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Different FL in flight.


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Hi guys,

Something's been bugging me and I can't find a clear answer to it: I've noticed several flight plans that include different flight levels throughout the flight that deviate from the assigned FL.

Example Amsterdam to Toronto: BERGI DCT AMGOD L602 SUPUR L60 PENIL M144 BAGSO DCT MALOT/M086F360 NATA NEEKO/N0488F380 N482A YRI DCT POLTY

As you can see are "MALOT" and "NEEKO" both dedicated to a different FL (for who can't see it, it's the F at the end + the number, so F360 and F380). So to get to the point: does that mean, from waypoint MALOT, continue the flight at FL360 or climb to 360 to be reached at MALOT and descend to the original FL after? (Last assumption makes no sense given fuel consumption but that's why I'm asking). 

Only thing I can assume is to maintain the same FL compared to ground as it did before MALOT, but again, couldn't find any concrete explaining on this.

Sorry if it's a silly question and looking forward to the replies.

- Alex

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Yes, those are step climbs for efficiency purposes on longer flights, as you rightly assume. As the plane consumes fuel and becomes lighter, it can climb higher and fly more fuel efficiently. It won't descend back to the level it started at because there is no reason to do it. The initial level is filed as the cruise level but it doesn't mean it will be kept for the whole flight. The way it works with ATC, you'd ask for a climb before reaching MALOT and get their permission. They will also change your flight plan accordingly.

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These can be step climbs, but in Europe a lot of routes have altitude restrictions, so some part of the route needs to be above a certain altitude and others below - even enroute, not just SIDs and STARs. If you really want to check these the RAD document from Eurocontrol is invaluable (https://www.nm.eurocontrol.int/RAD/). I think PFPX is the better planning tool compared to Simbrief in this regard, as the restriction are shown in PFPX (not all of them, but a good part at least), while Simbrief doesn't.

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Torben Andersen, VACC-SCA Controller (C1)

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These codes generally mean "from here onwards". So on this particular flight plan, you would (subject to ATC clearance):

  • Depart EHAM on a SID
  • Climb to your initial cruise altitude (which is almost certainly lower than FL360, but could, in theory, be higher)
  • Stay at initial cruise altitude until shortly before MALOT
  • Climb to FL360 to reach by MALOT
  • Stay on FL360 until shortly before NEEKO
  • Climb to FL380 to reach by NEEKO
  • Stay on FL380 until your calculated top-of-descent (TOD)

You would not descend back to your previous cruise altitude.

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On 1/23/2022 at 10:16 AM, Tobias Dammers said:

These codes generally mean "from here onwards". So on this particular flight plan, you would (subject to ATC clearance):

  • Depart EHAM on a SID
  • Climb to your initial cruise altitude (which is almost certainly lower than FL360, but could, in theory, be higher)
  • Stay at initial cruise altitude until shortly before MALOT
  • Climb to FL360 to reach by MALOT
  • Stay on FL360 until shortly before NEEKO
  • Climb to FL380 to reach by NEEKO
  • Stay on FL380 until your calculated top-of-descent (TOD)

You would not descend back to your previous cruise altitude.

Interesting. Then if I filed this route:

On 1/22/2022 at 9:05 AM, Alexander Streumer said:

BERGI DCT AMGOD L602 SUPUR L60 PENIL M144 BAGSO DCT MALOT/M086F360 NATA NEEKO/N0488F380 N482A YRI DCT POLTY

then ATC understands that I will climb to reach MALOT at FL360 without me explicitly requesting the new altitude?

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4 hours ago, Sebastien Bartosz said:

You have to request the new altitude. Just because it is filed it doesn't mean you do it. As a matter of fact, some real world ATC systems drop step climbs altogether. Controllers wouldn't even be aware of it in the first place.

That's interesting to know because I've often experienced ATC who were basically breathing down my neck for not paying attention to reach the FL at given way point, basically the exact opposite of what you're telling me. So in the case of vatsim it seems they do pay a lot of attention to corrected FL's 'to be reached at', apparently.

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It's more important for the oceanic controllers since they don't have radar and rely on altitudes to separate aircraft (as also in your example of Amsterdam to Toronto). Under radar coverage, they shouldn't care much what level you're at unless their airspace was totally saturated and they'd planned that level for you (more applicable to real world). It's mostly important to you as a pilot if you want to be fuel efficient. Now then there's China where you have to change to a metric level when crossing the border, that's important.

