Terminal Velocity is a short story by L.J. Goulding.
In the skies over Brakur IV, war rages. The tyranids of Hive Fleet Kraken have achieved air-superiority over the Imperial defenders, disrupting what should have been a simple extraction mission for the Scythes of the Emperor - and a lone battle-brother plunges from his wrecked dropship towards the planet's surface. With his life expectancy now measured only in seconds, he must find a way to slow his deadly freefall, or become just another name on a staggering list of fallen Chapter heroes...