2 Questions

[Singlecoil]

Well, I'll chime in on that one. They are minimum altitudes. You don't have to descend to them immediately, it is entirely at your discretion. There are plenty of times when you don't want to go down there, like descending into a low cloud layer that has ice in it. It is absolutely OK not to descend into that.

Also, in cold weather ops in mountainous areas you are going to want to stay high on things like DME arcs or non-precision approaches because your altimeter will be lying to you. You can add the appropriate correction to published altitudes and fly that. On the approach, you don't have to advise ATC you are doing that, but you do if you would like a fudge factor on an airway, obviously. Something else to think about, minimum vectoring altitudes are down to 1000 agl even in mountainous areas. On a -30 day, you could only be 400 agl even though you and ATC think you are 1000 agl.

 

[stillaboo]

As the unofficial 'reg' guy of this post, I'll chime in one last time. I'm with Singlecoil here. "Published altitudes apply to descent" means just that, the published altitude applies to descents. To go any lower than the minimum altitude would require a descent. But you aren't allowed to. Simple. I'd say your DPE, '172driver' is, how do we say this delicately . . . WRONG! I'd advise that you (rather than one of your students) take him up on this.

Singlecoil points out some benefits of remaining high. Here's another. The safest approach is a stablized approach, one which doesn't consist of descent, level-off, descent, like an ILS. On many ILS's, the GS intercept is 500-800 ft. below the intermediate approach altitude. "The glideslope is normally useable to the distance of 10 NM. However, at some locations, the glideslope has been certified for an extended service volume which exceeds 10 NM." (AIM 1-1-9d3) Interestingly, there appears to be no height restrictions mentioned, though there are for localizers (any comments on the lack of GS height restriction, other than the false GS's above the real one?). So, my point is, if you remain at the intermediate altitude (coming off the arc or PT), you are only required to make one descent configuration at GS intercept (even if it's outside the OM/FAF), rather than multiple ones, provided you're within 10 NM of the antenna (which is at most 1250 ft from the approach end of the runway (is the end the threshold, or what?). This method is usually safer than the 'dive and drive' method, and is the reason that VDP's exist for the big tin with VNAV vertical path computers, so that they make 1 descent to the runway from the FAF, rather than diving down to a low altitude with a high rate of sink in IMC only to level off at MDA(H) on non-percision approaches (What most pilots call VDP's are actually not, as a VDP is the DA(H) on a non-percision approach for VNAV equiped aircraft. See the note on Jepp plate for details)

So, fly higher and make less configuation changes (aka, fly safer) and intercept the GS at the intermediate altitude. It's easier too! I did it on my instrument and multi-instrument commercial rides and passed both. Just explain to the examiner why you're not descending.

Now, the issue of MVA's. MVAC (MVA charts, the ones controllers use to vector pilots) are supposed to provide 1000 ft and 3 miles in Part 95 non-mountainious areas and 2000/3 in DMA (FAR 95 designated moutainious areas). These can be reduced down to as low as 1000/3 to help controllers radar vector smoothly onto approaches. It has been found that many tracons have simply bypassed TERPS regulations in constructing their MVAC's (ATL Center reduced the required 2000 ft clearance in ther DMA's to 1500 w/o approval from anyone, and is now under an NTSB investigation for it) to make their lives easier, putting pilots at risk. One example, ILS 16 in Ashville, NC, shows an inital approach segment that the FAA says requires a minimum altitude of 6800 ft. for proper FAR 91.177 obstacle clearance. The MVA for this same area, which is in a DMA and has a 4,858 ft mountain in it, not to mention the additional height of any trees . . . 5,300 ft.! In short, if you are about 1 mile east of the depicted course and are maintaining your altitude EXACTLY, you're less than 450' above the ground, and likely less than 350' above the trees in an area where you are required to have 2000' ft b/t you and terra firma. And I didn't even mention the 5339 ft. mountain that's about 3 miles east of you (and 39 ft. above you!). And that's if it's not a colder than standard day. Hope you have radar altimeters, boys.
MVA's are not held to the same standards as instrument approaches are in reality, though they are legally. If you're flying into Ashville under vectors, you just busted FAR 91.177a2, while your controller just violated the ATC Handbook (7110.65). Neither of you knew it, but that's cold comfort when the FAA comes calling.
[Note: all info about MVA's was blatently plagerized from the April 2003 IFR Mag. article by Wally Roberts, former chairman of ALPA's TERPS Committee]

A Squared - you're right. After further review, my pie is still uneaten. I don't think we'll ever have an answer on the descent w/o authorization issue. I'm always asking for a descent clearance from ATC (not to MVA though!) and putting my pie in the freezer so it doesn't get stale.

-Boo!