In Larry J's post:

http://www.habitablezone.com/space/messages/28532.html

he referred to the declassified pilot's manual showing an altitude versus Mach number flight envelope plot:

http://www.sr-71.org/blackbird/manual/5/5-9.htm

This plot showed an upper altitude of 85 kft. In an earlier post I claimed the upper altitude was 110 kft. I learned my number when I was touring Beale AFB many years ago. During that tour, I was taken to a room where they extracted flight data from the SR-71's flight recorder (one of the few military aircraft to carry a flight recorder). They read the flight recorder by plotting all of its parameters on a long piece of paper and then comparing the distance of the different traces to an axis using a template card (1950's analog technology). I examined the template card and saw the maximum altitude was 110,000 feet. I concluded from this that whoever designed the SR-71's flight recorder did not think the SR-71 could fly beyond 110,000 feet altitutde.

The maximum flight recorder value of 110 kft does not necessarily contract the pilot's manual value of 85 kft. The pilot's manual value was probably the maximum allowed with the engines still providing thrust. If the SR-71 flew beyond 85 kft then the inlets would probably unstart.

There is a manuever that flighter pilots and birds know called the "zoom climb". This is where the aircraft trades the specific energy from velocity into altitude by flying along a line of constant specific energy. I think(?) the equation was

specific energy = h + v^2 / (2 g)

Plotting out zoom dives and climbs for fighter planes on a flight envelope diagram was something we did in graduate school.

I think 110 kft is the maximum altitude allowed after a zoom climb. The maneuver would be a very desperate one, e.g. to avoid a SAM. The pilot would pitch up the aircraft and begine the zoom climb while throttling down both engines. He would deliberately unstart both engines at the same time to avoid an uncontrolled unstart of one engine (a very dangerous situation). The plane would zoom climb to the desired altitude and then begin a controlled descent. The SR-71 would have to descend to a much lower altitude and velocity before the inlets could be restarted and the engines spun back up (probably subsonic).

Gary