Cuin5 wrote "In reality the cockpit crew probably would not have heard until they arrived in HKG." - sorry to rain on his parade, but this was incorrect.
Actually the crew I was with, as did many others, knew there was something untoward unfolding during the early part of our flight back to HK.
On that date, I was leaving the US to fly west across the Pacific. We had just become airborne when the first impact occured.
Air Traffic control started making gradually but increasingly different calls to inbound aircraft. As we were outbound, we were of little consequence, however, those who were coming towards us with the intention of landing in N America, were it appears, being categorized as those who had sufficient fuel to do a 180' and return westbound to land in Japan, or, those who had passed their point of no return and would have to land somewhere on the N American continent.
There was significant lack of understanding by some of the non-native English speaking Asian airlines, who couldn't comprehend or just didn't realise, that when they were told to land in Whitehorse or Fairbanks for example, that it was not a request! The terms in which they communicated to these other flights were becoming increasingly firm.
The other area of co-ordination which I thought was well handled, was the integration of a whole swag of east-bound aircraft being turned back and joining (our) west bound routes, but avoiding confliction at the same time. In general, I'm not a great lover of seppo ATC, but credit where it's due, they played the part that I listened to extremely well, Canadians too eh? but thats expected!
Such occurences are fairly unique, and although that night I never heard anyone on VHF or HF say the reason for the closure of US airspace, it was obviously something of considerable magnitude. Consequently, we were able to do two things. One of them was to tune one of our wireless' to the BBC world service, and the other was to send a "whats goin on?" message via ACARS back to our ops room in HK who were glued to CNN.
The news was confirmed, and a series of protective measures were taken. Additionally, the aspect of informing passengers now or later was also discussed, and it was decided not worry passengers with the news so early on in the flight. as there would be little they could do for the next 9 hours or so. Their access to certain media was also limited.
So there you have it, a mini version of one crews abbreviated observations of the period in question.
Good luck with the book.