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-   -   Good day for GPWS (https://www.airlinepilotforums.com/safety/110739-good-day-gpws.html)

galaxy flyer 02-08-2018 11:50 AM


Originally Posted by CBreezy (Post 2522890)
You don't get that option in a place like ATL or LGA or ORD. You don't get to stay a few hundred feet above assigned altitudes. Like I said, we do it so much in flatland that I can understand a crew misinterpreting a potentially illegal clearance. Doesn't excuse them for not flying the approach but I'm not relieving ATC of any blame. The non-standard clearance is what caused the confusion during an already high workload environment.

Agreed in places like ATL, ORD, LGA where US crew’s are very familiar, low threat terrain. Try that assumption at places like Bishkek (multiple conversions, metric altimeter to inches, QFE to QNH); a night transit of Petropavlovsk (huge terrain and poor English); or Gorno Altsk in Russia (mountains and Russian navigator translating) or Dillion, MT for the first and only time with customer crew new to the plane and you are a “ dead man walking”. I spent most of my career in those places, not ATL, ORD or LGA.

I’m old enough to remember the C-141, taking the clearance meant for another call sign (controller mixed clearance and call signs) and hitting the Cascades and TW 514 at IAD.

Might look at this recent close call, good for EGPWS

https://aviation-safety.net/wikibase/wiki.php?id=205811

Or this hull loss in AK after an erroneous altitude assignment.

https://aviation-safety.net/database...?id=20130308-0

GF

ATCBob 02-08-2018 01:27 PM


Originally Posted by galaxy flyer (Post 2522873)
ATCBob,

No argument with your ATC experience, I was referencing 4-8-1 Note 1, which says,

"The altitude assigned must assure IFR obstruction clearance from the point at which the approach clearance is issued until established on a segment of a published route or instrument approach procedure."


So, you looks to my pilot’s eye that being in a 7800’ MVA between the SKW flight and CEGAN that might be legal, if exceedingly unwise.

GF

Except note 3 states the aircraft isn't established on the approach until it is "at or above an altitude published on that segment of the approach." Crossing the IAF at or above 7800 here doesn't "assure IFR obstruction clearance" because they could cross it at 7800 and wouldn't be established until well past the high terrain and higher MVA.

It's not a legal clearance.

galaxy flyer 02-08-2018 01:30 PM

Thanks, ATCBob.. I’m not, even on the internet, a .65 expert.

GF

TCASTESTOK 03-26-2018 12:40 AM

Skywest
 
Whats your take on this Skywest flight that descended below the minimum segment altitude?

https://www.youtube.com/watch?v=FMUJnFr99rY

Cefiro 03-26-2018 04:05 AM

Already been discussed

https://www.airlinepilotforums.com/safety/110739-good-day-gpws.html

aaatwood 08-05-2022 12:28 PM

NTSB weighs in
 
https://www.avherald.com/h?article=4b3d8f81

joepilot 08-06-2022 12:23 AM

Many, many years ago, when I was a new Captain on the 737, I was coming from SFO to LAX. Twas a dark and stormy night, and the OAT was about 4 Degrees C. We were being vectored for the ILS 24R, and told to descend to 2,500. Presumably that was MVA. Being retired, I no longer have access to current approach charts, but at the time there was a terrain feature at 1,488 feet about 15 miles on final for 24R. If I remember correctly this was actually a quarry with rapidly rising walls.

The F/O was the PF, and he was highly experienced, (ex-TWA instructor). We briefed the approach, including the 1,488 obstruction. We got a vector to about a 22 mile final at 2,500. We were cleared to intercept the localizer, and cleared for the approach. We did NOT believe that meant that we were cleared to climb to the higher altitude depicted on the approach plate for the R24R approach plate. We both knew that LAX approach routinely vectored aircraft across the 24 runways approach at 3,500.

Predictably, we got a GPWS at the quarry. I saw the rapidly rising radar altimeter going up thru 1,000, and I said simply "do it", and the F/O did as we trained. The GPWS stopped within 100 feet, so we stopped the climb before we got 200 feet off altitude. We reported the incident to ATC, but they did not seem particularly interested.

I did do an ASRS report to the FAA, and also a safety report to the company. The company did not seem interested, but the FAA did call me back. They seemed to be most interested in what repercussions may have occurred with the company. They seemed to lose interest when I said that their were no company repercussions, but that I was most concerned that their was a potential for a midair collision if somebody followed the GPWS maneuver too far, with the aircraft performing the escape maneuver climbing into a higher aircraft being vectored for a runway 25 approach.

Joe

rickair7777 08-06-2022 07:35 AM

We get in the habit of accepting ATC descents below published MORA, route, or even arrival altitudes because ATC has min vectoring altitudes which are not published for our reference.

Also ARRIVAL crossing restrictions are usually there for airspace management reasons, ex separate departures from arrivals. ATC can waive those if there's no traffic conflicts and they often do.

But APPROACH restrictions are often there for terrain clearance purposes, especially closer in. If you're actually established on the approach course, you should question any clearance to descend below published altitudes.

If given at or above, might as well just comply with published, especially in mountains on a non-precision approach :eek:


As always, maintain terrain awareness at all times.


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