“speed 270kts，rod 2500ft/min” so bad？
Thread Starter
Joined: Oct 2013
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From: uk
“speed 270kts，rod 2500ft/min” so bad？
Hi，Guys，just ask you about one thing，is it really so bad that you give a A320 or A380 on decent this instruction：“speed 270kts，rod 2500ft/min” ，is it really hard to operate for pilots and why？
Thanks a lot～
Thanks a lot～
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From: Omnipresent
Think of a kid going down a slide. If the slide is at a certain angle, the kid will go down at a certain speed. If you want the kid to slow down, they can either put their hands out and try to slow down (not very efficient), or you could reduce the angle of the slide.
The same with aircraft. There can be a bit of extra drag available through various means, but it is not efficient. The best way of controlling the speed (assuming the aircraft is already at idle thrust in descent) is by controlling the angle of descent, which is easy to do. The usual phrase is that you can't get an aircraft to go down and slow down at the same time...
The same with aircraft. There can be a bit of extra drag available through various means, but it is not efficient. The best way of controlling the speed (assuming the aircraft is already at idle thrust in descent) is by controlling the angle of descent, which is easy to do. The usual phrase is that you can't get an aircraft to go down and slow down at the same time...
Joined: Nov 2001
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From: London
Think of a kid going down a slide
Thanks, "think of a kid going down a slide" is a very good way of explaining the problem to new controllers, I'll try and use that one on my next trainee.
However I never use "they cannot go down and slow down at the same time" as they obviously have to be able to do that to land. I would suggest they cannot do both quickly at the same time.
However I never use "they cannot go down and slow down at the same time" as they obviously have to be able to do that to land. I would suggest they cannot do both quickly at the same time.
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From: Always changing
Never hear the Emirates guys complaining about that kind of thing in the desdi/bubin vicinity. We know it's not ideal but they seem to deal with it very professionally - ie no complaints. Much appreciated btw.
Thread Starter
Joined: Oct 2013
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From: uk
thx
thank u very much，but is there any basis of theory to support it？I know its not comfortable for them to do it，but someone never said impossible，few dispised me。。awful things they said just upset me。。what I really wanna find out is the possibility to operate where data I downloaded didnt really cover。。
Per Ardua ad Astraeus
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From: UK
I would have thought it would be a 'doddle' actually (two button presses for the ML kids - speed and vs) , but they must be wondering why you ask for that, especially since your post suggests you might do it regularly. Why the RoD restriction? Why not 'level by'?
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From: London
I'll continue to give you both instructions at once and expect you to comply with them in any order you wish unless I specify the order. I don't expect you to expedite a descent and a speed reduction at the same time.
If you claim you cannot go down and slow down it makes a mockery of continuous decent approaches, unless you think you can land without actually slowing down.
If you claim you cannot go down and slow down it makes a mockery of continuous decent approaches, unless you think you can land without actually slowing down.
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From: Berkshire, UK
Interesting to see two captains with opposite views! I only ever used RoD instructions in procedural control withoiut radar and I never heard my radar colleagues at London Control give such instructions so presumably it's new?
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From: Hampshire
Ask the Cathay Pacific drivers who had to get their B747 into Bahrain from London. Dhahran would not allow them through their air space below something like 30,000 ft. And the controllers in Bahrain wanted them at around 3,000 ft! Just before crossing Dhahran, the Captains used to make an announcement, informing the passengers what was about to happen and reassuring them there was "nothing to worry about". Then it was wings full of flaps, air brakes or whatever and down we went, in a virtual nose dive! It was incredible to see how much an aircraft could rattle and shake without falling apart!
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From: In the rain
On a little bus it can be difficult to maintain 2500fpm at 270kts under certain conditions, for example if the aircraft is light or the wind is changing quite rapidly.
Slowing to 270 while maintaining 2500fpm is near enough impossible to do effectively even with the brakes out. We don't like using brakes much as it can be considered throwing away energy. If it's subsequently to fly level for miles that's a waste of fuel.
The only reason little busses slow down effectively on final approach is because of the gear + drag flaps. London TMA example: slowing from 180 to 160 once established on the glide can be near enough impossible without lowering the gear or having a helpfully strong headwind. Don't mind so much at 6-8DME but any further out is a bit... noisy.
Slowing to 270 while maintaining 2500fpm is near enough impossible to do effectively even with the brakes out. We don't like using brakes much as it can be considered throwing away energy. If it's subsequently to fly level for miles that's a waste of fuel.
The only reason little busses slow down effectively on final approach is because of the gear + drag flaps. London TMA example: slowing from 180 to 160 once established on the glide can be near enough impossible without lowering the gear or having a helpfully strong headwind. Don't mind so much at 6-8DME but any further out is a bit... noisy.
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From: Canada
Happy to help out controllers when I can but the bottom line is don't make your poor planning, my crisis.
Thread Starter
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From: uk
happy to know why pilots are reluctant。If I have to keep the rod，whats the min speed I may reduce？for example，A320 B737 on FL220 descending to FL130 when Short of Time and you would not like to make any dogleg？
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From: Costa del Swanwick
I would suggest the RoD is required either for separation or to make an agreed level-something that is far more important than losing a mile or 2 in a stream. I don't think there are many of us in the area world who go for a really tight 5 miles in a stream, there's always a bit to play with. Make the level and then the speed is my modus operandi.
Last edited by 250 kts; 30th October 2013 at 19:46.
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From: etha
HD, I can vouch that there are more AC controllers using RoDs from time to time, either that or "be level in x minutes", both work just as good. They are being used quite regularly by some of our European colleagues too instead of actual level restrictions which I doubt we will ever understand why.
I would never give a speed instruction and a RoD as it would be far too easy for them to compromise each other. I'd pick whatever was more important and then coordinate whatever can't be done without the other.
I would never give a speed instruction and a RoD as it would be far too easy for them to compromise each other. I'd pick whatever was more important and then coordinate whatever can't be done without the other.
