Seatrend45

As long as you are in the green stab trim area on the stab position indicator, the chances of crashing the airplane due to it are really slim as a small input on the control column is all that is gonna be required for the proper attitude pitch setting during takeoff. It is not as critical as some people think. Nothing wrong with setting it exactly as per the book though! Save the pilots from having to do a trim correction on liftoff/initial takeoff phase.

Thanks Scott, This appears to confirm a small bug with the ANP settling at .05 or so when GPS update and radio update is turned off, instead of increasing based on the chart above. Hope you had fun in Hawaii before returning ! Nothing wrong in having enhanced navigation compared to the real thing! thanks for the feedback.Marc Bergeron

Thanks Scott!It will be nice to find out what your Hawaii flight reveals next time you have time for it! As shown on the chart below, even with radio update (IRS/DME), the ANP should not be below 0.2. It is important to mention the ANP is not a direct measurement of the IRS drift. Whatever the outcome is, it will not change my appreciation of the NGX a bit! I will at least know what the limitations are so I don't commit a navigational error that could lead me to a mountain side, in palm spring for example, while doing an RNP SAAR approach ! :( .05 is an excellent ANP factor and you can fly with confidence tight approaches, but only if it is in a serviceable condition !Marc Bergeron

Thanks Scott!It will be nice to find out what your Hawaii flight reveals next time you have time for it! As shown on the chart below, even with radio update (IRS/DME), the ANP should not be below 0.2. It is important to mention the ANP is not a direct measurement of the IRS drift. Whatever the outcome is, it will not change my appreciation of the NGX a bit! I will at least know what the limitations are so I don't commit a navigational error that could lead me to a mountain side, in palm spring for example, while doing an RNP SAAR approach ! :( .05 is an excellent ANP factor and you can fly with confidence tight approaches, but only if it is in a serviceable condition !Marc Bergeron

Thanks Scott!It would be nice when you have time if you could validate my findings. it will not change my appreciation of the NGX a bit but I would at least know it is not me that is missing something! :lol:See attached table that describes a typical expected ANP for the different sensor update inputs to the FMC.Marc Bergeron

Mine use to jump all over the place like yours is before I installed the Service pack: it is not what you want it to do because you would have to replace your FMC (45000$) if it did that in real life !! After I installed the service pack, the position does not jump all over the place anymore but the ANP stays steady in the .05 range... also not expected? Any more ideas?Thanks a lot for your feedback and video!!Marc Bergeron

Anybody knows if this feature is modelled?I tried it some more and also found out that if the radio update ( VOR and DME update is turned off ) is disabled, the ANP still stays at a pretty low value.Just curious,Marc Bergeron

To give an example, maintenance is required to replace the IRU unit before the next flight if it has drifted 20 miles on the previous 4 hour flight. For the same 4 hours flight, if the drift was 13 miles, the IRU can be released for an other flight without maintenance action. If during the second flight, the drift is 11 miles, looking at the graph provided on the previous post, we are still in the "Hatched" area, which requires maintenance to replace the unit prior to further flight.If the first flight had a drift of 13 miles, and the second one 5 miles, no action is required.As far as the GPS updating the IRU, the concept is the following : The GPS update and the Radio Update will line up the FMC position, but will not correct the IRU position. This is why you have a "Position Shift" page in the FMC that let you compare the different sensor positions relative to the FMC position. The GPS sensor position will be very close to the FMC position source that has the most impact in the algorithm used by the FMC software to compute the FMC position.Hope this makes sense.Marc Bergeron

My observation is the following :ANP on the ground by default, with all sensor position update selected to ON, is close to .06, which makes sense. Before the SP1, when I used to turn off the GPS update under the NAV OPTIONS section of the FMC menus, the sim frame rate would immensely suffer. This is now corrected.I am now turning the GPS update to OFF, and even after a 60 minutes flight, the ANP still lags around .06. Same result when I turn off in turn the VOR, DME and LOC update. The " IRS Nav only" messages then pops up in the scratch pad, which is normal. I was expecting the ANP value to start going up gradually as a result of an OPS software algoritthm that accounts for the IRS drifts and corrects the ANP accordingly.Is this feature simulated or is it designed as part of the sim product to keep the ANP value to a "Fictive" value?The 737-NGX is absolutely wonderful!Thanks,Marc Bergeron