Using LNAV/VNAV to carry out an approach

[markadeane 272]

I've seen some writings from one of our fellow drivers that touched on the use of LNAV/VNAV to carry out an approach independent of any ground based navaids.Does such a procedure exist in the 744 in real life? If not is it feasible? What steps would we need to carry out such an approach? Presumably program in the approach waypoints and heights required off the approach plate and treat it as a non-precision approach with a DH of 200 feet.I am trying to recall from the manual: can you enter custom waypoints into the FMC that are 'x' Miles from the threshold? Assuming so, what about speed control? Using Speed Intervention changes the mode to VNAV SPD so it wouldn't follow the computed path would it? Are manually entered speed contraints on the custom waypoints possible?If anyone has carried one of these out to their own satisfaction of accuracy standards, please share with us!

[Guest D17S]

Sure . . . but not ccertified, yet. Good question though. How low can you go with Vnav? But we can go as low as we want. Just set up a normal flight plan with it terminating in an approach to a runway from the FMCs DEP/ARR/ arr page. Most of the Approaches I've seen have 3 or 4 waypoints at short intervals. This makes a nice tight set of vertical destinations for Vnav to aim at during that last final approach leg. Heck, just use those. 200 foot DH, Chicken! I was ready to let it land. It really worked that well. Make sure the legs page shows a full route with your runway's waypoint correctly set to field's elevation. Go fly. Fly the route in LNAV/VNAV and just leave it alone. Might want to set a 180 k speed restriction at a ways back. Start getting the flaps down. At 25 miles from the runway, you will still be L/Vnaving along. Double check that your altimeter is set to field baro. This is critical. Tap MCP's airspeed window knob and you will open the window. Note that if you are within 25 miles of your runway, pitch will stay in VNAV PATH and thrust will stay in SPD. You can now start dialing down airspeed. Thrust will keep you on-speed and Path will keep you on-path. Get into landing configuration and then to Vref soon as you can. Path is a bit wobbly. You want to give the AFS as much time as possible to get stable. Then just sit back and watch.The ILS will have autotuned and will be displaying LOC and GS info in the PFD. Do not press APP! Watch the ND's path scale against GS. Make sure they are tracking the same. Watch LOC against versus the roll command bar. The roll bar is still displaying Lnav commands.At RA of 50 feet, look out the window. You are over the runway threshold (well, that's our 'make-a wish'). Disco the AP, flare and rollout normally. A GPS CAT 3a approach. Now you say, you don't even want to rely on satellites? As you roll out onto final, go into the PROG > Posit Ref and inhibit GPS updating. Now you are entirely self-contained. Haven't tried this one, but it should work just as well as a GPS updated approach . . . that is if your IRUs are sober that day.Got an MD11 sim ride over at Alteon in Long Beach tomorrow. I'll try it in the real sim. Let cha know.

[Guest petermcleland]

>>If anyone has carried one of these out to their own>satisfaction of accuracy standards, please share with us!Just doing the "Smitty" Tutorial flies a full LNAV and VNAV automated approach to touchdown.

[zubart 5]

Here are the steps to do an instrument approach using VNAV in a 737NG. This is one way of probably many and probably not much different in a 744. Recommended roll modes for final approach:RNAV, GPS or TACAN approach : LNAVLOC-BC, VOR or NDB approach: LNAV or HDG SELLOC, SDF, or LDA approach: VOR/LOC or LNAVFor LOC, LOC-BC, SDF or LDA approaches, ensure appropriate navaids are tuned and identified prior to commencing the approach and monitor raw data throughout the approach. For VOR and NDB approaches, raw data should be monitored, if available.FMC approach procedure................SelectSelect the approach procedure on the ARRIVALS page. DO NOT MANUALLY BUILD THE APPROACH OR ADD WAYPOINTS TO THE SELECTED FMC PROCEDURE. Add cold temperature corrections to waypoint altitude constraints as appropriate.Verify VANV glide path angle is displayed on the final approach segment on the LEG's page.RNP appropriate for approach (if required)...Verify/Enter, this allows appropriate alerting to occur if ANP exceeds RNP.Approximately 2 NM prior to the FAF and after ALT HLD or VNAV PTH engaged:MCP Altitude......................Set MDA(H)/DA(H), This allows VNAV to command descent in VNAV PTH. If the MDA(H)/DA(H) does not end in zero zero, for example, 1320, set MCP ALTITUDE window to the closest 100 foot increment above the constraint. There may be a level segment beyond the FAF before intercepting the descent path.Prior to reaching FAF:AFDS roll mode ...............Verify/Select, verify appropriate roll mode annunciates.VNAV switch (if required) ....................Push, select VNAV if in ALT HLD. Verify VNAV PTH annunciates.Autopilot......................Verify engaged, the autopilot should remain engaged until suitable visual reference is established.Prior to reaching MDA(H)/DA(H) and when the airplane is at least 300 feet below the missed approach altitude:MCP altitude....................Set missed approach altitude.At MDA(H)/DA(H)/Missed approach point:If suitable visual reference is not established, execute a missed approach.After suitable visual reference is established:A/P disengage switch.......................Push, disengage the autopilot before descending below MDA(H)/DA(H).A/T disengage switch...............Push, disengage the autothrottle before descending below MDA(H)/DA(H).Floyd

