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Can anyone explain why this approach may sometimes be required please?  I fly the NGX in P3D.

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Because it is far easier than a non-precision approach, particularly the NDB, which in my opinion should have gone the way of the dinosaur years ago. As long as you have sufficient navigational accuracy and the vertical and lateral trajectories for the approach have been carefully checked, the RNAV approach is much easier than using an NDB as it's not susceptible to interference and has vertical deviation information just like the ILS.

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Can anyone explain why this approach may sometimes be required please? I fly the NGX in P3D.

 

Hi, Dave,

 

I'm not sure they are ever actually "required," but they certainly can be useful.

 

Often for an offset approach -- for example one approach for SFO 28R, or DCA 19, which involves a fairly sharp low level right turn. 

 

SFO:

http://flightaware.com/resources/airport/SFO/IAP/RNAV+(GPS)+PRM+X+RWY+28R/pdf

 

DCA:
http://flightaware.com/resources/airport/DCA/IAP/RNAV+(RNP)+RWY+19/pdf

 

Also any runway that either does not have GS or localizer, or for which one or both are not working.  Especially if there is no GS or it is inoperative, it is useful to have the vertical guidance of an RNAV approach.

 

Both the SFO and DCA approaches end in visual final approaches, which I believe is always the case for an RNAV approach. 

 

Somewhere on the PMDG forums there is a discussion of why you wouldn't want to combine an RNAV approach with an ILS approach, and why, for example the 777 won't autotune the ILS if an RNAV approach is selected.

 

Not meant to be an exhaustive explanation -- just a few examples.

 

Mike

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Thanks Mike. I thought maybe it was something to do with local terrain etc.?   Thanks for your explanation, much appreciated.

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Can anyone explain why this approach may sometimes be required please?

 

Airports are equipped with approaches based on necessity, along with other fluid requests (I'll explain the latter as we go).

 

 

 

The type of approach is highly dependent on the type of airport, and the types of operators into that airport. If it's a small general aviation airport, then it usually gets (at best) an RNAV approach, and/or perhaps a VOR approach if one is nearby. NDB approaches are also occasional, but usually only for airports that have been around for quite some time, and the NDB itself hasn't died yet (at which point they're simply decommissioned). Why do even the smallest of GA airports get an RNAV approach? They're the cheapest due to the lack of equipment. There's no LOC array, glide slope antenna, monitoring equipment, and so on.

 

Stepping up to a larger GA airport with more traffic and larger operators, you start to see LOC and ILS approaches. The reason is that, as mentioned earlier, these are more expensive to develop, set up, and maintain. Either the FAA or local government - or more likely, a combination of both - have a business and safety reason to install the equipment and maintain it. At this level, though, there's usually only one ILS approach to the most frequently used runway, with an RNAV approach on the reciprocal side.

 

Moving up to a regional airports and above, you usually see that there's generally a business reason to commission and maintain multiple approach types. Additionally, these approaches are set up to both ends of the runways, and potentially multiple runways. The RNAV approaches remain to handle ILS outages, or offer different routing options around terrain. As an example, KROA is buried in (low) mountains, which means that the "ILS" to Runway 6 has to be offset due to terrain, making it an LDA. Runway 34 has an ILS because the mechanics of the approach actually worked out. Runway 24 wasn't found to be used enough for landing to require setting up an LDA approach, but enough that an RNAV could be set up. Runway 16 can't have an approach at all due to terrain on the north side making the approach too steep. In this case, while the airport has more sophisticated options available, the curved paths of the RNAV are available to handle the terrain.

 

At international airports, you generally only see ILS approaches to each runway, along with RNAV for the same reasons as regional airports. There may be one or two VOR approaches as a last ditch effort back up. RNAV approaches are generally overlay-type approaches that are just about the same thing as the ILS approach, but navigated via GPS/INS. These approaches generally also have curved entries that help to smooth traffic flows off of the STAR, or navigate complex paths. An example of the latter case here is the RNAV Runway 19 approach to KDCA, which follows a relatively complex curvy approach following the Potomac River to the airport.

 

Taking this last point to a larger extreme are certain operators who are utilizing RNAV approaches to get into specific airports in specific situations. Alaska Airlines has a number of approaches that they have specifically sponsored up in Alaska (and since they've footed the bill, they're not public). Similarly, jetBlue paid a pretty penny to create an RNAV approach into Runway 13L at JFK, which they can use when conditions are jamming up operations in NY airspace. If JFK goes to the 13s, LGA also has to go to 13, which then causes issues for EWR for both the 4s or the 22s. As such, ILS 13L at JFK is avoided at all costs. jetBlue's RNAV approach, though, cuts in a lot closer to the airport than would be required for the ILS, so they can use a more favorable runway while other operators take a delay in trying to get in on the ILS, or take a less wind-favored runway.

