Narrative:

Position and hold on runway 26R. While waiting for takeoff clearance, ont tower asked us what type of climb we could give him. He said there was an aircraft in vicinity who had not cancelled his IFR clearance yet. I said we could given him 236 KTS (V2F) on climb and a rate of approximately 2000-3000' initially. I also said that we would wait, that we were in no hurry and, 'I don't want to get mixed up with a little guy out there.' about 1-1 1/2 mins later we received takeoff clearance. After takeoff, at V2F and climb power (approximately 4000-4500'), we were given a turn to heading 235 degrees. We were barely established on 235 degrees and the controller gave us another turn to 280 degree heading, direct pomona when able, reintercept the pomona 4 departure. Then controller said, 'traffic alert, 11 O'clock, less than 1 mi, same altitude (6400').' I said, 'we're IMC, but looking.' controller said, 'I think it's an erroneous signal--it just popped up on radar!' other conversation took place at this time on the frequency. Before changing frequencys, the controller came back to us and said it was an erroneous signal, but we as the crew weren't so sure of that due to other conversations we were hearing on the frequency. After landing in msp, I called the duty supervisor in ont departure control and discussed the matter with him. He said he would pull the tapes. He also said, 'I don't know if you are familiar with our area, but we did get a lot of erroneous signals (mode C) and are required to give traffic alerts. I told him it was not very comforting to be told you have traffic less than 1 mi, same altitude and in IMC conditions. What causes the erroneous mode C signals? Or was there an aircraft in our same proximity.?

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Original NASA ASRS Text

Title: ACR WAS ISSUED TRAFFIC WHILE IN IMC, THEN TOLD LATER THAT TARGET MIGHT BE AN ERRONEOUS SIGNAL.

Narrative: POS AND HOLD ON RWY 26R. WHILE WAITING FOR TKOF CLRNC, ONT TWR ASKED US WHAT TYPE OF CLB WE COULD GIVE HIM. HE SAID THERE WAS AN ACFT IN VICINITY WHO HAD NOT CANCELLED HIS IFR CLRNC YET. I SAID WE COULD GIVEN HIM 236 KTS (V2F) ON CLB AND A RATE OF APPROX 2000-3000' INITIALLY. I ALSO SAID THAT WE WOULD WAIT, THAT WE WERE IN NO HURRY AND, 'I DON'T WANT TO GET MIXED UP WITH A LITTLE GUY OUT THERE.' ABOUT 1-1 1/2 MINS LATER WE RECEIVED TKOF CLRNC. AFTER TKOF, AT V2F AND CLB PWR (APPROX 4000-4500'), WE WERE GIVEN A TURN TO HDG 235 DEGS. WE WERE BARELY ESTABLISHED ON 235 DEGS AND THE CTLR GAVE US ANOTHER TURN TO 280 DEG HDG, DIRECT POMONA WHEN ABLE, REINTERCEPT THE POMONA 4 DEP. THEN CTLR SAID, 'TFC ALERT, 11 O'CLOCK, LESS THAN 1 MI, SAME ALT (6400').' I SAID, 'WE'RE IMC, BUT LOOKING.' CTLR SAID, 'I THINK IT'S AN ERRONEOUS SIGNAL--IT JUST POPPED UP ON RADAR!' OTHER CONVERSATION TOOK PLACE AT THIS TIME ON THE FREQ. BEFORE CHANGING FREQS, THE CTLR CAME BACK TO US AND SAID IT WAS AN ERRONEOUS SIGNAL, BUT WE AS THE CREW WEREN'T SO SURE OF THAT DUE TO OTHER CONVERSATIONS WE WERE HEARING ON THE FREQ. AFTER LNDG IN MSP, I CALLED THE DUTY SUPVR IN ONT DEP CTL AND DISCUSSED THE MATTER WITH HIM. HE SAID HE WOULD PULL THE TAPES. HE ALSO SAID, 'I DON'T KNOW IF YOU ARE FAMILIAR WITH OUR AREA, BUT WE DID GET A LOT OF ERRONEOUS SIGNALS (MODE C) AND ARE REQUIRED TO GIVE TFC ALERTS. I TOLD HIM IT WAS NOT VERY COMFORTING TO BE TOLD YOU HAVE TFC LESS THAN 1 MI, SAME ALT AND IN IMC CONDITIONS. WHAT CAUSES THE ERRONEOUS MODE C SIGNALS? OR WAS THERE AN ACFT IN OUR SAME PROX.?

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.