Question #306 for the NG drivers here.
When you guys ask for descent from cruise altitude, I assume you ask for it somewhat in advance of the VNAV profile descent?
Reason I ask this is because I've seen several cases of a WJA airplane at 410 or 390 ask for descent, then don't actually start descending for 15-20 miles.
Sometimes with the phrase "WJA XXX leaving 390 for 290 now"
Works well and good if you're issued PD to 290, but if you request 290 and are issued "Descend FL290" without PD involved, a pilot should begin their descent as soon as practicable. Normally it's not really an issue but just a procedural thing.
More than once I've seen this occur then a controller have to check if the airplane is actually vacating the altitude.
Also another question here, when you guys hit TOD does the airplane maintain altitude while it slows to descent speed then descend, or does it slowly begin descent while backing the speed off?
Also if a controller asks you to pick up your Rate of descent or climb for that matter, do you have to switch to LVL CHG or do you just dial up a set Vertical rate, or is it something you can set in the FMS (Max Rate/Angle etc)
VNAV Descent
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invertedattitude
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"When you guys ask for descent from cruise altitude, I assume you ask for it somewhat in advance of the VNAV profile descent?
Reason I ask this is because I've seen several cases of a WJA airplane at 410 or 390 ask for descent, then don't actually start descending for 15-20 miles.
Sometimes with the phrase "WJA XXX leaving 390 for 290 now"
Works well and good if you're issued PD to 290, but if you request 290 and are issued "Descend FL290" without PD involved, a pilot should begin their descent as soon as practicable. Normally it's not really an issue but just a procedural thing.
More than once I've seen this occur then a controller have to check if the airplane is actually vacating the altitude. "
Sounds like someone forgot to start the descent. However, In the aircraft, a yellow FMC Alt light turns on if you go within 10 NM of the TOD without a lower altitude set. About 1 NM mile prior is where the NFP usually asked for lower. So is it exactly 11 miles, or approx. 20?
"Also another question here, when you guys hit TOD does the airplane maintain altitude while it slows to descent speed then descend, or does it slowly begin descent while backing the speed off? "
In VNAV it slows and descends at the same time. If we start down prior to 3:1 or the set VNAV path the aircraft goes down at 1000 FPM unitl it flies in to the descent path then goes flight idle.
"Also if a controller asks you to pick up your Rate of descent or climb for that matter, do you have to switch to LVL CHG or do you just dial up a set Vertical rate, or is it something you can set in the FMS (Max Rate/Angle etc)"
That's a preference depending on pilot. In climb, you can ask for max rate or max angle via FMC, you can also just request a slower speed and guess if it will give you a better rate.
In descent it goes down in LVL CHG, VS, or VNAV, or VNAV w/Speed Intervention. Myself I go Level Change unless it's in a condition where it may pull some G's, then I'll press V/S and manage the speed myself.
Reason I ask this is because I've seen several cases of a WJA airplane at 410 or 390 ask for descent, then don't actually start descending for 15-20 miles.
Sometimes with the phrase "WJA XXX leaving 390 for 290 now"
Works well and good if you're issued PD to 290, but if you request 290 and are issued "Descend FL290" without PD involved, a pilot should begin their descent as soon as practicable. Normally it's not really an issue but just a procedural thing.
More than once I've seen this occur then a controller have to check if the airplane is actually vacating the altitude. "
Sounds like someone forgot to start the descent. However, In the aircraft, a yellow FMC Alt light turns on if you go within 10 NM of the TOD without a lower altitude set. About 1 NM mile prior is where the NFP usually asked for lower. So is it exactly 11 miles, or approx. 20?
"Also another question here, when you guys hit TOD does the airplane maintain altitude while it slows to descent speed then descend, or does it slowly begin descent while backing the speed off? "
In VNAV it slows and descends at the same time. If we start down prior to 3:1 or the set VNAV path the aircraft goes down at 1000 FPM unitl it flies in to the descent path then goes flight idle.
"Also if a controller asks you to pick up your Rate of descent or climb for that matter, do you have to switch to LVL CHG or do you just dial up a set Vertical rate, or is it something you can set in the FMS (Max Rate/Angle etc)"
That's a preference depending on pilot. In climb, you can ask for max rate or max angle via FMC, you can also just request a slower speed and guess if it will give you a better rate.
In descent it goes down in LVL CHG, VS, or VNAV, or VNAV w/Speed Intervention. Myself I go Level Change unless it's in a condition where it may pull some G's, then I'll press V/S and manage the speed myself.
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Rotten Apple #1
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Normally the descent mach speed will be very near, if not identical to the cruise mach just prior to Top of Descent. As WJ700 pointed out, if a lower descent mach speed was manually entered, it would slow first, then descend.Also another question here, when you guys hit TOD does the airplane maintain altitude while it slows to descent speed then descend, or does it slowly begin descent while backing the speed off?
Tactile John
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invertedattitude
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Thanks for all the info guys, in regards to when they descend, I've seen them carry on for 20 miles or maybe even a little more before starting down.
This is not an everyday thing by any means, just curious if it was because of the VNAV system, seems like it may be just that.
Thanks very much.
This is not an everyday thing by any means, just curious if it was because of the VNAV system, seems like it may be just that.
Thanks very much.
there's a very obvious 't/d' symbol on the nav display that the FMC calculates. So the pilot knows exactly when the plane want's down, according to the profile it has. Sometimes guys do ask for descent 15-20 miles before, and just sits there. Guys with good airmanship let the controller know what he's planning, too bad not everyone's doing it.
I dont fly a 737 but i do fly a jet with FMS. Our VNAV gives us a "Top of Descent" Alert about 12 miles before the VNAV actually captures. We usually ask for descent and arm the VNAV at this point. 12 miles later the descent is started. Which is usually less than 2 minutes. Hope that helps.
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invertedattitude
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This is probably what I've seen. Like I said it's never usually a problem, chances are if a controller needs you down for sep, they wouldn't wait for a pilot to ask for lower to begin with, but a pilot not starting down when they ask for it could change a controllers plan for other traffic.Four1oh wrote:there's a very obvious 't/d' symbol on the nav display that the FMC calculates. So the pilot knows exactly when the plane want's down, according to the profile it has. Sometimes guys do ask for descent 15-20 miles before, and just sits there. Guys with good airmanship let the controller know what he's planning, too bad not everyone's doing it.
