Originally Posted by
MEM_ATC
Compare the BEERT 1 Arrival with the GILMORE 3 Arrival. Now take a look at the FSM Transition from FSM to HERTZ Intersection. The GILMORE Arrival indicates the FSM R-076, while the BEERT Arrival indicates the the FSM R-082. That's six degrees difference over the course of 103 miles between FSM and HERTZ.
We have a tool at the sector that allows us to plot these angular differences. According to my plots last night at work, there is a 9.53 mile difference in the location of HERTZ between the two arrivals. I'm not up to speed on the formulas required to calculate this by hand. 9.53 miles is fairly significant in my world of ATC.
OK, HERTZ is a good example. The printed chart for the GILMORE 3 Arrival shows HERTZ at N35 34.8 W092 10.8. The textual descrition I have for the BEERT 1 Arrival (RNAV) also shows HERTZ at the same exact coordinates. Now, how we get from FSM to HERTZ is another story. Jeppesen may calculate one radial off of FSM using data published 8 years ago, and LIDO might take a different chart and different data and come up with a different number. I honestly don't know who is the more accurate, but we've gone from using the former to the latter. The only people that use that information anyway are the VOR-only airplanes, and they won't be doing the RNAV approaches. The airplanes already equipped with INS aren't using those numbers (R-076 or R-082) to get to HERTZ, they're just going direct to a LAT/LONG. I see those radials not as definitions of the waypoint, but as an aid to get there.
But for the sake of conversation, I'm going to go out on a limb and postulate a possible explanation for the apparent discrepancy. If I'm using the VOR to navigate, I should use the FSM R-076 radial. Since VORs don't get regular maintenance, it's likely that the alignment of that NAVAID has drifted off of magnetic north since it was last certified. It's likely cocked a bit to the east, say, maybe even as much as 6 degrees. What's important, though, is that to get to HERTZ, I should set the 076 degree course on my cockpit instrument and keep that course centered.
If, on the other hand, I'm not using that cockpit instrument, I might find that the actual magnetic course between FSM and HERTZ is 082 degrees. I might find this by plotting the course on a chart, or I might flight test it. Either way, the magnetic course between the points is different from the magnetic course that I would set off of the FSM NAVAID. They both would get me to the same geographical fix, HERTZ.
I do NOT know that the above IS the case, but I believe that it MIGHT be the case, and it would explain the apparent discrepancy.
Originally Posted by
MEM_ATC
Yes, it's all very unusual to me as well. I've seen a number of chart changes, additions and updates over the years, but never the number of slight differences that exist with these 8 overlying procedures.
I believe we'll see more and more of these RNAV procedures as time gose on. I think it's important to understand what's going on now so we can keep up as the pace of change quickens.
Originally Posted by
MEM_ATC
These types of procedures are supposed to reduce workload and help pilots and ATC by reducing the frequency congestion, as well as provide standardized routings in/out of the Terminal area. If I have to guess or ask each aircraft which STAR Procedure he's flying, or if I fall back into the habit of issing a heading at the "pivot point" and then relaying this information to the next sector -- then I've negated some of the positive benefits of implementing these new RNAV STAR Procedures.
Well, you don't HAVE to assign a heading at the pivot point, at least from my perspective. The procedure on the STARS is to turn to the published heading at those points, period. There's no "EXPECT" caveat attached to them. The only thing different is the heading. In the case of the old arrivals, we'll turn and drift; in the case of the RNAV arrivals, they'll go directly to the opposite pivot point. Depending on the crosswinds, you should be able to pick out who's doing what by the direction they're going.
Originally Posted by
MEM_ATC
I'll post anything unsual from the ATC side.
Thanks. This should be a good learning experience for us all.
.