Selecting a realistic approach procedure

[martinBerlin 0]

Hello gentlemen,

 

I think this question is bugging me for quite some time and now I will ask it here as I am sure some people will be able to give me a good answer. When I am looking at a lot of airports these days I find something like this list when it comes to selecting an approach:

 

Note this is taken from SFO for runway 28R:

 

a) ILS OR LOC RWY 28R

b ILS RWY 28R (SA CAT I)

c) ILS RWY 28R (CAT II - III)

d) RNAV (RNP) Y RWY 28R

e) RNAV (GPS) X RWY 28R

f) RNAV (GPS) Z RWY 28R

g) LDA/DME RWY 28R

h) LDA PRM RWY 28R

i) RNAV (GPS) PRM X RWY 28R

j) QUIET BRIDGE VISUAL RWY 28L/R

k) TIPP TOE VISUAL RWY 28L/R

 

From what I understand, in the real world for normal commercial operations

 

(a) Radar required, is the most common approach used in the real world, when the weather is fine

(b,© Radar required and other requirements, is used when visibility forces us to use them

(d) Authorization required, RF, GPS, Radar required. Why do you need an authorization for this? Why wouldn't all airlines use this procedure on a day with fine weather instead of (a)

(e) Radar required, DA is 1140 ft, ok (a) has a lot lower minimums, but with nice weather why wouldn't I use this one instead of (a)?

(f) Radar required, DA is 287 ft for LPV, and 641 ft for LNAV/VNAV, 760 ft for LNAV. Could somebody explain what LPV is?

(g) Radar and DME required, this is a special localizer-based instrument approach, why does an airport with ILS do need this at all? 

(h) Radar, DME and dual VHF comm required, again a special localizer-based app, I guess this is all about seperation and movements per hour

(i) Radar and dual VHF comm required, why do I need this when I have (g) and (h), just in case LDA is unavailable?

(j),(k) ok, this would be a choice when weather is fine and I should take care of my seperation myself

 

My question is: In normal operations, nice weather conditions, is it like airlines use (e), (f), (d) or (i) instead of ILS-based approaches? One small question regarding the naming, what is the difference between a RNAV RNP (d) and RNAV GPS (e) approach?

 

Thanks for your help.

 

Best regards,

Martin Schiewe

[scandinavian13 5,192]

 

 

(a) Radar required, is the most common approach used in the real world, when the weather is fine
(b,© Radar required and other requirements, is used when visibility forces us to use them
(d) Authorization required, RF, GPS, Radar required. Why do you need an authorization for this? Why wouldn't all airlines use this procedure on a day with fine weather instead of (a)
(e) Radar required, DA is 1140 ft, ok (a) has a lot lower minimums, but with nice weather why wouldn't I use this one instead of (a)?
(f) Radar required, DA is 287 ft for LPV, and 641 ft for LNAV/VNAV, 760 ft for LNAV. Could somebody explain what LPV is?
(g) Radar and DME required, this is a special localizer-based instrument approach, why does an airport with ILS do need this at all? 
(h) Radar, DME and dual VHF comm required, again a special localizer-based app, I guess this is all about seperation and movements per hour
(i) Radar and dual VHF comm required, why do I need this when I have (g) and (h), just in case LDA is unavailable?
(j),(k) ok, this would be a choice when weather is fine and I should take care of my seperation myself

 

Radar required refers to the requirement to be under ATC radar coverage, not have radar on-board your aircraft.

 

a) is false, because visuals are the most common in good weather.  ILS is common for poor weather all the way down to terrible weather (which is covered by some of b and c).

b) is SA (special authorization) so that operators can use lower minimums on 28R with the use of a HUD

c) CAT II and III approach (for lower minimums and those that require autolands)

d, e, f) are different variations on an RNAV approach that uses GPS (thus, "RNAV GPS")

g) LDA approach at SFO to allow for the simultaneous use of 28L and 28R during poor weather

h) same approach as g, but with the use of Precision Runway Monitoring (PRM) for even closer spacing during simultaneous 28L and 28R operations

i) same approach as h, but using RNAV (GPS), instead of an LDA

j and k) used during the night to lessen the noise impact to surrounding communities

 

Again - as always - visual approaches are the most common approach to just about any airport.  ILSs are next.  You generally don't see the rest too often.

 

 

 

One small question regarding the naming, what is the difference between a RNAV RNP (d) and RNAV GPS (e) approach?

