Tips for NPA approaches

[musefan 363]

So I've just started flying some non precision approaches and while I'm getting better at it, I'm still stuggling with some aspects of it.

 

First of all, when coming in to land do I need to make adjustments to the thrust levers to control pitch or should I just leave in climb CL until 20 feet above (like an ILS approach)?

 

Also, is it correct to assume that I have to manually pitch up/down in order to keep the glide blip centered (I know it's not the glideslope indicator, it's a rectangle rather than a diamond but I don't know the correct terminology). In which case, do I need to disengage the AP and fly manually in order to keep it centred?

 

Same goes for banking the aircraft. Is this done manually as well? A symbol (like a cross section of a plane) appears at the bottom of the PFD. I'm not really sure if I need to be paying attention to it. And if I should be paying attention, I don't understand how it works, or what it represents.

 

I suppose what I'm asking for is an idiots guide to flying an RNAV approach or something like that. It's also quite possible that I don't have the plane configured properly. I normally just select the RNAV version of the runway I intend to land on when setting up my arrival on the flight plan page. Maybe I need to do something else.

 

Sorry for all the questions. I intended to make this simple, but the more I typed, the more I thought of.

 

The step by step guide does brush on it, but it doesn't go into any great detail like the main tutorial flight.

[Tom A320 4915]

You might want to have a look on the video belonging to the step by step guide:

 

 

 

More of the videos:

https://www.youtube.com/channel/UCIIBJ0coVzXGmNxfn3sP4FQ/videos

 

[musefan 363]

Thanks Tom. Believe it or not, it was actually after watching this video that led to the above questions 

 

If you look through the comments you'll see that I asked the same questions, but Rolf ask me to post here instead. His videos are brilliant, and I have learned a lot more from him than than any other videos. However, he does very little talking about describing what he's doing of the screen or why he's doing what he's doing, if you know what I mean.

[Andy320 77]

I'm going to speak from things iv read and the various videos Iv watched of bus pilots although I believe SOPs may vary airline to airline.

Regarding the A/T from what I know you can use it to its limitations (wind, inoperative systems etc) down to the flare. AP should be switched off before or at minimums meaning you must hand fly, iv also read that you must switch off the F/D if AP is off and A/T is on to avoid the A/T hanging at idle power which is dangerous at low levels, by the way I haven't read into the logic of this yet but I thought I would still include that in here and here is an example of a A330 NPA demonstration the above

, many SOPs state AP off, A/T must also be switched off... there are hundreds of videos of pilots landing with AP off and A/T on, I believe it is up to the captain if the SOPs allow.

 

When flying the magenta rectangle I always use the VS selecter to follow it down with heading mode (personal choice). Funny enough the video also demonstrates this in Track and FPA mode selected which gives you that fighter jet heads up display angle of attack indicator thingy thing on the PFD rather than the FD bars, you can fly that if you know how to, You could say they are like flight direction bars, where that points is where your aircraft will hit the ground, so if it's level with the other green line then you are bang on profile, I recommend watch some heads up display landings to understand what it's meant to simulate (watch aircraft carrier landings also if you have time).

 

In terms of flying the aircraft I fly with A/T on  if the wind allows just like the video above, so I pitch up and down accordingly after switching off the AP at minimums so fly as if you turned off the AP at your normal 1-4 mile final on an ILS approach and fly the runway PAPI lights. For a circle to land a recomandation is to use a flap 3 config approach for the purpose of the final turn especially when landing at places like Maderia where it's gusty, I occasionally use a flap 3 config for Gibralter runway 09 (Captain's discretion). 

 

Im not an Airbus pilot but this is my understand so far flying the aerosoft busses and reading what I can find as well as videos on the bus.

Also I find that the video quality is better on YouTube.com than viewing it from the forum.

[FraPre 89]

Hi,

you speak german? I can write better in my mother language for this difficult and profound theme.

 

Best regards

Frank

[skelsey 103]

Big topic, and probably (certainly!) one that is beyond a single forum post (in fact, this topic would form a large portion of the Instrument Rating in real life!), but I will try and cover the basics.

 

Firstly, before we start talking about the intricacies of flying one, techniques in the Airbus etc - let's go back to basics. What is a non-precision approach?

 

Non-precision approaches exist because not every airport/runway has the demand for a precision approach (i.e. almost always an ILS -- some RNAV RNP approaches are classed as precision approaches as well, but these are very rare so we'll ignore them for the moment).

