Blind Encoder

[meritflyer]

Can someone explain a blind encoder to me? Attached to the autopilot and/or xponder? Basic function, attached to the static ports, ect?

I have heard way to many conflicting descripitions.

Thanks.

[DE727UPS]

It's attached to the static ports and transponder, fer sure...

It's an altimeter but only gives an electronic output to the trasponder for mode C, receives input from static line.

[flyguy]

Its a component of the pitot static system and is how the transponder reads altitude. Inside the encoder is a pressure altimeter which is connected to the static line. Its basically an anneroid berometer, just like the altimeter, but there is no Kolesman(sp?) window, and it reads only pressure altitude. Also inside the encoder, there is a digitizer that measures the pressure altimeter to determine altitude, and converts it into an electronic signal, which gets sent via a data link cable to the transponder.

[TFaudree_ERAU]

To add, the conversion from 29.92 to the actual barometric pressure is done by the computers at the ATC facility. Makes things interesting when the controller tells you that you're 200 feet higher than what your altimeter is showing you. Now you have to figure out whether its your altimeter or encoder that needs a whack with the sledge hammer.

[ananoman]

Normally you will have a blind encoder which is a separate part, about the size of a soda can wired to the transponder, or you will have an encoding altimeter. An encoding altimeter looks just like the altimeter you are used to, but is wired to the transponder and performs the same function as the blind encoder.

[JayRay]

Originally Posted by TFaudree_ERAU

To add, the conversion from 29.92 to the actual barometric pressure is done by the computers at the ATC facility. Makes things interesting when the controller tells you that you're 200 feet higher than what your altimeter is showing you. Now you have to figure out whether its your altimeter or encoder that needs a whack with the sledge hammer.

This is probably the reason that there is a mandatory 24 month transponder check.

[todd584]

The blind encoder on a C172 I fly is hooked up to the autopilot; I checked the POH to make sure. So if it only reads pressure altitude, how does the autopilot's altitude match up with the altimeter?

[meritflyer]

Originally Posted by todd584

The blind encoder on a C172 I fly is hooked up to the autopilot; I checked the POH to make sure. So if it only reads pressure altitude, how does the autopilot's altitude match up with the altimeter?

On the 172s I've flown you have to enter the altimeter setting into the AP. This would digitally correct the PA for barometric pressure.

[todd584]

Oh duh I forgot about that, thanks

[Bandit_Driver]

Originally Posted by todd584

The blind encoder on a C172 I fly is hooked up to the autopilot; I checked the POH to make sure. So if it only reads pressure altitude, how does the autopilot's altitude match up with the altimeter?

If I am think of this correctly, the A/P doesn't care about your altimeter in this situation. It will maintain the pressure altitude that ALT HOLD was engaged at.

I am not sure how the more advanced ones work, that will capture an alttitude.

[meritflyer]

See what I wrote a few posts ago. You enter the altimeter setting into the AP.

[Bandit_Driver]

Originally Posted by meritflyer

See what I wrote a few posts ago. You enter the altimeter setting into the AP.

DOH !