"If you turn off the A/T arm switch on the glareshield, then Auto Throttle will not come on at all until you turn the A/T arm switch back on and then select a vertical mode."
Besides A/T arm switches there's an A/T engage pushbutton. Today the NTSB said the A/T switches were armed, but did not say whether the A/T pushbutton was on.
The PF was an Airbus captain from 2005 to a few months ago. Does the Airbus A/T activate whether its A/T pushbutton is on or not? On Boeing must the A/T pushbutton always be on for A/T to work? Is it conceivable the A/T switch was off but his ingrained Airbus experience coupled with fatigue made him forget it must be on?