Descent Planning
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Descent Planning
Hi all.. I was having a bit of a discussion with a captain of mind as to the best method of desent planning ro make a smooth transition all the way from tod to final approach course. Okay if atc allows it it can be done but was wondering if any of you had any special methods of techniques you used? Any rules of thumb I have not heard before?
Cheers guys..
Ollycopter
Cheers guys..
Ollycopter
Descend
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1) Altitude to lose x 3 gives distance to descend
ie 30,000' to lose 30 x 3 = 90 miles + 10 as above = 100 miles
2) Ground speed x 5 gives ROD to give a 3deg descent
ie 300kts GS 300 x 5 = 1500'/min
3) Also, distance out x 3 gives height (x100') above level off point or runway if on 3 deg descent/glideslope
ie 20 miles before level off point
20 x 3 = 6000'
or if on glideslope
8 x 3 = 2400'
4 x 3 = 1200'
ie 30,000' to lose 30 x 3 = 90 miles + 10 as above = 100 miles
2) Ground speed x 5 gives ROD to give a 3deg descent
ie 300kts GS 300 x 5 = 1500'/min
3) Also, distance out x 3 gives height (x100') above level off point or runway if on 3 deg descent/glideslope
ie 20 miles before level off point
20 x 3 = 6000'
or if on glideslope
8 x 3 = 2400'
4 x 3 = 1200'
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On the Boeing family I used
Altitude x 3
+1 mile for each 10 knots of Tail wind (-1 for Head)
+1 mile per 10 knots above 200 kts to allow for slowing down. (200 to 220 is where you get the flaps. It is a an easy figure to use too).
decending at 280 kts on passing 25000' with 25 kts tail gave me
3x25000 + 8 + 3 (rounding 25kts to 30) = 86 miles and no speedbrake needed.
Now that I fly the Citation XL, I would say slowing down is not a problem so I am adapting the formula as there is no real need to allow as much for deceleration.
For the rate, I divide by 2 the ground speed (same as multiply by 5 but I find it less demanding). 280/2= 140(0') fpm
Altitude x 3
+1 mile for each 10 knots of Tail wind (-1 for Head)
+1 mile per 10 knots above 200 kts to allow for slowing down. (200 to 220 is where you get the flaps. It is a an easy figure to use too).
decending at 280 kts on passing 25000' with 25 kts tail gave me
3x25000 + 8 + 3 (rounding 25kts to 30) = 86 miles and no speedbrake needed.
Now that I fly the Citation XL, I would say slowing down is not a problem so I am adapting the formula as there is no real need to allow as much for deceleration.
For the rate, I divide by 2 the ground speed (same as multiply by 5 but I find it less demanding). 280/2= 140(0') fpm
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What do you guys use as quick recalculations for if, say, you get a short cut through a star?? I find it a pain and just want to get down to final intercept rather then plan it on short notice...
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All depends upon the direction you're approaching. Unless it's a straight in app I use this... dme distance direct to the field plus double what ever distance final you expect. Now use you ROD Calcs to sort the rest.
Take the first two Numbers of the G/s then divide by 2 ie G/s 300kts =30/2 = 15(x100'/min) 1500'min
Just try and build up a mental Circuit in your mind then 'unfold it'
All about trying to see the picture
Take the first two Numbers of the G/s then divide by 2 ie G/s 300kts =30/2 = 15(x100'/min) 1500'min
Just try and build up a mental Circuit in your mind then 'unfold it'
All about trying to see the picture
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For shortcuts the best thing is to be prepared. ie to expect/suspect it but of course it is only with some experience you get that.
On the other hand when it happens and I need a distance to help me achieve a CDA, I ask for a "Direct Intercept the Final course"(Not Direct the Waypoint) on the FMS. Pretty good and gives you a distance from position to, say the Final Fix then RWY.
Or look at your Nav Display and the Distance Rings from your position to the some point you have in the FMS, located on the final course (such as the FF).
You can the visualise how much you have to go before reaching the Final course, then read the distance from the FF to the RWY.
If I have time, I prefer the first option as this entry will tidy up what is displayed. If not, number two suits me too.
As for being prepared, I would tend to reduce the speed (if possible/allowed), say from 250 to 220Kts at the moment I think is opportune. That way, I save fuel (and noise) then if my plan comes to fruition (get the shortcut), I will convert this energy into ROD to recover my flight path (the one I work out as I hit the FLC, V/S button or whatever it is called).
No excessive fuel burn here too and the noise level in the cabin remains low as the engines are idling (bearing in mind PAX confort during pitch change, ie. what FLC as opposed to V/S).
