Narrative:

When leaving den at about 500' AGL, tower told us to climb to 9000' and go to departure. I started to call departure when I saw the airspeed decreasing. I yelled to the captain 'airspeed, it keeps decreasing.' I called 'airspeed' again, and reached up to the throttles to push them to the firewall because we were about -40. At the same time, I looked at the captain's airspeed and it showed 160 KTS, and mine was at 110 KTS, so at that time I looked at the standby airspeed and altitude and the airspeed showed 180 KTS and the altitude showed 11100. I looked up at the captain's altitude and it showed 7500', and mine was at 8000'. I said to the captain you should leave off because the standby altitude said 11100'. We were light and climbing at about 4000-5000 FPM. I called departure and asked our altitude. They said 11100'. We came back to den using only the standby altitude and airspeed. The WX was -X 1/2 s-f. Supplemental information from acn 131714: due to light snow flurries we were deiced 5 mins before takeoff. Very shortly after takeoff we lost both left and right altimeters and speed indicators, as well as all indications from both left and right air data computer. Realizing that the failures were probably caused by deice fluid, I didn't know whether or not to trust the standby altimeter and airspeed, so I kept a climbing attitude. We told departure that we had altimeter problems and that we had to come back immediately. Controller said he showed us at 11500'. He thus confirmed both the validity of our standby altimeter and that we had overshot our altitude. Since, during the failure, our altimeter showed 3 different altitudes, it was impossible to determine which was the right one until we could confirm one of them with ATC.

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Original NASA ASRS Text

Title: ACR MLG HAS ERRONOEUS READINGS ON CRT. CAPT AND FO READINGS DISAGREEING. EQUIPMENT CAUSES ALT DEVIATIONS. USING STANDBY AIRSPD AND ALTIMETER, RETURN TO DEP ARPT.

Narrative: WHEN LEAVING DEN AT ABOUT 500' AGL, TWR TOLD US TO CLB TO 9000' AND GO TO DEP. I STARTED TO CALL DEP WHEN I SAW THE AIRSPD DECREASING. I YELLED TO THE CAPT 'AIRSPD, IT KEEPS DECREASING.' I CALLED 'AIRSPD' AGAIN, AND REACHED UP TO THE THROTTLES TO PUSH THEM TO THE FIREWALL BECAUSE WE WERE ABOUT -40. AT THE SAME TIME, I LOOKED AT THE CAPT'S AIRSPD AND IT SHOWED 160 KTS, AND MINE WAS AT 110 KTS, SO AT THAT TIME I LOOKED AT THE STANDBY AIRSPD AND ALT AND THE AIRSPD SHOWED 180 KTS AND THE ALT SHOWED 11100. I LOOKED UP AT THE CAPT'S ALT AND IT SHOWED 7500', AND MINE WAS AT 8000'. I SAID TO THE CAPT YOU SHOULD LEAVE OFF BECAUSE THE STANDBY ALT SAID 11100'. WE WERE LIGHT AND CLBING AT ABOUT 4000-5000 FPM. I CALLED DEP AND ASKED OUR ALT. THEY SAID 11100'. WE CAME BACK TO DEN USING ONLY THE STANDBY ALT AND AIRSPD. THE WX WAS -X 1/2 S-F. SUPPLEMENTAL INFO FROM ACN 131714: DUE TO LIGHT SNOW FLURRIES WE WERE DEICED 5 MINS BEFORE TKOF. VERY SHORTLY AFTER TKOF WE LOST BOTH LEFT AND RIGHT ALTIMETERS AND SPD INDICATORS, AS WELL AS ALL INDICATIONS FROM BOTH LEFT AND RIGHT AIR DATA COMPUTER. REALIZING THAT THE FAILURES WERE PROBABLY CAUSED BY DEICE FLUID, I DIDN'T KNOW WHETHER OR NOT TO TRUST THE STANDBY ALTIMETER AND AIRSPD, SO I KEPT A CLBING ATTITUDE. WE TOLD DEP THAT WE HAD ALTIMETER PROBS AND THAT WE HAD TO COME BACK IMMEDIATELY. CTLR SAID HE SHOWED US AT 11500'. HE THUS CONFIRMED BOTH THE VALIDITY OF OUR STANDBY ALTIMETER AND THAT WE HAD OVERSHOT OUR ALT. SINCE, DURING THE FAILURE, OUR ALTIMETER SHOWED 3 DIFFERENT ALTS, IT WAS IMPOSSIBLE TO DETERMINE WHICH WAS THE RIGHT ONE UNTIL WE COULD CONFIRM ONE OF THEM WITH ATC.

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.