Several things spring to mind.
The ATC clearance to cross CEGAN at or above 7,800' implies that the crew is safe all the way down to 7,800.' It appears that ATC took the position that the procedure required 10,000 at CEGAN, and therefore a clearance to cross at or above 7,800 didn't prevent them from following the published numbers. This is a very dangerous slippery slope, and I don't buy it. What if ATC had said "at or above 1,000?" Clearly it's not possible, but it implies that the crew may commence the procedure at the ATC altitude. ATC frequently provides vectors at altitudes lower than procedure altitudes, such as vectors to a localizer or ILS. The approach guidance with a glideslope is nearly always intercepted from below. In this case, I'd be leary of beginning the approach at CEGAN at anything less than 10,000. That said, one might look at the arc and the high points along the arc to note that The highest point to be encounered is joining the inbound course from the arc, and that altitude is 7655. One might be forgiven for hearing the altitude restriction, glancing at the chart, and believing that based on the presented data, the clearance and arc imply guidance safe from terrain. At the same time, neither crewmember had flown this procedure or routing before? While the arc is beyond the 25 nm MSA radius, the radius for that area varies between 8,800 and 10,700; a crucial clue that 7,800 may be unwise, despite the potentially disasterous clearance. Another important clue is that BRKET (27 DME OED) is published at 10,000, the next fix inbound is SERTE (21 DME OED) at 8,500. Clearly at that point in the approach one is still restricted well above 7,800, and a review of the procedure and briefing of the procedure should be enough to convince to fly the published altitudes. Another observation is that both crewmembers heard the clearance and both agreed to the decision to descend below published altitudes, apparently. The narrative doesn't suggest one crewmember voicing an objection. This reminds me somewhat of the B757 mishap in Colombia years ago, American 965, in which the crew was cleared via an NDB, but entered the wrong one. Both crewmembers bought into the decision, and ultimately they did get a GPWS alert prior to impact. If this procedure was database selectable, were they not seeing the segment altitudes in more than one place; procedure charts or displays as well as on the FMS/FMC? |
Holy crap....
|
A quick glance at the chart shows about a 20 mile arc and a 20 mile final. Why would they want to get down and close to the terrain and get bounced around when not necessary if they had any vertical navigation awareness? The FMC might also have given them some vertical navigation info if time permitted finger fking it.
|
Originally Posted by 1wife2airlines
(Post 2509225)
A quick glance at the chart shows about a 20 mile arc and a 20 mile final. Why would they want to get down and close to the terrain and get bounced around when not necessary if they had any vertical navigation awareness? The FMC might also have given them some vertical navigation info if time permitted finger fking it.
Worth noting that a SLC 900 probably had a very, very senior CA (who grew doing a VOR approaches into mountain holes in a metro), so there's likely some cultural misunderstanding about how those at-or-above clearances work. |
Originally Posted by JohnBurke
(Post 2509033)
The ATC clearance to cross CEGAN at or above 7,800' implies that the crew is safe all the way down to 7,800.' It appears that ATC took the position that the procedure required 10,000 at CEGAN, and therefore a clearance to cross at or above 7,800 didn't prevent them from following the published numbers. This is a very dangerous slippery slope, and I don't buy it.
Originally Posted by JohnBurke
(Post 2509033)
If this procedure was database selectable, were they not seeing the segment altitudes in more than one place; procedure charts or displays as well as on the FMS/FMC?
But I don't think awareness of the stepdown altitudes was the problem. I think the problems were... - Assuming that they were good down to 7800 based on an MVA. - Lack of awareness of actual terrain (this is all on them). When I worked there, I could have gotten sucked into this right up until that last part... I like to read the terrain highlights on approach plates... especially doing DME arcs to a VOR approach in mountains in IMC. |
Lots of valuable lessons here. Pilots Must query ATC if a clearance does not make sense or is unclear.
|
Originally Posted by rickair7777
(Post 2509232)
They're used to getting slam dunked in places like that, so they're spring-loaded to get down sooner rather than later, especially on a complicated approach.
Worth noting that a SLC 900 probably had a very, very senior CA (who grew doing a VOR approaches into mountain holes in a metro), so there's likely some cultural misunderstanding about how those at-or-above clearances work. |
Originally Posted by rickair7777
(Post 2509239)
But I don't think awareness of the stepdown altitudes was the problem. I think the problems were...
- Assuming that they were good down to 7800 based on an MVA. - Lack of awareness of actual terrain (this is all on them). When I worked there, I could have gotten sucked into this right up until that last part... I like to read the terrain highlights on approach plates... especially doing DME arcs to a VOR approach in mountains in IMC. A firefighting operator (no longer in business) that used P-3's accepted a dispatch to Missoula a number of years ago. Conditions required the use of an approach at Missoula. The nature of that kind of operation means very short notice dispatches or diversions; it's a constant thing. On arrival, the crew found that they did not have a printed chart for the procedure, and ATC provided it for them verbally. Without the ability to see the procedure in front of them, they did not have the situational awareness. The arc at Missoula arrives to final from two directions, at two altitudes. They were fine at their arrival altitude on the arc, and fine if they made the correct turn to final and completed the approach. They were not fine if they missed the turn and continued on the arc into rising terrain, which is what happened. The altitude worked for one segment of the approach, but not all...much like an MVA in the case of the procedure in this thread, which was acceptable at CEGAN perhaps, but not for the remainder of the procedure. The two cases are not identical, but do draw on some salient points. The procedure doesn't help much if not followed. The diagram and details aren't much use if not used. While an ATC clearance should be flown when received, the old adage to trust but verify seems cogent. The entire procedure should be reviewed, particularly in mountainous terrain. Deviations from published procedures, even on vectors, can be invitations for Murphy. We got vectors to the procedure in Kabul one night, which means off course in very tall mountainous terrain. It ought not be a problem, but heavy jamming was taking place with difficult communications; ATC was in and out. At some point, we lost all electrical, dark cockpit, loss of displays. We found ourselves going to memory items then trying to rebuild the system by checklist, and unable to copy additional vectors, with other aircraft nearby. Dominos. At what point, when accepting deviations from what's published, or even when getting to what's published, do we find the gates starting to close? At the point it becomes critical to know the high points, know the terrain, and know the details, it's already too late to begin looking it up. Hence prebriefing. Ultimately, all that could have been avoided here by simply flying the published procedure in accordance with the clearance, which was "at or above 7,800." 10,000 on the arc is at or above, and hides a multitude of sins. |
|
|
All times are GMT -8. The time now is 02:07 AM. |
User Alert System provided by
Advanced User Tagging v3.3.0 (Lite) -
vBulletin Mods & Addons Copyright © 2024 DragonByte Technologies Ltd.
Website Copyright ©2000 - 2017 MH Sub I, LLC dba Internet Brands