 

 

 

Short version?

Contrary to the common sim belief that the ILS is the King of All Approaches, the RNAV offers a more consistent and wide-spread approach to airports. The only true advantage that you get with the ILS is its current approval for autolands, if your aircraft is so equipped and it's necessary (another sim misconception...autolands are very very infrequent). RNAV hasn't been approved for autoland yet.

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Thanks Kyle, I was rather hoping you'd notice this one. lol

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Thanks Kyle, I was rather hoping you'd notice this one. lol

 

You're welcome.

 

...and to tack on - again - to Mike's earlier post, the SFO example is actually pretty unique and important. Since the runways are so close together, maintaining proper radar separation is tough if you want to keep the arrival rates up to help avoid huge delays ("Oh SFO is delayed today? Color me surprised..." is a common line for me at work when I look at the OIS). To combat this, they have a few different tools, from an offset ILS approach and an offset RNAV approach, to a further offset - beyond the capabilities of an ILS at this airport - RNAV approach that allows the aircraft to get below the clouds, visually acquire the leading ILS approach, and proceed visually. This, of course, is something that we have the advantage of doing over here that isn't something you'd see elsewhere, as many other places still require minimum radar separation even when pilots have visual contact with the preceding traffic.

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RNAV approaches are generally overlay-type approaches that are just about the same thing as the ILS approach, but navigated via GPS/INS.

 

Hi, Kyle,

 

Thanks for your very thorough discussion.  I am curious though as to why many airports have RNAV approaches that are virtually identical to the ILS approaches to the same runways.  Are these only for equipment failures, either on the ground or on the aircraft?  Is there any reason why, in the particular situation of a working ILS/GS, that a pilot or controller would prefer an RNAV approach to an ILS one for the same runway?

 

Thanks,

Mike

 

PS: Kyle, I think I got the particular RNAV SFO 28R approach from one of your earlier posts.

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Thanks for your very thorough discussion.  I am curious though as to why many airports have RNAV approaches that are virtually identical to the ILS approaches to the same runways.  Are these only for equipment failures, either on the ground or on the aircraft?  Is there any reason why, in the particular situation of a working ILS/GS, that a pilot or controller would prefer an RNAV approach to an ILS one for the same runway?

 

Part of it is just the idea that most of the work is already done. An ILS approach is a lot more stringent in terms of requirements than an RNAV, so the site survey is already complete for the environmental impact, noise studies, and so on, so you might as well get a "free" approach out of it. As a controller, you can't assign an approach that doesn't exist, and if you have an ace up your sleeve in the case equipment goes out (intentionally or unintentionally), or something else of the sort, you have a little more fault tolerance. For a good number of them, the fixe names don't even change.

 

 

 


PS: Kyle, I think I got the particular RNAV SFO 28R approach from one of your earlier posts.

 

Probably - SFO and JFK were big examples we used when we were floating the idea of "Best Equipped Best Served" over the "first come first served" concept. The other one was a MDW and ORD example, but it got less discussion time.

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Similarly, jetBlue paid a pretty penny to create an RNAV approach into Runway 13L at JFK, which they can use when conditions are jamming up operations in NY airspace. If JFK goes to the 13s, LGA also has to go to 13, which then causes issues for EWR for both the 4s or the 22s. As such, ILS 13L at JFK is avoided at all costs. jetBlue's RNAV approach, though, cuts in a lot closer to the airport than would be required for the ILS, so they can use a more favorable runway while other operators take a delay in trying to get in on the ILS, or take a less wind-favored runway.

 

Hi Kyle,

 

Strangely, I have had the impression that the 13L (visual, VOR or RNAV) approach is used quite often when the wind is from the sector E-SSW when looking at the traffic in flightradar24 but statistics would be interesting. I can see even traffic coming from Europe directed to the 13L instead of rwy 22s which doesn't look logical...

And by the way, the RNAV approach is published so all traffic other the Jetblue may use it also but do you know what is the most given approach on the 13L? VOR, RNAV or visual?

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Because it is far easier than a non-precision approach, particularly the NDB, which in my opinion should have gone the way of the dinosaur years ago.

 

John,

 

How many real world NDB approaches have you flown?

