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View Full Version : VSI and altimeter contradict each other??

cja
03-16-2006, 08:45 AM
Cessna 150
“Stick” back open throttle intending to climb.
Vertical speed indicator shows 300 ft per minute, altimeter stays the same. What is happening? All instruments are functioning normally.


This relates to an actual event while I was in the right seat.
LRJet Guy
03-16-2006, 03:08 PM
Instantaneous VSI. Very common for the VSI to show a climb / descent while the altimeter isn't moving. Just that the altimeter hasn't caught up with the change.
cja
03-16-2006, 03:36 PM
Instantaneous VSI. Very common for the VSI to show a climb / descent while the altimeter isn't moving. Just that the altimeter hasn't caught up with the change.

Even after a minute or so?
LRJet Guy
03-19-2006, 12:24 AM
Altimieter could be stuck, or something up in the pitot static system.

Either that or the VSI was showing a minor climb / descent and it was corrected before the altimeter started to move.
cja
03-19-2006, 08:22 AM
[QUOTE=LRJet Guy]Altimieter could be stuck, or something up in the pitot static system.

Ok thanks for answering. Not, it would seem, such a mystery after all.

Cheers

Chris
nwaA330
04-12-2006, 05:56 AM
actually, the VSI lags 1 or 2 seconds behind the altimeter. At least that's how it is in a Piper Warrior or Cessna 152, small pistons, etc. Something must have been wrong with the altimiter.
thecloudbuster
04-17-2006, 07:26 PM
The altimeter is just a barometer, calibrated in feet. It will have a connection to the atmosphere via a tube which exits the aeroplane as a little hole. If the tube gets blocked then the altimeter will not experience any change in pressure and therefore will not show any change. I'm digging back some way now into my memory, but I seem to recall that on some altimeters if the static tube gets blocked then breaking the instruments glass will subject it to the cockpit pressure (which in an unpressurised aeroplane will be roughly the same as what is outside) and therefore make it work!!!