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Guest bvdtol

PMDG 737-XXX flying an orbit

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Dear all,I'm flying on Vatsim for a while now, and lately I recieved an instruction from atc I did not hear before: 'Fly a full orbit'.I now know that this is a procedure to fly multiple 360 turns around a fixed point until cleared to leave the orbit. But it is not the same als a holding pattern on present pos. How do you fly it in the PMDG 737-800? Is there a way to fly it by fmc and LNAV? Or do you simply keep turning around you HDGselect button (this would be a somewhat strange method I think)?I don't think I will be instructed to do this again soon, but it might always be helpful to know the procedure if it happens to me a next time.Help would be greatly appreciated, so thanks in advance.Bart van den Tol

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Really?!? I've never heard that one before, it certainly is not standard ATC phraseology in the FAA 7110.65 "ATC Bible." ATC should give you vectors and state something like "for separation."Anyway, in that situation I would use autopilot CWS mode to put her in a constant bank (maybe 15-20 deg) with some nose up to maintain altitude and autothrottle to maintain a safe maneuvering speed (maybe 210-220 clean). We are definitly VFR in this situation.Interesting.

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I think you are talking about a hold, which as Dan said is usually used for aircraft separation on approach. You usually hold at a navaid fix and just circle til released. This happens quite often heading into Boston where you hold around Providence. You can even program one with the FMC.

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The OP is correct - he is referring to an 'ORBIT'.This is basically just a 360 degree turn in the direction specified.I am ATC now for 12 years, and use it often. When I want delaying action longer than a dog-leg, but shorter than a hold, I issue the 'orbit' instruction. I only use it below about F250 when the speed is low 220~250 otherwise an orbit is huge and defeats the object.So, for instance, if you're flying on heading 360, or tracking direct to XYZ, then you will execute a 360 degree turn (either left or right specified by ATC) and continue either on the heading 360 or track back to the XYZ.I have always flown this manually, and as far as I know there isn't a way of programming the FMC for this...Cheers!

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I was indeed instructed to fly the orbit in a certain direction, namely to the right. In the documentation I've read, it seems to be a VFR procedure, but obviously I was flying IFR. It was however in the vicinity of the airport (alt around 3000 feet AGL and somewhere around 230 knots, lots of traffic).Of course a 360 degrees turn is easy to fly by hand, but the thing is that I understood the fixed center point of the ORBIT to be important. When I fly a 360 turn by hand and winds are interfering, it's practically impossible to make a perfect circle around that point.So: is the fixed center point really important, or does ORBIT just mean 'make a 360turn in direction X starting now'?Regards,Bart van den Tol(EHAM)

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ICAO phraseology explains why it's not used in the US, and isn't in the 7110.65. Actually seems like a good tool to use for VFR pattern traffic but I'm still surprised that it's used for air carrier operations. Wow, boggles my mind.

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1- A hold doesn't necessarily require a fix. Nearly all aircraft are FMS equipped and are able to fly a PPOS hold, or alternatively give a radial DME for a non-standard hold.2- I work Area Control only, and use orbit often, for the reasons I gave earlier. My ACC sectors do 90% of the sequencing for the approach sector, so that is why.3- I have a fully functional radar, so I have absolutely no need for a pilot to report end of orbit. I know of no requirement in our regs for a VFR to report end of orbit either. If I don't ask for a report then I don't want one. Working giant sectors, my frequencies are often coupled/combined, and frequency congestion sometimes a big problem.4- 360/orbits can be flown by autopilot, just manipulating the HDG select to keep you in the required turn. One thing an ATC must remember is that the radius of the turn might reduce putting the aircraft offset if they roll out onto a pre-assigned heading. This is especially true if the aircraft is descending and the GS is bleeding off.CheersBryan

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>I was indeed instructed to fly the orbit in a certain>direction, namely to the right. In the documentation I've>read, it seems to be a VFR procedure, but obviously I was>flying IFR. It was however in the vicinity of the airport (alt>around 3000 feet AGL and somewhere around 230 knots, lots of>traffic).>>Of course a 360 degrees turn is easy to fly by hand, but the>thing is that I understood the fixed center point of the ORBIT>to be important. When I fly a 360 turn by hand and winds are>interfering, it's practically impossible to make a perfect>circle around that point.>>So: is the fixed center point really important, or does ORBIT>just mean 'make a 360turn in direction X starting now'?>>Regards,>Bart van den Tol>(EHAM)>>As I mentioned prior, the centre of the orbit point is not important. ATC *should* understand that as IAS and relative GS reduce, the orbit will not place you right back at the same point as a hold would.Orbit means make a 360 to the right, and return to your previous heading.

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With no fix involved, do we care about the wind drift effect? Does ATC consider this?

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See my replies above - we do know and cosider this. Wind drift should be of no consequence to the pilot.

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