When the Soyuz started aerobraking in the upper reaches of the atmosphere, the combined spacecraft sought the most aerodynamically stable position - nose forward, with the heavy descent module facing directly into the air stream with only its light metal entry hatch at the front to protect it. The gaskets sealing the hatch began to burn, filling the compartment with dangerous fumes and smoke. The deceleration, while normal for reentry, pulled Volynov outward against his harness rather than against the padded seat. As the thermal and aerodynamic stresses on the combined craft increased, struts between the descent and service modules broke off or burned through before the hatch failed. The descent module immediately righted itself once the service module was gone, with the heat shield forward to take the brunt of re-entry.