Narrative:

We were climbing out of slc and received vectors to intercept J15 between slc and jnc. Our original altitude clearance was 16000'. As we were intercepting the arwy (slc 109 degrees) and approaching 16000', slc departure cleared us over ZLC. The center controller cleared us to climb to what all 3 of us in the cockpit heard, '2-9-0.' I was controling the aircraft, and set 29000' in the altitude alerter, while the captain read back the clearance as 'cleared to two niner zero.' there was no response from the controller. As we climbed through FL255 we noticed aircraft lights in our 1 O'clock, moving to 2 O'clock, fairly close. (Position slc 109 degrees/ 65 DME.) as we leveled off at FL255 to avoid getting any closer to the other aircraft, ZLC asked us to confirm our altitude clearance, the captain stated we had been cleared to FL290, and that's what he had read back after receiving the clearance. The controller said our clearance had been for FL250, and that a possible altitude violation would be forthcoming after review of the tapes. He gave the captain a phone # to call after our return to slc on 2/tue/89. He also confirmed that the other aircraft was at FL260, but did not give us its latitude distance from us (we estimate 5000' for what it's worth). The other aircraft had us in sight, as he flashed his landing lights at us when we questioned center about the traffic in our 1 O'clock position. About 30 mins later ZDV relayed to us that the tapes had been reviewed and that we were not involved in an altitude violation. Apparently the controller had cleared us to FL250. We interpreted it as '2-9-0,' and the controller failed to catch our error when we read back 'two niner zero.' a bit more vigilance on the controller's part would have avoided this incident, VMC conditions at altitude allowed us to avoid a near miss situation before it developed. We were lucky.

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Original NASA ASRS Text

Title: CTLR FAILED TO CATCH ALT ON READBACK.

Narrative: WE WERE CLBING OUT OF SLC AND RECEIVED VECTORS TO INTERCEPT J15 BTWN SLC AND JNC. OUR ORIGINAL ALT CLRNC WAS 16000'. AS WE WERE INTERCEPTING THE ARWY (SLC 109 DEGS) AND APCHING 16000', SLC DEP CLRED US OVER ZLC. THE CENTER CTLR CLRED US TO CLB TO WHAT ALL 3 OF US IN THE COCKPIT HEARD, '2-9-0.' I WAS CTLING THE ACFT, AND SET 29000' IN THE ALT ALERTER, WHILE THE CAPT READ BACK THE CLRNC AS 'CLRED TO TWO NINER ZERO.' THERE WAS NO RESPONSE FROM THE CTLR. AS WE CLBED THROUGH FL255 WE NOTICED ACFT LIGHTS IN OUR 1 O'CLOCK, MOVING TO 2 O'CLOCK, FAIRLY CLOSE. (POS SLC 109 DEGS/ 65 DME.) AS WE LEVELED OFF AT FL255 TO AVOID GETTING ANY CLOSER TO THE OTHER ACFT, ZLC ASKED US TO CONFIRM OUR ALT CLRNC, THE CAPT STATED WE HAD BEEN CLRED TO FL290, AND THAT'S WHAT HE HAD READ BACK AFTER RECEIVING THE CLRNC. THE CTLR SAID OUR CLRNC HAD BEEN FOR FL250, AND THAT A POSSIBLE ALT VIOLATION WOULD BE FORTHCOMING AFTER REVIEW OF THE TAPES. HE GAVE THE CAPT A PHONE # TO CALL AFTER OUR RETURN TO SLC ON 2/TUE/89. HE ALSO CONFIRMED THAT THE OTHER ACFT WAS AT FL260, BUT DID NOT GIVE US ITS LAT DISTANCE FROM US (WE ESTIMATE 5000' FOR WHAT IT'S WORTH). THE OTHER ACFT HAD US IN SIGHT, AS HE FLASHED HIS LNDG LIGHTS AT US WHEN WE QUESTIONED CENTER ABOUT THE TFC IN OUR 1 O'CLOCK POS. ABOUT 30 MINS LATER ZDV RELAYED TO US THAT THE TAPES HAD BEEN REVIEWED AND THAT WE WERE NOT INVOLVED IN AN ALT VIOLATION. APPARENTLY THE CTLR HAD CLRED US TO FL250. WE INTERPRETED IT AS '2-9-0,' AND THE CTLR FAILED TO CATCH OUR ERROR WHEN WE READ BACK 'TWO NINER ZERO.' A BIT MORE VIGILANCE ON THE CTLR'S PART WOULD HAVE AVOIDED THIS INCIDENT, VMC CONDITIONS AT ALT ALLOWED US TO AVOID A NEAR MISS SITUATION BEFORE IT DEVELOPED. WE WERE LUCKY.

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.