Climb predictions on ND vs MCDU page (A320)
Join Date: Jan 2014
Location: Europe
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
If ATC gives you a descent rate, do you use V/S or open descent?
Same question for climb rate, what mode do you use?
A good pilot should ALWAYS monitor the energy level of the aircraft, especially in climb or descent. This means eyes on thrust, PFD, etc. Normally you wouldn't have any problems in V/S mode if you apply this correctly.
And to the guys getting personal and offensive because they disagree with a certain point of view: really mature.
Same question for climb rate, what mode do you use?
A good pilot should ALWAYS monitor the energy level of the aircraft, especially in climb or descent. This means eyes on thrust, PFD, etc. Normally you wouldn't have any problems in V/S mode if you apply this correctly.
And to the guys getting personal and offensive because they disagree with a certain point of view: really mature.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,404
Likes: 0
Received 0 Likes
on
0 Posts
pineteam
Instead of experimenting with VS there is more accurate and safer way given in airbus document of getting the best climb performance from the FMS. Since climb is the most fuel expensive phase if you change cost index to zero it operates at a speed which makes this phase shortest. But don't forget to change the CI at TOC otherwise it will cruise at snail's pace.
Instead of experimenting with VS there is more accurate and safer way given in airbus document of getting the best climb performance from the FMS. Since climb is the most fuel expensive phase if you change cost index to zero it operates at a speed which makes this phase shortest. But don't forget to change the CI at TOC otherwise it will cruise at snail's pace.
Join Date: Aug 2013
Location: PA
Age: 59
Posts: 30
Likes: 0
Received 0 Likes
on
0 Posts
vilas... that is correct, for CI=0.
Unfortunately, in many cases, not an option with airspace/noise constraints..
All;
While it is a higher workload, understanding the ac parameters does have value, for when to use the settings, the associated parameters, and understanding the variables, albiet brute force.
For TOD, optimized descent is a much different animal.
Unfortunately, in many cases, not an option with airspace/noise constraints..
All;
While it is a higher workload, understanding the ac parameters does have value, for when to use the settings, the associated parameters, and understanding the variables, albiet brute force.
For TOD, optimized descent is a much different animal.
Join Date: Aug 2013
Location: PA
Age: 59
Posts: 30
Likes: 0
Received 0 Likes
on
0 Posts
Jimmy, thanks for the input. As you note, the cost is relative.
Saving fuel has been a marketing ploy for quite some time (dont forget the carbon you save!)
TOC is far more difficult to show benefit, for all the reasons you mention, with all of the real time variables, especially winds and bleeds.
Time of flight that must be considered to see potential value if cost is the issue vs time.
TOD has far more value, especially in a coded procedure. The original 'idle descent' sales pitch was crap, especially mixing RNP and non-RNP traffic in the terminal environment, with ATC managing the flow.
Quickly learned there was no value, and actually penalties.
TOD management to FL10, now that is much different. A simple waypoint on the STAR to the system to calc and one at FL10 will optimize TOD for the ac real time (we can add a time constraint), will provide the optimum fuel, time and flow management for the flight.
Driving as fast as you can, to sit in a hold pattern?
Saving fuel has been a marketing ploy for quite some time (dont forget the carbon you save!)
TOC is far more difficult to show benefit, for all the reasons you mention, with all of the real time variables, especially winds and bleeds.
Time of flight that must be considered to see potential value if cost is the issue vs time.
TOD has far more value, especially in a coded procedure. The original 'idle descent' sales pitch was crap, especially mixing RNP and non-RNP traffic in the terminal environment, with ATC managing the flow.
Quickly learned there was no value, and actually penalties.
TOD management to FL10, now that is much different. A simple waypoint on the STAR to the system to calc and one at FL10 will optimize TOD for the ac real time (we can add a time constraint), will provide the optimum fuel, time and flow management for the flight.
Driving as fast as you can, to sit in a hold pattern?
