Need help writing ILS approach

[scott967 62]

I am working on the ILS approaches to the new VTBS. The problem I am haivng is in the missed approach procedure. For example ILS 01L has "climb on R-015 SVB to 3000 ft and hold or as directed by ATC". I have a CA leg that gets me out on 015, but there doesn't seem to be any good way to do the hold. The plate shows a waypoint symbol at the 10 DME from SVB as the base for the hold, but there isn't an official waypoint there.Do I have to create a terminal_waypoint in the correct position for the hold, or is ther some other way to get from the CA leg to an HM? I tried playing with a CD leg but didn't get that to work, and at any rate it seems like you need a waypoint for the HM.scott s..

[mgh 89]

In the real world, according to my copy of Supplement 17 to ARINC Specification 424 Attachment 5 Para 1.3 Leg Sequencing neither a CA or CD leg is permitted before a hold (HA, HF, HM) This is because a waypoint is required to define the hold.The only legs allowed before a hold are:AF, CF, DF, IF (only when the altitude constraints at each end of the "HX" leg are different), RF, and TF. Note that these are all routes to a fix.

[scott967 62]

I guess I will have to create some waypoints then. thanks.scott s..

[wsieffert 0]

You might try disassembling a similiar airport with approaches to see how MS made the approaches. Don't get to creative for several reasons:1. The approaches are only used for practice when NOT using ATC for vectors. ATC will vector your aircraft, if you are using them, and they will not use the holds.2. MS doesn't use all the ARINC Specification 424 codes in their procedures.Lastly, you need the actual published approaches. You need to add any additional waypoints, etc. to your scenery files, if they don't already exist. I added new approaches to KMCO just after FS2004 was delivered and KMCO opened up RW 17L/35R. I found it beneficial to disassemble KMCO to see how MS designed the existing approaches and then replaced the entire KMCO with a new KMCO with the new RW and approaches.W. Sieffert

[scott967 62]

The authors of the VTBS scenery included a waypoint file with all the new waypoints. All the default procedures (that I recall) end the missed approach with a hold. In the US (at lesat in programing for FMS for example) it seems like these holds are all bsed on a named waypoint. The charts for this airport, though, give a text description, and on the plan view indicate a waypoint symbol at a certain DME from the VOR at the airport. My plan is to just create unnamed terminal_waypoints in the approx location as a fix for the hold.Here is one of the plates:http://forums.avsim.net/user_files/158295.jpgscott s..

[jvile 1]

ScottYou can write the missed approach exactly as it is shown on the chart. There are certain type legs that will give you the runway heading to a certain point and then another leg that will turn you to 30 degrees. There are additional legs that will use a DME from a specific point to make the fictitious waypoint where the hold begins.In this way you do not need a TERMINAL_WAYPOINT for the hold. The legs that are used must accept rho and theta values which give you the proper distance and recip headings to accomplish a hold without a waypoint fix.This is one of the advantages of rho and theta because it will map the heading and distance which simulates the 10 DME value where the holding pattern is specified.ARINC is a world standard so if a country does not use a waypoint for the holding pattern then other math means can be used based on a distance value that comes from rho.

[scott967 62]

Thanks Jim, I will give it some more work. I kind of got sidetracked on another project (must have ADD) and will have to get back to this one.scott s..

[mgh 89]

Does FS follow ARINC's rules on leg sequencing?If so, the only legs that can precede a hold (HA, HF, HM) are AF, CF, DF, IF, RF, and TF. All these terminate in a fix.

[jvile 1]

hi mqhFS follows the rules in most cases. However in order to get the User Plane to auto fly some of the GPS receiver approach legs there are acceptions coded.I agree with you (based on ARINC) if a holding pattern has a required waypoint but, ARINC also has acceptions for a missed approach holding procedure code if there is no missed approach holding fix.In this case a different set of legs can be used with rho and theta to establish where the holding pattern is located in respect to the MAP of the Approach procedure. ARINC says the approach procedure owns the MAP waypoint (when it is needed) and that waypoint fix can be placed before, at or after the threshold of the runway.If a MAP waypoint is used, the entrance to the holding pattern is based on a distance from that waypoint fix (MAP) and not a holding pattern waypoint which as you said is leg specific.I could be wrong but I am reading the full ARINC document with the lastest attachments that came from the working group that met in Toulouse, France.

[mgh 89]

JimThanks, that's helpful.You're more likely to be right than I am - I'm working from only part of ARINC 424 and that could well be out of date.