GTC until take-off
Guppy, don't doubt what you are saying, just wondered why you would keep the GTC running until take-off. What was the purpose for that. I am presuming you had an ATM for electrical power (20KVA) and the Emergency System Hydraulic Pump plus a one-way "Pineapple" check valve which would close the GTC air delivery duct when engine bleed was available.