 

RNAV RNP (required nav performance) is a technology that utilizes GPS in addition to inertial navigation (and other sources) to allow the aircraft to determine its location very precisely.  RNP is a concept related to using multiple types of RNAV simultaneously.

 

RNAV GPS simply requires that you use GPS as a source of RNAV.  GPS is a type of RNAV.

[dravid kenyala 6]

Here I see. Kyle and his very fast and perfect answering. Thanks. Learnt a bit by both of you guys.

[martinBerlin 0]

Hi Kyle,

 

thanks for your answer. Why to have RNAV approaches at all when they are so rarely used?

 

Best regards,

Martin Schiewe

[jag heter jan 2]

(edit: brain farting ensued. sorry for that.)

 

(edit 2: RNAV is an just a way to move more metal in a limited airspace simultaneously. You not only have the classic VOR & DME ground-based radio stations available, but airborne equipment like INS/IRS and GPS as well to aid you in determining your position.)

[dcgator29 37]

I'm far from an expert but I'll provide what info I know.

 

ILS are the standard approaches because most aircraft have them and they follow the standard 3 degree guideslope. In good weather atc will often vector you onto final and it's your choice if you follow the ILS or fly a visual approach. The cat II and III ILS's have lower minimums used for bad weather and autolandings and as such the radios on the aircraft are under stricter rules and inspections. There must also be failure redundancies on board. On a cat 3 approach in zero visibility, your ILS radios can NOT fail. Here is a good video on cat approaches; long and dry but good if you're interested. http://forum.avsim.net/topic/440291-cat-iii-instructional-video/#entry2972723 Sometimes the vertical glideslope component of an ILS is out at the airport. You would only be able to follow the localizer then. You'll notice for LOC only the mimimum is higher.

 

RNAV is simply a GPS approach. Some commercial aircraft have an FMS/CDU/GPS, some don't. Some may have that equipment but not the approach in the database. RNAV approaches are gaining in popularity but the status quo is to still offer an ILS as the least common denominator. You also notice the RNAV approaches don't generally provide alternate approach fixes. This is where you start the approach, no exceptions. The RNAV approaches have different letter designators X, Y, Z for different initial approach fixes (IAF), missed approach procedures, and decision heights/altitudes.

 

RNP is required navigation performance. It's simply a measure of how precise your GPS can calculate your position. On your PFD you should see RNP/ANP; required and actual navigation performance. You'll see on RNAV Y a RNP .10 and .30 DA; ANP must be within 1 tenth and 3 tenths of a nautical mile. On that Y approach, you see how the descent path are GPS fixes with altitudes. There's no ils signal or glidepath the aircraft is following. The FMS is calculating a descent based on those fixes. Again your FMS must be updated with the approach and fixes to follow it; again why an ILS approach is the least common denominator. The X approach I guess is simply less precise; no RNP requirements so the DA is much higher. It also has a missed approach that turns to the right, which is likely only possible if you've gone missed sooner at a higher altitude. X would likely be used in better weather.

 

This brings us into LPV. LPV is localizer perfomance with vertical guidance. It's like a virtual ILS glideslope. Your aircraft and gps must be able to utilize it. LPV should designate on the PFD. If not, you must follow the decision altitude for your approach; LNAV/VNAV, or LNAV.

 

On the LDA approaches. It stands for localizer type directional aid. It is used when the localizer signal does NOT line up directly with the runway. If you look closely on the LDA 28 approach, it is offset to the right of the runway. It is likely a backup if the main ILS fails. The LDA can get you close enough to the runway that you can land visually. Often terrain is the reason for an offset localizer; you simply can't fly straight in because of a hill. Juneau is an example of this.

 

Hope this helped some. If anything is wrong or not completely correct I'm sorry and hopefully someone can correct or elaborate.

 

 

The RNAV GPS approaches are designated that way to provide for commercial aircraft FMS's as well as panel mounted GA GPS receivers.

Edited June 21, 2014 by dcgator29

[77west 139]

Interesting you mention KSFO, every time I go in there on VATSIM I set up for nice long approaches with ILS and then they give me the damn Tipp-Toe Visual anyhow. Well, it is kinda fun, I think I might enjoy it more one SP1 is out.

[kevinh 409]

Hi Kyle,

 

thanks for your answer. Why to have RNAV approaches at all when they are so rarely used?

