Geometric Path Descent on Boeing a/c

[moscho999]

Hello everybody,

operating 737NGs I found out that my company is planning to upgrade the FMC to be capable of a geometric path descent.
According Boeing this change provides commonality with other Boeing Airplane models and allows VNAV to be used for approach operations at non-standard temperatures.

The last part about temperatures is puzzling me a bit. Up to now - w/o the option installed we are already doing VNAV-approaches and for lower temp. than ISA we are correcting the minimum crossing altitudes during final approach.

So, could anybody explain me what the differences are?

Thanks a lot for the help...

Moscho

[alexban]

APP using VNAV:
"when appropriate,crews should make cold temp altitude corrections by applying a correction from an approved table to the waypoint altitude constraints.The FMC obtains the GP angle displayed on the legs page from the nav data base.This GP is based on standard atmosphere......If cold temperature alt corrections are not made,the effective GP angle is lower than the value displayed on the LEGS page.
When cold temp alt corr are made,VNAV PATH operation and procedure tuning function normally;however,the a/p follows the higher of the GP angle associated with the app or the geometric path defined by waypoint alt constrains.
NOTE: Temp corrections redefine the GP only if the FMC has the geometric path option installed."
from FCTM 5.41 (31 oct 4004)

this is for using VNAV to land,for ex instead of ILS. Not for using VNAV for app,then followed by a ILS proc,for ex.
Brgds
Alex

[moscho999]

Thank you Alexban,

crazy enough I already read this part of the FCTM - however it never reached my brain.

You have been a great help!!

Moscho