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Guest jaseman

At what point do I engage VNAV & LNAV

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Guest jaseman

Hi everyone, this may have been asked in previous posts but I would like to know when you are to activate VNAV and LNAV after departure. Could someone please help with this?Jason

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Well the simple way is to clean up first, retract flaps speed up and engage the A/P...You can ARM the modes prior to A/P engagement too. LNAV on the grnd if within limits and VNAV I believe at 400' AFE.. [h4]Randy J. Smith[/h4]


Randy J Smith

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Guest

I like to climb in VS mode and use heading select when the atc gives me vectors to climb. Once they say "proceed on course" I engage LNAV but keep it in VS until I reach my climb. VNAV climbs too fast and doesn't give me any options if I want to climb slower at higher alittudes, etc.

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Guest neeraj.pendse

I think VNAV does a great job of climbing, personally. What I do typically is take off, and engage AP in VNAV and HDG after gear is pulled up. VNAV keeps the plane pitched up at 18 deg or so at V2+20 for a while which is the right way to do it. The speeds are managed by the FMC here and you do not need to reset speeds as you retract flaps.On descents though, if you want to follow ATC instruction, then you can not use VNAV PATH, which sucks. So you have to use VNAV Speed, which is great because it will hold a speed at IDLE throttles, and is immunte to the acceleration effects as it will constantly adjust VS.I have heard people using FL CHG for descents, but I think it is really inteneded for 3-4 thousand foot climbs and descents in the flight levels (hence the name FL CHG) ... and might descend you at 5000 foot per minute some times. So I end up using Vertical Speed mode for descents. Sometimes VNAV SPD.$0.02- Neeraj

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VNAV climbs too fast and doesn't give me any options if I want to climb slower at higher alittudes, etc.Alex, The airplane will climb slower as it climbs to higher altitudes because of the thinner air, even when using VNAV. When I first engage VNAV, I'm usually climbing at about 3000fpm. When I get to about 30,000ft, I'm climbing at about 1200-1500fpm. Ken.

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Guest McGraw

I am at the early stages of learning to use the NG and last night VNAV kept having to dip it's nose to regain speed to climb.I was on 96% manual throttle. Is that why?

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Guest hlm65

Hi,best use with VNAV is with autothrottle.And VNAV/LNAV engagement is dependent on many factors, including SID, ATC requirement, weather, noise abatement procedure etc etc.I usually use an ICAO B standard departure sequence, that calls for VNAV engaged when cleaned up. This can occur usually about above 1500 ft AGL. LNAV is engaged when you're in a suitable heading to the first relevant point of your SID or flight plan. Usually I engage autopilot in HDG SEL (rwy heading or first assigned heading) climbing thru 1000-1500 ft AGL. Could be that for wx or ATC you need to keep the HDG SEL mode till further down on your route.

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Guest tmetzinger

Operators vary the use of the autopilot and the modes used, so there's no one "right" way to do it.After takeoff, a typical flight profile is flown in four phases:Initial climb, flown at V2 to V2+20 to about 400 feet AGL. This phase is to get you away from the ground quickly, for safety and noise abatement reasons.Acceleration is usually from 400 feet AGL to 1000 feet AGL, and this is where the airplane is cleaned up (flaps retracted) and accelerated to the speed limit for the airspace.Intermediate climb runs from 1000 AGL to wherever the speed restrictions disappear (10000 in the USA), and is flown at climb thrust and at the speed limit.Cruise climb then starts and the airplane generally accelerates to 300 knots or so, climbs at that speed and eventually ends up at cruise altitude and cruise mach (and there's a speed switchover from KIAS to Mach in the mid 20's).In GENERAL, the initial climb is flown manually, but the flight director may be set to LNAV or VNAV. Autothrottles are used if installed (TOGA mode which changes to N1)Some operators engage the autopilot for the acceleration, others don'tAutothrottles usually stay in N1 but sometimes a speed mode.Most operators engage the autopilot for the intermediate and cruise climb.www.smartcockpit.com has good briefings on the subject.Best wishes,

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Guest

I'm wondering what the general rule is for climbing. How fast of an ascent is too fast and visa versa? I usually climb around 2000 fpm + after takeoff and scale that back to 1500 or so until around 20 thousand feet or so then it goes back to 1000. Should I be using a higher/lower rate? Thanks for any help Tim or anyone with the knowledge of real world ops

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I am at the early stages of learning to use the NG and last night VNAV kept having to dip it's nose to regain speed to climb.I was on 96% manual throttle. Is that why? Hi McGraw,The nose pitches down to maintain the 315 knot target speed set by the FMC. The reason for the nose to pitch down is because as the plane climbs to a higher altitude, the air is thinner and you'll notice that the rate-of-climb is less. You should use the auto-throttles so that the correct power is used calculated by the FMC. The auto-throttles are usually enganged after taxing onto the runway. The pilot manually advances the throttles to 40% N1 and when everything stablilizes, the TO/GA is engaged. The auto-throttle then advances to the N1 calculated by the FMC. Ken.

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Guest skefford

>I am at the early stages of learning to use the NG and last>night VNAV kept having to dip it's nose to regain speed to>climb.>>I was on 96% manual throttle. Is that why?>...Why are you on manual? As a previous poster said, LNAV works best with AT.Steve

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Guest McGraw

I was having problems with the Autothrottle but I've sorted them now.Cheers.

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hi i just took off now in the 737/800 and i had an awefully slow climb to FL350 it was like 400fpm with Lnav and Vnav engaged, anyone know why this could be the issue?it doesnt happen often just sometimes,rgds

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Guest benhoffman

Fellow Captains;Most operators do not allow the use of vertical speed mode in the climb or cruise due to the safety issue; i.e. climbs as a function of set rate rather than speed so I can set +7000fpm and the airplane will do its darndest to adhere to +7000fpm and it's liable to fall out the sky.I personally use the FPV, FD, trim and yoke to fly up to cruise manually -yes that's right, I don't engage Otto until I am at cruise; it is more fun! :)I DO however, arm LNAV/VNAV on the ground.

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The 'trouble' with the PMDG744 is that a lot of us are used to using the old default MS autopilot where we had to set VS in the climb and manually change things from there. In the PMDG744 there is NO need to climb according to a specific rate of climb. In fact to do so is largely unrealistic and potentially very dangerous. Leave that technique in the default 'Microboeing 737' where it belongs, gentlemen! :-)VS mode is really ideal for descents as you can adjust the rate of descent to cross a given point at a given altitude (using the green altitude arc on the ND). HOWEVER, using VS in the climb poses certain risks. You can ask the autopilot to climb at an impossible angle and it will do its best until the aircraft gets dangerously slow. As stated elsewhere, the 747 is not an aircraft you want to be slow in!Some flight crews will use VS for the climb to comply with ATC requests or other factors, but only in the context of thousands of hours of experience in the aircraft and a good knowledge of the its limitations.For us regular Joes, EITHER engage VNAV and let it handle the climb OR engage FL CHG and set the appropriate speed for the phase of the climb. The autopilot then sets a nose angle and hold sthe speed, at least that way you don't run the risk of stalling.Note that you can engage VNAV or FL CHG and still fly the aircraft using the flight directors.


Mark Adeane - NZWN
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