That sounds like a reasonable explanation to me!
When cleared to climb to a flight level I set STD BARO, and cleared to descent to an altitude I set the QNH.
I have 3 places to set the pressure (G1000, the standby altimeter and in the KAP140 autopilot).
With the G1000 you can quickly flip between STD BARO and last used QNH.
Having two altimeters displaying different values could be potentially dangerous when flying IFR.
lenthamen wrote:
Having two altimeters displaying different values could be potentially dangerous when flying IFR.
And it kind of reduces the redundancy to absurdity.
I change between QNH and STD when passing transition level/alttitude. Changing when getting clearance can lead to unwanted change of altitude when flying on autopilot and changing baro coupled to it.
Alt1 and the Alt selecter are set to whatever I’m cleared to, or QNH if VFR.
Cross-checked against Alt2 (which is always on QNH) if flying attitude, and against the xpder if flying standard setting.
Imagine your primary altimeter goes stuck or fails. What would you like the second one to show you?
Michael_J wrote:
Imagine your primary altimeter goes stuck or fails. What would you like the second one to show you?
The problem is that when the two altimeters show different values (deliberately or not) you will never notice that the one you use for flying is defective or set wrongly. This is why real airplanes have a comparison monitor that will display a big red/orange/amber alert across the primary flight display if the two (or more) altimeters show different numbers.
That’s clever but possible only if they are all encoding types.
“Simple” planes have non-encoding ones because they are cheap – below €1000 normally.
The cheapest encoding one is perhaps the KEA130A which is about $5000 new (can’t find a price right now). These are normally used as #1 and they drive the autopilot, and maybe the transponder, TCAS, etc. Then #2 is a cheapo one.
On a long high altitude flight the QNH is soon meaningless so both of mine with be set to FL. And then the Q becomes: what do you do about terrain clearance in an emergency? A: use the GPS altitude 
Peter wrote:
The cheapest encoding one is perhaps the KEA130A which is about $5000 new (can’t find a price right now).
Wow. For less than that price you can get a proper TSOed air data computer that can do much more for you than just encode an altitude (e.g. http://www.aircraftspruce.com/catalog/avpages/sandia735.php?recfer=5964). I guess the days of the 5000$ encoding altimeter will soon be over.
Number of accidents because of broken altimeter = ?
Number of accidents because of defect in pitot-static system = ?
Number of accidents because of lack of altitude awareness when flying at a low flight level = ?
All are rare; the number of accidents because of pitot/static failure are probably a magnitude higher than the other two, though. So a completely seperate pitot-static system would make the second altimeter hugely more useful than just the altimeter.
C.
