# 737NG Psuedo-ILS

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I'm wondering what other people do to help them land at obscure airports in less than favourable weather conditions and without ILS. I set up a psuedo-ILS by adding a fix point/navaid to my legs page between 8-10nm from, and lined up with, the destination runway. If such a fix point/navaid is not available, I create a user waypoint (ie. lat/long) to achieve the same objective. I then set a speed restriction of 180kts for this waypoint and put in an altitude constraint that gives me a 3 degree glideslope. I calculate the 3 degree glideslope using some good old high school math (anyone remember SOH CAH TOA?), which is a function of the distance the way point is from the airport and the elevation of the runway. If anyone is really interested, the Excel spreadsheet formula I use is =ROUND(((TAN(RADIANS(3))*D21*6076.12)+D22)/10, 0)*10, where D21 is the waypoint distance from the rwy threshold in nm and D22 is the runway elevation in feet and the answer is to the nearest 10 feet.This now gives me an LNAV and VNAV path which is pretty close to what a real ILS approach would have me do. It can acually be flown on A/P nearly all the way to the ground in VNAV/LNAV, but I find that the A/P has a tendency to fly too shallow on the calculated glidepath which can cause grief if there are tall buildings on the final approach path. Because of this, I handfly the whole approach using the VNAV path indicator as my "glideslope" and the LNAV path and runway centreline extension as my "localiser". When the VASI lights and runway come into view, there is usually only a small correction required to make a greaser landing. Works a treat!As a practical example, I have attached a few screenies of my recent approach into navaid-bereft Mogadishu (HCMM) on my world tour. The first shows the user waypoint (WPT1), speed constraint and 3 degree glideslope altitude calculation result I used. The second, shows map view of me approaching WPT1 and the third shows me on psuedo-ILS approach final. I'm interested to read any comments on my procedure and also any suggestions of other ways to achieve the same result.Gary

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Hey Gary,A simpler way to do this same thing is available (and the simpler you keep things in the air the better):- Go to the Dep/Arr pages and select the landing runway (don't EXEC yet).- Once selected all the other runways (if any) dissapear from the right side and you are left with the selected runway displayed in 1R and 'RWY EXT' with some dashes below it in 3R- To keep things simple enter 10 into this field and EXEC- This now adds a waypoint (named 'RX-') 10nm away from the threshold of selected runway on the extended centerline.- Since a 3

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Funny I was about to post the same RNWY EXT lol. I would like to add if I may, The selection of a rnwy ext will give you 2 DISCONs so simply get clearance and perform a DIR TO to lighten the heads down work load. [h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/forum/betaimg.jpg

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Thanks Randy, forgot about that bit :)David

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David,I know the excel formula looks a bit complicated but I took it as a personal challenge to create it using my fading math knowledge. Since I have excel running when I fly (for my flight logging) anyway, I just pop the two numbers (distance and rwy elev) in their respective cells and instantly get the more exact answer.Thanks for the tip on RWY EXT usage. Certainly a heck of a lot easier than creating user waypoints. I have seen RWY EXT on the Dep/Arr page before, but couldn't find any reference to the use of it in the PMDG manuals. In fact, after looking again I still can't find it! Can you please provide me a reference?Gary

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Hey Gary,I don't think I remember seeing it in any of the manuals, I probably just tried it out sometime to see what it did :) I'll have a look though.CheersDavid

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Yes I am not sure it's even in there but certainly is in the AOMs CBTS etc. Of course it's only offered in the FMC for RNWYS not ILSs etc...[h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/forum/betaimg.jpg

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Here is an extract from a 737 AOM regarding the runway extension function:http://forums.avsim.net/user_files/69700.jpgThat's about all there was on it, out of nearly 2000 pages :-eek CheersDavid

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In addition you can also monitor the descent page. And when you see the V/B(vertical bearing) near 3.0 degree's you can use V/S to control your descent and follow the 3.0 degree angle, this works when there is no additional waypoint between your aircrat and and the runway ,as is the case when a runway extension is selected.http://forums.avsim.net/user_files/69713.jpg

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Thanks for the responses everyone: there's a great depth of knowledge here in this forum. I'll be executing the most precise non-precision approaches from now on. :-hah Gary

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