CBreezy

You're right. We should refuse clearances that descend below platform altitudes.

JohnBurke

No, we shouldn't, as MVA is a useful altitude with a purpose. A vector, however, which is the function of the MVA, presupposes that the controller is taking responsibility for terrain clearance and traffic separation. When assigned to an approach segment, in which the pilot ultimately has responsibility, the pilot should determine the altitude to fly...especially an "at or above" clearance.

The controller has NO business including the MVA in that clearance, however, as it serves NO purpose in that application, and it dangles a very dangerous carrot. It so happens in this case that the crew tried to take a bite.

CBreezy

It was sarcasm. GF was insinuating that anyone accepting a clearance below the platform altitude of an approach is a "dead man walking."

ATCBob

No it was not a legal clearance and the controller violated the 7110.65 "in my personal opinion."

See the example (below) from 4-8-1-b-2 that shows specifically an approach clearance commencing at an IAF where the MVA is below the published altitude at the first segment (as was the case in this incident).



Both aircraft are direct LEFTT and the MVA here is 3000. Aircraft #1 is at 4,000 and the clearance here is to cross LEFTT at or above 3500 (note altitude on the first segment, not the MVA) and cleared the approach.

Aircraft #2 is at 3,000 but cannot be cleared the approach commencing at LEFTT because they're below the altitude of the first segment, so to get them from LEFTT to CENTR (where the segment altitude is at 3,000) you have to clear them either direct CENTR, or in this example direct LEFTT direct CENTR and cleared the approach beginning at CENTR. (Not shown here you can also climb them to 3,500 to begin the approach at LEFTT, but the way they show is easier).

In this event, Skywest was either at or above 10,000 when the clearance was issued prior to the IAF so would have been the aircraft #1 example, where the controller was required to issue CEGAN at or above 10,000 (not the MVA of 7800).

Or Skywest was below 10,000 already prior to CEGAN in which case the controller could not issue the approach beginning at CEGAN without a crossing restriction at or above 10,000 (there's no other IAF on that approach with an altitude below 10,000).

So no, not a valid clearance.

Maybe the controller or his instructor came from a facility in a non-mountainous area where the MVA was always at or above the IAF altitudes and that's how he was taught to do it, and never encountered problems with this particular approach because the pilots always caught it. But the above requirements to issue an altitude at or above the IAF altitude is in the 7110.65 I'm sure to help prevent situations exactly like this.

galaxy flyer

Do it often enough and you could be the SKW crew. Do it in the days before EGPWS and the outcome won’t be good. I’d be real careful about accepting altitudes below “platform” which is the intermediate segment. There’s only 1,000’ ROC on the intermediate segment, potentially not much clearance. I never did unless I knew exactly where the terrain was; no harm staying a couple hundred feet high.

GF

galaxy flyer

ATCBob,

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

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

WesternSkies

Really dude?

CBreezy

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.

galaxy flyer

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

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.