just pointing this out since the discussion here seems to alternate from vectors to non-vectors. I'm not sure to what degree an opinion that starts off by saying it is addressing the rule in a non-radar environment can be used as an indicator of what is permitted when vectoring.
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It helps to know the background of the letter. I didn't post most of Wally's stuff, but he talks about when he was part of ALPA's TERPS committe, they solicited this letter from the General Counsel's office for their own purposes. That office consulted *someone* in Flight Procedures, and they produced the first version of this letter that you have on your Summit CD. Wally said that letter was disastrous. They reissued the request and the General Counsel's Office researched further, talking with the "right person" at Flight Procedures and produced this second letter. The ALPA committe did not want the ruling on the DME Arc, but the flight procedures guy found a few approaches in mountainous areas where descent gradients could not be met if the arc were intercepted at some of the airway/arc intersections.

So the context of the letter is from a Flight Procedures perspective. The only significance to them of a radar environment to them is that radar can vector you to final, eliminating any published initial segment. Without the vectoring function, you're "non-radar."

This is why the question of "Are you being vectored to final" becomes important. If you're not, then you're a non-radar arrival.

Wally's argument, and I'm doing some interpretation here, is that if ATC were authorized to vector the aircraft to an initial segment that was not aligned with the final approach course, then it would be legal. However, he says that since ATC's authority to do such things has been since limited by the 7110.65, it becomes "marginally legal," whatever that means.

MidlifeFlyer said:
For example, I know his position (before the AIM change, anyway) on whether ATC can clear you for a straight-in approach (avoiding a depicted PT) without vectoring you was a clear "no" because, in part, ATC personnel are not versed on TERPS requirements. I never could quite understand how, assuming you were sitting on the FAF at the proper altitude, it could conceivably make any difference whether you continued straight in or made a series of turns to bring you back to the exact same place before continuing.
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I believe he'd agree that you were *safe* doing what you propose, but you were legally bound to fly what was published, and ATC didn't have the authority to waive that.
 
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