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LNAV engagement on the ground

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I'm flying with the 738 and trying to make a rolling takeoff from KSEA with full FMC programmed, F/D and A/T engaged and TO/GA mode. I set LNAV on the ground since this is a very common procedure. Everything works fine but the LNAV switch light should extinguish once TO/GA engaged until 400 feet AGL, as per the below Boeing 737 AOM (official document). Can anybody tell if below LNAV behavior is strictly modeled in PMDG aircraft or such details have been omitted?"LNAV engagement criteria on the ground:• origin runway in flight plan• active route entered in FMC• track of first leg within 5 degrees of runway heading• LNAV selected prior to TO/GA. Once TO/GA is engaged, the LNAVswitch light is extinguished until 400 feet AGL• LNAV guidance becomes active at 50 feet AGL"

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I'm flying with the 738 and trying to make a rolling takeoff from KSEA with full FMC programmed, F/D and A/T engaged and TO/GA mode. I set LNAV on the ground since this is a very common procedure. Everything works fine but the LNAV switch light should extinguish once TO/GA engaged until 400 feet AGL, as per the below Boeing 737 AOM (official document). Can anybody tell if below LNAV behavior is strictly modeled in PMDG aircraft or such details have been omitted?"LNAV engagement criteria on the ground:• origin runway in flight plan• active route entered in FMC• track of first leg within 5 degrees of runway heading• LNAV selected prior to TO/GA. Once TO/GA is engaged, the LNAVswitch light is extinguished until 400 feet AGL• LNAV guidance becomes active at 50 feet AGL"
Good question. I know ever the Level 3 sims have some discrepancies in this regard.

Matt Cee

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All all of the following is operational and can be found in the NG Manuals which can be downloaded from the PMDG website. :( http://www.precisionmanuals.com/pages/downloads/docs.htmlTo answer your question, the following is modeled:07 Systems Operations, Section 7-72:LNAV provides steering commands to the next waypoint. If selected, LNAV engages when laterally within 3 nautical miles of the active route leg. If outside of 3 nautical miles of the active route leg, LNAV engages if on an intercept heading of 90 degrees or less and the intercept will occur before the active waypoint. FMC LNAV guidance normally provides great circle courses between waypoints. However, when an arrival or approach from the FMC database is entered into the active route, the FMC can supply commands to fly a constant heading, track, or follow an arc, as required by the procedure.From Section 7-21:LNAV engagement criteria on the ground:

  • origin runway in flight plan
  • active route entered in FMC
  • track of first leg within 5 degrees of runway heading
  • LNAV selected prior to TO/GA

From the 09 AFDS System Manual, section 9-6:LNAV: Commands bank to follow active FMC route as displayed on the navigation display. If on ground, LNAV mode will arm to engage when passing through 50 feet AGL.Section 9-13LNAV will engage as long as the aircraft is above 50 AGL and within 2.5 miles of the planned track. If the aircraft is outside of these parameters, LNAV mode will arm and engage when the aircraft moves within these parameters (e.g.- after takeoff).LNAV mode will be displayed in green on the PFD if LNAV mode is engaged. If LNAV arms, but the aircraft is not on an intercept heading to planned track, the FMC scratch pad will show the text NOT ON INTERCEPT HEADING, and the previously armed roll mode will remain active.Additional information from the 07 Systems Operations manual, section 7-21:LNAV engagement criteria in flight:

  • active route entered in FMC
  • within 3NM of active route, LNAV engagement occurs with any airplane heading
  • outside of 3NM, airplane must:
  • be on intercept course of 90 degrees or less
  • intercept route segment before active waypoint

LNAV automatically disconnects for following reasons:

  • reaching end of active route
  • reaching a route discontinuity
  • intercepting a selected approach course in VOR LOC or APP modes (VOR/LOC armed)
  • selecting HDG SEL

George Morris

 

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All all of the following is operational and can be found in the NG Manuals which can be downloaded from the PMDG website. :( http://www.precision...loads/docs.htmlTo answer your question, the following is modeled:07 Systems Operations, Section 7-72:LNAV provides steering commands to the next waypoint. If selected, LNAV engages when laterally within 3 nautical miles of the active route leg. If outside of 3 nautical miles of the active route leg, LNAV engages if on an intercept heading of 90 degrees or less and the intercept will occur before the active waypoint. FMC LNAV guidance normally provides great circle courses between waypoints. However, when an arrival or approach from the FMC database is entered into the active route, the FMC can supply commands to fly a constant heading, track, or follow an arc, as required by the procedure.From Section 7-21:LNAV engagement criteria on the ground:
  • origin runway in flight plan
  • active route entered in FMC
  • track of first leg within 5 degrees of runway heading
  • LNAV selected prior to TO/GA

From the 09 AFDS System Manual, section 9-6:LNAV: Commands bank to follow active FMC route as displayed on the navigation display. If on ground, LNAV mode will arm to engage when passing through 50 feet AGL.Section 9-13LNAV will engage as long as the aircraft is above 50 AGL and within 2.5 miles of the planned track. If the aircraft is outside of these parameters, LNAV mode will arm and engage when the aircraft moves within these parameters (e.g.- after takeoff).LNAV mode will be displayed in green on the PFD if LNAV mode is engaged. If LNAV arms, but the aircraft is not on an intercept heading to planned track, the FMC scratch pad will show the text NOT ON INTERCEPT HEADING, and the previously armed roll mode will remain active.Additional information from the 07 Systems Operations manual, section 7-21:LNAV engagement criteria in flight:

  • active route entered in FMC
  • within 3NM of active route, LNAV engagement occurs with any airplane heading
  • outside of 3NM, airplane must:
  • be on intercept course of 90 degrees or less
  • intercept route segment before active waypoint

LNAV automatically disconnects for following reasons:

  • reaching end of active route
  • reaching a route discontinuity
  • intercepting a selected approach course in VOR LOC or APP modes (VOR/LOC armed)
  • selecting HDG SEL
Very good and appreciated. This is a confirmation that PMDG is pretty much good with 737 NG operations and actual system simulation. Still I can observe the LNAV switch light is not extinguishing when TO/GA is engaged. Can you please tell if this is due to some fault in my FMC setup or is it just an omitted 'detail' of the beautifully simulated AFDS? If so it's not a big issue, the whole aircraft is definitely a top-class simulation but, please, remind to add this little touch of additional realism in the next product release/service-update, if any.

