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Guest alex_m

Fine tuning crossing restrictions...

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Guest j-mo

I realize there have been many posts on this subject, but I don't remember seeing these (apologies if I've missed them).This is the 747-400X in FSX (naturally) and Vista 32, using Radar Contact, and default airport and scenery.My flight was LFPG-KBOS. All was fine until RC issued a crossing restriction of '12,000 and 250 kts' 40 nm before BOS. BOS wasn't on my flightplan, and my approach (SCUPP3, which is vectors) didn't add it. However, it was easy enough to add BOS, The issue was adding the restriction as per the manual "exactly as issued from ATC." When I went to enter BOS/-40 I got the NOT IN DATABASE message. I noticed on the LEGS page that the leg from SCUPP to BOS is only 37 nm, so I tried entering SCUPP/-3 and that worked.So, question #1 is: is this the procedure when a crossing restriction would precede another WP?Next, after working this out, as soon as I hit the EXEC button, the plane began to snake around something fierce trying to find and track the path (this was in LNAV and VNAV modes). The plane deflected as much as 90-degrees off course at bank angles as much as 45-degrees. I limited the bank at this point, but the plane never 'found' and stayed on track. I was at 14,000 and 275 kts at the time, with at least 25 nm to hit my restriction. Winds were 20-25 kts no more than 20-degrees off the nose. No problems tracking before this leg or after reaching SCUPP.In hindsight, I probably should have switched to HDG mode. I've been trying to figure out what was caused this, but can't seem to get it. There were no issues getting to 11,000 or 250kts (I was there is plenty of time), it was just lateral tracking that was problematic.So question #2 is: what caused this behavior?Thanks in advance for any feedback!Regards,

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Hi Alex,The way many of us use any FMC enabled aircraft with Radar Contact's crossing restriction is to use the "Fix" page on the FMC. Create a fix BOS with a distance of /40 which will put up a green range-ring on the ND, showing exactly where 40nm is on your FP. If you're using realistic STARS or approach-plates, the intersection will usually coincide with a FP waypoint. The reason this works better is because Radar Contact's crossing-restriction is 40nm Line of sight (LOS) from the airport or the last VOR (within 5nm of the airport) in the flight plan. The LOS meathod aleviates issues with FP's having numerous turns or extended segments within 40nm of the airport. Then you can downselect the point the FP crosses the range-ring on the FMC Fix page, and upselect to the Legs page and associate any restriction with it, such as 250/11000. This also sets up your Top of Descent (T/D) nicely and after inputing Forecast winds on the VNAV-3 page, you'll have a golden VNAV descent, coinciding perfectly with Radar Contact.As for snaking around the track, do you have the 744X service pack installed? Where you using third-party weather such as ASX?


Regards,
Al Jordan
------------
KMLB

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Guest j-mo

Hello, Al-Thanks for your reply. I'll use the FIX page next time and see how that goes for me.To answer your questions, yes I have the service pack installed, and yes, this was ASX, which I thought I put in my original post, but realize that I overlooked doing so.Regards,

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Guest j-mo

OK, got it. And... works like a charm. I can remember reading a while back about range rings, but I wasn't flying the PMDG nor using RC. It's all coming together for me now.Thanks again!

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