 

A precision approach normally gives you some form of externally-derived vertical profile (e.g. the glideslope element of the ILS) to fly in order to bring you out at the DA/H and enable you to land the aeroplane on the touchdown point if you continue the same trajectory.

 

This is not the case with a non-precision approach, and that is why they are non-precision!

 

Non-precision approaches could include VOR, NDB, LOC only (or backcourse) approaches, or most RNAV approaches (again, ignoring the very occasional RNAV RNP approach).

 

Because there is no proper vertical profile below MDA, the AFDS cannot provide you with sensible guidance. For this reason, in the Airbus the autopilot will disconnect (whether you want it to or not!) when you descend below MDA, so you are hand-flying from this point onwards. At this point you must have the appropriate visual references (i.e. the runway) to continue in any case.

 

Whilst we're talking about MDA -- an important point to note is that unlike a precision approach (like an ILS) which has a DA/H (Decision Altitude/Height), an NPA has an MDA -- Minimum Descent Altitude. The MDA is similar to the DA in that this is the altitude at which we must be able to see the required visual references (very basically -- the runway) to continue the approach. However, if we're flying down the glideslope on an ILS, get to the DA and then commence a go-around because we don't have the visual references we need, inertia means that the aircraft will momentarily dip below DA whilst the engines spool up etc. This is fine, because the obstacle clearance etc for the missed approach takes this in to account. However, the MDA for a non-precision approach does not have this protection, and therefore we must not dip below MDA during the go around. This means that we must actually make the decision and commence the go-around prior to reaching MDA to ensure we will not bust it - generally 50ft is a good additive for these purposes (some operators have approval at some airfields to treat MDAs like DAs, but we won't get in to that now).

 

The MDA for a non-precision approach is generally higher than that for a precision approach. Why? Because the approach itself is inherently less accurate. Full deflection of the CDI when an ILS Localiser beam is tuned, for instance, indicates a deviation of 2.5 degrees from the centreline. When a VOR is tuned, full scale deflection is ten degrees. Because VORs and NDBs are inherently less accurate than ILS localisers, and RNAV relies on the accuracy of the aircraft's navigation system unless backed up by some form of ground-based system (GBAS) it's not possible to determine the path an approaching aircraft will take so accurately -- therefore obstacles in a wider area have to be taken in to account for both the final approach and the missed approach phases.

 

Now, to fly an NPA in the Airbus we have three options:

 

Selected/Selected

This is where are manually altering the heading and altitude to follow the approach as depicted on the chart (i.e. in HDG | VS (or TRK | FPA if you prefer).

 

Managed/Selected

Here we're letting the AFDS follow the lateral path of the approach using LOC or NAV, but we are still manually controlling the descent using V/S or FPA.

 

Managed/Managed

If the approach is appropriately coded in the navigation database, and we have the required navigation accuracy (i.e. HIGH), then the Airbus can manage both the lateral and vertical paths for us (using FINAL APP mode, as shown in the tutorial video).

 

Things to remember:

In the Airbus, the autopilot will disconnect below MDA, therefore you must hand-fly to the runway (by looking out the window). The general rule of Flight Director usage is that if you are not intending to follow them -- turn them off (as they will be giving both you and the rest of the autoflight system erroneous commands). So generally speaking, at or just before MDA you would want to disconnect the AP (better technique to do it yourself prior to MDA rather than waiting for it to trip off) and turn OFF the flight directors.

 

At this point, you may wish to select TRK/FPA mode as this will give you the Flight Path Vector on the PFD -- aka "the bird". The bird is useful because it tells you where your aeroplane is actually going -- so, for instance, if you want to fly a 3 degree descent, you simply adjust the pitch until the bird is sitting on the 3 degree down line on the ADI. Likewise, the bird will show you your drift (i.e. from a crosswind) -- if you set the runway course on the track selector, you'll notice a little green mark extending upwards from the compass that sits immediately below the ADI. Turn so that the vertical lines that extend up and down from the bird are lined up with this green mark, and that is the track you are flying (obviously this is not an indication that you are lined up -- just that your ground track is parallel with that of the runway centreline).