Edited by Dace Nicmane
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Another case would be when you're crossing from a country that uses the East/West semicircular rule into one that uses North/South. Or certain airways where level restrictions exist (wouldn't often be filed by VATSIM pilots but ATC would have you change it anyway). 

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Breathing down your neck for a step climb? Or to meet a constraint on a STAR for example? 2 different things. They shouldn't be breathing down your neck for any step climb things.

And it's pretty simple, regardless if you are or aren't under radar coverage or regardless if you cross into a country with a different semi-circular rule or anything else for that matter: You were previously cleared to a certain level and that is the level you are to maintain until told otherwise. If you need/want something else, just ask.

Edited by Sebastien Bartosz
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New York ARTCC

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38 minutes ago, Sebastien Bartosz said:

Breathing down your neck for a step climb? Or to meet a constraint on a STAR for example? 2 different things. They shouldn't be breathing down your neck for any step climb things.

And it's pretty simple, regardless if you are or aren't under radar coverage or regardless if you cross into a country with a different semi-circular rule or anything else for that matter: You were previously cleared to a certain level and that is the level you are to maintain until told otherwise. If you need/want something else, just ask.

No they were genuinely expecting me to reach the appointed level as per flight plan. Had nothing to do with crossing semi's or SID/STARS unfortunately.

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ATC doesn't (or shouldn't) care for step climbs that only benefit the pilot themselves (fuel efficiency).

They do care at what level you cross your oceanic entry (this one, I think, is the pilot's responsibility to request but I may be wrong) or the border of a country with a different flight level system or semicircular rule and will give appropriate instructions (not sure if that counts as "breathing down one's neck"). Unless the aircraft comes from unicom and fails to take care of an appropriate level by themselves which may upset the ATC (but I think controllers of those countries where this is relevant are used to it).

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1 hour ago, Dace Nicmane said:

Unless the aircraft comes from unicom and fails to take care of an appropriate level by themselves which may upset the ATC (but I think controllers of those countries where this is relevant are used to it).

The change of semi-circular levels from West-East to North-South is - in my opinion - an advanced subject for pilots to know. As ATC I am absolutely happy if "my" pilots are able to comply with instructions to change course (heading, waypoint-navigation) and altitude/level with restrictions ("cross ABCDE at FLxyz"). If they are not aware of these special cruise level rules, I do not blame them. If I have time, I educate them by private chat, otherwise I simply ask them to change to an even/odd level. Done.

And: as long as you are flying outside active airspace, you can climb/descend to whatever level you like. It's not for nothing that we instruct pilots "continue own navigation, switch to UNICOM 122.80". The "navigation" bit includes level-changes.

I think we are having some luxury problems here. It's not that long ago that a significant number of pilots did not know how to use their FMS properly. Now they can and we are so spoilt by it that some vocal ATOCs are shifting their attention to such advanced topics.

I think that those of you who are not flying in Central Europe on a regular basis, should do so to better understand the confusion about active/inactive airspace. It's not that simple, especially when some map-applications are not able to depict active airspace accurately.

Luckily there are tools (e.g. Qutescoop) that actually can show the airspace correctly, for example the new division between Maastricht WEST and EAST:

sceenshot_01222022_001944.thumb.jpg.bce31803c6c6c734aced0c25a47fa152.jpg

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15 hours ago, Sebastien Bartosz said:

Just because it is filed it doesn't mean you do it

This ^ when in airspace with a controller online.  

You may be flying at FL360 and be looking to get FL380, but have you accounted for the opposite direction/crossing traffic at FL370?   Always ask and let the controller decide if it's safe for you to climb.

Depending on the traffic levels, I've now actually taken to checking a flight plan as soon as I get someone as step climbs are frequent in the sectors I control.  I've now started asking pilots if:

a. They can take their climb at that point or if not
b. "Advise ready for step climb"

Anyone who makes a step climb/descent is asking for a controller to call on frequency for them to check their cleared level.   

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Trevor Hannant

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32 minutes ago, Andreas Fuchs said:

The change of semi-circular levels from West-East to North-South is - in my opinion - an advanced subject for pilots to know.

