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Two (2) more descent techniques

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Since there's been some good discussions on descents lately, I thought I'd add two more RW examples that we used on this last trip.

 

Ex. 1

 

SEA-DEN on the MOLTN2. We were at cruise at FL370 and Denver Center wanted us to "Descend now to FL320, pilot's discretion FL240."

 

There are many ways to do this, but me having the attention span that I do, I like to have it ready now. Here's a clean/smooth way of doing it:

  1. Reset the MCP to FL240
  2. Enter a new cruise alt of FL320

If you're in VNAV PATH, the plane will descend and level at FL320 and at the T/D, it will start down to FL240. Sit back, enjoy the Pike Place, black, no sugar.

 

Ex. 2

 

DEN-SEA on the CHINS9. We're inside HUMPP, level at 15,000 and 270kts for AUBRN at 12,000 and 250kts. Since SEA wasn't too busy, they had us descend to 10,000. That way you get a little bit shorter downwind. We still needed to slow for 250 at AUBRN, but the 12,000 restriction was gone.

 

Here's what I did:

  1. Set the MCP to 10,000
  2. LVL CHG at the current 270kts
  3. Let the nose pitch down and V/S stabilize (around 2000fpm)
  4. V/S (now it locks in that 2000fps)
  5. Reset the MCP to 250kts
  6. Once the jet levels at 10,000, the speed slows to 250

Now, I could have done this with VNAV, but this was easy and smooth. I needed to reduce the V/S a bit as we descended to 1700fpm so the jet maintained 270. Had I been doing a VNAV approach, I probably would have staying in VNAV, but from this point it was all vectors, so I left VNAV behind for the day.

 

That's just how we did it, your mileage may vary.


Matt Cee

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Great write-up mate, thanks for sharing :)


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To add to scenario 2:

 

I could have done this:

  1. MCP 10,000
  2. LVL CHG 270kts
  3. Level at 10,000 and
  4. Select 250kts

This would have worked as well. I used the V/S procedure probably because it would take care of the speed change for me. It was also fair weather cumulus at SEA, so it was a bit bumpy in the descent. LVL CHG and VNAV (idle descent) would have been a bit "pitchy." V/S keeps a nice, constant deck angle.

 

If I wanted to go crazy, I could have used CWS Pitch!


Matt Cee

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Sit back, enjoy the Pike Place, black, no sugar.

 

Sign of a true airline pilot right there.


Joe Diamond

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Sit back, enjoy the Pike Place, black, no sugar.

You probably got black, no sugar and burned.

 

Thanks for the descent information.


Michael Cubine
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There was a question about whether Ex. 1 would require the use of ALT INT. No it does not, it appears.


Matt Cee

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There was a question about whether Ex. 1 would require the use of ALT INT. No it does not, it appears.

 

In that example if you pressed the ALT INT button I believe it would activate the descent mode and continue right through FL320 and level at FL240.

 

It's also worth noting that anytime you use the cruise descent to check the speeds on the cruise and descent pages as the box tends to drop the speed quite a bit if you are in ECON.  I've gotten messed up by that more than once.


Joe Diamond

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In that example if you pressed the ALT INT button I believe it would activate the descent mode and continue right through FL320 and level at FL240.

 

It's also worth noting that anytime you use the cruise descent to check the speeds on the cruise and descent pages as the box tends to drop the speed quite a bit if you are in ECON. I've gotten messed up by that more than once.

If you "re-cruise" it, it should still stop, right? I haven't flown a plane with ALT INT since 2011.

 

Our SOP is to overwrite the DESC ECON SPD with .78/280. That is often forgotten until the standard "Why is it slowing?" callout is made.


Matt Cee

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Our SOP is to overwrite the DESC ECON SPD with .78/280. That is often forgotten until the standard "Why is it slowing?" callout is made.

 

Loving how you call it a "callout" and the SOP-like thread title including "two (2)."


Kyle Rodgers

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If you "re-cruise" it, it should still stop, right? I haven't flown a plane with ALT INT since 2011.

 

Our SOP is to overwrite the DESC ECON SPD with .78/280. That is often forgotten until the standard "Why is it slowing?" callout is made.

It depends on the sequence of events.  If you set FL240 and press the ALT INT button it will go into descent mode and dump the cruise page altogether.  If you re-cruise it after pressing the ALT INT button it will stop at FL320 but all you have done is increase your workload as you could have accomplished the same thing by entering FL320 on the cruise page in the first place.

 

The cruise descent is another trap.  If you initiate one to close to the top of descent point it will blow right through the path.  My personal cutoff for a cruise descent is 80NM from the TOD.  If I am within that I'll initiate the descent with the ALT INT button.

 

Our standard descent is cruise mach transitioning to 290 KIAS.  Going into Miami we always get a clearance to cross a fix at FL240.  The fix is pretty far out so usually you re-cruise it at FL240.  At that point we are already at 290KIAS.  The box will keep the 290 but will drop the mach to something absurdly low like .5.  If you don't catch the change in mach number when you hit the new TOD the throttles retard followed by the obligatory "what the heck is it doing now" callout.


Joe Diamond

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It depends on the sequence of events. If you set FL240 and press the ALT INT button it will go into descent mode and dump the cruise page altogether. If you re-cruise it after pressing the ALT INT button it will stop at FL320 but all you have done is increase your workload as you could have accomplished the same thing by entering FL320 on the cruise page in the first place.

 

Yeah, that was my thought, was well. I don't want to push any more buttons than necessary - it's like working for free! ;)


Matt Cee

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Resetting the cruise can cause large speed changes depending on the cost index in use or choice of speed for the descent. We use a low cost index and descend at a low speed of around 250kts at transition to CAS. If we re-set the cruise, the aircraft would again accelerate to econ cruise speed when leveling off.

 

Edited to add: Oops! Joe already said this :P Note to self, read whole thread before opening gob.


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