 

Legally speaking you cannot "roll your own" approaches by building them with place/bearing/distance points, even with reference to the chart -- you must select the approach from the FMGS database (and you cannot modify any of the legs or altitudes that are coded). Therefore, it stands to reason you must check the approach you have selected from the database against the chart carefully. If it all matches up, happy days -- you may fly a managed/managed approach. If not, you will have to fly a selected approach and back it up with the raw data from the VOR or NDB. Likewise, if your Navigation Accuracy from the PROG page is not HIGH, managed/managed is generally out of the window.

 

Autothrust

Some discussion about autothrust here.

 

In the Airbus, you can use Autothrust in all phases of flight, and indeed autothrust usage is recommended by Airbus at all times, including when hand-flying. Many operators require autothrust to be used at all times when serviceable.

 

In the past (particularly with non-FBW types), A/T usage whilst hand-flying was generally discouraged. This is because underslung engines produce a thrust/pitch couple -- when you increase thrust, the nose will go up, and when you decrease thrust the nose will go down. In a conventional aeroplane like the older Boeings (e.g. 737/747/757/767), this meant that if you disengaged the autopilot but left the A/T in, you would invariably get in to quite uncomfortable pitch oscillations (because if you pitched the nose up, the speed would decrease, so the A/T would add thrust, which would cause the nose to pitch up more, so you'd have to counteract that by applying forward pressure, then the A/T would take some thrust away and the nose would want to drop.... you get the message. Tiring and uncomfortable for the pax). Therefore, on those types the recommendation was that if you took the A/P out you should also take the A/T out and manage the thrust yourself (because then you could adjust the thrust manually in concert with what you were doing, rather than fighting the A/T).

 

On the Airbus A320 series, however, the Fly By Wire implementation provides path stability and automatically corrects for the thrust/pitch couple. Therefore you can hand-fly the aeroplane quite stably with the autothrust engaged without the uncomfortable pitching effects that conventional aircraft have. Therefore, you can leave the A/THR in all the way to the flare (and indeed this is recommended as it gives you things like GS Mini protection in managed speed). Boeing's newer offerings such as the B777 and B787 also include thrust/pitch couple correction in the FBW, and therefore the A/T can be left in whilst hand-flying these types as well.

 

Hope that helps answer some of your questions, and feel free to ask more...

[musefan 363]

2 hours ago, 320Ski said:

I'm going to speak from things iv read and the various videos Iv watched of bus pilots although I believe SOPs may vary airline to airline.

Regarding the A/T from what I know you can use it to its limitations (wind, inoperative systems etc) down to the flare. AP should be switched off before or at minimums meaning you must hand fly, iv also read that you must switch off the F/D if AP is off and A/T is on to avoid the A/T hanging at idle power which is dangerous at low levels, by the way I haven't read into the logic of this yet but I thought I would still include that in here and here is an example of a A330 NPA demonstration the above

, many SOPs state AP off, A/T must also be switched off... there are hundreds of videos of pilots landing with AP off and A/T on, I believe it is up to the captain if the SOPs allow.

 

When flying the magenta rectangle I always use the VS selecter to follow it down with heading mode (personal choice). Funny enough the video also demonstrates this in Track and FPA mode selected which gives you that fighter jet heads up display angle of attack indicator thingy thing on the PFD rather than the FD bars, you can fly that if you know how to, You could say they are like flight direction bars, where that points is where your aircraft will hit the ground, so if it's level with the other green line then you are bang on profile, I recommend watch some heads up display landings to understand what it's meant to simulate (watch aircraft carrier landings also if you have time).

 

In terms of flying the aircraft I fly with A/T on  if the wind allows just like the video above, so I pitch up and down accordingly after switching off the AP at minimums so fly as if you turned off the AP at your normal 1-4 mile final on an ILS approach and fly the runway PAPI lights. For a circle to land a recomandation is to use a flap 3 config approach for the purpose of the final turn especially when landing at places like Maderia where it's gusty, I occasionally use a flap 3 config for Gibralter runway 09 (Captain's discretion). 

 

Im not an Airbus pilot but this is my understand so far flying the aerosoft busses and reading what I can find as well as videos on the bus.

Also I find that the video quality is better on YouTube.com than viewing it from the forum.

Thanks for this. It's very helpful. But I'll need to watch it a few more times. I never thought of using the VS and the heading knob. I know it's a sad state of affairs, but I've gotten so used to flying in managed mode I'm always under the impression I need to fly manually when managed mode won't get the job done.

