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Posted

After numerous CADC failures (not the issue here) the question arises in my mind - Why no back up airspeed indication? Or invalid reading indication on the HUD? Is this the situation in the real A-10C?

The altimeter has an pneumatic mode in case of CADC failure.

In the Manual under Emergency Procedures for CADC failure it says "

Corrective Action: Select STBY or PNEU on the altimeter and monitor pitot-static airspeed indicator." I've never seen the airspeed indicator show anything but 0 after CADC failure and switching to pneumatic.

Of course a backdoor backup method is setting CDU rotatry to "Position" and using the GS reading in the display. Not a good solution for a primary flight instrument.

Posted

I've had CADC failures where I can get secondary indication by switching to PNEU. I don't believe you can get the HUD to show PNEU indication, however.

Posted
I've had CADC failures where I can get secondary indication by switching to PNEU. I don't believe you can get the HUD to show PNEU indication, however.

 

Both correct!

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Posted

The pitot-static tube on the wing connects to a pressure transducer with an output voltage based on the current dynamic pressure. The computer system converts this voltage into a speed reading, so if the computer fails, the airplane cant give you a speed indication from the transducer anymore.

 

The only other way your airplane could give you a speed reading from the pitot system is if the pressure tubes went all the way through the wing to the speed indicator. Since this is never converted into a digital signal, your HUD wouldnt be able to read it.

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Posted
The pitot-static tube on the wing connects to a pressure transducer with an output voltage based on the current dynamic pressure. The computer system converts this voltage into a speed reading, so if the computer fails, the airplane cant give you a speed indication from the transducer anymore.

 

The only other way your airplane could give you a speed reading from the pitot system is if the pressure tubes went all the way through the wing to the speed indicator. Since this is never converted into a digital signal, your HUD wouldnt be able to read it.

 

Thanks for info. I looked for a schematic of the system put only found a very primative input/output diagram.

On the other hand they do make tee fittings that would allow both to happen. Does seem that a tube running the length of the right wing might be pretty battle damage prone.

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