Airbus A320 Fully Managed Non Precision Approach (NPA).

[Haseen]

Dear:

I am not a real world pilot, I am an Avionics Engineer at Biman Bangladesh Airlines Ltd. I do flightsimming in my PC. I would request for your kind help regarding above.

I am talking about how a fully managed (lateral and vertical) NPA is flown in a A320 and what are its prerequisites.

I saw a you tube flight deck video relating to the subject. After arming APPR button and pushing the HDG-V/S/TRK-FPA, on the FMA it shows APP NAV in the roll window and ALT in the pitch active window, FINAL is shown in the pitch arm mode window. FCU altitude is set at 2000. At certain point, may be, at FAF, pitch active mode window changed from ALT to FINAL. The pilots didn't reduce the FCU altitude value, as if, the plane is capturing a typical ILS Glide slope. But there is no radio GS as it is a VOR approach.

My questions are:

1. What logic makes the plane descend without any further pilot action?

2. Is the plane following a line drawn between FAF altitude say 2000 ft and the MDA say 450 ft?

3. If there is no approach procedure in the FMGC nav database and if I make place/bearing/distance way points along the runway center line approx. and set speed/alt constraints, will this NPA procedure work?

Thanks for your time and best regards,

Haseen Ahmad
Bangladesh.

[FlightDetent]

Hello Haseen,

1) The FINAL APP (blue) mode which is armed. Similar to GS (blue), no FCU action is needed, once all self-activation prerequisites are met.

2) Yes, not exactly what you describe (MDH) but geometrically similiar. Vertical profile is assembled in the FMGS, based on the database coded waypoints and legs, and the AP/FD then follows it.

3) No. The vertical profile between the waypoints needs to be in the database too - this is the way how the machine recognizes the FAF. The FMS db coding standard provides both waypoints and legs inbetween them (path & terminator concept). The technology present on the flight deck only allows us to enter the waypoints, possibly with constraints, as you describe, but not legs. In turn, this is not enough for FINAL APP to arm or engage.

Nice explanation of path-terminators here, page 10 onwards: http://www.icao.int/safety/pbn/Seminar%20Material/Montreal,%20Canada%2013-15%20June%202007/D.3.pdf

[Haseen]

Dear FlightDetent:

Thank you very much for your reply.