Tutorial: Approaches

[Aquila]

Hi there,
Does an Approach also work without an ILS?
And which Approach do AI-Aircraft use to Approach?

 

[jvile]

Hi there,
Does an Approach also work without an ILS?
And which Approach do AI-Aircraft use to Approach?

Hello Aquila

That is a excellent question and one that does not get asked very often. All approaches work with out a actual ILS but it is a little bit more complex then just saying yes.

We need to review what a ILS added to a runway actually does. When a full ILS (LOC + GS + DME) is added to a runway it serves only one purpose. The purpose is for the User Airplane. Inside the User Airplane is a radio and instruments that lock on to the Localizer and GS (with option DME) so the User can fly these beams. That is the only thing the ILS does. It has nothing to do with any type approach and nothing to do with any type AI Plane.

In a nutshell the ILS added to a runway allows the User Plane to fly the ILS to a runway and nothing else. That presents another problem. As long as the weather is VMC at the airport ATC will vector the user and AI plane to that runway for landing if the winds are conditioned correctly. However ATC says to use the visual runway because ATC does not see the runway as a ILS. If weather at the airport becomes IMC (IFR conditions) then ATC will not keep that runway open since only the User Plane sees the ILS on the instrument panel and ATC knows nothing about the runway.

If the User plane and Pilot (you) want ATC to vector you to the ILS then an approach code must be written so ATC understands a ILS exist.

Normally the 2 go hand in hand meaning if a ILS exist for the runway then there is/should be a companion ILS approach code so ATC understands a ILS exist. That way the runway stays open if weather deteriorates to IMC condidions.

Up to this point we have been talking about the User Plane and you the Pilot. We need to talk about the approaches.

There are 3 catagory's of approaches for planes on IFR Flightplans. VFR FP's have different rules.

1. Hardcoded FS9/FSX approach
2. Non-Weather related approaches
3. Weather related approaches.

No 1 means, if a airport exist and there are no approaches in the database for the runways then ATC directs the User and the AI plane on a fake hardcoded vectors to final approach. This fake approach is written in the .dll files. It uses a standard 2000 ft AGL for the approach and a runway heading to vector the plane to. Since ATC sees this runway as a visual runway the approach controller will say 'runway is at your xx O'clock position do you have the runway in sight' (yes or no).

No 2 means, if the airport has a ILS and companion ILS approach code then ATC will use and say to both the user and AI plane fly the ILS approach. The FAF altitude, the missed approach altitude, the heading is runway heading + - the missed approach turn, etc. all comes from the XML approach code so the hardcode is not used.

We call this a non-weather related approach because it is the fundamental approach used regardless of what the weather is. The weather can be severe clear and ATC is going to say fly the ILS approach and give instructions for the approach based on what is written in the XML (ADE Approach Mode).

Remember, the User Plane needs a ILS beam to lock on to which is the ILS that is part of the runway. The AI Plane uses all the written XML but does not know anything about the ILS added to a runway. The AI Plane does not know anything about a ILS added to the runway because there is no Pilot flying the AI Plane. You the Pilot look at your instruments and use your eyesight to fly the ILS beams. Since no pilot is flying a AI Plane it has no reason to process the ILS beams into the aircraft. Who's going to see them.

Now I can answer your question that says which approach does the AI aircraft fly.

1. If there is no approach code in the database the AI flys the hardcoded .dll approach.

2. If a ILS exist in the approach code (with or without a actual ILS beam) the AI Plane flys it in both clear weather (VMC) and severe weather (IMC).

So what is and when is a weather related approach used.

There are many different type approaches in the database that FS understands. These many type approaches also have a priority or pecking order that is used. We now know that by default regardless of what type weather is at the airport the AI and User Plane is instructed to fly a ILS approach if it exist (regardless of weather).

The priority order is as follows and what FSX honors

ILS (instrument landing system) <<<<<<======== Non-weather related
GPS (Global Positioning System type approach) <<<<<<======== From here down are all weather related approaches
RNAV (Area Navigation type approach)
LOC (Localizer)
LDA (Localizer Directional Aid)
SDF (Simplified Directional Facility)
LBOC (LOCALIZER_BACKCOURSE)
VORDME (very high frequency omnidirectional range with Distance Measuring Equipment type approach)
VOR (same as above without DME)
NDBDME (nondirectional beacon with DME type approach)
NDB (same as above without DME)
RW (runway visual)

Not Used by FS

IGS (Instrument guidance system) not used in FSX but we offset a ILS as much as 90 degrees and make it appear to be a IGS
LORAN (not used)
TACAN (tactical air navigation approach not used in FSX)

My small GA home airport has a 16/34 runway. The runway does not have a ILS or ILS approach code. However my small home airport has a VORDME and a NDB approach as per Jeppesen approach charts and FS9/FSX has these 2 approaches in the database.

If I am on a IFR FP (including IFR AI Planes landing) and the weather at my airport is IMC then the FS ATC controller will look down through the list to find an approach for me and the AI Planes to execute. It does not see a ILS approach so ATC searches further into the approach databse and sees 2 other type approaches. VORDME is a higher priority then a NDB so ATC vectors me and the AI Planes toward a vectors to final (or Transition if I select it) for the VORDME approach to runway 16.

To summarize

1. User and AI Planes are told by ATC to use a ILS Approach if it exist regardles of weather

2. In good weather if no ILS exist then ATC uses a hardcode in the .dll to get you and the AI plane to the runway

3. In bad weather if no ILS exist then ATC looks for another approach in the pecking order of the database.

4. You can write a ILS approach code and ATC will use it even if a runway does not have ILS added to the runway as seen with ADE

Many airports and runways in FS could use the No.4 because of my No. 2 above.

