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tyketto they were cleared to cross cegan at or above 7800
quite a bit after that comes the mountain with 7300 feet elevation.

so your logic does not apply here.

Then something else is completely off, because they would have to be on a published IAP or STAR or airway to get the call for such a crossing restriction. CEGAN is on V122, which has an MEA of 8500ft westbound and 9000ft eastbound, with an MVA of 7900 in the area. The call in this case to cross AoA 7800 would be questionable, because of the MVA in the area. You should not receive a crossing restriction that would be below the MVA. That's asking for trouble. However, with "at OR ABOVE", the call is still valid. I would have questioned the altitude, especially with the MVAs in the area.

The mountain in question is southwest of CEGAN, roughly on the OED R-141, at 7265ft. The problem here is that after crossing CEGAN, if they were truly at 7800ft, they were below the MVA for the area. The question here is what was the call AFTER they crossed CEGAN.

Hence why I said that while given a "cross <fix> at/maintain or at/above <altitude>" doesn't necessarily mean you should immediately descend. You can remain at your given altitude for as long as you want as long as you cross that fix at the restrictions given.

BL.


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tyketto they were cleared to cross cegan at or above 7800
quite a bit after that comes the mountain with 7300 feet elevation.

so your logic does not apply here.
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18 Jan: Cessna 180J (N180V). Aircraft scraped wing tip on runway at Santa Fe
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Aviation Audio Clips / 18 Jan: Delta 1594 Emergency Landing at LAX
« Last post by lajim on January 20, 2018, 01:40:23 AM »
Delta 1594 took off from LAX and had to return and make emergency landing due to losing left hydraulic system.  Tower saw smoke coming from left side during landing. The aircraft sat on the runway (25R) for a while figuring things out and waiting for a tow which caused some traffic concerns. Unfortunately, can't hear responses from fire rescue vehicles (too far away from my location) but sounds like they were seeing a thermal anomaly (mentioned 300 degrees).  Recorded from personal scanner (wasn't able to find on the 127.85 LAX archive).  Good clear communications between all parties though must have been stressful for the crew. 
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Certainly the "above" part gives me the option to cross higher if I choose to, but that's not the point here.  If I'm trying to get down, I could choose to descend to the lowest altitude allowed, which is 7800 in the example.  Are you saying that I would need to plan my descent to hit my altitude (or above) right at the fix?  In other words, I can't reach 7800 before I get to the fix?

Basically "cross <fix> at or above 7800" means this: I don't care what you do, or when you start your descent; you need to cross <fix> at 7800ft or above. If you immediately descend, that's okay. If you take your time, that's okay. To be honest, you could cross that fix at FL210, and would still meet the requirement for what you were told to do.

What it doesn't mean is that you are immediately cleared to descend to that altitude. Take, for example, "reduce your speed to 230kts, then cross <fix> at or above 7800."

You wouldn't be immediately able to descend (which would basically be at pilot's discretion) until the speed restriction is met.

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Another question long these lines, what would be the difference between the clearance given, and "descend at pilot's discretion to 7800"? They seem to mean the same thing here - I own all the altitude between where I am and 7800.

Are you on a STAR? If so, what "cross <fix> at/maintain" would be primarily used for is to meet a crossing restriction as depicted on a STAR. Take for example, the KEPEC6 or the CLARR3 arrivals into KLAS:

http://155.178.201.160/d-tpp/1801/00662KEPEC.PDF
http://155.178.201.160/d-tpp/1801/00662CLARR.PDF

Both have the 13000ft and 250K crossing restriction at CLARR. And seeing that you'd be joining the STAR anywhere from 60 to 120nm away, you definitely would not want to be immediately descending to 13000, especially if it may take you below the MVA/MOA for the segment in question.

If not on a STAR and receiving vectors, "cross <fix> at/maintain" wouldn't be a good call to give, because you'd either have to be properly equipped to know where <fix> is, or check if it is a non-RNAV fix, meaning that it should be defined by a radial from a given VOR and DME from that VOR. Regardless, you "should" be on a published chart to be given that call to cross a given fix.

BL.
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Aviation Audio Clips / 18 Jan: Tukan Trike N907T crashed on landing at KEIK
« Last post by GeoffSM1 on January 19, 2018, 06:29:09 PM »
Substantial damage to the aircraft but thankfully only minor injury to the pilot.
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Certainly the "above" part gives me the option to cross higher if I choose to, but that's not the point here.  If I'm trying to get down, I could choose to descend to the lowest altitude allowed, which is 7800 in the example.  Are you saying that I would need to plan my descent to hit my altitude (or above) right at the fix?  In other words, I can't reach 7800 before I get to the fix?

Another question long these lines, what would be the difference between the clearance given, and "descend at pilot's discretion to 7800"? They seem to mean the same thing here - I own all the altitude between where I am and 7800.
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Listener Forum / If KOMA is gone could some zmp frequencies move to other feeds?
« Last post by 777lrf on January 19, 2018, 04:43:03 AM »
Hello too bad KOMA has been gone for a long time. Is it possible for some of the zmp feeds to be added to other active feeds in the area? A large portion of zmp is missing from KOTM to KDEN. Thank you for this service.
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Yeah, this one got me thinking, too.  If I were told to cross a fix "at or above 7800", I'm cleared to descend to 7800' - even if that leg of the approach is charted at something higher. This happens all the time. Controllers have MVA charts that tell them how low they can vector a flight in a given area, and those numbers are usually lower then the published minimums on the charts, so I wouldn't have thought twice about it. The only explanation I can come up with is that the controller just messed up here.  Yes, maybe the pilot should have questioned it if he was (and should have been) aware of the surrounding terrain. But in my opinion the clearance was just fundamentally flawed.  Yeah, trust but verify - especially when the descend-to altitude is below the published numbers for the approach. A nice lesson here - thanks Geoff!

Not necessarily.. If you are told to cross a fix at or above 7800, that doesn't give you clearance to descend immediately to 7800; the call means exactly what it says: "I don't care when you have to start your descent, but be sure to cross this fix at or above 7800ft. You can cross it at 8500, or even 15000; as long as you cross it at or above 7800ft, you're good. However, if the chart has published minimums for the segment of the chart, and the fix you are told to cross is below the published minimums on the chart, than that would be a problem.

The rest, you are absolutely correct, but it should be stressed that a clearance to cross a fix at a given altitude does not necessarily mean that you are given clearance to descend directly to that altitude, especially if you have traffic along that segment, for example, converging at the same fix.

BL.
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