Join Date: Apr 2007
Location: The Woodlands
Age: 64
Posts: 175
Likes: 0
Received 0 Likes
on
0 Posts
A bit more expanded from my previous post:
The best Rate of Climb occurs at a speed where there is Maximum Excess Power. As jet engines directly produce Thrust, not Power, it is necessary to consider Thrust multiplied by speed (Power = Force X Velocity). Thus, for a given Thrust setting, Power increases as TAS increases. Thrust actually ‘dips’ as speed increases, but then there is significant Ram recovery at higher Mach Numbers, thus further increasing Power at higher speeds. If we examine a Power Required and Power Available graph for a jet aircraft (about the only time that we’re interested in Power for a jet), it is observed that at the higher speeds, Power Available Vs Power Required (thus excess Power) is close to parallel with minimal divergence over a fairly wide speed range. Speed variation of the order of about plus and minus 20 to 30 knots from the optimum, shows only a slight reduction in excess Power with this speed variation.
For a fairly Light jet aircraft such as the A320, a fairly typical best Angle speed is 250 KIAS, best Rate 280 KIAS, and a typical Economy climb speed is 300 KIAS. Best Angle speed is at a somewhat lesser Rate than best Rate speed, so, if the two are compared, the low speed climb will take longer and consume more fuel to Top of Climb. Then, for a climb time of, say, 30 minutes at a difference of 50 KIAS (about 80 KTAS), there will be an incremental cruise of 40 nm required to just achieve the point where best Rate of Climb would have ended. Therefore, in the comparison between climb at best Angle and best Rate, the lower speed will cost you both time and fuel. The best Rate of climb can be refined further to optimize time and fuel. Remembering that up to 20 to 30 Knots ‘Off Optimum’ have only minimal effect upon excess Power, an Econ Climb speed a little above best Rate (+20 KIAS for the A320) will have a negligible effect upon Rate of Climb, but put the aircraft 30 miles or so further down track at Top of Climb. The very slight increase in climb Time and Fuel is more than off-set by the extra distance covered in the ‘fuel expensive’ climb, and elimination of the incremental cruise. If we consider operations for a Maximum Range profile (absolutely minimum fuel), it’s not at all uncommon to see a Climb speed in EXCESS of the initial Cruise speed.
The best Rate of Climb occurs at a speed where there is Maximum Excess Power. As jet engines directly produce Thrust, not Power, it is necessary to consider Thrust multiplied by speed (Power = Force X Velocity). Thus, for a given Thrust setting, Power increases as TAS increases. Thrust actually ‘dips’ as speed increases, but then there is significant Ram recovery at higher Mach Numbers, thus further increasing Power at higher speeds. If we examine a Power Required and Power Available graph for a jet aircraft (about the only time that we’re interested in Power for a jet), it is observed that at the higher speeds, Power Available Vs Power Required (thus excess Power) is close to parallel with minimal divergence over a fairly wide speed range. Speed variation of the order of about plus and minus 20 to 30 knots from the optimum, shows only a slight reduction in excess Power with this speed variation.
For a fairly Light jet aircraft such as the A320, a fairly typical best Angle speed is 250 KIAS, best Rate 280 KIAS, and a typical Economy climb speed is 300 KIAS. Best Angle speed is at a somewhat lesser Rate than best Rate speed, so, if the two are compared, the low speed climb will take longer and consume more fuel to Top of Climb. Then, for a climb time of, say, 30 minutes at a difference of 50 KIAS (about 80 KTAS), there will be an incremental cruise of 40 nm required to just achieve the point where best Rate of Climb would have ended. Therefore, in the comparison between climb at best Angle and best Rate, the lower speed will cost you both time and fuel. The best Rate of climb can be refined further to optimize time and fuel. Remembering that up to 20 to 30 Knots ‘Off Optimum’ have only minimal effect upon excess Power, an Econ Climb speed a little above best Rate (+20 KIAS for the A320) will have a negligible effect upon Rate of Climb, but put the aircraft 30 miles or so further down track at Top of Climb. The very slight increase in climb Time and Fuel is more than off-set by the extra distance covered in the ‘fuel expensive’ climb, and elimination of the incremental cruise. If we consider operations for a Maximum Range profile (absolutely minimum fuel), it’s not at all uncommon to see a Climb speed in EXCESS of the initial Cruise speed.
Join Date: Apr 2007
Location: The Woodlands
Age: 64
Posts: 175
Likes: 0
Received 0 Likes
on
0 Posts
Perhaps you would care to enlighten us with a intelligent response other than obnoxious Games of Thrones sardonic nonsense.
By the way;
The quote was originally said by Ygritte in Chapter 15 of A Storm of Swords. In the chapter, Ygritte says the line to Jon Snow in anger. This happens because Jon asks why she was crying because of a song about “the last of the giants” when he had just seen hundreds of them.