 

Best regards,

Martin Schiewe

I'm not sure Kyle meant it quite like that. RNAV approaches are becoming increasingly common. They will eventually replace all non-ILS approaches in FAA controlled airports. They don't require ground-based radio aids and can be used to give accurate guidance where ILS is inappropriate (ILS requires a straight in approach path with no terrain obstructions). RNAV procedures can steer you around terrain and are not subject to radio interference. At the moment the lowest decision height is 200 ft, equivalent to Cat I conditions. So RNAV approaches can't be used for autoland ... yet.

[scandinavian13 5,192]

 

 

thanks for your answer. Why to have RNAV approaches at all when they are so rarely used?

 

Kevin beat me to it, and summarized it nicely, but I'll add a little detail in parts:

 

Much like NDBs and VORs, ILS equipment (the LOC array and GS antenna) needs to be maintained.  That maintenance costs money, obviously.  In the same way the FAA is just letting NDBs die off, VORs will eventually meet the same demise in favor of RNAV-type navigation (again, remember that RNAV is simply a larger term to imply the idea that you can go direct to any point in space from any point in space - unlike you can when tied to VORs, NDBs, and even LOCs).  With this will come a decrease in the costs to maintain the NAS infrastructure.  I doubt the ILS will meet the same demise of VORs and NDBs at all airports relatively soon, but I have a feeling they will, eventually.

 

The RNAV RNP approach can also vastly improve traffic flows in certain areas dramatically.  Go here, and select LGA's ILS Runway 13 approach.  Note how the traffic interferes with both EWR and TEB.  RNAV RNP approaches could help avoid that situation by altering traffic flows into all three airports, in ways that the ILS cannot.

 

The main reason RNAV approaches aren't used, currently, is the amount of aircraft that require the ILS outnumber the number of aircraft that can fly RNAV.  Over time, this will change, and the majority will be flying RNAV approaches with ILS as the exception.  When that will occur is anyone's guess...

 

 

 

So, the main thing for everyone to take from this thread is that approaches aren't just tools to meet aircraft equippage; they're also tools to help with traffic management (particularly at SFO, with the close parallel 28L/R situation - thus the PRM approaches).

[martinBerlin 0]

Hi Kyle,

 

the number of aircrafts requiring ILS outnumbers the ones with RNAV capabilities? I thought it's the opposite looking at any modern airliner. OK GA might be different but that's another story.

 

Martin

[Cristi_Neagu 134]

Hi Kyle,

 

the number of aircrafts requiring ILS outnumbers the ones with RNAV capabilities? I thought it's the opposite looking at any modern airliner. OK GA might be different but that's another story.

 

Martin

I have the slight feeling that with all the low cost operators around these days, the vast majority of airlines have old fleets. Don't quote me on this, it's just my opinion.

[scandinavian13 5,192]

 

 

the number of aircrafts requiring ILS outnumbers the ones with RNAV capabilities?

 

Yep.

 

Looking at the charts, you have to pay close attention to what the chart calls for:

RNAV (GPS)?  A good number of UAL's 757s can't fly them (no GPS, though they have RNAV because they're IRU/IRU/DME)

RNAV RNP?  A good number of airlines can't fly those entirely (SWA is one of them - mixed fleet between 73 classics and NGs)

 

 

I have the slight feeling that with all the low cost operators around these days, the vast majority of airlines have old fleets. Don't quote me on this, it's just my opinion.

 

Bingo.

[kevinh 409]

I have the slight feeling that with all the low cost operators around these days, the vast majority of airlines have old fleets. Don't quote me on this, it's just my opinion.

Old fleets or not they can't fly without meeting local RNP standards. So they have to have up to date avionics. Low cost airlines in Europe often have very modern fleets to reduce costs. Holiday airlines have to fly into ill equipped airports so RNAV capability is a big plus.

 

Many full service carriers have older fleets that aren't economic to update.

 

ILS is still the approach of choice if you might need Cat II or Cat III limits.

[Cristi_Neagu 134]

Old fleets or not they can't fly without meeting local RNP standards. So they have to have up to date avionics.

Not if:

1. They can ensure that RNP using the current avionics, which is always the case if...

2. They never fly RNAV procedures, which they can avoid doing cause there aren't that many RNAV procedures to start with.

[kevinh 409]

Not if:

1. They can ensure that RNP using the current avionics, which is always the case if...

2. They never fly RNAV procedures, which they can avoid doing cause there aren't that many RNAV procedures to start with.

2 is not always the case at all. RNP doesn't just apply to approaches after all.

 

As I said, low cost airlines often have the most modern fleets.