Simple question -- VNAV and RNAV

Stormflyer · August 21st, 2004, 18:16

I'm just a high school student and I've never taken any flying lessons before, so right now I'm just an enthusiast, so there are many simple things I don't know. I've bought a few books, and I've searched the Internet a little, but I still don't quite understand VNAV and RNAV and what they are supposed to be. [img]/ubbthreads/images/graemlins/banghead.gif[/img]

A300Capt · August 21st, 2004, 18:34

[ QUOTE ]
I still don't quite understand VNAV and RNAV and what they are supposed to be.

[/ QUOTE ]

VNAV refers to Vertical (up and down) navigation for meeting altitude and speed constraints whether your in the climb, cruise or descent phase.

RNAV refers to lateral navigation (left and right). Navigating from point A to B.

Using both gives a pilot 3 dimensional navigation capability.

Stormflyer · August 21st, 2004, 18:47

Thanks for the reply, but how are VNAV and RNAV actually used? For example, if I'm not mistaken, they are options on the autopilot, but don't you already have heading, altitude, and vertical speed options as well as autothrottles?

A300Capt · August 21st, 2004, 19:32

[ QUOTE ]
Thanks for the reply, but how are VNAV and RNAV actually used

[/ QUOTE ]

Modern aircraft with "glass" cockpits usually come equipped with one or more FMC's (Flight Management Computers). These computers have an internal database which consist of not only navigational charts but also an aircraft specific performance database.

Using inputs from GPS and/or IRS systems for positional updates, the FMC, using it's internal nav and performance databases, along with the aircraft's autopilot and autothrottle systems, can control all aspects of the flight. VNAV controls, or provides, vertical information in the climb, cruise and descent phases of flight along with any crossing and/or speed constraints within those 3 phases.

RNAV or LNAV (Lateral navigation), as we called it on the B757, uses the FMC's database and the autopilot/flt director to steer the aircraft on a prescribed course. All airways/navaids/fixes and approaches are within the FMC's database. Selecting "LNAV" tells the autopilot/flt director to follow the route selected in the database the pilot has chosen. This route is also depicted on the pretty little moving map in front of the pilot.

Selecting "VNAV" ties the FMC to control the autopilot/flt dir to give automatic "pitch" guidance during the climb, cruise and descent.

The "LNAV" and "VNAV" buttons tie the aircraft's autoflight system together. They're the only two buttons that need the FMC to guide them. Basically, the FMC's databases automatically controls the autopilot and autothrottles along the entire 3 dimensional flight.

Using vertical speed or heading select removes the FMC from directly controlling the aircraft's vertical and lateral direction. The pilot then becomes the "middleman" between the FMC and the aircraft's autoflight system. Using LNAV and VNAV lets the FMC to talk directly to the autoflight system.

THERE! Clear as mud, huh? [img]/ubbthreads/images/graemlins/cwm27.gif[/img] [img]/ubbthreads/images/graemlins/insane.gif[/img]

Stormflyer · August 21st, 2004, 20:02

Thanks so much A300Capt, that's exactly what I wanted to know!
[ QUOTE ]

Clear as mud, huh? [img]/ubbthreads/images/graemlins/cwm27.gif[/img] [img]/ubbthreads/images/graemlins/insane.gif[/img]

[/ QUOTE ]
Actually, that made quite a bit of sense. Thanks again! [img]/ubbthreads/images/graemlins/smile.gif[/img]

August 21st, 2004, 18:16	#1
Stormflyer Junior Member Join Date: Feb 2004 Location: Phoenix, AZ Posts: 86	Simple question -- VNAV and RNAV I'm just a high school student and I've never taken any flying lessons before, so right now I'm just an enthusiast, so there are many simple things I don't know. I've bought a few books, and I've searched the Internet a little, but I still don't quite understand VNAV and RNAV and what they are supposed to be. [img]/ubbthreads/images/graemlins/banghead.gif[/img]

August 21st, 2004, 18:34	#2
A300Capt Senior Member Join Date: Oct 2000 Location: Louisville, Kentucky Posts: 709	Re: Simple question -- VNAV and RNAV [ QUOTE ] I still don't quite understand VNAV and RNAV and what they are supposed to be. [/ QUOTE ] VNAV refers to Vertical (up and down) navigation for meeting altitude and speed constraints whether your in the climb, cruise or descent phase. RNAV refers to lateral navigation (left and right). Navigating from point A to B. Using both gives a pilot 3 dimensional navigation capability.

August 21st, 2004, 18:47	#3
Stormflyer Junior Member Join Date: Feb 2004 Location: Phoenix, AZ Posts: 86	Re: Simple question -- VNAV and RNAV Thanks for the reply, but how are VNAV and RNAV actually used? For example, if I'm not mistaken, they are options on the autopilot, but don't you already have heading, altitude, and vertical speed options as well as autothrottles?

August 21st, 2004, 19:32	#4
A300Capt Senior Member Join Date: Oct 2000 Location: Louisville, Kentucky Posts: 709	Re: Simple question -- VNAV and RNAV [ QUOTE ] Thanks for the reply, but how are VNAV and RNAV actually used [/ QUOTE ] Modern aircraft with "glass" cockpits usually come equipped with one or more FMC's (Flight Management Computers). These computers have an internal database which consist of not only navigational charts but also an aircraft specific performance database. Using inputs from GPS and/or IRS systems for positional updates, the FMC, using it's internal nav and performance databases, along with the aircraft's autopilot and autothrottle systems, can control all aspects of the flight. VNAV controls, or provides, vertical information in the climb, cruise and descent phases of flight along with any crossing and/or speed constraints within those 3 phases. RNAV or LNAV (Lateral navigation), as we called it on the B757, uses the FMC's database and the autopilot/flt director to steer the aircraft on a prescribed course. All airways/navaids/fixes and approaches are within the FMC's database. Selecting "LNAV" tells the autopilot/flt director to follow the route selected in the database the pilot has chosen. This route is also depicted on the pretty little moving map in front of the pilot. Selecting "VNAV" ties the FMC to control the autopilot/flt dir to give automatic "pitch" guidance during the climb, cruise and descent. The "LNAV" and "VNAV" buttons tie the aircraft's autoflight system together. They're the only two buttons that need the FMC to guide them. Basically, the FMC's databases automatically controls the autopilot and autothrottles along the entire 3 dimensional flight. Using vertical speed or heading select removes the FMC from directly controlling the aircraft's vertical and lateral direction. The pilot then becomes the "middleman" between the FMC and the aircraft's autoflight system. Using LNAV and VNAV lets the FMC to talk directly to the autoflight system. THERE! Clear as mud, huh? [img]/ubbthreads/images/graemlins/cwm27.gif[/img] [img]/ubbthreads/images/graemlins/insane.gif[/img]

August 21st, 2004, 20:02	#5
Stormflyer Junior Member Join Date: Feb 2004 Location: Phoenix, AZ Posts: 86	Re: Simple question -- VNAV and RNAV Thanks so much A300Capt, that's exactly what I wanted to know! [ QUOTE ] Clear as mud, huh? [img]/ubbthreads/images/graemlins/cwm27.gif[/img] [img]/ubbthreads/images/graemlins/insane.gif[/img] [/ QUOTE ] Actually, that made quite a bit of sense. Thanks again! [img]/ubbthreads/images/graemlins/smile.gif[/img]

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