737ng FMC SID turn construstion
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Join Date: Aug 2014
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737ng FMC SID turn construstion
Hello!
Can anybody advice how exactly turns of SID's on ND are being constructed? Especially initial turns? Are there any parameters that take into account bank angle limitations?
For Example, if we take UDYZ SEVAN3E SID (P-RNAV), we have an initial turn to the right for about 130 degrees. The note on the chart says that it should be done at 210kts or less and with bank angle 20.
OK. I'm loading the SID from FMC database and see a nice looking magenta turn to the right, that looks pretty close to the one on the chart. Does this turn take into account 20 degree bank? Does it's radius account for acceleration etc?
Took-off with LNAV + VNAV and to my surprise, to follow the magenta turn, LNAV commanded 25 to 30 degrees of bank. I would have understood this if I was somehow deviating from pre-programmed flightpath (started early acceleration, for example, or exceeded 210 knots). But that was not the case. Switching to HDG SEL - 20 degree bank placed me far outside of the LNAV path on turn exit.
So, it seems that LNAV can violate the RNAV SID routing. Is it normal? Or was I doing something wrong?
Yeah, we always should monitor and intervene with AFDS doing stupid things, but shouldn't the FMS path construction follow the published limitations in "ideal comditions"?
Thanks folks
Can anybody advice how exactly turns of SID's on ND are being constructed? Especially initial turns? Are there any parameters that take into account bank angle limitations?
For Example, if we take UDYZ SEVAN3E SID (P-RNAV), we have an initial turn to the right for about 130 degrees. The note on the chart says that it should be done at 210kts or less and with bank angle 20.
OK. I'm loading the SID from FMC database and see a nice looking magenta turn to the right, that looks pretty close to the one on the chart. Does this turn take into account 20 degree bank? Does it's radius account for acceleration etc?
Took-off with LNAV + VNAV and to my surprise, to follow the magenta turn, LNAV commanded 25 to 30 degrees of bank. I would have understood this if I was somehow deviating from pre-programmed flightpath (started early acceleration, for example, or exceeded 210 knots). But that was not the case. Switching to HDG SEL - 20 degree bank placed me far outside of the LNAV path on turn exit.
So, it seems that LNAV can violate the RNAV SID routing. Is it normal? Or was I doing something wrong?
Yeah, we always should monitor and intervene with AFDS doing stupid things, but shouldn't the FMS path construction follow the published limitations in "ideal comditions"?
Thanks folks
