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Guest BushPilot

Airbus VNAV Approach

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I've build an RNAV approach (which is not yet available in the latest NAV DATA Pack)for a local airport, and added the WPTs into the FPLAN. The FMC calculated WPT crossing altitudes are higher than the published crossing altitudes, which is great, because the FMC calculated a 3 deg descent gradient (I assume this). However, during the descent the aircraft does not maintain the correct vertical path, starting of much to high, then all of a sudden much to low. My sequence of events are as follows:1. Before TOD I dial in the MDA into the MCP and then right click on the altitude button. Which then decelerates the aircraft to descent speed, but the aircraft does not follow the vertical path indicator.2. When descending the aircraft basically dives at 3000+ fpm but passes throught the VPI and then ends up way to low on final approach.3. I give the FAF a hard altitude, and it appears the aircraft tries to get to that altitude, and therefore bust the IAF and IF altitudes.How can I get the aircraft to maintain a nice 3 deg descent path from TOD until at least to the RWY THR? Do I need to give the FAF a hard altitude or is the THR elevation sufficient for the FMC to calculate the 3 deg descent path? I need the maintain 3 deg all the way down to THR, and at MDA be able to complete a visual approach or execute the missed approach.Stephen

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Hello to you!If you want the plane to follow the FMC profile, you have to "left clic" the alt button (not right-clic).Left clic will make "DES" appear on FMA, indicating you are in managed mode: the airbus starts a descent according to the FMC profile, and your vdev indicator will stay centered. To strictly follow this profile (by defaut 3

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catIIIdualThanks for the reply. The left click worked. Thanks. Why doesn't the a/c maintain a 3deg descent path all the way down to runway threshold? If there is no waypoint crossing restrictions in the approach, why does the a/c level off at each waypoint at it's own calculated crossing level, and then continue the descent afterwards. I see this happens with sids and stars too, and one gets a type of occilated descent profile. It does keep within 300 feet of the descent path but then levels off or descents in order to maintain the correct path.I also do not put in any minimas during the approach, just to check whether the aircraft will maintain a 3deg descent profile to threshold height, and according to the VPI it does, but when breaking the cloud the aircraft is way to low (all 4 papi's red). I thought the aircraft should be able to maintain a constant descent path all the way to threshold elev +50ft, but it does not. There is this up and down flight path to try and catch the VPI and the final approach glide slope is very close to the 3deg standard, but way too low according to the visual slope indicaters (papi). Maybe I'm just doing something wrong, but the same procedure works 100% in the PMDG B737-700. On the correct VNAV path, slight low in ILS (half a dot), but good enough to execute a visual approach. Stephen

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