Flying DME Arc, lose DME, now what?
 

Hey I have a Skywest interview soon and one of the gouges lists one of the possible questions as:

You are flying a DME arc in IMC and you lose DME. What do you do?

Does anybody know the right answer? I know in the real world I'd tell ATC and ask for vectors to set up for another approach, but what should the correct interview answer be?

And if you're at non-radar approach controlled Helena, Montana, served by SKW, flying the DME arc, what will you do?

You have to break off the approach because one of the required navigation facilities is not working. If you were on an ILS and lost glide slope you would discontinue the approach but continue to the missed approach and go missed.

However on a DME arc it is not quite so clear. The ARC is there to protect you from an obstruction or other traffic so you can't turn towards the missed approach point and then go missed (you might hit something)

It still seems to me even in a non radar control environment you break off the approach. Contact ATC for more instructions while climbing to MSA (via what heading or direction though?)

It's really not that clear. :confused:

I would say turn direct to the VOR, climbing to the missed approach altitude, then execute the missed. DME arcs are designed to keep you away from high terrain outside the arc, not inside the arc. If there was high terrain inside the arc, you wouldn't have picked up the DME in the first place.

If asked such a question in the interview, my first response would be "do I have any approach certified area navigation equipment onboard (that's a fancy way of saying FMS/GPS).

If so, you don't need the DME.

What about situations where the VOR/DME is located on a hillside and the airport is in a valley? I personally wouldn't assume anything... especially if you're outside of the US.

The best thing to do is call ATC and ask for instructions/vectors. Even in a non-radar environment, they can provide minimum safe altitudes for whatever sector your in.

On GA aircraft a certified GPS can also substitute for DME. You would have this already set up as supporting nav gear anyway, so just use that.

Good point.

Yeah and fly what heading or direction? I've seen ATC so busy that it could take 1 to 2 minutes to get a word in?

It would be nice if part 121 aircraft had GPS but 95% of the aircract at Mesa have no GPS. Without DME you would have no distance information.

Climb to the MSA that appears on the approach plate. This is the quickest way to assure terrain separation. Then you can proceed to the missed approach point or to the holding pattern depicted on the missed approach. Notify ATC as soon as practical but remember, Aviate, Navigate, then Communicate.

depart the arc and attempt to find runway VFR

Not if you declare an emergency and squawk 7700 to light up his board, which this definitely is unless you have the sectional charts out (or know the area) and are 100% satisfied that a straight-ahead or dead reckoning climb around the arc to the MSA will keep you from hitting something.

I think it's clear that the question assumes no GPS that can substitute or it wouldn't be asked (although asking "what other equipment do I have on board" would be a good question). Even a handheld GPS would be a lifesaver in this situation.

Out of ATC communication also? Hope you have those sectionals. I would not turn to the VOR for the reasons already stated.

The original question was how to respond to the question, if asked. Of course, assumptions like, "the VOR has to be in a lower MSA, so fly over there" are a great way to paint yourself in a corner during the interview.

Don't make it up. If there's not a prescribed procedure in regs, SOP, etc, then use ALL the tools at your disposal. Ask the other crew member. Ask ATC. If no obvious answer is immediately apparent, I'd say CLIMB and get to the missed approach (assuming you are below the MA altitude). Obviously, any missed will require specifics from the approach to determine how to do that. Maybe there is a NOTATION on the chart just for the possibility of loss on a navaid signal.

If asked the question, methodically think it through if you don't know the answer. Guessing, assuming... bad plan.

Sure hoping you forgot the sarcasm smiley! :cool:

With that answer, what does the interviewer ask next? "What would you do now that the weather just went to mins?"

If the field is VMC, and you have it in sight in VMC, sure, visual is not a bad choice. I suspect the interviewer won't make it that simple.

Not in Helena, Montana, it won't. It may be an emergency, and you may squawk 7700, but unless you have two way radio communication with Helena, and tell them, they probably won't have a clue.



I don't recommend your answering being to bring in unapproved electronic devices into the cockpit and then using them for an emergency with no briefing, no company procedures or training, etc.



Unless the airline has sectionals specifically for VFR flight, I don't recommend that being your answer.

Ok barring GPS, FMS, VFR reversion, ATC vectors, radar coverage, backup DME units, or VFR sectionals at your disposal it seems all you can do is climb back to MSA as quick as you can. So what heading am I to recommend with that climb? Back to the missed approach hold?

Ah, you're looking for an answer that will satisfy an interviewer in an office on the ground. I'm giving an answer that will save my life.

You already mentioned Helena MT. I'll mention the middle of the Colorado Rockies. You're now postulating a situation with no DME, no radar contact, no ATC communication.

Heck, I'd pull out my smartphone with it's internal GPS and geo-referenced sectional charts and use that if it was my best option. I'd rather be alive without a job than dead with one, so the company can say, "he's dead, but he died in accordance with proper procedures".

The interviewer may not care, but hopefully the pilot does. But if it's all about checking off the right box, I'll defer.

The problem is that there's no one-size (real) answer. What you do in fact do is going to be based on your equipment (both aircraft and avionics) and the conditions.

The climb to MSA is somewhat obvious but the direction you take is going to be based in large part on the climb performance of your aircraft, the surrounding terrain and the weather conditions (the VFR option already mentioned), all of which you, of course briefed.

try to raise ARINC on HF

I believe my answer, climb to MSA, go to Missed Approach holding point, satisfies both.

