Z,
Yes a B200 out of Leavesdon UK on a crew training flight.
Went up to 30+ and did a decompression.
They had mask on but the B200 had the O2 cylinder in the aft fuselage operated by a wire cable from the cockpit.
They put on the masks and opened the valve but the valve on the O2 cylinder had frozen and did not open. the cockpit lever was in the open but the cable "bunched"
The aircraft flew on A/P over the south of England and crashed in Northern France when it ran out of fuel.
GTS