B. Failure of the Hycon II Camera Mount during the previous flight, resulted in that experiment being deleted until further notice. Redesign is in progress.

B. Drop tanks were installed for this flight.

C. A high temperature measuring probe installation was incorporated at the top leading-edge of the upper vertical. Two sensors were used, a Rosemont probe and a Honeywell fluidic probe.

B. The periodic refurbishment of the pilot seat stabilization booms was accomplished at Talley Corporation between August 28 and September 18. The booms were reinstalled in the seat on Tuesday, September 19.

C. System preflight functional tests were begun on Saturday, September 16, and completed on Wednesday, September 20. The external drop tanks were installed on Monday, September 18.

D. An APU ground run was made on Wednesday, September 20. No engine ground run was made for this flight, but a full load of LOX and NH3 was serviced and chilled leak checks were made. A propellant external to internal flow check was also made to verify proper propellant transfer from the external tanks.

E. The X-15 was closed out for flight on Friday, September 22, ablative coating touch-up repairs were made Saturday, September 23, and the X-15 was mated on the following Monday.

F. Wet weather made Mud Lake unusable for X-15 operations during the week of Monday, September 25, and flight 2-53-97 was scheduled for Tuesday, October 3. The flight was made on that date.

Engine operation and propellant feed system operation during boost phase were excellent. The pilot's NH3 helium flow indicator was, as in the past, rather slow in responding, but the "Paddle Switch" flow indicators responded instantly in external flow, and confirmed proper propellant feed sequencing.

C. The ramjet separated prematurely during the turn to downwind leg over Rogers Lake, at approximately 32,000 feet and approximately Mach 1.0. The ramjet impacted in the Edwards Bombing Range and was recovered. Due to the high separation speed the parachute failed and impact damage was great. Certain major pieces of the ramjet are salvageable however. It appears that aerodynamic heating caused the explosive bolts (which attach the ramjet to the pylon) to fire prematurely (see item D below).

D. Post flight inspection shows that local aerodynamic heating of the ramjet pylon, especially the leading-edge area, was too great for the ablative coating installed in that area, and virtually all of the ablative coating dissipated down to bare metal. Skin failure followed, and several holes were burned in the skin and substructure. The excessive heating propagated upward into the lower fuselage area, causing an over-temperature indication in the engine H202 compartment, failure of a control-gas line, and loss of helium control-gas. As a result, residual propellants could not be jettisoned.

It appears that the excessive heating of the unprotected pylon eventually "cooked off" the explosive bolts attaching the Dummy Ramjet, (inspection shows all four to have fired) resulting in premature separation as reported above. The design of the pylon is now under scrutiny and a new leading-edge design, able to withstand the Ramjet shock wave heating, will probably be incorporated prior to the next flight.