Narrative:

The northbound crj, which has a notoriously slow climb rate, checked in climbing to an altitude not reflected in the data block. The readback was not caught by me and the erroneous data block not caught by handoff sector. I witnessed FL241 in data block and climbed B757 using observed leaving rule. Separation was lost.

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Original NASA ASRS Text

Title: ZBW CTLR EXPERIENCED OPERROR AT FL240.

Narrative: THE NBOUND CRJ, WHICH HAS A NOTORIOUSLY SLOW CLB RATE, CHKED IN CLBING TO AN ALT NOT REFLECTED IN THE DATA BLOCK. THE READBACK WAS NOT CAUGHT BY ME AND THE ERRONEOUS DATA BLOCK NOT CAUGHT BY HDOF SECTOR. I WITNESSED FL241 IN DATA BLOCK AND CLBED B757 USING OBSERVED LEAVING RULE. SEPARATION WAS LOST.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.