PS: I Really can't spell
On the other hand when it happens and I need a distance to help me achieve a CDA, I ask for a "Direct Intercept the Final course"(Not Direct the Waypoint) on the FMS. Pretty good and gives you a distance from position to, say the Final Fix then RWY.
Or look at your Nav Display and the Distance Rings from your position to the some point you have in the FMS, located on the final course (such as the FF).
You can the visualise how much you have to go before reaching the Final course, then read the distance from the FF to the RWY.
If I have time, I prefer the first option as this entry will tidy up what is displayed. If not, number two suits me too.
As for being prepared, I would tend to reduce the speed (if possible/allowed), say from 250 to 220Kts at the moment I think is opportune. That way, I save fuel (and noise) then if my plan comes to fruition (get the shortcut), I will convert this energy into ROD to recover my flight path (the one I work out as I hit the FLC, V/S button or whatever it is called).
No excessive fuel burn here too and the noise level in the cabin remains low as the engines are idling (bearing in mind PAX confort during pitch change, ie. what FLC as opposed to V/S).
PS: I Really can't spell
Last edited by PPRuNeUser0215; 31st Jan 2007 at 06:18.
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3 times your height to loose minus ten miles if theres a headwind, plus ten if theres a tailwind. but always add an extra 5 miles to this as a safety net and to slow down and set up prior to intercepting approach, thats very important, theres nothing worse than hitting the loc at 250 knots 1000 ft high and clean. done it loads and it aint worth for the extra 1 minute 20 seconds you save.
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It also depends on the weight of the aircraft you are trying to descend efficiently.
A "H" aircraft near or at MLW will need a max of 3 deg decent path. If it is empty with minimum fuel you could be looking at more.
A "M" aircraft, 3 degs power off will not really be 3 degs. 3.5 or more if you are light with wind considerations.
Just my 2 cents worth having operated heavy, medium and light aircraft.
Weight plays a very big part in this. Ask your selves why a glider takes on ballist to increase speed for a given range.
A "H" aircraft near or at MLW will need a max of 3 deg decent path. If it is empty with minimum fuel you could be looking at more.
A "M" aircraft, 3 degs power off will not really be 3 degs. 3.5 or more if you are light with wind considerations.
Just my 2 cents worth having operated heavy, medium and light aircraft.
Weight plays a very big part in this. Ask your selves why a glider takes on ballist to increase speed for a given range.
CDA
All of the above work but mostly for arrivals at airfields without formal proceedures.
I find the best way to achieve a CDA is to work out your groundspeed for your chosen descent speed and then set a RoD to achive the next STAR or waypoint desired height. When cleared direct to a point set the RoD which will get you there at the published or desired height. This will normally give you a CDA from ToD to touch down but you will need to vary your RoD throughout the approach.
For example if you are cleared to FL90 and you can see a point on the chart which states FL90 there is no point using the descent profiles above if they get you down to FL90 before the point as it is probably a controller change point, so aim to arrive so you will be passing the ht at the point and you will be more likeley to achieve a smooth descent profile.
None of these proceedures works every time at every airfield, airmanship dictates and be prepared to switch between techniques.
Regards
MM
MM
I find the best way to achieve a CDA is to work out your groundspeed for your chosen descent speed and then set a RoD to achive the next STAR or waypoint desired height. When cleared direct to a point set the RoD which will get you there at the published or desired height. This will normally give you a CDA from ToD to touch down but you will need to vary your RoD throughout the approach.
For example if you are cleared to FL90 and you can see a point on the chart which states FL90 there is no point using the descent profiles above if they get you down to FL90 before the point as it is probably a controller change point, so aim to arrive so you will be passing the ht at the point and you will be more likeley to achieve a smooth descent profile.
None of these proceedures works every time at every airfield, airmanship dictates and be prepared to switch between techniques.
Regards
MM
MM
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All the above suggestions achieve the TOD calculation simply.
For my halfpenny's worth, I use all the same calcs but disregard the additional 10 miles for slowing down at 10,000ft/ lowering flaps, slats and gear. I gain the 10 miles by increasing the RoD in the early part of the descent (where there is less drag and higher TAS), and then reduce RoD and IAS as I get into the lower and denser air at say 15,000ft.
If you descend at 2,500-3,000fpm from top of drop (above FL350) till you reach FL150 then decrease the RoD to 1,500 fpm without changing power, everything works out beautifully for a constant power approach.
