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FLS vs RNAV approaches on A320

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FLS vs RNAV approaches on A320

Old 22nd Jun 2021, 09:43
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FLS vs RNAV approaches on A320

Hello all,

In the airline I fly for on the A320 we regularly do RNAV approaches and soon RNP-AR obviously using FINAL APP.

Have been recently made aware that the A320 can have the option of doing an FLS approach using F-G/S and LOC. Just wondering if anyone has any experiences of using this system, it’s use on the line and the benefits or negatives compared to an RNAV app?

I understand you can’t do curved final approaches like with RNP-AR with FLS but to me ( with very little knowledge of this system so please correct me) if you can do RNAV approaches is there any point in FLS. Also what airlines use this system?
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Old 22nd Jun 2021, 12:01
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Fls is not a procedure is guidance for the approach calculated by FMS , you select an Rnav procedure and if the GLS is available for that procedure you will see the info displayed like an ILS with pesudo Loc and Glide so you will fly it like an ILS .
Also in case of ILS with inoperative glide slope , the GLS is able to calculate a glide and present the info in the PFD like an ILS with glide , you will flight it arming APP with Loc and ( pseudo ) Glide. There is even no need to take into account temperature below the maximum shown on chart , because the FMS with the temperature inserted will make the correction in presenting the calculated glide , so it is a simplified and safer mode to fly all non precision approach.
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Old 22nd Jun 2021, 12:57
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FLS presentation.
https://www.airbus-win.com/wp-conten...fHIupD1xDn6sgA
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Old 22nd Jun 2021, 14:54
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I think one of the advantages of FLS is that it's automatically temperature compensated.
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Old 22nd Jun 2021, 15:28
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Interesting information here.

I have no first hand experience on FLS, but on the system that Airbus essentially copied and improved upon, Boeings IAN. IAN has quite a few advantages in my view, it gives a pseudo ILS indication so it can be used with or without FD allowing "raw data" flying on any kind of (straight in) approach, there is no procedural change from precision approaches like ILS or GLS to non precision approaches like overlay or RNP (non AR) approaches as long as they are straight in. Everything is flown in approach mode instead of LNAV/VNAV or VORLOC VS. The big downside for IAN is that it is not temperature corrected and that non-straight in approaches have to be flown using LNAV/VNAV, which is still fully managed but not using ILS procedures, which does include RNP AR approaches.

From what i read above FLS seems to have the same restriction on being usable on straight in approaches only, but is temperature corrected, which is a huge improvement in my view. Now, if airbus would only implement a 5 and 2,5NM range mode and vertical situation display on the A320, but sadly, it would also need to implement quite a bit bigger screens for that.
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Old 22nd Jun 2021, 20:18
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Thanks for the replies and especially the airbus video which has cleared a lot up for me.

I fly for a pretty big A320 outfit and was surprised thereís no mention of it but guess it hasnít been optioned. The focus seems very much on RNAV. Certainly having temperature corrections would be great at the time of cold temperatures. Can see a big benefit for doing a back course approach although canít think of any in Europe unless anyone knows of one ( I know a small section can be used for 08 Innsbruck).

Thanks for your help.
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Old 23rd Jun 2021, 18:21
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Our line has one Airbus fleet that is FLS equipped. We only have one non-ILS approach in the route system that does not allow FLS, which is trained specifically in the simulator. For that fleet, FLS does dramatically simplify the process of approach preparation and execution. The only disadvantage would be the inability to use FINAL APP to perform RNP approaches, as previous posters have mentioned. From what I understand an upcoming MMR upgrade will eliminate that limitation.
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Old 25th Jun 2021, 00:16
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I think one of the advantages of FLS is that it's automatically temperature compensated.
RNP-AR is only designed for uncompensated Baro-VNAV....
The flightpath is already corrected for NA above and NA below...
it is dangerous to attempt to add temperature correction...aerodrome temperature is meaningless aloft...,

I dont see many aerodromes with compensated VNAV approach...what temperature would you be compensating for, the aerodrome temperature on the ground? or temperatures aloft?

the pattern would be a mess flying compensated and uncompensated approaches with the associated altitude differences...and min required separation

The only disadvantage would be the inability to use FINAL APP to perform RNP approaches, as previous posters have mentioned. From what I understand an upcoming MMR upgrade will eliminate that limitation.
Even if the ac can do it, I doubt if the pattern can monitor separation standards...

BTW...agree with Nick 1...
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Old 25th Jun 2021, 09:36
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turbidus

You cannot fly RNP AR with FLS as it uses F-LOC and F-G/S. The temperature correction is to the FLS beam. RNP AR would be flown in FINAL APP.
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Old 25th Jun 2021, 12:11
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https://www.airbus.com/content/dam/c...agazine_23.pdf
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Old 29th Jun 2021, 12:56
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Nick1, please donít confuse FLS and GLS, they are two entirely different systems.

FLS uses the FMS to calculate a pseudo LOC and GS beam and effectively uses the same indications as when flying an ILS approach albeit with a ďdouble diamondĒ.

When flying a GLS approach the MMR uses the local GBAS system / channel.

FLS is entirely FMS generated whereas the GLS still uses GBAS which is an external system.

Both are highly accurate although a three degree FLS beam in very hot conditions might end up being misleading, GLS doesnít have this issue.

Have flown both approaches and done autolands of GLS approaches which with an FLS approach equally is not possible.
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