Fly-by fly-over

5 Answers

1. Best Answer
   
   

   
   

   John D Collins on Dec 31, 2015

   Jeppesen does not determine if a fix is “fly over” or “fly by”. That is determined by procedure or airway designer. The MAP is a “fly over fix”. When the fix is a “fly by fix”, the GPS or FMS can provide guidance to apply turn anticipation. This cutting of the corner can result in an aircraft flying outside of the obstacle protected area. A route based on VOR’s assumes that the aircraft will pass over the fix and then turn, so this area is evaluated for obstacles on the outside of the turn at a greater distance than on the inside of the turn. When using turn anticipation, the turn is on the inside of the course change.

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   Mark Kolber on Dec 31, 2015

   miladmaz, you have me curious. Why do you think “they can’t actually be fly-by”?

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   miladmaz on Jan 01, 2016

   thanks Mr. collins for the reply
   dear @mark
   i did some more research and find out (in Airway manual ATC section doc 8168 pages 205-208)that turns are made after the fix as Mr Collins said and there is a obstacle clearance zone for each turning point (TP) . but what has got me wondering is that in airway manual general section (airway-general-symbols) there is a fly-over FIX symbol ( a triangle with a circle around it) so my question is this: if we are required to turn after the FIX (not waypoint , waypoints turning procedures are determined by FMS,GPS,GNS…) so why there is such thing as a Fly-over FIX symbol?

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   Mark Kolber on Jan 01, 2016

   The turning procedures are not determined by the GPS/FMS. What the GPS/FMS does is guide you into the turn based on whether the waypoint is fly-by or fly-over as established by the procedure designer.

   I don’t follow you on the difference between a “waypoint” and a “fix.” A “waypoint” is just a geographical point in space. While it is defined in terms of latitude/longitude coordinates, there’s no reason it can’t be associated with existing navaids, intersections, or fixes. A “fix” is just a geographical location defined by reference to the surface or a navaid. GPS uses “waypoints” defined as lat/long simply because that’s all GPS understands. For example, it doesn’t receive a VOR signal; it “sees” a VOR based on the VOR’s latitude/longitude coordinates. So, to your GPS, a “fix”, VOR, NDB, intersection, etc is just another “waypoint”. In terms of the practical difference between “fly-by” and “fly-over”, the FAA uses the terms “fix” and “waypoint” interchangeably.

   Why is there a fly-over waypoint? As John explained, the difference between the two is that, with a “fly-by” you (and your GPS/FMS) may anticipate the turn, start the turn before you get to the waypoint, and “fly by” it without ever crossing it. With a “fly-over” you need to wait until you “fly over” the waypoint before beginning the next segment, whether turn or straight ahead. The difference in their use is based on the required tolerances for the segment. In the typical GPS approach, for example most of the waypoints are fly-by, but the MAP is fly-over, I think for obvious reasons.

   If this makes no sense, perhaps I am not understanding the question you have. Do you have a specific approach in mind you can point us to?

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   miladmaz on Jan 02, 2016

   dear mark . you are right! about all that , let me tell you this way…
   lets assume we are going to fly a “Non-Rnav” route so it’s a simple victor-airway with only VOR-DME as a navigation guidance. on our aircraft we only have VOR-DME receiver.
   so basically we cannot identify “waypoints” but we can identify FIXes .
   now my question is this: since there is no waypoint (only Fixes) how do we navigate along FIXes , do we fly-by them or Fly-over them?
   FIX is different from waypoint , this we all know. i believe if an intersection, turning point,reporting point or whatever is defined by a FIX , we have to fly-over it , but if the opposite is true (it’s defined by waypoint) turning procedure is either fly-by or fly-over which the designer specifies it.
   what’s your idea?

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