777's PFC reset (volcanic ash C/L)
I was recently taught that in the (unlikely ?) event of an "Airspeed Unreliable" within Volcanic Ash, it is better not to reset PFC at the end of the Volcanic Ash C/L (whereas it is explicitly written to do it in the FCOM) because the reset will be based on unreliable airspeed.
That makes sense to me but where it is written ? Where can I find information on PFC reset ?
Thanks