Here's a timeline of the flight:
Flight Track Log ? N900KN ? 05-Sep-2014 ? KROC - KAPF ? FlightAware
EDT Alt Crs
8:26:00 1,100 215 First radar return
8:46:00 28,000 199 Cruise flight
10:04:00 28,000 193 Problem indicated. Cleared to descend to FL250
10:05:00 27,000 193
10:06:00 25,000 172 Levelled off. Turning 30 degrees left
10:07:00 25,000 164 Turn complete. Course and altitude remain for the duration of flight
14:11:00 25,000 207 Last return. Heading and altitude erratic over the last 2 minutes
And a summary of the tape:
http://archive-server.liveatc.net/kg...2014-1400Z.mp3
Offset Alt
0:04:17 FL280 Pilot: "We need to descend to about 180. We have an indication that is not (?) correct in the plane"
0:04:22 FL280 ATC: "Standby"
0:04:30 FL280 ATC: "Descend and Maintain FL250"
0:04:33 Pilot: "250 we need to get lower"
0:04:37 ATC: "Working on that"
0:04:52 ATC: "If you have to get down, 0KN, turn 30 degrees left"
0:04:58 Pilot: "30 left"
0:06:35 FL250 ATC: (Broken) "FL200" (Assumed it was clearance given)
0:06:42 FL250 Pilot: "FL200 0KN"
0:07:15 FL250 ATC: "Cleared direct Taylor"
0:07:30 FL250 ATC: (Repeats) "Cleared direct Taylor"
0:07:33 FL250 Pilot: "Direct Taylor 0KN"
0:08:05 FL250 ATC: "N900KN Copy that altitude 200"
0:08:10 FL250 Pilot: (Unintelligible)
0:08:37 FL250 ATC: "N900KN Descend and Maintain FL200 and cleared direct Taylor"
0:08:42 FL250 Pilot: (Slow voice - last contact) "Kilo November 900 Kilo November"
0:09:50 FL250 ATC: "Understand FL200, FL200 for 900KN"
0:10:10 FL250 ATC: "TBM, TBM, Zero Kilo November, descend and maintain FL200"
0:11:49 FL250 ATC: "Zero Kilo November, if you hear this, transmit and ident"
0:12:15 FL250 ATC: (Attempts contact through other air traffic)
And the time of useful consciousness:
https://en.wikipedia.org/wiki/Time_o..._consciousness
So:
- Within 2.5 minutes of reporting the problem at FL280, descending to FL250, he ceased responding to the ATC directive to descend to FL200.
- After a further 2 minutes, still at FL250, his voice was very groggy and it was the last response given.
Hypoxia is so insidious. Very sad.