Perform a LNAV/VNAV approach (A320)[PDF]

INTRODUCTION

This briefing shortly describes the basic procedures to perform RNAV (GNSS) approaches with LNAV/VNAV minima. The differences with LNAV only, are mainly based on the criteria of design:

  • LNAV/VNAV requires a V/DEV indicator as the primary source for vertical navigation, provides a DH as low as 250ft depending on the obstacles around, and ensures the maximum vertical deviation along the Final Descent (75ft max).
  • LNAV only ensures vertical obstacle clearance by crossing specific altitudes over specific fixes along the approach. It’s like a conventional NPA which provides a more exact lateral navigation due to the accuracy of the GPS receivers

In Airbus philosophy, there are two types of Autopilot/Flight Directors modes used during the approach, commonly referred to as “Guidance" (See table below in Aircraft Guidance Management section).

The Guidance used for LNAV/VNAV approaches must be FINAL APP.


FLIGHTPATH MANAGEMENT

LATERAL FLIGHT PATH

RNAV GNSS approaches are procedures based on GNSS lateral navigation to follow a defined track. The lateral flightpath will be monitored by a cross track deviation value indicated on the Navigation Display (or L/DEV in some aircraft).

A lateral deviation of 0.1nm is accepted as a standard value during the approach.

The required system accuracy must be 0.3NM maximum of lateral error.
Sometimes the final approach track is not totally aligned with the runway center line.

VERTICAL FLIGHT PATH

For LNAV/VNAV minima approaches, a V/DEV indicator on the Primary Flight Display (PFD) is required to be followed as the main source of vertical navigation.

In LNAV/VNAV, a deviation of ½ a dot in the V/DEV vertical scale is accepted as a standard value. 1 dot equals to a deviation of 100ft.

NAV/FPA mode cannot be used in LNAV/VNAV.


PREPARATORY WORK

CHART READING

Approach Chart Reading

RNAV (GNSS) APPROACH 13R

Final Approach Course: 134o

FAF: BO612 at 12000ft

Glide path: 3.0o

DA: 8682ft


DESCENT PREPARATION

Use the “TOP HAT” method as per AIRBUS SOP for descent preparation. Follow the flow from left to right.

Prepare the approach at least 80NM before Top of Decent (TOD)
Top Hat Flow


  1. Pay particular attention to the F-PLN sequence. Select the appropriate RNV approach (RNAV GNSS). Make a vertical revision and check altitude and speed constraints for each point along the approach. Press key R2:
Vertical Revision


Cross check with the charted values.
Constraints vs Chart


Cross check the final approach track, the Final Descent Point (FDP) and the final descent angle on the MCDU with the information in the chart. A difference of 0.1o in the vertical path, and 1.0o for the lateral path between the chart and the MCDU is acceptable.
Values


2. Check that the reported temperature at the airport is within the limits for the procedure.

If the temperature is out of the charted range, LNAV/VNAV minima cannot be used and the FINAL APP mode might not engage (Non-baro compensated aircraft).
Insert the most accurate temperature and QNH information in PERF (Approach page), along with the other relevant data.
Temperature compensation: The baro-VNAV navigation system should be capable of automatically adjusting the vertical flight path for temperature effects.


3. On PROG page, insert the reference runway threshold in order to monitor the position during the approach.

Check “GPS PRIMARY” passing 10000ft during descent.
Values


4. It’s always a good idea to have a back up plan. You may prepare another type of approach on the SEC F-PLN, a different suitable runway or simply make a copy of the primary flight plan.
Values



AIRCRAFT GUIDANCE MANAGEMENT

This table will help you understand the overall guidance management considerations highlighted for LNAV/VNAV mínima approaches, using FINAL APP mode.

