Originally Posted by PFactor

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!

Originally Posted by Cubdriver

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.

Originally Posted by f16jetmech

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

Originally Posted by clipperskipper

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

Originally Posted by forumname

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.

Originally Posted by clipperskipper

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.

Originally Posted by forumname

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.

Originally Posted by FlyerJosh

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.