Narrative:

Air carrier X assigned and acknowledged 11000', in level flight. Air carrier Y, opp direction level 10000'. I observed air carrier X descending through 10800' and told controller. Controller instructed air carrier X, 'maintain 11000'.' pilot said, 'roger, out of 11 for 10000.' controller: 'negative, climb and maintain 11000, traffic 12 O'clock...air carrier X, turn left--air carrier y--turn left!!!' pilot given hell over the air and replied, 'when I read back a wrong altitude, I expect feedback.' controller, trnee and handoff scared and mad, informed supervisor. Air carrier X called supervisor and whole event covered over because 'it wouldn't look good chewing out a pilot on the air' (good grief). No explanation from supervisor as to why pilot started descent.

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Original NASA ASRS Text

Title: ACR MISINTERPRETED CLRNC AND STARTED DESCENT TO AN ALT OCCUPIED BY ANOTHER ACFT.

Narrative: ACR X ASSIGNED AND ACKNOWLEDGED 11000', IN LEVEL FLT. ACR Y, OPP DIRECTION LEVEL 10000'. I OBSERVED ACR X DSNDING THROUGH 10800' AND TOLD CTLR. CTLR INSTRUCTED ACR X, 'MAINTAIN 11000'.' PLT SAID, 'ROGER, OUT OF 11 FOR 10000.' CTLR: 'NEGATIVE, CLB AND MAINTAIN 11000, TFC 12 O'CLOCK...ACR X, TURN LEFT--ACR Y--TURN LEFT!!!' PLT GIVEN HELL OVER THE AIR AND REPLIED, 'WHEN I READ BACK A WRONG ALT, I EXPECT FEEDBACK.' CTLR, TRNEE AND HDOF SCARED AND MAD, INFORMED SUPVR. ACR X CALLED SUPVR AND WHOLE EVENT COVERED OVER BECAUSE 'IT WOULDN'T LOOK GOOD CHEWING OUT A PLT ON THE AIR' (GOOD GRIEF). NO EXPLANATION FROM SUPVR AS TO WHY PLT STARTED DSCNT.

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.