By the way;
The quote was originally said by Ygritte in Chapter 15 of A Storm of Swords. In the chapter, Ygritte says the line to Jon Snow in anger. This happens because Jon asks why she was crying because of a song about “the last of the giants” when he had just seen hundreds of them.
Last edited by jimmyg; 3rd Sep 2017 at 08:57.
Join Date: Sep 2016
Location: USA
Posts: 803
Likes: 0
Received 0 Likes
on
0 Posts
If this is a response to Jimmyg's post above yours, I'm also curious what found incorrect (or "confused") about it. It all checks out, as far as I can tell.
(Except this part: "As jet engines directly produce Thrust, not Power, it is necessary to consider Thrust multiplied by speed (Power = Force X Velocity). Thus, for a given Thrust setting, Power increases as TAS increases." also applies to piston engines.)
(Except this part: "As jet engines directly produce Thrust, not Power, it is necessary to consider Thrust multiplied by speed (Power = Force X Velocity). Thus, for a given Thrust setting, Power increases as TAS increases." also applies to piston engines.)
Thread Starter
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 946
Likes: 0
Received 0 Likes
on
0 Posts
Vilas, Jimmyg and the others, thank you for your valuable inputs.
I was aware of the CI O as equivalent to best ROC but it looks like the reality with the ATC restriction and the wind always changing, an heavy A321 with a high IAS of around 280/290kt often gives you a very poor sometimes zero ROC for few seconds as the aircraft is pitching down to keep the speed. Flying in Hong Kong airspace every day, we have to reach cruising altitude before exiting their airspace. Sometimes, especially in winter with very strong tail wind increasing as we climb, even flying at Green dot speed the whole way we can't make it. But with a fairly light A321 or A320, I like using vertical speed for the last 5000 feet or so as you can aim to reach your cruising altitude exactly at the waypoint required by ATC. No need to workout what is the Best IAS, just set the required vertical speed with a safety margin as you might need to reduce the ROC at higher altitude. Works pretty well. On A319 I always fly managed speed unless restriction from ATC as its climb performance is never a concerned.
I was aware of the CI O as equivalent to best ROC but it looks like the reality with the ATC restriction and the wind always changing, an heavy A321 with a high IAS of around 280/290kt often gives you a very poor sometimes zero ROC for few seconds as the aircraft is pitching down to keep the speed. Flying in Hong Kong airspace every day, we have to reach cruising altitude before exiting their airspace. Sometimes, especially in winter with very strong tail wind increasing as we climb, even flying at Green dot speed the whole way we can't make it. But with a fairly light A321 or A320, I like using vertical speed for the last 5000 feet or so as you can aim to reach your cruising altitude exactly at the waypoint required by ATC. No need to workout what is the Best IAS, just set the required vertical speed with a safety margin as you might need to reduce the ROC at higher altitude. Works pretty well. On A319 I always fly managed speed unless restriction from ATC as its climb performance is never a concerned.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,404
Likes: 0
Received 0 Likes
on
0 Posts
It can also be done by reducing flying select speed. PERF page will give you the ETA and distance required to reach. This is actually the preferred method by airbus and demonstrated in type rating.
Join Date: Apr 2007
Location: The Woodlands
Age: 64
Posts: 175
Likes: 0
Received 0 Likes
on
0 Posts
Dear Pinteam,
Absolutly, applying an AOC with VS and managing the slow bleed off of airspeed to TOC is IMHO a decent technique a very acceptable way to manage your climb profile. Back in the day AOC was/is the primary instrument. We tend to get lost in push the button pull the button flying for dummies process now adaays.
This old adage that V/S is taboo in climb in nonsense. Sure do you have to manage your A/C, of course. Chasing a strict speed around the sky can at time be a unreasonable way to manage you A/C.
I say when, I say where, I say how much :ok
Absolutly, applying an AOC with VS and managing the slow bleed off of airspeed to TOC is IMHO a decent technique a very acceptable way to manage your climb profile. Back in the day AOC was/is the primary instrument. We tend to get lost in push the button pull the button flying for dummies process now adaays.
This old adage that V/S is taboo in climb in nonsense. Sure do you have to manage your A/C, of course. Chasing a strict speed around the sky can at time be a unreasonable way to manage you A/C.
I say when, I say where, I say how much :ok