This is actually a good question, all joking aside. Me personally, climb to MSA while still on arc as best as possible (engaging climb mode and continuing 5 degree heading cuts to maintain the arc for another 5 minutes ain't gonna kill anybody while you climb to MSA), then proceed to the holding pattern and obtain ATC clearance.

making a hard bank to the station the nanosecond I loose DME? Nah don't know about that one....

All joking aside, this dead reckoning around the arc as you climb to the MSA appears to me be the best answer assuming your hands are as tied as others have suggested - no ATC, no radar, no other equipment (official or not). Even in an aircraft with poor climb capability (the issue I have with Tony's answer), this will probably keep you from hitting something as you get up there (including the mountain between the arc and the MAHF).

The one thing I did not see in these answers is to make the mandatory call to ATC of "Missed Approach".

I agree with dead reckoning the arc while climbing to MSA (which may be higher than missed approach altitude), and then flying the approach path to the missed approach point while trying to contact ATC for a different clearance.

Joe

The only problem I have with Noy's (sensible) solution is that a situation as common or possible as this one would seem to merit a specific procedure of some kind. Since aircraft performance would be known factor in this scenario, it seems like a company ops manual would address it. So at an interview I would give that as my primary response, and if the interviewer replies there is no company solution, THEN I would ask if we could get back to MSA and how fast we could get there.

I wouldn't over think the question too much for an interview. They just want to know what you would do to keep the airplane intact and satisfy regulatory requirements. I wouldn't be pulling out sectional charts, your handheld GPS, Ipad or any of that silly BS. Just fly the airplane.

This is the best answer.

So wait, did we just lose the DME, or the VOR and DME?

Required obstruction clearance (ROC) along the arc
depends on the approach segment. For an initial
approach segment, a ROC of 1,000 feet is required in
the primary area, which extends to 4 NM on either side
of the arc. For an intermediate segment primary area
the ROC is 500 feet. The initial and intermediate segment
secondary areas extend 2 NM from the primary
boundary area edge. The ROC starts at the primary
area boundary edge at 500 feet and tapers to zero feet at
the secondary area outer edge.

The total width of an arc intermediate
segment is 6 NM on each side of the arc. For obstacle
clearance purposes, this width is divided into a primary
and a secondary area. The primary area extends 4 NM
laterally on each side of the arc segment. The secondary
areas extend 2 NM laterally on each side of the primary area.

So let's say you're flying the arc at 150kts...2.5 miles/min. I'd say "dead reckoning" for a few moments to begin the climb and reconfigure is your best bet. Just figured it would be good to see the obstacle clearance figures. Although, I can't say what the obstacle clearance limits are in other parts of the world. Don't forget to check the approach chart for your highest obstacles in the area either!

Great info. I must admit that the original question is indeed one that made my mental gears turn. Sadly (my fault?) those gears are cobwebbed up and it takes these kinds of discussions to clear them up.

Realizing that may make no sense to the normal reader, what I mean is that these types of discussions are good to stimulate thought.

Absolutely. Sometimes the best answer is a question that clarifies. Not all questions give all the information necessary to answer it.

Lost DME on an Arc
 

Anyone have a textbook answer for what to do if you lose DME on an arc? e.g. how would one execute "the missed" on an arc?

Assuming not in radar contact or on with atc, I would say climbing to msa, proceeding direct to the VOR and holding as published. Normally holds on arcs are over the VOR. Personally though, turn ten and twist ten and you will be fine. I'd keep shooting the arc in a real world situation. Not the textbook answer though

We seem to use dme on the arc about once a week around here. The GNS530W now becomes your dme, continue with the approach.

Assuming you are not on arc for very long and/or there isn't a strong crosswind.

Works great, probably better than the turn 10 twist 10, especially if you can couple the LNAV/VNAV and have it loaded properly.

Unless you're company doesn't have it approved in their ops specs to shoot a DME ARC or your getting line check, etc.

Sure would suck to be in the hearing if you used your GPS to fly the approach AND something else went wrong, now you're trying to explain the CP/Feds why you did what you did.

The Garmin 530W can be used freely as a DME substitute and as a substitute for ADF on ADF-required approaches. DME substitution also applies to precision approaches. RTM.

With all due respect, I'm not sure you fully read the back half of my post.

For clarification purposes, does "RTM" stand for Read the manual?

In the part 91 world, that my acceptable. But if your operating at an air carrier, the Op Specs may not allow you use/substitute GPS data in the even of a conventional nav DEM failure. In which case, I'd say "RTOS"

Also, I'm not sure how using the GPS for distance info on ADF approaches applies to the topic at had. You know, what to do if you have a DME failure on a DME arc.

If I have GPS, regardless of ops specs, I'm going to fly the arc utilizing whatever guidance I can, as I climb to the missed approach altitude and contact ATC.

Don't over think it and feel free to exercise command authority, but ALWAYS err towards the safer course of action. Nobody will question you if you take the safer path.

Even in a light GA aircraft, you should be able to climb from whatever circling altitude is assigned to the arc to the MSA or Missed Approach Altitude before you leave the confines of the protected arc just by taking a WAG at it.

I NEVER said I wouldn't use it if I had a failure and it the sole means of distance information.

I was simply responding to the poster that said he'd use it on the approach.

With all due respect, you didn't fully read the post either.