Soyuz 18a was the first Soyuz 18 mission. Launched on April 5th, the mission ended in the first in-flight abort of a human space mission. At 4 minutes 48 seconds into launch, at an altitude of 146 km, the Soyuz rocket launching the mission failed to fully separate its first and second stages. The stages finally tore apart as the second stage engine ignited, but that event threw the second stage off course. The Soyuz 11 spacecraft's onboard computers detected the deviation and activated the abort systems to pull itself and its two-person crew free from the failing rocket. Because the rocket was failing to keep itself pointed in the correct direction, Soyuz 11's abort engines fired when the craft was pointing toward the ground. The accelerated descent imparted 21 Gs of force onto the crew instead of the certified 15 Gs for Soyuz aborts. Despite the increased speed and force, Soyuz 11's parachute deployed and unfurled as designed. Twenty-one minutes after launch, it landed thousands of kilometers away from its launch site on a steep incline. The capsule tumbled down the embankment. Its still-attached parachute caught on a tree and the capsule jerked to a stop just meters from a 152 m plunge into a gorge. The crew were in contact with recovery forces within minutes but the steep terrain meant they had to spend the night in the capsule enduring -7 C temperatures. They were rescued the following day. Lazarev was injured in the abort and landing; he never flew again. Makarov went on to fly two more missions. The mission's failure was disclosed to NASA as part of inter-agency preparations for the Apollo-Soyuz Test Program mission just a few months away.