For my halfpenny's worth, I use all the same calcs but disregard the additional 10 miles for slowing down at 10,000ft/ lowering flaps, slats and gear. I gain the 10 miles by increasing the RoD in the early part of the descent (where there is less drag and higher TAS), and then reduce RoD and IAS as I get into the lower and denser air at say 15,000ft.
If you descend at 2,500-3,000fpm from top of drop (above FL350) till you reach FL150 then decrease the RoD to 1,500 fpm without changing power, everything works out beautifully for a constant power approach.
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As you all know, we work all the problems out in our head for the planning(7 to the 8th power divided by 3.14 X TAS + 5nm - 6% blah blah blah) program the FMS, get it all set up nice and neat. Then ATC changes everything!!
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And another one...
Example:
FL400
GS 450
FL: 40 X 3 = 120 nm
GS 45 - 15 = 30 nm
TOTAL: 150 nm
Easy to check as you descend...
As you approach FL300 at GS 400 you figure out that you need 115 nm. If reaching FL300 you are closer then that then just increase your ROD a bit or vice versa if you're further out.
I do this quite frequently during descent to ensure I stay on profile... Normal requires very few corrections.
Works for the CL604 as well as for the Airbus family...
Will
FL400
GS 450
FL: 40 X 3 = 120 nm
GS 45 - 15 = 30 nm
TOTAL: 150 nm
Easy to check as you descend...
As you approach FL300 at GS 400 you figure out that you need 115 nm. If reaching FL300 you are closer then that then just increase your ROD a bit or vice versa if you're further out.
I do this quite frequently during descent to ensure I stay on profile... Normal requires very few corrections.
Works for the CL604 as well as for the Airbus family...
Will
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G550 descent planning
Any tips on the G550?? The programmed speeds are pretty useless. MAN speed to the rescue..
Yes, set the FMS to give a 2.5% descent.
Always ensure you plan for a direct approach, by looking at the DME distance to airport, and plan to make that distance your track miles.
In Moscow especially, plan for the short approach. In geneva, expect the "can you accept the base tune now".
Manual speed is to be avoided, whenever possible, (FLCH provides the protection.)
Worst case, a little speed brake, (just a little).
if you wait for the VPATH prompt, you are too late.
The G550 is slippery as an ice cube. One problem is that the G450 G350 has the same type rating, and the differences course does not address this important difference. The G4 airframe can never be accused of being slippy.
glf
Yes, set the FMS to give a 2.5% descent.
Always ensure you plan for a direct approach, by looking at the DME distance to airport, and plan to make that distance your track miles.
In Moscow especially, plan for the short approach. In geneva, expect the "can you accept the base tune now".
Manual speed is to be avoided, whenever possible, (FLCH provides the protection.)
Worst case, a little speed brake, (just a little).
if you wait for the VPATH prompt, you are too late.
The G550 is slippery as an ice cube. One problem is that the G450 G350 has the same type rating, and the differences course does not address this important difference. The G4 airframe can never be accused of being slippy.
glf
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We always worked on a 3 degree profile but nearly always found ourselves getting in the way of boeing/buses on the same route invariably 2/4000 feet below us at the same cruise speed. Invariably we ended up getting vectored all over the place to make room for the pax jets that would hinder our descent. Anyway over the three years or so we have been operating the thing we have refined our descent FPA to 3.7 degrees, this gives us a TOD at the same point that most of the commercial transports do which give us a more or less Throttles Closed CDA, we can be 305 knots at the beginning of the descent with TL's closed and end up at 270 @ Fl100 which works well with our 270 restriction a through FL80.
Up until recently I've always been a 3x ALT + 10 kind of bloke, however our avionics are very good (Honeywell Epic) and frustratingly on our particular type it generally does a good job.
In the transition to becoming a child of the magenta one of the factors was the 160kg we saved per sector in doing so, saving the operation £15-20k per year in fuel.
Nothings carved in stone though and the Geneva/Barcelona turn ins can show anybody up all down to experience and being more cunning than those Damn Air Trafickers
Ollycopter whats the birdstrike Airspeed figure through FL80 you need to make in a 750
Up until recently I've always been a 3x ALT + 10 kind of bloke, however our avionics are very good (Honeywell Epic) and frustratingly on our particular type it generally does a good job.
In the transition to becoming a child of the magenta one of the factors was the 160kg we saved per sector in doing so, saving the operation £15-20k per year in fuel.
Nothings carved in stone though and the Geneva/Barcelona turn ins can show anybody up all down to experience and being more cunning than those Damn Air Trafickers
Ollycopter whats the birdstrike Airspeed figure through FL80 you need to make in a 750