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EGLL Heathrow - strange approach in 737NGX

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So I programmed in the following route into the FMC of the PMDG 737 and when I got to the STAR it had the following...







Before I fill out the INIT REF page the approach looks like the charts over at NATS but as soon as I fill that out and execute it puts in this 'loop'?


I'm using the latest Airac cycle 1513. Cruise altitude of FL190 so not too high for an easy descent.

Pax 150 and cargo 2000lbs split between front and back holds.


If anyone can shine light on this I'd be grateful :) Thanks



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A screenshot of the leg page of the CDU would help a well but my first guess is that there is something wrong in the way the nav data are encoded by the provider or the way they are decoded by the FMC. 


The INTC waypoint is definitely not right as the procedure is a right turn to intercept the localizer at BNN D19 which seems to be "D128S" in the FMC.

It may because the FMC anticipates that the right turn would be too tight to be able to catch the localizer. Check also that the speed restriction of 180kt is still displayed on the leg page for D128S.


I got also a strange loop when approaching Heathrow to the ILS 27R but coming from BIG. I just switched to HDG SEL slightly before the beginning of the loop to keep the aircraft on the approach track.

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It's not interesting until you are actually moving and the FMS has updated the path predictions.  I've used this arrival in the past few months and it is ok; however, keep in mind the path will require pilot intervention in most cases and in reality ATC is providing vectors so you'll not be following the magenta trail.

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I found out that the waypoint causing the issue was the (intc) waypoint shown above. Removing this caused the plan to be correct.


I did not have to modify altitudes or speeds for this to correct itself so that was good too.


Looks like a quirky feature of the NGX and that transition.




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