It was around this point in the descent that the last Apollo command module to enter space ran into problems. During their return from the first international linkup in Earth orbit, the Apollo-Soyuz Test Project, the crew failed to switch on the Earth landing system at the right time. This episode illustrates how quickly an otherwise nominal mission can be derailed by a small operational error. Vance Brand was flying in the left couch with ‘l orn Stafford in command occupying the centre couch and working through the checklist with him. Somehow, they missed the step where the Earth landing system should have been powered and. all too quickly, they realised that the apex cover was still attached when it should have already departed. Brand punched the button to manually jettison it, and did the same for the drogue chutes. Unfortunately, in the rush, the RCS jets were not disabled, and when the drogue deployment caused the spacecraft to sway, the RCS jets began to lire to damp out these motions. By this Lime, the cabin pressure relief valve had begun to admit air from outside and, as it did so. exhaust from the jets, including a fraction of unburnt propellant, entered the cabin where the highly noxious chemical irritated the skin and eyes of the crew and caused them to cough. After struggling through the remainder of the descent and a hard landing that left the spacecraft upside-down. Stafford found Brand to be hanging in his straps unconscious. He struggled to get oxygen masks on his crewmates and gain control of the ship.