A NASA DC-8, equipped as an in-situ sampling aircraft, flew in the exhaust wake of a Boeing 757 on May 4, 1996 over Kansas. Ice crystal samples were collected by impaction technique and replicated twice about 8 to 17 km behind the aircraft at an altitude of 11.8 km. The ice crystals in the contrail (after about 1 minute of growing time) had a unimodal size distribution, with an equivalent volume radius of less than 10 &mgr;m and an effective radius of about 2 &mgr;m. The crystal habits at the observed temperature of -61C were predominantly hexagonal plates (75%), columns (20%) and few triagonal plates (<5%). The habit was already well defined for crystals about 0.5 &mgr;m in radius. ¿ 1998 American Geophysical Union