[Jeff Nielsen 1,385]

Floyd,Thanks for the info. For a GPS appr...A couple of questions...What about the speed intervention during the approach? Is that pressing the middle of the speed dial then selecting the speeds needing during the approach?Also, I'm assuming you're meaning the published DH for the MCP alt window or the last published approved VNAV alt? I'm assuming you're meaning the DH's here so you can actually fly the GPS approach as if it were an ILS?Thanks.

[zubart 5]

I think they want to sign your name according to the forum rule....With VNAV engaged, the MCP window will of course be blank and the AFDS will fly the FMC speeds on the LEGs page. Yes, selecting speed intervention like you said might be necessary in situations where FMC speed is not appropriate. This will probably be interference by ATC when they want faster or slower speeds before the FAF.LNAV/VNAV uses a DA(H)on an approach plate. Usually to use a DA(H), your airline must be an approved carrier. The approach plate will usually make a note about this. DA(H) is a minimum that the airplane that may actually descend through (like an ILS) during a missed approach whereas the airplane can never descend below a MDA(H)minimum during the miss approach. You'll only see DA(H) on a LNAV/VNAV approach. A LNAV approach uses only a MDA(H). One technique to treat a MDA(H) like a DA(H) is to add 50 feet to the MDA, for example, if MDA is 420 feet then add 50 feet to make the MDA 470 feet. As the airplane descends through 470 feet, the missed approach is started so the airplane will descend no lower than the 420 feet published minimums.Floyd

[Jeff Nielsen 1,385]

Floyd,Not sure if you're talking about me, but you can clearly see my name in my post in the sig block.Again, thanks for the info.

[zubart 5]

I meant to take it off and forgot, apologies.Floyd

[markadeane 272]

EDIT: The links for the approach lists haven't worked and I can't fix them, make sure you include the bracketed date and the .xls bit in the URL, or alternatively access these links via the main one: http://gps.faa.gov/index.htm For those who wish to try their hand at some approaches!GPS approach list:http://gps.faa.gov/Library/Data/GPS_(12.22.05).xlsLNAV only approaches:http://gps.faa.gov/Library/Data/LNAV_(12.22.05).xlsLNAV/VNAV approaches:http://gps.faa.gov/Library/Data/LNAV.VNAV_(12.22.05).xlsLots of interesting info at this site:http://gps.faa.gov/index.htmI might try and write a few approaches for the sake of a demonstration. Any approaches specifically requested? I'd prefer major airports serviced by one of the FTG virtual airlines so I can incorporate it into one of my sectors.

[markadeane 272]

I've picked an approach to try out!I'm flying a Cathay service from Hong Kong to San Fransisco overnight on Saturday evening (NZDT).Having written the procedure of required, I'll make an LNAV/VNAV approach to 10R with a missed approach in the mix for the sake of some fun (I don't often do these unless asked to by ATC!)10R is my particular choice because it has no ILS to follow and there is high terrain to clear on relatively short final. I'll do it VMC and do some screen captures to demonstrate how it went.The approach plate is available here for those that want to try it:http://204.108.4.16/d-tpp/0513/00375RY10R.PDF

[Guest D17S]

How about one to the old VHHX Hong Kong airport. I wonder if a full L/Vnav approach would be enough to get ya around the corner at the checkerboard? Sounds like fun. I sure am having a heck of a time doing it by hand. Need a little modern automation.

[markadeane 272]

That's abut the best idea I've heard all day!