I was using this workaround method when flying into airports that do not have stars or have stars but ATC radar vector instead, because of the high traffic volume!!, and the controllers vector you everywhere, I found this to be the best technique personally for a idle path 3 degree descent for some high traffic airports in SE Asia
To follow my logic here goes!!
Following the FMC programming from below, this technique is based on using the landing RWY threshold height from the legs page data to calculate a dynamic 3 degree descent profile
Hope this helps and my explanation is understood! PS this technique takes a little practice but is great once the operator can master this technique (best practiced after line training!!) and will always give a 3 degree profile in relation to the rwy threshold
say we are at fl330 or whatever altitude (calculate the approx TOD mentally 3 * rule) set up the fmc des page for the anticipated arrival rwy, remain in vnav till the controller starts vectoring you for the approach or start the descent using the value of
VB 3.1 approx on the FMC des page, when the controller issues a descent at pilot discretion to the intially ATC step down alt), then we are looking for a
VB of approx 3.1 degrees on the DES page which equates to a approx 3:1 descent rate) us VS or FLCH to maintain this
VB, by using the VS associated with this
VB on the FMC des page. If you see that you are being vectored away from the airport for a while your
VB will start to show a
VB of say 3.0, 2.9, 2.8 etc.... to maintain the the
VB of 3.1 reduce the VS initially to approx a value less than the current VS
VB ie (say we have
VB 2.8 reducing with a VS of 500FPM use say a value of 200FPM to maintain the
VB 3.1 relation) use VS and or FLCH as your tools to refine the VS to equal the desired
VB.
Similarly if you get vectored a short dog leg (short cut vector due traffic sequencing) on to final app course the
VB trend will start to get high ie 3.1, 3.2, 3.3 etc... use FLCH and speed brake if needed as a way to get down back to the
VB 3.1 profile. when you are starting to approach 2 thousand feet above the commencement of the approach, Make the
VB 2.5 now to capture the g/s from 1 dot below (to prevent you from paralleling the ils G/S for capture) or use a
VB of 2.0 = 2 dots below the ils g/s on the b737 classic and NG presentations, this will ensure a idle path des and that the throttles open up when you start adding more drag and the final flaps.
The key to remember is to try and maintain the VB3.1, so if you are slightly low ie (
VB 2.7-2.9) use VS to fine tune, and say you are way high (
VB 6.0 -8.0) use FLCH and speed brake. (practice will refine this technique)
The above technique really does help to always know the req ROD to achieve for any RWY and is particularly useful for a late runway change (ie parallel runway)
FMC input technique below
Example rwy: 27 threshold height from fmc 434’
To create a rwy
vb using fmc u5.0 software b737 classic
1. Legs page
2. Enter rw27/-.1
3. Place above rw27 waypoint on legs page
4. Then from the entry above rw27 new waypoint (rw201)
5. Downselect this new waypoint (rw201) to the des page (lsk 3r)
6. Add 30’ to calculation ie… rw201/0464 (-.1 =1/10 nm in front of rwy threshold) des page lsk 3r or fix lsk 1l
7. Go back to legs page to erase the waypoint “(rw201)”
Example rwy: 27 threshold height from fmc 434’
To create a rwy
vb using fmc u10.6 software (b737 ng)
1. Legs page
2. Enter rw27/0434
3. Downselect this new waypoint (rw27) to the des page
4. For the
vb calc enter this format into the des page rw27/0434 (lsk 3r)
5. You do not need to worry about deleting the waypoint from the legs page like in the previous u5.0 example
Example rwy: 04 threshold height from fmc 56’ (made by the pilot from the nav supp) fmc d’base does not contain this rwy yet! Only the icao airport codes
To create a rwy
vb using fmc u5.0/u10.6 software from a pilot made rwy input from nav/supp page
1. Legs page
2. Locate the rw04 waypoint
3. Downselect this new waypoint (rw04) to the fix page (lsk 1l) or des page (lsk 3r)
4. For the
vb calc enter this format into the des page rw04/0056 (lsk 3r)
5. You do not need to worry about deleting the waypoint from the legs page like in the first u5.0 example, this also applies for u10.6 software