 

blaustern

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Because it is far easier than a non-precision approach, particularly the NDB, which in my opinion should have gone the way of the dinosaur years ago. As long as you have sufficient navigational accuracy and the vertical and lateral trajectories for the approach have been carefully checked, the RNAV approach is much easier than using an NDB as it's not susceptible to interference and has vertical deviation information just like the ILS.

RNAV approaches, including those with LPV minimums are non-precision. RNAV approaches with Ground based augmentation system (LAAS) also known as GLS approaches are the only satellite based precision approaches.

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Is there any reason why, in the particular situation of a working ILS/GS, that a pilot or controller would prefer an RNAV approach to an ILS one for the same runway?

 

Not entirely sure whether it's still the case but at Gatwick any aircraft following an A380 is/was offered the RNAV.

 

The reason is because the A380 infringes the ILS critical areas for a much larger period of time when vacating the runway and therefore much greater spacing (14 miles) would be required between a landing A380 and a following aircraft to ensure that the critical area is protected. Putting the following aircraft on the RNAV approach means that the ILS critical areas no longer need to be protected and therefore the spacing can be reduced to the usual 8 miles.

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Strangely, I have had the impression that the 13L (visual, VOR or RNAV) approach is used quite often when the wind is from the sector E-SSW when looking at the traffic in flightradar24 but statistics would be interesting. I can see even traffic coming from Europe directed to the 13L instead of rwy 22s which doesn't look logical...

And by the way, the RNAV approach is published so all traffic other the Jetblue may use it also but do you know what is the most given approach on the 13L? VOR, RNAV or visual?

 

Hi, Romain,

 

I don't see an RNAV approach for 13L at Flightaware.com - just the VOR, the Parkway Visual and the ILS.  Strangely, there is an RNAV approach to 13R, a runway normally used for takeoffs.  It starts much more to the west than the 13L Canarsie and Parkway approaches -- also odd, since this brings it close to the approach path for LGA 4.   My assumption is that the Canarsie VOR and Parkway Visual, among other things, provide for noise abatement since, like 4L/R AND 31L/R they are flown mostly over water.

 

 

 


The reason is because the A380 infringes the ILS critical areas for a much larger period of time when vacating the runway and therefore much greater spacing (14 miles) would be required between a landing A380 and a following aircraft to ensure that the critical area is protected. Putting the following aircraft on the RNAV approach means that the ILS critical areas no longer need to be protected and therefore the spacing can be reduced to the usual 8 miles.

 

Thanks, Simon.  Very interesting example!

 

Mike

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Actually it is called VOR or GPS RWY 13L/13R on the chart.

 

Hi, Romain,

 

I always thought of it as just a VOR approach but you are quite right -- it meets the definition of an RNAV approach -- indeed I've flown it that way many times.  Although I think the altitude for DMYHL in the Navigraph data, 800 ft, is too low, and does not agree with the chart you linked to or previous versions I've looked at.

 

Mike

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The good think of the RNAV approach is that it provides me a vertical path guidance while the VOR does not.

In fsx, I find this kind of approach with a turn to the rwy in short final quite difficult to fly regarding the vertical path without glide path indication especially when the altitude at the beginning of the turn is quite low.
In Nice (LFMN) you have the same kind of VPT approach but the beginning of the turn is higher and it gives a better situational awareness.

Plus the path to the runway is clear of any obstruction, while in JFK, you have some buidings in the way.

 

In real life, I find it easier to get good visual reference for altitude and path than in the simulator (at least with GA aircraft, as I'm not a commercial pilot).

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Although I think the altitude for DMYHL in the Navigraph data, 800 ft, is too low, and does not agree with the chart you linked to or previous versions I've looked at.

 

800ft is the MDA and DMYHL is the MAPt for the procedure. The vertical profile has been calculated, according to the LIDO chart, for a CDA to reach MDA at the missed approach point (i.e. 800ft at DMYHL). DMYHL is 3.6NM to 13L and 2.6NM to 13R, so you will be slightly low for 13L and about on profile for 13R.

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Strangely, I have had the impression that the 13L (visual, VOR or RNAV) approach is used quite often when the wind is from the sector E-SSW when looking at the traffic in flightradar24 but statistics would be interesting. I can see even traffic coming from Europe directed to the 13L instead of rwy 22s which doesn't look logical...

 

The charted Parkway Visual (hereafter "Visual") and VOR are used quite frequently for the 13s, if - and for as long as - they can be. The one angle that a lot of people forget about is minimums. The Visual to the 13s obviously has the highest minimums at 2500. The VOR is an approximation of the Visual that carries lower mins, but they're still up at 800. The company RNAV gets those mins down to 300-500ish (from what I remember - since it's a company approach, it is not published).

