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# Help - ROC/ROD calculation

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# Help - ROC/ROD calculation

9th Jan 2019, 19:19

Join Date: Sep 2017
Location: Europe
Posts: 13
Help - ROC/ROD calculation

Hi guys,

I've ran into this during selection process for ATC and it's been bothering me. Maybe you can give me explanation for dummies.
We were given an exercise where we had the following information provided:
- two aircraft, their rate of climb/descent was known and flight levels they were at and flight levels they were climbing/descending to ...
E.g. Aircraft 1 - FL 300 climbing to 400, rate of climb 1000ft/min, Aircraft 2 - descending from FL 350 to 250, 1000ft/min ROD
Now, those planes were flying either towards each other or behind each other on the radar and we had to determine whether they were gonna "overfly/underfly" before passing each other/before reaching passing point.
On the radar screen you could see their speed and also how far away they are -- you could determine whether they were let's say 5 minutes apart.
Supposedly there were more than one way to make the calculation.
One of the easiest ways was apparently calculating difference of FLs and then dividing it from ROC/ROD?!? That way we should've found out how much time it will take for the planes to climb or descend and then compare it to radar data.... So let's say our calculation would tell us that planes will reach their FLs in 4 minutes and they were 5 mins apart on the radar, then we would have to answer that yes, they will overfly/underfly each other before passing each other/before reaching passing point - the point where they meet.
Anyway, does that make any sense to you? How would you work with that? How to calculate this step by step?
Now we had about 30 seconds to make a decision and I felt quite overwhelmed, doubting if I could do this job. Is this kind of math on daily basis for you?
Or what kind of math do you need as APP?

Sorry for long, boring, confusing post . I hope you know what I mean by overfly/underfly .. I don't know exact English synonyms for words they gave us during an exercise.

ETA: if you have tips for some online sources or books where basic ATC math operations are well explained, I'd be happy to learn about that

9th Jan 2019, 20:13

Join Date: Nov 2005
Location: River Thames & Surrey
Age: 70
Posts: 7,778
Easiest way is forget the mental arithmetic and turn each aircraft 10 deg right.

9th Jan 2019, 20:44

Join Date: Jul 2004
Location: On the wireless...
Posts: 1,849
It's procedural vertical separation gone mad. It'll all end in tears...

9th Jan 2019, 22:00

Join Date: Nov 2005
Location: River Thames & Surrey
Age: 70
Posts: 7,778
He's got radar so why do it procedurally?

9th Jan 2019, 22:30

Join Date: Jan 2008
Posts: 9,109
If all else fails, there's always TCAS.

10th Jan 2019, 01:38

Join Date: Jan 2019
Location: EU
Posts: 4
Originally Posted by DaveReidUK
If all else fails, there's always TCAS.
Unless their TCAS is on MMEL at the moment.

10th Jan 2019, 05:04

Join Date: Sep 2017
Location: Europe
Posts: 13
Originally Posted by Talkdownman
It's procedural vertical separation gone mad. It'll all end in tears...
I feel that way as well LOL

10th Jan 2019, 05:11

Join Date: Sep 2017
Location: Europe
Posts: 13
Originally Posted by chevvron
He's got radar so why do it procedurally?
We were working in pairs where one of us was in the role of planner (reading instructions, flight levels, rod/roc to executive) and the other one in the role of executive in front of the radar (simulator).
I guess I shouldn't overanalyze this exercise as most likely they were trying to see how we will cooperate with each other, but I'm just curious what would be the best way to handle it within short time

10th Jan 2019, 10:06

Join Date: Jul 2004
Location: On the wireless...
Posts: 1,849
Originally Posted by ajl165
the best way to handle it within short time
Reject it as 'too difficult' with high risk of error. Use the radar set instead.

10th Jan 2019, 10:50

Join Date: Feb 2000
Location: solent-on-sea
Posts: 423
It's not exactly rocket science, but you need to pull out the actual useful data.
'Combined rate of crossing' is 2000fpm (1000+1000), vertical difference is 5000ft (FL350-FL300), so two and a half minutes until both at FL325, and have either 'crossed', or let's hope not collided. If we're talking separation required, and assuming we need 1000ft, we need to add another 30 seconds (1000ft/2000fpm rate), so 3 minutes.
Do I do this on a daily basis? Not really. Maybe a couple of times a week I actually look at rates of climb/descent, think to myself for example '4000fpm closure, 6000ft to go, less than 2 minutes, that's fine', so I won't need to separate with headings.
I know it's easy to say but try not to overthink things.

10th Jan 2019, 15:52

Join Date: Sep 2017
Location: Europe
Posts: 13
Originally Posted by Not Long Now
It's not exactly rocket science, but you need to pull out the actual useful data.
'Combined rate of crossing' is 2000fpm (1000+1000), vertical difference is 5000ft (FL350-FL300), so two and a half minutes until both at FL325, and have either 'crossed', or let's hope not collided. If we're talking separation required, and assuming we need 1000ft, we need to add another 30 seconds (1000ft/2000fpm rate), so 3 minutes.
Do I do this on a daily basis? Not really. Maybe a couple of times a week I actually look at rates of climb/descent, think to myself for example '4000fpm closure, 6000ft to go, less than 2 minutes, that's fine', so I won't need to separate with headings.
I know it's easy to say but try not to overthink things.

11th Jan 2019, 15:11

Join Date: Mar 2002
Location: Scotland
Age: 69
Posts: 107
I can see why they put the question to you, but would agree with others that you should not over-think the situation.
In the real world you'd do well to remember that an a/c's rate of climb might not be maintained - this might lead to some embarrassment in the absence of an imposed restriction. We've all been there.
So, it would indeed be wise to use your radar. Probably use less RTF time too.

11th Jan 2019, 16:15

Join Date: Sep 2017
Location: Europe
Posts: 13
Thank you :-) I will keep that in mind and try not to over-analyze things
I would always opt for using radar but I know that students have to learn procedural control during training too

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