2 hours ago, FraPre said:

Hi,

you speak german? I can write better in my mother language for this difficult and profound theme.

 

Best regards

Frank

Sorry, no I don't speak German, but thanks for offering to help

18 minutes ago, skelsey said:

Big topic, and probably (certainly!) one that is beyond a single forum post (in fact, this topic would form a large portion of the Instrument Rating in real life!), but I will try and cover the basics.

 

Firstly, before we start talking about the intricacies of flying one, techniques in the Airbus etc - let's go back to basics. What is a non-precision approach?

 

Non-precision approaches exist because not every airport/runway has the demand for a precision approach (i.e. almost always an ILS -- some RNAV RNP approaches are classed as precision approaches as well, but these are very rare so we'll ignore them for the moment).

 

A precision approach normally gives you some form of externally-derived vertical profile (e.g. the glideslope element of the ILS) to fly in order to bring you out at the DA/H and enable you to land the aeroplane on the touchdown point if you continue the same trajectory.

 

This is not the case with a non-precision approach, and that is why they are non-precision!

 

Non-precision approaches could include VOR, NDB, LOC only (or backcourse) approaches, or most RNAV approaches (again, ignoring the very occasional RNAV RNP approach).

 

Because there is no proper vertical profile below MDA, the AFDS cannot provide you with sensible guidance. For this reason, in the Airbus the autopilot will disconnect (whether you want it to or not!) when you descend below MDA, so you are hand-flying from this point onwards. At this point you must have the appropriate visual references (i.e. the runway) to continue in any case.

 

Whilst we're talking about MDA -- an important point to note is that unlike a precision approach (like an ILS) which has a DA/H (Decision Altitude/Height), an NPA has an MDA -- Minimum Descent Altitude. The MDA is similar to the DA in that this is the altitude at which we must be able to see the required visual references (very basically -- the runway) to continue the approach. However, if we're flying down the glideslope on an ILS, get to the DA and then commence a go-around because we don't have the visual references we need, inertia means that the aircraft will momentarily dip below DA whilst the engines spool up etc. This is fine, because the obstacle clearance etc for the missed approach takes this in to account. However, the MDA for a non-precision approach does not have this protection, and therefore we must not dip below MDA during the go around. This means that we must actually make the decision and commence the go-around prior to reaching MDA to ensure we will not bust it - generally 50ft is a good additive for these purposes (some operators have approval at some airfields to treat MDAs like DAs, but we won't get in to that now).

 

The MDA for a non-precision approach is generally higher than that for a precision approach. Why? Because the approach itself is inherently less accurate. Full deflection of the CDI when an ILS Localiser beam is tuned, for instance, indicates a deviation of 2.5 degrees from the centreline. When a VOR is tuned, full scale deflection is ten degrees. Because VORs and NDBs are inherently less accurate than ILS localisers, and RNAV relies on the accuracy of the aircraft's navigation system unless backed up by some form of ground-based system (GBAS) it's not possible to determine the path an approaching aircraft will take so accurately -- therefore obstacles in a wider area have to be taken in to account for both the final approach and the missed approach phases.

 

Now, to fly an NPA in the Airbus we have three options:

 

Selected/Selected

This is where are manually altering the heading and altitude to follow the approach as depicted on the chart (i.e. in HDG | VS (or TRK | FPA if you prefer).

 

Managed/Selected

Here we're letting the AFDS follow the lateral path of the approach using LOC or NAV, but we are still manually controlling the descent using V/S or FPA.

 

Managed/Managed

If the approach is appropriately coded in the navigation database, and we have the required navigation accuracy (i.e. HIGH), then the Airbus can manage both the lateral and vertical paths for us (using FINAL APP mode, as shown in the tutorial video).

 

Things to remember:

In the Airbus, the autopilot will disconnect below MDA, therefore you must hand-fly to the runway (by looking out the window). The general rule of Flight Director usage is that if you are not intending to follow them -- turn them off (as they will be giving both you and the rest of the autoflight system erroneous commands). So generally speaking, at or just before MDA you would want to disconnect the AP (better technique to do it yourself prior to MDA rather than waiting for it to trip off) and turn OFF the flight directors.

