Quote:
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Originally Posted by flying pig
.... Once this happens the traincrew aren't allow to try to raise it again until a Fitter has checked it....
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Quote:
Originally Posted by hairyhandedfool
...The air is fed directly from the main air resevior.... From my knowledge of the ADD on 319s, the driver would be unable to raise the pan if it activated, nevermind being allowed to raise it!
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Not so. That may be the simplified version that the Training School puts out, but it's rather more involved than that. It really wouldn't be a smart idea to have the Main Res Pipe venting directly to the world. Main Res Air is far too precious !
On a 319, a leak in the Air Gallery in the pan head, or operation of the Height Limit Valve effectively causes a leak in the feed to the Servo Piston Assembly, which operates the Pan Air Motor. As a result the Pan Air Motor doesn't function and the Pantograph Dropping Springs quickly bring the pan down.
However if you turn the ADD Isolating Cock it shuts off the 'leak' to the Height Limit Valve and Air Gallery line, allowing the Servo Piston to resume operation. Therefor operating the ADIC will cause the Pan Air Motor to function again. This is considerably more powerful than the Pantograph Dropping Springs, so provided that the pan isn't too mangled from its previous encounter it will go back up.