 

As far as runway selection goes, you have to remember that - for larger and busier airports - this has a lot less to do with the wind than you'd immediately think. Selection of a runway configuration will greatly affect your ability to accept and dispatch traffic. Since I'm not anywhere near an expert with N90 airspace, I'll leave you to the flow tools that were created to help visualize the unique interplay of JFK, LGA, EWR and TEB.

 

Here are the planning numbers of what to expect with each config: http://www.fly.faa.gov/Information/east/zny/jfk/frames.htm

 

And by the way, the RNAV approach is published so all traffic other the Jetblue may use it also but do you know what is the most given approach on the 13L? VOR, RNAV or visual?

 

The RNAV approach is not published. The RNAV approach you're seeing is not the one I'm referring to.

 

The most common is the Visual and VOR. The RNAV is used tactically, but it's not as advantageous as the company RNAV that jetBlue has to 13L, which cuts in closer to where the VOR exists. When the weather drops, they have to coordinate airspace with LGA and EWR to get an approach to the 13s via the ILS is most low weather cases. Of course, if you're already hosing up the airspace and someone can fly an RNAV approach, you might as well hand a few people the RNAV to 13R.

 

I don't see an RNAV approach for 13L at Flightaware.com - just the VOR, the Parkway Visual and the ILS.  Strangely, there is an RNAV approach to 13R, a runway normally used for takeoffs.  It starts much more to the west than the 13L Canarsie and Parkway approaches -- also odd, since this brings it close to the approach path for LGA 4.   My assumption is that the Canarsie VOR and Parkway Visual, among other things, provide for noise abatement since, like 4L/R AND 31L/R they are flown mostly over water.

 

Correct. It's unpublished. jetBlue footed the bill of that procedure's development, so it's exclusive to them until someone else wants to pony up money to make a public version of the approach.

 

The RNAV to 13R is tactically used to offload traffic onto that runway where it can be worked in: no departure to get out, RNAV capable, and usually when airspace is already backed up because they're on the ILS. As you've noticed, it's not in a great spot with regard to LGA and the city, so it's not the best assignment unless there's some tactical advantage to assigning it in that circumstance.

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Additional Information About All of This:

 

Something a lot of the sim crowd doesn't realize - related to the "ILS TO EVERYTHING" fallacy - is that your selection of runways and approaches has a huge impact on the rate at which you are able to handle aircraft.

 

In visual conditions, aircraft are assigned the visual because this allows the controller to defer separation to the flight crews. This relives the 3NM minimum radar separation requirement, which allows more aircraft to occupy the same parcel of airspace, which results in a relatively high airport arrival rate (AAR). Do note, however, that the controllers are still monitoring closure rates and any aircraft that may be on an errant path to ensure that - even though 3NM is not being maintained - aircraft are not at risk of blundering into each other. This is also still subject to FAR 91.111a separation ("no person may operate an aircraft so close to another aircraft as to create a collision hazard").

 

If the weather is still good enough for the visual, but with the aid of some other technology to get down under the clouds, the AAR dips slightly (the LOW VMC column of the AAR chart). Again, this requires some leading separation, but once under the clouds the preceding aircraft can be called in sight, which relieves the larger separation requirement, allowing for a still relatively high AAR.

 

When the weather drops to where instrument approaches are used, the AAR further decreases as radar separation is required essentially down to the runway. In the LOW IMC column, you're seeing an "approach down to minimums" example. The AAR doesn't drop too much between the two in most cases because of the separation requirements not being too different. The AAR might drop slightly due to the difficulty of the approach, or difficult airspace coordination.

 

 

 

A traffic manager is concerned a good deal about being able to move traffic efficiently. This lowers EVERYONE's workload. Along these lines, the runway configuration that moves the most traffic is the one that will be preferred. This includes the approach type to those runways. Visual is always going to move the most traffic, so it will be preferred at all times it's available. Only when the weather dips down will the facility start using instrument approaches. If there are airspace conflicts, higher min approaches with larger visual segments will be preferentially selected until weather drops lower.

 

Using JFK as an example:

The wind is blowing straight down the 13s at 20 knots.

Clear Day: Parkway Visual

Overcast at 2499 (below the Visual): VOR/GPS 13L/R

Overcast at 799 (below the VOR/GPS): ILS 13L with tactical offshoots to RNAV 13R

 

At any point the weather allows for an approach higher in the list, it will be chosen.

