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Driver170

Takeoff Acceleration Altitude, Thrust Reduction Altitude. Takeoff page.

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Does the 737 NGX reference the altitude for the above AAL or is RA? I know in the real NG The FMC actually uses AAL (barometric height above aerodrome), not RA. As RA is not suited for that purpose as it shows height above the ground the aircraft is currently over, which can vary a lot from the altitude the runway is at, think of a valley or hill right behind the runway or something!

 

The reason i ask is, looking at the RA after takeoff everything switches over exactly on the RA..

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The reason i ask is, looking at the RA after takeoff everything switches over exactly on the RA..

 

It's most possibly because the ground below you is at the same elevation as the departure airport.

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Yeh pretty much straight and level. So the NGX does use AAL then?

Just did a takeoff from Madeira, my conclusion is yes. The airport elevation is 200ft and thrust reduction height was set to 1500ft AGL. The plane flew over the sea and reduced to CLB power at 1700ft (while RA indicates 1700).

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David if you have Madeira addon i will send you all my notes about how to fly the VOR 05 approach that i got from a pilot.

 

Thankyou for testing this :)

Email...

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I'm going to assume the 73 is the same as the 74 as far as system logic in VNAV.  During your take-off acceleration at 100KIAS the computer does a "barometric snapshot" of the current conditions for VNAV purposes.  These would include switching to LNAV @ 50' VNAV at 400' both two and single engine acceleration and depending if you choose a flap setting or an altitude thrust reduction.  It does not use radar altimeter but the altitude sensed at the 100KIAS.  That about as clear as mud? I just woke up so I hope I make sense.

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David if you have Madeira addon i will send you all my notes about how to fly the VOR 05 approach that i got from a pilot.

 

Thankyou for testing this :)

Email...

That's very nice of you! So far I only flew the visual app to rwy 05 once and I it wasn't a beautiful one. Please check PM.

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This reminds me of the lengthy thread on using RA for takeoffs not too long ago. Nothing has changed.

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