Narrative:

Widebody transport X was over eastern wa in a climb to FL370 on a flight from sea to ord. Large transport Y was in level flight northbound on J3 south of geg at FL350. Widebody transport X was turned northeast, direct mlp to cross behind large transport Y. The jet stream was over the area from the southwest at over 100 KTS. The turn caused the speed on widebody transport X to increase by over 80 KTS and put the projected course even closer together. Widebody transport X was in a very slow climb of under 500 FPM but was already out of FL332. The radar controller turned widebody transport X to a heading 020 degrees to parallel large transport Y. Widebody transport X was told to resume own navigation direct mlp upon reaching FL370. A few mins later mode C on widebody transport X indicated FL367. The radar controller instructed widebody transport X to proceed direct mlp. Both data and radar controller had their attention off the scope for approximately 20 seconds looking at an overhead map. The data blocks began flashing on the scope indicating a ca. Mode C on widebody transport X then indicated FL360. Mode C was verified by the pilot who was then turned and told to expedite climb. Sep minima was lost. Supplemental information from acn 88325: one aircraft was turned to avoid the problem, but misread mode C and turned one aircraft too soon.

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Original NASA ASRS Text

Title: CTLR MISREAD MODE C READOUT AND ALLOWED ACR-WDB TO PROCEED INTO CONFLICT WITH ACR-LGT BEFORE ALT SEPARATION EXISTED.

Narrative: WDB X WAS OVER EASTERN WA IN A CLB TO FL370 ON A FLT FROM SEA TO ORD. LGT Y WAS IN LEVEL FLT NBOUND ON J3 S OF GEG AT FL350. WDB X WAS TURNED NE, DIRECT MLP TO CROSS BEHIND LGT Y. THE JET STREAM WAS OVER THE AREA FROM THE SW AT OVER 100 KTS. THE TURN CAUSED THE SPD ON WDB X TO INCREASE BY OVER 80 KTS AND PUT THE PROJECTED COURSE EVEN CLOSER TOGETHER. WDB X WAS IN A VERY SLOW CLB OF UNDER 500 FPM BUT WAS ALREADY OUT OF FL332. THE RADAR CTLR TURNED WDB X TO A HDG 020 DEGS TO PARALLEL LGT Y. WDB X WAS TOLD TO RESUME OWN NAV DIRECT MLP UPON REACHING FL370. A FEW MINS LATER MODE C ON WDB X INDICATED FL367. THE RADAR CTLR INSTRUCTED WDB X TO PROCEED DIRECT MLP. BOTH DATA AND RADAR CTLR HAD THEIR ATTN OFF THE SCOPE FOR APPROX 20 SECS LOOKING AT AN OVERHEAD MAP. THE DATA BLOCKS BEGAN FLASHING ON THE SCOPE INDICATING A CA. MODE C ON WDB X THEN INDICATED FL360. MODE C WAS VERIFIED BY THE PLT WHO WAS THEN TURNED AND TOLD TO EXPEDITE CLB. SEP MINIMA WAS LOST. SUPPLEMENTAL INFO FROM ACN 88325: ONE ACFT WAS TURNED TO AVOID THE PROB, BUT MISREAD MODE C AND TURNED ONE ACFT TOO SOON.

Data retrieved from NASA's ASRS site as of August 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.