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Guest CutiePie

Im sorry, but the PMDG AFDS is extremely far from realism, if we compare it with the latest FMC updates Boeing releasedYou cannot arm VNAV from ground...indeed LNAV doesnt extinguish..and it doesnt arm like in real life, it becomes active on groundRay Fahitas

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Im sorry, but the PMDG AFDS is extremely far from realism, if we compare it with the latest FMC updates Boeing releasedYou cannot arm VNAV from ground...indeed LNAV doesnt extinguish..and it doesnt arm like in real life, it becomes active on groundRay Fahitas
Why do you think it engages on the ground?

George Morris

 

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Guest CutiePie
Why do you think it engages on the ground?
Because the button remains lit, the F/D bars appear, also the LNAV indication appears green on the FMA, rather than white as in armed

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Because the button remains lit, the F/D bars appear, also the LNAV indication appears green on the FMA, rather than white as in armed
Are you running the latest version of the 800/900? Its been awhile since I flew the NG, but I thought after the last update everything was working properly. I will try to check out tonight.

George Morris

 

Boeing777_Banner_BetaTeam.jpg

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You cannot arm VNAV from ground...
While you can arm VNAV on the ground with the Honeywell MCP, Boeing released an op bulletin instructing crews not to arm VNAV on the ground, so whether or not it works in the PMDG is not an issue.

Joe Sherrill

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While you can arm VNAV on the ground with the Honeywell MCP, Boeing released an op bulletin instructing crews not to arm VNAV on the ground, so whether or not it works in the PMDG is not an issue.
I guess you're referring to the latest FMC U10.8 release from Boeing which indeed allows VNAV armed on ground but its installation has been stopped due to various "anomalies". Well, I'm not expecting PMDG programmers to release FMC service updates for each Boeing release, although it would be great and very professional. Let's stick to an older FMC version but in that respect it would be nice to have a fully realistic behavior.So, let's go back to my original question about LNAV. Can anybody please tell me whether or not it's correctly simulated when engaged on the ground? Here we're not talking about MSFS limitations which could prevent a realistic simulation, that's a pure piece of FMC software...quite challenging but still possible.

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Out of curiousity, what would these be?sig.gif
http://www.b737.org.uk/fmc_u108.htmVersion 10.8A will fix the following:
  1. VNAV commanding the airplane to descend below the expected path on approach, Ref Flight Crew Operations Manual Bulletin, TBC-79.
  2. Give proper descent path predictions/guidance for VNAV operation into airports above 10,000 feet.
  3. Allow full CLB thrust after a derate takeoff thrust has been uploaded via ACARS when the PERF Option code Zero is enabled.
  4. The FMC ACARS data buffer from filling up with a subsequent FMC restart.
  5. Position Hold Symbol displayed on the right display and expanded hold is displayed on the left display.
  6. FMC Disagree for certain vector/waypoint combinations (Dual FMC only).
  7. New advisory level message "FMC DISAGREE - VERTICAL" during VNAV Path Descents (Dual FMC only).
  8. A fix to correct a condition where an up linked Flight ID is not stored properly in the right FMC (Dual FMC only).
  9. Various in-service flight plan related software exceptions.

U10.8A is out in RW, just waiting for the POM Bulletin from the company to start using some of the new toys. I think they include VNAV on the ground and engine out SIDs. That will be huge.


Matt Cee

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I did KSAN LNSAY2 SLI J134 LAX J5 TILTS CANN2.FMG KRNO this morning.I did a few screenshots of my LNSAY2 departure, RWY 9, with LNAV armed before TOGA.Then the climb to 4000 before the left turn to 275 to pick up the MZB R-314.1-GroundArm.jpg2-N1.jpg3-1300feet.jpg4-CMDA.jpg5-left-turn.jpg


Best Regards,

Vaughan Martell - PP-ASEL KDTW

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I did KSAN LNSAY2 SLI J134 LAX J5 TILTS CANN2.FMG KRNO this morning.I did a few screenshots of my LNSAY2 departure, RWY 9, with LNAV armed before TOGA.Then the climb to 4000 before the left turn to 275 to pick up the MZB R-314.
Hello Vaughan, just a quick note. LNAV does not 'ARM' it 'ENGAGES' as it should. Its important to note the differences ;)>. As for the MCP switch light - its correct that the light should go out in TOGA as suggested. On another note, the behavior minus the light switch is spot on and should not really distract from a sim made years ago for it's price tag! On another note - I'm certain Rob will make sure (if not already) that the new baby is unlit on cue ;p

Randy J Smith

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Im sorry, but the PMDG AFDS is extremely far from realism, if we compare it with the latest FMC updates Boeing releasedYou cannot arm VNAV from ground...indeed LNAV doesnt extinguish..and it doesnt arm like in real life, it becomes active on groundRay Fahitas
Hey Ray, can you provide any proof that LNAV ever shows ARM anywhere anytime on the FMA? LNAV is either engaged or its not period. It certainly does "engage" on the ground just like "real life".

Randy J Smith

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