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737NG Bank Angle at Cruise?

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LNAV enroute bank angles seem excessive... I've been flying it for three months and every course change surprises me with up to 30 deg bank angles. Seems excessive at cruise speeds and never noticed it as a passenger (fairly often). I always assumed they limited their bank angles to 15 deg, which of course means a much longer radius turn but no one is trying to maintain std rate turns at 0.80M.


Dan Downs KCRP

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Guest neeraj.pendse

The bank limit can be controlled by a knob which is colocated with the HDG SEL knob. You can set the limit to AUTO or to any value up to 30 deg. Is it on AUTO?Some times, if the flight plan calls for a sharp turn (like more than 90 degrees) the airplane might bank more to keep on the center of the magenta line ... so check if you have the same bank behavior for turns that are 30 degrees heading changes.Hope that helps,- Neeraj

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And remember that BANK LIMIT will not work in LNAV mode. In LNAV mode the FMS will determine best bank angle up to max bank angle.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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Affirmative: Bank Limit works in HDG mode only, I observed a 30 deg banks on course change of 33 deg at FL400 0.78M; that just doesn't seem right. However, if you guys say that this is an accurate sim then I can live with it.I've read someplace that high altitude/speed course changes use a half-standard rate turn, but I can't find that source. The closest thing I found was in AC90-45 where the math behind airway and terminal route design can be found. The protected airspace for the course change expands above 10,000, and the inside of the turn has a "splay" (cut-the-corner) to increase the protected area with an angle 1/2 the angle of the course change. Aircraft flying above 290 kts are provided extra room around the turn as well.Having said all that... the enroute structure is designed for shallow banked turns, and I really thought that's how the jet's flew them. To reiterate: I'm only referring to enroute.


Dan Downs KCRP

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The PMDG Sim is accurate. The real airplane AFDS behave's the same way. Pilots can't controll bank angle when in Lnav mode. Lnav mode will bank the airplane as necessary up to about 33 degrees ignoring altitude in order to maintain the computed Lnav track. At or near maximum altitude with a very heavy airplane, it is possible to get or approach stick shaker warning, espeacially in turbulence, when Lnav rolls into a 30 degree bank angle. Floyd


John Floyd

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Thanks very much. I imagine there's a significant loss of momentum going on there at those speeds (p=mv^2).


Dan Downs KCRP

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We are currently getting the 10.6 FMC software for our 737s and one of the things it addresses is that high bank angle. 10.6 is supposed to tame that. Now if someone could figure out how to apply 10.6 to the PMDG simulation.


Tom Landry

 

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