Originally Posted by Bluestar51
100PP,
Is it SOP for the Airbus to fly NPAs using a constant rate of descent? Is the NPA flown in MAP mode (not sure about the Airbus term) with the raw data being monitored?
BS
There's a lot of guff on this thread, so I'll take the opportunity to explain in
simple terms how you fly an NDB in an A320 (the A330 I understand is identical in this respect - if any 330 guys want to point out any differences then that would be good). Small details have been omitted.
The bus has a small button which flips between HDG/VS and track/FPA (flight path angle). In track/FPA the heading window now displays a track and the VS window displays FPA in degrees. The flight director changes and a little "bird" appears, which is a flight path vector.
You can see that this is a very powerful set of controls. At the FAF you can just select a track that is the same as the approach track, and a descent angle (typically 3 degrees), taking you accurately down the approach. As the wind shifts direction and speed, the aircraft will maintain the track. As you slow down, or the wind changes, you will maintain your FPA. No need to worry about V/S!
Now, you also have a choice whether to use this "pilot selected" method, or let the FM system steer you laterally (NAV) and/or vertically (FINAL APP) - "managed" modes. In this case the airline required/allowed managed lateral and selected vertical, so we shall look at how that is flown.
You would always use the autopilot and autothrust.
Before the approach, you prepare the FMC by checking the approach, missed approach point, MDA (normally +50 on published) missed approach and auto-selected navaids. You tell it that you want Vapp at the FAF, and you put your ND into map mode, with the NDB needle displayed. You plan to fully configure the aircraft just before the FAF, so you fly the final approach fully stabilised. This minimises the workload so you can concentrate on the 2 or 3 important jobs on the way down.
On an intercept heading you would select track/fpa. You would push the heading knob to arm NAV, so that the aircraft will intercept and follow the FMC inbound track. Configure the aircraft, and just before the FAF you preselect your FPA (-2.6 degrees here) and when you want to start down you pull the knob and you will get 2.6 degrees down.
Exactly when you pull the knob is a complex subject and will vary by type, available aids and maybe some more accurate points that you can generate yourself (more accurate than a marker beacon).
You can vary your FPA on the way down to keep in line with your height/distance checks. On this NDB there are none, so you have to just maintain the rate. You cross check the raw data (NDB needle) to make sure the NAV mode is working correctly. In real life, NAV is deadly accurate.
At MDA +50 you decide and either:
- Disconnect the AP and FDs, and land.
- Move the thrust levers all the way forward. This gives you TOGA thrust and the AP will pitch up and fly the go around. You will follow the track you are on when you move the levers forward until you push the heading knob to engage NAV, whereafter you will fly the missed approach in the FMC.
If you descend below the database (or pilot entered) transition altitude on STD, then "STD" is boxed and flashed on the PFD. You can't miss it.
When the radalt becomes alive, you both cross check the reading with your calculated height (by subtracting approximate terrain altitude from your indicated altitude).
Hope this helps.
Some pics from the FCOM (it all looks nicer in real life!):
