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Guest BAW1085

The TOD VNAV dive

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Guest BAW1085

This is about the only niggle I have with the 744 and it applies to both versions.I always see a mad dive to recover the first 500-1000 ft deviation.(Usually in the region of 3000-3500fpm) Thereafter once the deviation has reduced below 200ft the descent rate slows to a more acceptable 2000-2300fpm I religously set the winds aloft in the forcast page and this happens regardless of whether I have any gates progrommed or not.I seem to remember somewhere an SOP saying 1000fpm above FL300 thereafter as required. Is this anything anyone recognises? it would imply that setting a Manual ROD is the way to go ?David MilesAirbus

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I don't recall any such thing in terms of VNAV's function. The only 1000 FPM I know of is when entering an early descent until the original path is intercepted. Even if an SOP would actually reqiure that (Highly unlikely) this does not mean that the AFDS follows SOPs. SOPs differ in regards to procedures for a particular airline but not always in terms of aircraft capabilities or mechanical functions. Also, I would not call 3000-3500 FPM a "mad dive". In VNAV one expects a dive or sorts to capture the path without concenn for PAX. This is one reason why under 10'000 one should use other modes for small altitude changes..Best,Randy J. Smith<<>>


Randy J Smith

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Additionally, 3000fpm at FL330 & above is pretty normal because it takes that kind of descent rate to maintain target mach due to thin air. The required descent rates drop rapidly below 14000 such that at 10000 you might see 1300-1800 fpm maintaining 240 kts. Half the weight of the air column is below 14000 ft, it get's pretty thin way up there.


Dan Downs KCRP

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Guest BAW1085

Ok guys thanks for that, I'll revisit this and try to find some supporting documentation.David MilesAirbus

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