Many users are familiar with TNCM and runway 09 that does not have a ILS. Many 3rd party AI Planes have problems trying to land at TNCM (and many other airports) because the AI Plane has no set of ILS approach codes to work with in clear weather.

Of course if weather is not considered clear (VMC) the AI plane landing on RWY 09 uses the VORDME instruction code at TNCM. Many designers and users never look at the flyability of a AI Plane when weather is IMC and they only watch AI planes landing in clear weather.

For TNCM we write an approach code for a ILS even though the runway does not have a ILS and now ATC will instruct the AI plane to fly the XML coded values which are much more precise then the hardcode and AI Planes will stop going missed and land everytime on the runway.

Any Questions?

 

[highflight1985]

...I smell a sticky...

Nice article, Jim!

 

[scruffyduck]

I stuck it!

 

[Aquila]

I can find no RW Type in ADE, but there is an UNKNOWN Type, what is that?? When i use this and try to compile, there is a error.
I want to write an Approach for EDRY.
It'S difficult but I hope you can help me.

 

[teite]

Hi,

I want to write an Approach for EDRY.

As Speyer (EDRY) is a VFR only airfield, I wonder why you want to write an approach for?
Do FSX vfr only airfields have approaches too?

cu,
Stefan

 

[Aquila]

I like this airport, because there was the G-OFOA of the Formula 1 and it's very spectecular, when this aircraft approaches there and take-off. And i want my AI-Planes to Land there.

 

[jvile]

I can find no RW Type in ADE, but there is an UNKNOWN Type, what is that?? When i use this and try to compile, there is a error.
I want to write an Approach for EDRY.
It'S difficult but I hope you can help me.

There are many runway types to choose from in ADE. You right click and highlite the runway and then a menu allows you to choose the type surface.

UNKNOWN type is the same as concrete. I do not get a compiler error using the UNKNOWN. You need to see what the error is.

If you want AI Planes to fly the VFR Pattern based on your picture you write Touch and Go (TNG) Flightplans with a utility like TTools.

 

[Aquila]

No, i dont mean the surface, i mean the Approachtype.
I want, that my ai-planes approach over the river to RWY17.
I also tired this at LSZS,LSGK,EDRY and EDFX.
Maybe i should upload my .bgl files od these airports, so you can see, how i made my approach.

 

[jvile]

Aquila

Your post says

I can find no RW Type in ADE, but there is an UNKNOWN Type, what is that?? When i use this and try to compile, there is a error.

My post was addressing your problem with runway type and you say your ADE will not compile.

Then you ask about writing an approach but say nothing about what type of approach

I want to write an Approach for EDRY

If your airport will not compile then you cannot write an approach. You have to fix problems first.

 

[jvile]

No, i dont mean the surface, i mean the Approachtype.
I want, that my ai-planes approach over the river to RWY17.
I also tired this at LSZS,LSGK,EDRY and EDFX.
Maybe i should upload my .bgl files od these airports, so you can see, how i made my approach.

Now you are saying you do not mean a runway type.

By default the AI Planes will fly an approach over the river to rwy 17 if they are on a IFR Flightplan.

 

[Aquila]

RW (runway visual)

That is, what i mean with "Runway Type", but in the List in ADE, there is no RW Approach Type, only an unkown type.
So, i have to change the Aircraft Flightplans from VFR to IFR?

 

[jvile]

Aquila

ADE does not work directly with bgl's like all other airport design tools. You must open a stock airport and Save As a .ade extension.

Now open the airport .ade and do all your work with that file compiling from time to time. That way we never open a bgl and loose certain type .ade data.

AI Planes on a VFR FP fly a downwind, base or straight in final based on the direction they are coming from. If you want all the AI planes to fly a ATC approach you have to set the FP to IFR.

In my original post I said

There are 3 catagory's of approaches for planes on IFR Flightplans. VFR FP's have different rules.

Any AI Plane on a VFR FP does not fly approaches built with the ADE Approach Mode but as per FSX fly full downwind patterns or a partial pattern (base or short final)

 

[Aquila]

have you got a look on my files?
should i upload my .ade files?

 

[jvile]

Aquila


You have 2 RNAV 17 Approaches for EDRY. You must delete one.

Your RNAV 17 Approach Header should have CFSP2 as the IDENT and your "IF leg Ident should be IFSP1. The next 2 DF legs are ok.

RNAV is a weather related approach (see my original post) and will not be used unless the airport is IMC weather conditions.

Your CFSP2 FAF is too close to the runway for a altitude of 1500 ft. It should be about 4 miles from the runway. The IFSP1 should be about 7-10 miles from the runway.

For proper placement of runway T_Waypoints see the following post

http://www.fsdeveloper.com/forum/showthread.php?t=13751&page=2

Are you trying to make the AI Plane fly down the river and land?

 

[Aquila]

yes, i trie to make this and so i have to place the waypoints near to the runwat like in the approach card

 

[jvile]

Aquila

OK!!

Now I understand. We call that a Curved Approach to runway 17.

Where can I get the Approach card (chart) you have that shows the Terminal_Waypoints?

 

[Aquila]

Yes
but i have created the waypoints myself, by looking it up in the chart and then in FSX to place them.
I have also done it at EDFX (i pimped that airport). There the planes should fly the highway along and then turn right to the RWY.

 

[jvile]

Yes
but i have created the waypoints myself, by looking it up in the chart and then in FSX to place them.
I have also done it at EDFX (i pimped that airport). There the planes should fly the highway along and then turn right to the RWY.

Aquila

No problem if you created the waypoints yourself. What I am going to do is use your EDRY and make a post on how to get AI Planes to fly a curved approach. Everyone can then use that post to make curved approaches anywhere in the world for any reason such as high mountains on final.

 

[Aquila]

Thank you very much, i think this is what i am looking for.