What should the controller have done?

[Palmpilot]

You're missing that the profile view on the FAA charts is not to scale, and regardless of depiction, the altitudes depicted are only on glideslope if they have a lightning bolt or are a glideslope check altitude like the small "2500" above the FAF. 3600 is not glideslope intercept at HUBJU, nor is 3000 at FIKOX. The line preceding the FAF is notional, representative only, and is not to scale or used to indicate anything about the glideslope. It's not the greatest depiction, especially since the glideslope feather extends well up final.

This is clear when you think more about it, though - HUBJU to FIKOX is 600 feet over 4.2 nm, and FIKOX to BLKEY is 500 feet over 2.9 nm. Obviously those are different slopes, and ILS glideslopes don't bend like that. A 3.0 degree glideslope like published here is about 318 feet per nm. So the glideslope altitude at FIKOX is about 2500 + (2.9 x 318) = 3422, and the glideslope at HUBJU is about 3422 + (4.2 x 318) = 4758. In other words, well above the charted altitudes, as is desirable to be able to intercept the glideslope from below.

Not flying IFR for two-and-a-half years has apparently made me rusty at reading approach charts! I was misinterpreting the stepdown altitudes as glide slope altitudes.

So if he was at 6000 MSL two miles outside HUBJU, that gave him about nine miles to reach the 2500 MSL glide slope intercept altitude by BLKEY. That's about 389 feet per mile, which shouldn't require a heroic effort.

 

[roncachamp]

Looking at the profile view on the chart, that doesn't look right. The GS intercept altitude at HUBJU is 3600 msl, and 4.2 nm later at FIKOX, the GS is shown as being only 600 feet lower, so two miles outside HUBJU, the GS should be approximately 3600+300 = 3900 msl. What am I missing?

The 3600 MSL altitude is not the GS intercept altitude at HUBJU, it's the minimum altitude outside of HUBJU. The GS intercept altitude is shown by the lightning bolt, it's 2500 MSL at BLKEY. BLKEY is 7.3 DME, HUBJU is 14.4 DME, so two miles from HUBJU is 9.1 miles from BLKEY. A three degree slope is about 320'/mile, 320' x 9.1 miles would be about 2900' above the 2500 MSL altitude at BLKEY, 5400 MSL.

 

[GeorgeC]

LTNS, roncachamp.

 

[Palmpilot]

The 3600 MSL altitude is not the GS intercept altitude at HUBJU, it's the minimum altitude outside of HUBJU. The GS intercept altitude is shown by the lightning bolt, it's 2500 MSL at BLKEY. BLKEY is 7.3 DME, HUBJU is 14.4 DME, so two miles from HUBJU is 9.1 miles from BLKEY. A three degree slope is about 320'/mile, 320' x 9.1 miles would be about 2900' above the 2500 MSL altitude at BLKEY, 5400 MSL.

Thanks - my mistake.

 

[Clip4]

Was flying IFR from PDK-GAD this weekend and was given the ILS 24 at GAD. The plate is attached for reference.

I was still w/ ATL center at roughly 5 miles from the IAF and was cleared direct HUBJU. They hadn't descended me from 6,000 yet. For the last 15 miles or so, I asked twice to descend so that I could make the approach, and the controller said "I can't give it to you...you'll have to request lower from Birmingham approach when I hand you off." I asked if there was traffic, and she just said "No, Birmingham approach will have to descent you." I told her that if I didn't get lower I wouldn't be able to get down in time, and all I got was "You can request lower from Birmingham."

Another 2 miles or so go by and she finally hands me off. I check in with Birmingham and get "2 miles from HUBJU, cleared the ILS 24."

Now, in IMC with <1,000ft ceilings, I had to descend at more than twice the normal rate I'd fly on an ILS since they had me roughly 2,500 feet above the GS. In retrospect, I should've asked to hold or for vectors to go through and come back so I had time to get down. I made it in without having to go around, but it was hairy getting down.

Before I switched to unicom, I told the controller "I don't know why you had me at 6,000 at the IAF, but getting down from there was almost impossible."

The controller responded "Yeah, we were wondering why Center had you so high. There was no traffic. You should've asked for lower." I told the controller that I did twice, and he said "Strange."

Obviously the ATL Center controller screwed something up, but my question is this: What should the Birmingham Approach controller have done? Was it the right call to just clear me for the ILS? Should he have vectored me around to get down? Should he have at least asked if I needed to hold to get down?

Of course, it's ultimately on me to ask for something if I need it, but I'm just curious if you guys think the controller should've done something different.

Ultimately, I wasn't comfortable starting the approach from that altitude in IMC with low ceilings, and I should've done something about it. A good learning experience.

Maybe I am confused, but if you were two miles from Hubju at 6000 ft, you had ~7 miles to descend to the 2500 ft at Blkey. At 80 knots, that is a descent rate of <700 fpm, less than 800 fpm at 90.

You could have just advised ATC of your speed change prior to the handoff.
Requested to descend in the hold.
Or just descended at 800 ft per minute to Blkey.

 

[roncachamp]

LTNS, roncachamp.

Awww, didn't know I'd been missed!