I like to start my descent about 5 miles before TOD but when I hit des now, nothing happens.

Anyone else have this issue?

maveric751 wrote on Feb 14^th, 2019 at 11:21pm:

I like to start my descent about 5 miles before TOD but when I hit des now, nothing happens. Anyone else have this issue?

Did you dial in your new descent altitude in the MCP?

The problem with DES NOW is known, since there was already a thread here, but unfortunately can not find it anymore. With DES NOW enabled, only the speed goes back, but the 1000 ft / min descent is not initiated.

FraPre wrote on Feb 15^th, 2019 at 8:50am:

The problem with DES NOW is known, since there was already a thread here, but unfortunately can not find it anymore. With DES NOW enabled, only the speed goes back, but the 1000 ft / min descent is not initiated.

Not a single issue with DES NOW, as I just hit it in the -300 and voila! the -300 is descending as can be clearly seen in the attached cockpit screenshot

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I've also experienced this. Just yesterday I tried the DES NOW feature and nothing happened. I then used FLC for the descent and when I tried the VNAV function, the aircraft started to climb.

Colvale wrote on Feb 15^th, 2019 at 9:51pm:

FraPre wrote on Feb 15th, 2019 at 8:50am: The problem with DES NOW is known, since there was already a thread here, but unfortunately can not find it anymore. With DES NOW enabled, only the speed goes back, but the 1000 ft / min descent is not initiated. Not a single issue with DES NOW, as I just hit it in the -300 and voila! the -300 is descending as can be clearly seen in the attached cockpit screenshot

That looks like an issue on it's own....-4000 fpm and overspeeding...

I'm also having an issue where "descend now" doesn't appear to actually do anything. I've already lowered my altitude in the MCP but nothing happens.

Something is not quite right somewhere.

Just for testing purposes, as I am right now in a 757-300 pax at 36000ft, I selected 10000, hit FL CH, and voila! she is descending as cane be seen by attached

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Colvale wrote on Feb 27^th, 2019 at 8:55pm:

Something is not quite right somewhere. Just for testing purposes, as I am right now in a 757-300 pax at 36000ft, I selected 10000, hit FL CH, and voila! she is descending as cane be seen by attached

I'll give it another shot -- but these issues stem from the DES NOW button in the FMC and not so much the FL CH (I'll test both though).

I do own the 757-300 but haven't flown it yet. All the issues I've had to date have been with the -200 variant. I almost always have to revert to V/S mode to get the aircraft to descend.

Edit: You cropped out your speed from that screenshot  :'(

Here it is then

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Just an update -- I did a test flight today and it actually worked the way it should! This is the first time it's worked for me...my procedure didn't change so I'm not sure what clicked this time around...

It's worth noting that it did take a moment to kick in (~10 seconds), but it was able to work itself out.

I had a video recording going but it's not needed as it was rather uneventful this time around. I'll record the next few descents just in case it happens again.

Here's the recording for those who are curious:https://youtu.be/9csYRFQyGl8
Note that you can't see my cursor which might make it hard to see what I'm doing and when.

This 757 is a cruel mistress....on the same flight, it completely blew through the speed restrictions at 10,000 feet. It went from 260 knots during descent, but tried to go up to 426 knots after descending below 10,000 feet, despite having SEL SPD at 260 and SPD TRANS at 240/10000.  :o

I'll have to start a seperate thread for that I think.

Mission.Control wrote on Mar 1^st, 2019 at 2:50am:

This 757 is a cruel mistress....on the same flight, it completely blew through the speed restrictions at 10,000 feet. It went from 260 knots during descent, but tried to go up to 426 knots after descending below 10,000 feet, despite having SEL SPD at 260 and SPD TRANS at 240/10000.  :o I'll have to start a seperate thread for that I think.

Has been answered elsewhere. This is a double post from you.

I think the whole thing did not work better than before. The distance to TOD was probably quite low the moment you started DES NOW, as well as the turn could have had an influence. Initially, only the speed goes back to the new setpoint, but no sink rate, which should now be 1000 ft until the normal path is captured. Later you can see a sink rate of 2000 ft on the FO side, at the same time the vertical path deviation indicates that you are still on top of the path. For DES NOW, the deviation would indicate that you're below the path, diamond up. Approaching the normal path, the diamond moves towards the center, with trapping the normal path it should stay in the middle, but with an increasing rate of descent.