Disclaimer:
▪︎This content is Not an official document and does not represent the views of Airbus or any other aviation authority.
▪︎The information provided may be incorrect or misinterpreted and should not be relied upon for decision-making.
▪︎Always refer to official documents and consult with a qualified aviation professional before making any decisions based on the information provided in this blog post.
▪︎The information provided in this blog post is based on personal study and review.
GUIDANCE MODES PER APPROACH TYPE
FLS enables flying RNAV(GNSS) approaches with LNAV or LNAV/VNAV minima,
As well as conventional approaches based on VOR or NDB using F-LOC and F-G/S guidance.
FLS enables ILS-like approaches even without a localizer-only approach database.
FLS does not authorize RNP(AR) or RNAV(RNP) approaches with the FMS.
RNP(AR) and RNAV(RNP) approaches are permitted only in the FINAL APPROACH mode.
FLS/FINAL APP coexistence
For this reason, FLS/Final approach coexists to preserve the capability to fly curved RNP AR approaches, which cannot be flown using FLS.
Importance of Correct BARO setting for approach
The correct BARO setting for an approach is crucial, especially when it comes to approaches using FLS or the final approach.
Hence, the FMS uses the aircraft's barometric altitude to compute the deviation of the aircraft's trajectory from the computed final descent path
Even the altitude-vs-distance checks can not detect incorrect flight path with erroneos altmiter setting.
1hPa altimeter error moves the F-G/S vertical profile about 30ft
ALTSM function (pilot alerting function)
According to the airbus safety megazine,
ALTimeter Setting Monitoring (ALTSM) function, there is The ALTSM function, currently available on some Honeywell EGPWS standards, compares the barometric altitude on the captain side with the GPS altitude.
Procedural difference between FLS and Final Approach Guidance. (FCOM) - not all.
INITIAL/INTERMEDIATE APPRAOCH
In the approach using FLS mode, we arm the approach mode when the aircraft is on the intercept trajectory for the final approach course.
In contrast, the approach using the final approach mode is initiated when the TO waypoint is the final descend point.
MANAGEMENT OF DEGRADED NAVIGATION
There is an FMA column in the PDF that indicates the FLS capability. Depending on this capability, specific procedures are outlined for the FLS approach.
If it downgrades to F-APP + RAW, the flight crew needs to confirm that the lateral navigation is correct using radio NAVAID raw data.
If it downgrades to RAW ONLY for VOR and NDB approaches, the flight crew must press the LS push button to OFF and revert to TRK-FPA guidance. For ILS G/S OUT and LOC ONLY approaches, the flight crew must disregard the F-G/S deviation and revert to vertical selected mode, with the LOC deviation remaining trustworthy.
The flight crew can then continue to perform the approach with the localizer and altitude/distance raw data.
However, for RNAV (GNSS) approaches with LNAV minima and LNAV/VNAV minima, the flight crew is required to discontinue the approach when F-APP capability is lost or GPS POS disagrees.
(This is because there is no RAW data available to crosscheck the position, etc.)
COLD weather operation
The virtual FLS beam is corrected for temperature below ISA for the approach using FLS. Therefore, the approach can be flown regardless of the Outside Air Temperature (OAT).
However, the altitude still needs correction before establishing the F-GS beam during the approach and when cross-checking the altitude and distance when the FLS capability is showing F- APP+RAW or RAW, as well as the minimum values on the MCDU.
In contrast, the approach using the final approach mode requires adherence to specific temperature restrictions. These restrictions are typically indicated on the Jeppesen chart, in accordance with the company's procedures.
In cases where there is no specified temperature restriction on the Jeppesen chart, some companies may impose a restriction, usually at 0 degrees, for the approach using the final approach mode.
Deviation callouts.
In case of deviation call out, there is a LOC or GLIDE callout when there's a deviation of more than half dot of the localizer and half dot of the of glideslope,
but when it comes to approach using final approch mode, it is not LOC or GLIDE,
but it is CROSS TRACK or V/DEV, (when more than 0.1nm and half dot)
and also, in case of approach using FLS mode , correct standard callouts for deviation is L/DEV or DEV.
though the deviation callout is at half dot for glide(VDEV) ,
for rnav approaches with lnav.vnav,
discintinue approach if the g-gs deviation exceeds half dot below the F-G/s beam.
(F-loc is 1 dot)
