We use airborne observations to extend a previous analysis by Lang and Rutledge (2008) of remotely sensed radar and lightning mapping array observations of the 11 June 2000 asymmetric mesoscale convective system (MCS) that moved through the primary observation region of the Severe Thunderstorm Electrification/Precipitation Study in northeastern Colorado and northwestern Kansas. We analyze in detail aircraft observations, radar, and remotely-mapped lightning discharges from a portion of the MCS that was starting to produce a bow echo during the time of the aircraft mission. The observations are interpreted to indicate the presence of a rearward and downward-sloping positive charge layer detraining from a mature cell in the leading convective region. In the convective cell the positive charge region was at an altitude of 10 km MSL. It then descended and crossed the 6 km MSL altitude plane 40 km to the rear of the leading convective region. A pattern of rearward and downward propagating lightning discharges from the upper convective region to trailing stratiform region was associated with this layer. The pattern persisted over a period of at least 8 minutes within which time 3 major lightning discharges initiated in the convective region and propagated rearward into the trailing stratiform region through the positive charge layer. Lightning initiation was not observed in the trailing stratiform region during the hour the aircraft was sampling it. The lack of lightning initiation in the trailing stratiform region is attributed to relatively weak electric fields there.