411A
In actual fact, the J47 jet engines on later B-36's could be (mostly) routinely restarted at 50,000 feet, to enable high speed bombing runs.
This was on the 'Featherweight' models, which had much equipment removed to attain these altitudes.
I thought the J47s were needed to get the B-36 off the ground in hot and high, Max AUW conditions.
Although I could be wrong as the picture below shows all ten engines running at height!