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Kyle,

 

Thanks! Such an explanation, I expected no less from you!

 

I understand perfectly the hierarchy of the approaches (do we say that in English?) and their use.
One last question if I may:

I know that the Ivao network may not reflect the real use of approach type, but even in VMC, I almost always get an ILS approach for a runway if there is one.

In real life, in international airports in VMC, where VPT/visual are not published, are pilot directed to the final for a visual approach or are they just given ILS?

I'm familiar with VFR circuit procedure (controlled/uncontrolled airport) for GAs flying VFR all the way, but I'm a bit confused about how to transition between a STAR/transition and a visual final approach/landing.

When looking at the flight pattern on flightradar24, it looks like the traffic are vectored to intercept the localizer rather far from the airports when ILS approaches.

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Thanks! Such an explanation, I expected no less from you!
 
I understand perfectly the hierarchy of the approaches (do we say that in English?) and their use.

 

You're welcome, and 'hierarchies' is correct, yeah.

 

 

 


I know that the Ivao network may not reflect the real use of approach type, but even in VMC, I almost always get an ILS approach for a runway if there is one.
In real life, in international airports in VMC, where VPT/visual are not published, are pilot directed to the final for a visual approach or are they just given ILS?

 

Online networks usually default to the ILS because most sim pilots usually don't know how to fly a visual. You're welcome (and encouraged) to have the ILS information dialed in as backup guidance. If it's not a charted visual, you just line up visually and land the plane.

 

 

 


I'm familiar with VFR circuit procedure (controlled/uncontrolled airport) for GAs flying VFR all the way, but I'm a bit confused about how to transition between a STAR/transition and a visual final approach/landing.

 

At large internationals airports, you don't fly a traffic pattern. The approach controller will guide you up to just about the base or final leg through vectors and then ask you to call the field in sight. Once it's in sight, advise, and once cleared, line up on the extended centerline and land. It's actually a lot simpler than people make it out to be. It's an unfortunate, but understandable misconception given how procedural and regimented aviation can be at times.

 

Think of it this way:

An instrument approach is a means of providing guidance to a point where you can see the runway. A visual approach sidesteps all of that because you already see the runway and can navigate on your own by looking outside. A charted visual allows you to execute a visual approach much farther out, or via a non-standard (not straight in) path by correlating items on a chart with ground features.

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Crystal clear, thanks again!

 

 

 


At large internationals airports, you don't fly a traffic pattern

 

And it is fortunate because much as flying a VFR pattern in a GA at 80kt is easy, joining it like I learned via overhead the airport with a pass along the runway on the dead side before joining the downwind (standard procedure) in a jet at 200kt gives much less time to react!

 

Anyways, I will probably request more Visual to the controllers, now I know it is that easy in IFR!

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I know that the Ivao network may not reflect the real use of approach type, but even in VMC, I almost always get an ILS approach for a runway if there is one.

In real life, in international airports in VMC, where VPT/visual are not published, are pilot directed to the final for a visual approach or are they just given ILS?

 

I don't know where you do most of your flying, Romain, but just to add a small caveat to Kyle's excellent post:

 

 

 

In visual conditions, aircraft are assigned the visual

 

...in the USA.

 

In Europe an instrument approach will normally be assigned if there is one available. Heathrow, for instance, have some tricks to get the arrival rate up in VMC -- mainly a thing called Reduced Separation In The Vicinity of the Aerodrome (RSIVA) which means that reduced separation minima can be applied if the Tower controller can see both aircraft and the aircraft can see each other -- but it's still all radar sequenced to the ILS. (For interest, the standard separation at Heathrow is 3NM applied to 4DME, which results in about 2.5NM at touchdown: under certain circumstances 2.5NM to 4DME can be applied which results in 2NM at touchdown -- obviously wake turbulence requirements override those minima where applicable). I'm not sure how assigning visuals would help with the arrival rate in those circumstances, really: you can pack them as close as you like on final approach, but the preceding aircraft still needs time to vacate the runway before you can clear the next one to land and 2NM is about the bare minimum that you can get away with for that. Time Based Separation has also recently been introduced to further increase the landing rate in strong headwinds.

 

In Italy, visual approaches have more or less reduced to zero for transport category aircraft after a Cessna Citation flew in to a mountain whilst on a visual approach to Cagliari -- the ATCOs who assigned it were sent to jail (because the court decided that the pilot calling the field in sight was not enough and the controllers should have taken more steps to make the pilot aware of the terrain). Silly decision but result: = no more visuals in Italy.

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