On 29 June 1971, the crew loaded scientific specimens, films, tapes, and other gear into Soyuz 11, then transferred manual control back from Salyut 1 to Soyuz 11 and returned to their ferry craft. Undocking occurred at 18:28 GMT. Soyuz 11 flew co-orbit for a while and retrofired at 22:35 GMT. The work compartment and service module were routinely cast off prior to entering the dense atmosphere. Radio communications abruptly ended at the moment of separating the work compartment (about 22:47 GMT), before the normal ionospheric blackout. Automatic systems landed the craft safely at 23:16:52 GMT. The total flight duration of the crew was 570.22 hours and involved 383 orbits—18 prior to docking, 362 docked, and 3 after undocking. On reaching the landing site and opening the hatch, the helicopter rescue crew discovered all three men dead in their seats. The official investigation results showed that the men died of pulmonary embolisms when the imperfect seal of the hatch between their command module and work compartment permitted the air supply to evacuate in the seconds after the two crafts separated.