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hmslion

Deceleration help needed

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Ok, I am a frequent flyer on Alaska Airlines so I spend a lot of time on the 700s, 800s and 900s they drive.I can't remember ever being on a flight where the pilot is sitting on the spoilers as much as I am having to do to slow the planes down in VNAV. I'm even having to use the spoilers when I'm at Flaps1 with the LE slats down.Are they starting their descent earlier than recomened by VNAV? It would have to be by 30 - 50 NM though to have much difference in the speeds on descent.I'm using TopCat to set fuel amounts so I'm not overloading the plane with fuel on descent.Would appreciate some help on how to slow these slippery birds down.Colin Ware - Seattle

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Sounds accurate to me! Though I have no issues letting VNAV handle the entire descent phase without spoilers. Are you sticking to the proper flaps/gear schedule?An experienced friend of mine told me (referring to the 73'classics) that you can slow down, you can descend, but you can't slow down and descend. Apparently the 727 was a different story.


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What is your cost index value? As far as I know, this can affect where your T/C and T/D are along your route. Correct me if I'm wrong, a higher CI will increase cruise speed and shorten decent path, making for a steeper decent to ALT restrictions on approach. This is just my opinion though.


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If you have a tailwind during descent, add about 20 percent more wind speed in the CDU than actually forecast.. Your T/D might be too close, just a guess though.. Good rule to follow is with tail wind, descent should begin about 120nm, about 100 with headwind..


Tony Fontaine

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CaptBillyBob talking about at 35,000ft that definitely sounds right

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What is your idle thrust below FL150 in a clean configuration (no flaps, no gears)?If it is near to 40% of N1 you are experiencing the idle thrust bug that will be fixed on the SP1b.If it is normal (around 34%) you have to check wheater and cost index. Fill the des forecast page and use a cost index between 20-40.A trick: fill the des forecast page with a tail wind a bit higher than what is present, it will change your TOD a bit, reducing the descent ramp.In the first case, you will solve by using the keyboard G key to rise/lower gear.


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Andrea Daviero

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The other thing that confuses the heck out of the FMCs is arrivals that don't have crossing restrictions and end on a long vector. The ROYIL2 at IAD is an example (it does show expected crossings, but those are generally not set in the FMC, though they occasionally are). Since the ROYIL2 does not have any hard crossing altitudes, and none of these expected crossings are hard-set in the nav database, the FMC will calculate its own descent, and you'll see the long vectors at the end, that essentially put the aircraft on a downwind for the airport. Because of this long vector, the FMC will assume you have more distance to travel and calc a slightly later descent. Drop the 11,000' expected restriction at DRUZZ (pronounced "Drew's" if it matters), and you'll see the T/D jump closer to you. That should help the descent some, first of all.Assuming all of that is out of the way, consider your Cost Index. The cost index will drive your descent speeds. If you use one that is too high, the plane will come booking down and have a tougher time pulling back on the reigns to hit 250 by 10,000 (or whatever other speed restriction you need to hit). Furthermore, you get a discrepancy between how the plane wants to descend (idle power using pitch for speed), versus how ATC wants you to descend (driven mostly by restrictions on STARs). Because of this, the T/D may calculate fine, but there's a steep segment between crossing restriction 1 and restriction 2. Most of the time (as outlined in a quasi-tutorial by one of the actual 737 pilots who peruses these forums indicated), you can get around using the speed brakes by using SPEED INT to temporarily dial in a higher descend speed, which will descend at a higher vertical speed. Once you make up for being high, and slightly overshoot the mark, you can bring the speed back to the VNAV calc, and let it go back on full VNAV on its own.


Kyle Rodgers

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My recommendation is, if the last part of your decent just before final approach is gonna be a steep one, so that you're gonna have problems slowing down, I recommend thisJust at top of descent, just press SPD INTV (speed intervention), and dial the speed up a bit e.g. 300 kts IAS. In this way, the airplane will do a steeper descent to maintain the speed you dialed in. This means you will reach your glide slope intercept altitude earlier (e.g. 2000 ft), giving you more time to slow down just before final approach.


Arjen Vandervelde

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My recommendation is, if the last part of your decent just before final approach is gonna be a steep one, so that you're gonna have problems slowing down, I recommend thisJust at top of descent, just press SPD INTV (speed intervention), and dial the speed up a bit e.g. 300 kts IAS. In this way, the airplane will do a steeper descent to maintain the speed you dialed in. This means you will reach your glide slope intercept altitude earlier (e.g. 2000 ft), giving you more time to slow down just before final approach.
No offense but that's extremely unrealistic.

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No offense but that's extremely unrealistic.
I've seen JackC (a real world pilot), doing this in his videos... Can't find it now. Perhaps you didn't understand what I mean. When you see on your chart that the descent before your final approach is gonna be steep, you can press SPD INTV at e.g. 20,000 ft, and increase the speed on the MCP a little. In this way, VNAV will descent a little steeper. At a later moment, you can decrease the speed on the MCP again, in this way, VNAV will make a less steep descent, giving you more time to slow down.

Arjen Vandervelde

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I've seen JackC (a real world pilot), doing this in his videos... Can't find it now. Perhaps you didn't understand what I mean. When you see on your chart that the descent before your final approach is gonna be steep, you can press SPD INTV at e.g. 20,000 ft, and increase the speed on the MCP a little. In this way, VNAV will descent a little steeper. At a later moment, you can decrease the speed on the MCP again, in this way, VNAV will make a less steep descent, giving you more time to slow down.
I understood what you meant. I'd love to see those videos.

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No offense but that's extremely unrealistic.
He's describing what I mentioned, just in the wrong way...I pulled what I was talking about from the pilot who mills about here. He posted two tutorials on YouTube outlining the procedure, but with much more finesse than you see in the above posts.Here it is:http://vimeo.com/27673259

Kyle Rodgers

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He's describing what I mentioned, just in the wrong way...I pulled what I was talking about from the pilot who mills about here. He posted two tutorials on YouTube outlining the procedure, but with much more finesse than you see in the above posts.
Yeah, I'm looking for those tuts now that Arjen mentioned them.

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