During its landing in April a Soyuz capsule carrying three astronauts returning from ISS became partially depressurized at about five miles altitude.
The partial loss of pressure did not put the crew in jeopardy, Stafford said. A valve normally opens once the capsule descends to an altitude of five kilometers to allow outside air into the capsule. The crewmembers were also wearing pressure suits, as is standard procedure on Soyuz landings.
The incident occurred when a buckle from the parachute system hit a welding seam in the capsule as the parachute deployed.
There is a reason the Russians require astronauts to wear pressure suits while in a Soyuz capsule. During the return to Earth in 1971 of three cosmonauts from the first Russian space station, Salyut 1, the capsule depressurized and the three men died of suffocation.