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Chris Catalano

737 - GPS approach question

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In the 737 NG, during an RNAV (GPS) approach, is there a way to program the GPS unit to automatically lock onto to the "artificial" glideslope and track it by pressing "Approach" on the MCP? (In other words, make it behave exactly like an ILS approach when "Approach" is pushed on the MCP.)ThanksChris Catalano

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Guest tmetzinger

>In the 737 NG, during an RNAV (GPS) approach, is there a way>to program the GPS unit to automatically lock onto to the>"artificial" glideslope and track it by pressing "Approach" on>the MCP? (In other words, make it behave exactly like an ILS>approach when "Approach" is pushed on the MCP.)>>Thanks>Chris CatalanoShort answer: No.Longer answer:RNAV approaches are flown in LNAV, and you can manage the pitch in several ways:VS/SPD, where you can set a constant rate of descent appropriate for your groundspeed.LVL CHG to get you down to the MDAVNAV. This is as close as you'll get to the ILS or the LPV-like experience. What you need to do is set up the appropriate altitude and speed constraints on the legs page, and then let the airplane fly in VNAV. Generally it will work well, but you've GOT to stay on top of it, and watch the DES page and the VNAV vertical deviation indicator on the ND. There are a few glitches with the PMDG implementation and when you pass a waypoint in VNAV sometimes the airplane won't resume the proper descent path - the cure is to watch it and be ready to disengage and re-engage VNAV the minute the deviation occurs. A key indicator for a well-programmed approach, the LEGS page will always show the glide path angle between the last waypoint and the runway. You want that to be in the 3 degree range if you want it to "feel" like a normal ILS, and you may want to play with the altitude constraints a little to make it work.The other tip is to get slow as early as possible. When you hit 1000 feet AGL you want to be completely squared away - landing flaps and gear down, speed at Vref+5 (or whatever correction factor), and you need to be poised to either land visually or to initiate a missed approach. Too many times folks come scorching onto the final approach course at 200+ knots. 180 is a better intermediate segment speed.Best Wishes,

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Tim,I have a question on the speed. I have used 190 as my LOC capture speed for most of the approaches I have ever flown. Is this a good speed. I see alot of times the FMC indicating 170 and flaps 10 or more (aircraft other than 737)at these speeds should I just have the appropriate flaps for the slower speeds and the gear down or keep using my 190 and what ever appropriate flap setting?Thanks


Andrew

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Guest tmetzinger

For the 737s, the operators who's specs I've seen call for 180 and flaps 5 when intercepting the localizer (and this normally assumes you're getting vectors to the final approach fix). Then at the FAF you drop gear, flaps, and slow to your final approach speed.When flying in real life or with online ATC, you may get requests to keep speed up to the final approach fix. In that case, be ready to add drag with spoilers when you reduce speed at the fix.

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Guest Lenny Zaman

As tim said, noIt is at the moment not 'allowed' to use GPS alitude data operationally. Only as information it can be used because at the moment the error is too big. At least that's what they told me. Then again, my theory exams (ATP) were some time ago so... maybe i'm allready getting rusty :s :)(passed though ;))

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Guest tmetzinger

>As tim said, no>It is at the moment not 'allowed' to use GPS alitude data>operationally. Only as information it can be used because at>the moment the error is too big. At least that's what they>told me. Then again, my theory exams (ATP) were some time ago>so... maybe i'm allready getting rusty :s :)(passed though>;))The updates needed for LPV (Localizer Precision with Vertical guidance) are in the works. I'm not sure whether the approaches will be flown in APPR (since it's as smooth as an ILS) or in LNAV/VNAV (which would be consistent with other RNAV approaches). My money is on LNAV/VNAV, as it's easy to feed the vertical steering to the autopilot that way.I've got about 12 LPV approaches in a Mooney equipped with the Garmin 480 system coupled to an STEC autopilot. It's every bit as good as an ILS, and in someways better since there's no "hunting" for the localizer.Best wishes.

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