Narrative:

Air carrier X received departure clearance from tower to climb and maintain 4000 ft. (Normal for pit is 5000 ft). After airborne we were told to contact departure control (119.35). On initial contact with departure control, we were told to climb to 5000 ft; and were issued VFR traffic advisory for small aircraft Y at 4500 ft. This clearance would have us climbing through his altitude but controller had us both in radar contact and we light (ferry flight) and climbing very fast. I assumed the controller thought we would be level at 5000 ft before the traffic became a factor. The 5000 ft altitude assignment was read back by first officer on radio and he set 5000 ft in altitude alerter. I confirmed '5000 ft'. As we climbed through 4500 ft I spotted the small aircraft Y off my left shoulder at approximately 1/2 mi. Controller simultaneously said 'maintain assigned altitude 4000 ft.' we were level at 5000 ft and told controller he had assigned us 5000 ft. He said he was saving tape to check. A couple mins later he confirmed on the radio that it was his mistake. Small aircraft Y stated that 'was too close.'

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Original NASA ASRS Text

Title: ACR X HAD LTSS FROM SMA Y. SYS ERROR.

Narrative: ACR X RECEIVED DEP CLRNC FROM TWR TO CLB AND MAINTAIN 4000 FT. (NORMAL FOR PIT IS 5000 FT). AFTER AIRBORNE WE WERE TOLD TO CONTACT DEP CTL (119.35). ON INITIAL CONTACT WITH DEP CTL, WE WERE TOLD TO CLB TO 5000 FT; AND WERE ISSUED VFR TFC ADVISORY FOR SMA Y AT 4500 FT. THIS CLRNC WOULD HAVE US CLBING THROUGH HIS ALT BUT CTLR HAD US BOTH IN RADAR CONTACT AND WE LIGHT (FERRY FLT) AND CLBING VERY FAST. I ASSUMED THE CTLR THOUGHT WE WOULD BE LEVEL AT 5000 FT BEFORE THE TFC BECAME A FACTOR. THE 5000 FT ALT ASSIGNMENT WAS READ BACK BY FO ON RADIO AND HE SET 5000 FT IN ALT ALERTER. I CONFIRMED '5000 FT'. AS WE CLBED THROUGH 4500 FT I SPOTTED THE SMA Y OFF MY L SHOULDER AT APPROX 1/2 MI. CTLR SIMULTANEOUSLY SAID 'MAINTAIN ASSIGNED ALT 4000 FT.' WE WERE LEVEL AT 5000 FT AND TOLD CTLR HE HAD ASSIGNED US 5000 FT. HE SAID HE WAS SAVING TAPE TO CHK. A COUPLE MINS LATER HE CONFIRMED ON THE RADIO THAT IT WAS HIS MISTAKE. SMA Y STATED THAT 'WAS TOO CLOSE.'

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.