It's actually quite simple but you have to have read about it to know it. I've sometimes forgotten it and controllers simply cleared me to a different level than what I was expecting, no problem on either side.

32 minutes ago, Andreas Fuchs said:

I think we are having some luxury problems here. It's not that long ago that a significant number of pilots did not know how to use their FMS properly. Now they can and we are so spoilt by it that some vocal ATOCs are shifting their attention to such advanced topics.

To be clear, I haven't encountered an ATC that was upset about this myself. Just trying to imagine a possible problem scenario as Alexander described. 🙂

Edited by Dace Nicmane
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30 minutes ago, Andreas Fuchs said:

It's not for nothing that we instruct pilots "continue own navigation, switch to UNICOM 122.80". The "navigation" bit includes level-changes.

"Own navigation" actually refers to termination of vectoring. I hope no pilot thinks that they can change level without asking ATC just because they have been instructed to resume/continue own navigation!

Obviously in uncontrolled airspace on VATSIM level changes are up to the pilot, but that has nothing to do with "own navigation".

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Martin Loxbo

Director Sweden FIR

VATSIM Scandinavia

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57 minutes ago, Martin Loxbo said:

"Own navigation" actually refers to termination of vectoring. I hope no pilot thinks that they can change level without asking ATC just because they have been instructed to resume/continue own navigation!

Obviously in uncontrolled airspace on VATSIM level changes are up to the pilot, but that has nothing to do with "own navigation".

Actually "own navigation" would in my eyes (re)direct to the already existing filed flight plan, therefore could never become a wild goose doing whatever they please. I hope 🙂

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1 hour ago, Martin Loxbo said:

"Own navigation" actually refers to termination of vectoring. I hope no pilot thinks that they can change level without asking ATC just because they have been instructed to resume/continue own navigation!

Obviously in uncontrolled airspace on VATSIM level changes are up to the pilot, but that has nothing to do with "own navigation".

Context....my explanation obviously only made sense in connection with pilots being sent off to UNICOM. I assumed that readers took this into account.

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23 minutes ago, Alexander Streumer said:

Actually "own navigation" would in my eyes (re)direct to the already existing filed flight plan, therefore could never become a wild goose doing whatever they please.

Correct, as Martin has explained correctly, under normal circumstances you are supposed to return to or continue on your filed routing.

Only when you are sent to UNICOM, you can also change level/altitude without asking anyone - because you are not with ATC anymore.

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I appreciate the discussion on this. I had someone change flight levels on me within vZAU airspace saying they had placed it in their flight plan as one of these fixes. It didn't make any sense to me that any air traffic control authority in the world would have thought that a good idea because, as has essentially been said above, ATC now has to protect the protect for the existing altitude through the new one between the fix with the new altitude and the fix that precedes it. Considering how far apart those two can be, that can add up to a lot of airspace to protect.

Then are pilots filing these fixes/altitudes in their flight plans for the benefit of ATC so they have advance notice that a pilot will be asking for a new flight level at a specific point in their FP?

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Well, a flight plan is just that - your plan how to fly. It can be useful for ATC to see e.g. if I need to change my flight level from even to odd, whether I'm planning to climb 1000 ft or descend 1000 ft. That way they can immediately give me the instruction without having to ask what I prefer. As for long haul step climbs, it's also there for ATC to see and plan, it's just unfortunate that some people don't realize you still need ATC permission for that, as has been stated several times in this thread. Nobody expects ATC to put up with unauthorized climbs! If it's a common problem perhaps it's a good idea to include it in the Pilot Learning Center.

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9 hours ago, Dustin Rider said:

Then are pilots filing these fixes/altitudes in their flight plans for the benefit of ATC so they have advance notice that a pilot will be asking for a new flight level at a specific point in their FP?

At least in some cases the pilots file these fix/altitudes as this is done by the flightplanning software or because of compliance to Eurocontrol validation, where many routes have these restriction and validation fails, if the fix/FL isn't flied in the ATC flightplan. When I plan using PFPX I always (when flying in Europe) validate the flightplan via Eurocontrol. I try to adhere to restriction given to me by the Eurocontrol validation tool - except for "hot" danger areas, which seldom are in effect at VATSIM. It takes time, but also takes the planning to the next level, instead of the blindly use of Simbrief I see these days as controller.

Torben Andersen, VACC-SCA Controller (C1)

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