Topic Author
Posts: 190
Joined: Mon Jun 25, 2001 8:56 pm

Lnav And Vnav?

Fri Sep 14, 2001 2:30 am

Still in deep shock, but i have a question "How do the LNAV and VNAV operate with the Autopilot and when are they operated?after purchasing PSS747-400
Any views much appreciated!
P.S RIP to all affected by the attack
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

RE: Lnav And Vnav?

Fri Sep 14, 2001 12:04 pm

Hi Springbok,
LNAV (lateral natigation) and VNAV (vertical navigation) operate using data from the flight management computer.
On a normal B747-400 operation with a SID programmed for departure LNAV and VNAV can be armed for departure.
At 50' TOGA will change to LNAV in the roll mode and the flight director will follow instructions from the FMC to fly the SID. When the autopilot is engaged it will follow these commands. LNAV can remained engaged, follow a programmed STAR right to the destination. Normally it is only disconnected for radar vectors (HDG SEL), weather diversions (HDG SEL) or Localiser intercept (LOC).
At 400' TOGA will change to VNAV in the pitch mode and the flight director will follow instructions from the FMC VNAV page. The first speed commanded is V2+10kts to +25kts depending on current speed. VNAV will then command acceleration for flap retraction at the appropriate altitude and programmed climb speed (VNAV SPD). VNAV will not climb through or leave an MCP entered altitude (VNAV ALT). If cruise altitude on the MCP matches the altitude on the VNAV CRZ page in the FMC you will hav VNAV PTH (path) displayed on the PFD. Approaching TOD calculated by the FMC you will get the message 'Reset MCP altitude'. If the MCP altitude is below the cruise altitude the thrust will reduce to idle and descent will commence in VNAV PTH. VNAV will maintain the path up to 15kts away from the programmed speed. Outside of this VNAV SPD will be displayed and the descent profile will be left. This will normally require speedbrake to resume path with the message 'Drag Required'. VNAV will follow the speed transitions entered in the VNAV DESCENT page, such as 240kts below 10000'. It will also attempt to comply with STAR altitude restrictions. If an intermediate altitude is captured on climb or descent VNAV ALT will be displayed. Once the MCP altitude is reset the selector button must be pushed to resume the climb or descent. VNAV can remain engaged until glideslope (GS/APP) intercept.
I don't want to make this too complicated, I hope this info helps!  Smile/happy/getting dizzy
Posts: 723
Joined: Thu May 17, 2001 12:02 pm

RE: Lnav And Vnav?

Sat Sep 15, 2001 8:12 am

Basically, the flight planner on MSFS is like programming the FMC, and using the NAV button is like hitting the LNAV. (With a few differences) On real aircraft, the closest thing to the NAV button is the VOR/LOC button which will fly to the airport LOC, or a VOR. Either way, the VOR or LOC frequency must be inputed in the radios.
Posts: 11
Joined: Thu Sep 13, 2001 4:13 pm

RE: Lnav And Vnav?

Sat Sep 15, 2001 5:19 pm

AJ-thanks for the superb explanation. Very informative-not boring at all! Smile
Posts: 11
Joined: Thu Sep 13, 2001 4:13 pm

RE:Rare To Find Aircraft Cut-away Drawings.

Sat Sep 15, 2001 5:33 pm

I already have around 300 cut-away drawings.Would like to have for the following types;
Antonov An-22
Tupolev Tu-16
Anyone with a similar interest,please respond. Smile
Topic Author
Posts: 190
Joined: Mon Jun 25, 2001 8:56 pm

RE: RE:Rare To Find Aircraft Cut-away Drawings.

Sun Sep 16, 2001 9:22 pm


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