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-   -   B737 "LAND ALT" selector (https://www.pprune.org/tech-log/273193-b737-land-alt-selector.html)

Agaricus bisporus 24th Apr 2007 09:52

B737 "LAND ALT" selector
 
A question for anyone who flies 700 - 900 series 737s.

When setting the LAND ALT before departure do you round up or round down the arrival rwy altitude? Does it matter - after all, only 50 feet is involved. What is Boeing Standard, and why?

My feeling is that as the cabin lands "slightly pressurised" ( Boeing OM Vol II) rounding it down could result in a landing pressure equivalent to up to 50 ft below the surface, plus the "slightly pressurised" element, plus any barometric variable, ie QNH about to change) which could cause a pressure bump in the cabin, whereas rounding up would minimise this. Previous company insisted vehemently that rounding up was essential, present one doesn't seem to have much of a view. Our trainers tell different stories.

Ideas?

alexban 24th Apr 2007 13:24

No problem whatsoever, otherwise Boeing would have specified which way to set it. The cabin will be 200' bellow land alt ,and 50' plus or minus won't make such a difference. It is not a pressure bump,it's a controlled depressurize of the cabin. So,if you add 50' ,it will take a 'bit' longer.

Permanent Standby 30th Apr 2007 13:41

LAND ALT selector? So thats why my ears keep popping on t'down....:mad:


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