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Old 26th Jan 2006, 15:19   #1 (permalink)
Byrna
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Mexico City MMMX ILS 5R approach-very sharp turns?

Hello,

I do flight simulation and used charts based on real-world charts (from Simplates 2004 and VATSIM) to do an ILS approach to runway 5R at Mexico City's Benito Juarez airport (MMMX).

The route was from Vancouver Intl CYVR to MMMX.

The approach to runway 5R using the GABTU ONE STAR is confusing in how sudden the turns are and after verifying if I misunderstood the charts by re-reading Charles Woods' instructions on ILS approaches, I found I had done it properly.

The approach was done with a heavy - the PSS 772LR and the autopilot made the turns though it was off on the last turn to the final, making my course misaligned so the next time, I'LL do the turns manually myself. Here are some of the sharpest turns on the approach:

Begins at PJT VOR with heading 137
Turns to RADEL intersection heading 074
Turns to SMO (Mateo) VOR heading 159
I then inserted an intersetion myself to make the turns more smooth - MALPA heading 177
CD05 heading 111
Then the final approach fix (FAF) with is MW (Plaza) NDB with heading 049.

The last turn from 111 to 049 is incredible as the distance to go is only about 3.9 NM!


Do pilots really do this in real life or have I done something wrong?

Please note, the approach to runway 23L has a "teardrop" turn but 5R does not.

Any help would be appreciated, especially from pilots who have flown to Mexico City before.



Can (John) Agbaba
 
Old 26th Jan 2006, 15:34   #2 (permalink)
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Yes, it's really like that. Remember as well you are at a pressure altitude of about 9500' flying on that base leg so your TAS is much higher than normal meaning turns are wider. If you mess up that turn, you mess it up big time. My first time on that base leg, I was heavily involved in flying the complicated procedure approach, checks, flap extension, dropping the gear, getting 'cabin OK' from the cabin crew, and chuntering down the base. The copilot asked 'have you actually looked at the runway?' and up until then I hadn't had time. It was the classic eyes wide, 'omigawd!', strangled call for full flap and get turn going quick. You're very very close, and landing at over 8000', over the threshold you suddenly become aware how much faster than normal you are going. Actually stopping on the runway is exciting too.
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Old 26th Jan 2006, 16:04   #3 (permalink)
 
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Yea it's quite a fun arrival and the runway has a skin of tyre rubber on it " slippery when wet" good job it's long even if pretty rough
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Old 26th Jan 2006, 22:23   #4 (permalink)
Byrna
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Thanks so much Rainboe and gooneydog for clarifying that!
Well, at least I know I am reasonably good at understanding charts at least! I used to be looking at them but really not using them until I started flying online on VATSIM doing IFR procedures (for real, or as real as it gets in FS2004 in any case) so I am much less confused ... and in fact getting to be quite knowledgeable about charts...but still have lots to learn.

I think the obvious question would also be - how is the approach from SLM (Lucia One) VOR with the teardrop crossing MEX VOR? Is doing a longer teardrop pattern very tight with the mountains (obstacles) around Mexico City or is this longer but less nerve-racking than the Mateo approach? My guess is it may be less tight because you have more time to prepare and align with your runway and to descend to the correct approach/landing altitude.


John
 
Old 27th Jan 2006, 08:54   #5 (permalink)
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Its not that, its just the airport is way too busy to allow that kind of procedure regularly. Mex is certainly entertaining! Even with Land flap at Vref+5 you will go through the LOC on a heavy.
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Old 27th Jan 2006, 09:57   #6 (permalink)
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Although these teardrop & extended approach procedures are published in approach charts and occasionally flown in the simulator checks, in reallife they are never actually achieved. As pointed out, everywhere is just too busy, and equiped with radar anyway. What happens is that approach control will issue during descent a clearnace at some stage on the lines of "proceed to xxx VOR, then yyy, then beacon zzz and commence approach ILS 05R"- the logical route in following the most convenient approach bearing in mind outbound routings and terrain. It's usually not difficult to work out what's going to happen. Alternatively they just take you on radar control to the base leg, turn you toward the ILS and clear you for an ILS approach. I honestly can't ever remember flying these teardrop patterns more than a couple of times in a long career.
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Old 27th Jan 2006, 14:28   #7 (permalink)
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Interesting about the "theoretical" but not very practical approach charts... Well, that is very logical to use radar and ATC-provided vectoring for a smooth, less risky landing. The mountains which the course to runway 5R intersects definitely are a bit of a problem.

Actually, I have not tested altitudes for landing by an approach from the mountains, but is it too high if one literally approaches runway 5R by flying at the lower point of the mountains or is there no time and distance to make a safe landing with an over-the-mountain approach? I assume not for otherwise, the charts would show a course over the mountains onto 5R.

MMMX reminds me of another very dangerous and nerve-racking approach - Kathmandu's Tribhuvan (VNKT) where the alignment of the runway (or so it is in FS2004) is NOT at the LOWEST point of the mountains but at a slightly elevated portion (for the South approach to runway 2). This makes proper altitude when crossing the mountain range into the valley where Kathmandu is located (not too high) absolutely crucial or one is too high on the final - something I still need to master, at least with a heavy. I will probably try that again but with a more reasonable-sized 737-700 or program my VNAV to an exact altitude using approach charts.

Thank-you all again for your very helpful comments - your will to share your knowledge with "laymen" like myself (albeit informed laymen as I have a fair amount of simulation experience of well over 2 years now) is wonderful and very rewarding...in fact priceless.

John
 
Old 27th Jan 2006, 15:08   #8 (permalink)
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Not done Kathmandu but i suspect there will be an option to descend in the hold before starting the procedure in real life. MMMX is "entertaining" you need to start the turn and the descent spot on to hit the glide.
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Old 27th Jan 2006, 16:53   #9 (permalink)
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There are very tight minimum altitudes during the approach that have to be carefully monitored at all stages. There is no latitude for slackness in commencing descent at each stage. The approach brings you over the city too. Long straight approaches over mountain ridges often just won't work- the GPWS would not like it and cause go-arounds. Places that spring to mind are Mauritius 13 over the centre of the island and steep approach paths, and Seychelles where we used to get away with it on a visual approach, but you couldn't do an instrument approach on a straight in. Seychelles was very stimulating- you had to handfly in the dark a curved approach monitoring lighthouses- just like a yachtsman- until you could make out the runway nestled against enormous mountains. In daylight standing at the airport and looking up, you suddenly discovered what you'd been mussing with! Very sobering.
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