Soyuz 7K-T No.39, also known as Soyuz 18a or Soyuz 18-1, was intended to be the next crewed mission to the Salyut-4 space station. The mission launched on April 5, 1975, 11:04:54 UTC, but due to a failure of the Soyuz launch vehicle during ascent it was aborted. Safety system initiated separation of the spacecraft, and the crew of commander Vasili Lazarev and flight engineer Oleg Makarov experienced overloads of up to 21.3 g. The capsule landed safely at 11:26:21 UTC, followed by a successful rescue of the crew members.