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Loss of Ess AC Power

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Hi all.

In our dash 1 under \"Loss of Ess AC Power\" there is a statement about what systems we will loose. One of them is Normal Brakes ( on the Ground).

For the life of me I cannot understand what they mean? with the engines at NGI on the ground we would still have the Main AC Tru\'s working to give us Main DC power and Esst DC for the brakes. All the circuts are DC, for the brakes. Only AC in the Normal Brake system is the 26 volts of Antiskid so if thats a player why not turn it off.

So who would it say we will not have normal Brakes when on the ground??


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if you went to LSGI and just had the APU or GTC running, then you would loose all TRU\'s if you had the ESST AC Buss isolated or lost and be on the Battery to prvide power for DC via the Touch Down System (not good).

So if you left 1 engine up and 1 gen on line you would get Main AC Buss power and then all the DC busses powered via the 2 Main TRU\'s, so you would still have normal brakes available...

So back to the original Flight Manual #3 statement of No normal brakes when on the ground for loss of ESS AC. Why???


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You were getting close to the answer in your first post. Loss, or partial loss of the ESS AC bus could cause problems with the Anti Skid system. It\'s been found that in a couple of instances, faulty power caused the Anti Skid to act as though there was a skid on all the wheels, thus causing loss of normal brakes. I\'m not sure which flight manual you\'re using, but it should include the step of turning the Anti Skid off in the corrective action, like ours does.

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  • 2 weeks later...

In reference to \"Normal brakes\", it implies fully operational anti-skid. So, when you turn off the anti-skid, it\'s no longer a \"normal\" system. The only difference between the normal brakes & emergency brakes is essentially then only the system supplying the pressure. Yes, the intent is you leave the brake select switch in normal unless you have reason to believe there\'s a problem with the utility hydraulic system. Just turn the anti-skid switch off.


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