 

At this point, you may wish to select TRK/FPA mode as this will give you the Flight Path Vector on the PFD -- aka "the bird". The bird is useful because it tells you where your aeroplane is actually going -- so, for instance, if you want to fly a 3 degree descent, you simply adjust the pitch until the bird is sitting on the 3 degree down line on the ADI. Likewise, the bird will show you your drift (i.e. from a crosswind) -- if you set the runway course on the track selector, you'll notice a little green mark extending upwards from the compass that sits immediately below the ADI. Turn so that the vertical lines that extend up and down from the bird are lined up with this green mark, and that is the track you are flying (obviously this is not an indication that you are lined up -- just that your ground track is parallel with that of the runway centreline).

 

Legally speaking you cannot "roll your own" approaches by building them with place/bearing/distance points, even with reference to the chart -- you must select the approach from the FMGS database (and you cannot modify any of the legs or altitudes that are coded). Therefore, it stands to reason you must check the approach you have selected from the database against the chart carefully. If it all matches up, happy days -- you may fly a managed/managed approach. If not, you will have to fly a selected approach and back it up with the raw data from the VOR or NDB. Likewise, if your Navigation Accuracy from the PROG page is not HIGH, managed/managed is generally out of the window.

 

Autothrust

Some discussion about autothrust here.

 

In the Airbus, you can use Autothrust in all phases of flight, and indeed autothrust usage is recommended by Airbus at all times, including when hand-flying. Many operators require autothrust to be used at all times when serviceable.

 

In the past (particularly with non-FBW types), A/T usage whilst hand-flying was generally discouraged. This is because underslung engines produce a thrust/pitch couple -- when you increase thrust, the nose will go up, and when you decrease thrust the nose will go down. In a conventional aeroplane like the older Boeings (e.g. 737/747/757/767), this meant that if you disengaged the autopilot but left the A/T in, you would invariably get in to quite uncomfortable pitch oscillations (because if you pitched the nose up, the speed would decrease, so the A/T would add thrust, which would cause the nose to pitch up more, so you'd have to counteract that by applying forward pressure, then the A/T would take some thrust away and the nose would want to drop.... you get the message. Tiring and uncomfortable for the pax). Therefore, on those types the recommendation was that if you took the A/P out you should also take the A/T out and manage the thrust yourself (because then you could adjust the thrust manually in concert with what you were doing, rather than fighting the A/T).

 

On the Airbus A320 series, however, the Fly By Wire implementation provides path stability and automatically corrects for the thrust/pitch couple. Therefore you can hand-fly the aeroplane quite stably with the autothrust engaged without the uncomfortable pitching effects that conventional aircraft have. Therefore, you can leave the A/THR in all the way to the flare (and indeed this is recommended as it gives you things like GS Mini protection in managed speed). Boeing's newer offerings such as the B777 and B787 also include thrust/pitch couple correction in the FBW, and therefore the A/T can be left in whilst hand-flying these types as well.

 

Hope that helps answer some of your questions, and feel free to ask more...

Very informative post. Thanks a million. I'll have to study it in a bit more detail though lol

[Andy320 77]

Thank you so much Skelsey to be honest I didn't want your reply to end, it was so detailed and has given me a much more structured and overall better understanding of how to make best use of the systems. Thank you for sharing your knowledge :-)

[Andy320 77]

Nealmac you may find it easier to practice using selected mode from TOD and flying the ILS on selected mode, a tip is try not to make excessive VS changes for example if 1000 fpm is to steep then try 800 fpm etc make sure you monitor your speed when descending to steep. But again there are plenty of videos out there of real world pilots fly in selected mode at some point during an approach to final.

[musefan 363]

yeah ive no problem flying an ils approach in selected mode. my question was based on runways that dont have an ils.

[Andy320 77]

Sorry last one from me for this topic and anyone else that may find this useful for NPA, just after 18 minutes will explain in video form some of what Skelsey was explaining earlier, happy landings :-)

[LLL33 5]

Airbus is indeed recommending A/T at all times, as skelsey wrote. However, many operators, including the biggest European airline, require to switch it off prior of disengagement of the autopilot. This wasn't the case, when the 320 was introduced, but some fatal accidents did lead to this change in SOP.

The awareness of crews of the power setting did go down in the busses compared to conventional planes. This can end fatal, especially at very low level.

There have been runway overruns due to unnoticed power increase, and short landings due to help of the A/T. Sometimes airlines learn from accidents quicker than Airbus.

So prior MDA you switch off 1. A/T 2. A/P 3. F/D

The change from manual to automation goes the other way around.

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