You can also find it useful for LNAV mínima approaches using both FINAL APP and NAV/FPA modes. (Refer to Perform a LNAV approach (A320) for LNAV ONLY info)

Guidance Management.jpg


1. When the Final Descent Point (FDP) has been sequenced as the “TO WAY POINT”, and the approach clearance has been received, ARM THE APPROACH by pushing the APPR button on the FCU.
Arm the app


As mentioned earlier during descent preparation, the FDP can be identified as the point on the MCDU F-PLN with the value of the Final Descent Angle (usually -3.0o). It can also be identified by looking at the blue “hockey arrowed stick” over the FDP. Sometimes the FDP and the charted FAF are the same, but there are some cases where the FDP might be located at a different point, before the FAF. (See the picture below)

FDP on ND


2. Check APP NAV and FINAL are engaged in green or armed in blue.
FINAL APP


3. When FINAL APP mode engages, set the Go Around Altitude.
FINAL APP ENGAGED


4. Monitor vertical and lateral deviations. It’s very important to cross the FAF with a maximum deviation of 75ft.
Deviations during the approach cannot be greater than ½ dot of V/DEV on the PFD and 0.1nm of X-TK on the ND.


5. Monitor flight parameters in order to maintain a stabilized approach. Call out for any deviation that might affect the stabilization criteria.
Stabilized App


COMMON PARAMETERS FOR STABILIZATION DURING THE APPROACH

The stabilization criteria shown here are just a reference. They may vary depending on each operator.
  • Speed: between VAPP -5kt // +10kt
  • V/S: Max -1000ft/min in descent
  • Bank: Max 7o
  • Pitch: Max -2.5o // +10o
  • Cross Track: Max XTK (lateral deviation) of 0.1NM
  • V/DEV: Max ½ dot


6. At DA, announce MINIMUM or monitor auto callout.
With enough visual references, continue the approach, otherwise perform a GO AROUND.



7. Disconnect the A/P at the latest when passing the MAPt or MINIMUM HEIGHT (250ft AGL), whichever comes first.
Flight Directors (FD) can still be used down to the MAPt when it’s located over the RWY threshold. They are very useful especially in low visibility. However, If they are not relevant or not followed, or simply useless due to, for example, the final approach segment and the RWY track not aligned, switch BOTH FLIGHT DIRECTORS OFF. After the MAPt, disregard the FDs as they revert to basic mode (HDG/VS).
8. Switch the “BIRD ON” by pressing the TRK/FPA button on the FCU anytime the flight directors (FD) are not intended to be used, and the approach will be continued under visual references (as per A320 SOPs). In this case, on the FCU set the RWY TRK .
BIRD ON
ATTENTION! Due to variations in the software and add ons, you might find differences in your flight simulator features with the explanations given here. For example, some add-ons allow you to keep the FINAL APP mode engaged only until passing the DA/MDA, no matter the position of the MAPt. At DA/MDA, you might expect an automatic disconnection of the Auto Pilot, and the mode reversion to HDG/VS. Closely monitor the FMA at all times, which in fact is one of the GOLDEN RULES in Airbus Philosophy. Check your add-on


AIRCRAFT CONFIGURATION MANAGEMENT

As per A320 Standard Operating Procedures, the aircraft configuration management should be as follows:
  • At Green Dot speed, select Flaps 1
    • Flaps 1 should be set more than 3nm from the FDP
    • Check deceleration towards S speed
    • For decelerated approach, reach the final descent path with F1 and S speed.
  • Set Flaps 2
    • This flap setting must be set by the latest at 2000 feet AGL.
    • Check deceleration towards F speeed.
  • When Flaps at 2, “Landing Gear Down”
    • Set Landing Gear Down
    • Check auto brakes
    • Arm the spoilers
    • Turn on “Taxi Light and RWY turn off” switches
  • Flaps 3 and Flaps Full as required
  • Landing checklist
Always check speed limits for flap and landing gear operations


See also

Reference

  • A320 FCOM/FCTM
  • Getting to grips with PBN

Author

  • VID 109661 - Creation

DATE OF SUBMISSION

  • 07:19, 23 February 2021

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.