Shytorque - it had nothing to do with windshear and everything to do with external visual cues overshadowing instrument indications - the pilot perceived the same groundspeed when he looked outside (a good thing at low level) but missed the airspeed dropping off as he turned downwind. The classic demo started at between 30 and 40 kts on a 15 to 20 kt day so that as the IAS bled off on the downwind turn, ETL was lost and a RoD built up (low IAS + RoD = potential VRS).