Narrative:

At FL310 we started a descent to FL260. At a descent rate of 2000-3000 FPM; and initial power setting of approximately 50%; both airspeed indicators read the same and showed an abnormal decrease that did not correlate with the current aircraft confign. At this point; wind noise in the cockpit had risen and helped confirm that both airspeed indications were erroneous. Power was reduced to idle and the aircraft was leveled off. Shortly thereafter; the speed tape on the captain's side jumped suddenly and had a significantly higher value than the first officer's. At that time the high speed alert sounded. As we began a descent to 13000 ft; the autoplt disconnected and we received an associated autoplt failure message on the EICAS. The message quickly disappeared; however. It was shortly after this time that the cockpit started to fill with smoke; originating from underneath the instrument panel. Memory items and appropriate checklists were performed. An emergency was declared and we proceeded directly to ZZZ. The smoke lasted less than 5 mins and had cleared before we landed visually. Callback conversation with reporter revealed the following information: reporter stated that he attempted to determine what caused the equipment failures and smoke but was unable. The last time he flew this aircraft; the log page covering this event had already been replaced because the book was beyond 60 days. He said the air carrier also played down the incident and so did not send respond.

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Original NASA ASRS Text

Title: AN EMB135 DECLARES AN EMER FOLLOWING ERRONEOUS AIRSPDS; UNCOMMANDED AUTOPLT DISCONNECT; AND FINALLY INST PANEL SMOKE.

Narrative: AT FL310 WE STARTED A DSCNT TO FL260. AT A DSCNT RATE OF 2000-3000 FPM; AND INITIAL PWR SETTING OF APPROX 50%; BOTH AIRSPD INDICATORS READ THE SAME AND SHOWED AN ABNORMAL DECREASE THAT DID NOT CORRELATE WITH THE CURRENT ACFT CONFIGN. AT THIS POINT; WIND NOISE IN THE COCKPIT HAD RISEN AND HELPED CONFIRM THAT BOTH AIRSPD INDICATIONS WERE ERRONEOUS. PWR WAS REDUCED TO IDLE AND THE ACFT WAS LEVELED OFF. SHORTLY THEREAFTER; THE SPD TAPE ON THE CAPT'S SIDE JUMPED SUDDENLY AND HAD A SIGNIFICANTLY HIGHER VALUE THAN THE FO'S. AT THAT TIME THE HIGH SPD ALERT SOUNDED. AS WE BEGAN A DSCNT TO 13000 FT; THE AUTOPLT DISCONNECTED AND WE RECEIVED AN ASSOCIATED AUTOPLT FAILURE MESSAGE ON THE EICAS. THE MESSAGE QUICKLY DISAPPEARED; HOWEVER. IT WAS SHORTLY AFTER THIS TIME THAT THE COCKPIT STARTED TO FILL WITH SMOKE; ORIGINATING FROM UNDERNEATH THE INST PANEL. MEMORY ITEMS AND APPROPRIATE CHKLISTS WERE PERFORMED. AN EMER WAS DECLARED AND WE PROCEEDED DIRECTLY TO ZZZ. THE SMOKE LASTED LESS THAN 5 MINS AND HAD CLRED BEFORE WE LANDED VISUALLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE ATTEMPTED TO DETERMINE WHAT CAUSED THE EQUIP FAILURES AND SMOKE BUT WAS UNABLE. THE LAST TIME HE FLEW THIS ACFT; THE LOG PAGE COVERING THIS EVENT HAD ALREADY BEEN REPLACED BECAUSE THE BOOK WAS BEYOND 60 DAYS. HE SAID THE ACR ALSO PLAYED DOWN THE INCIDENT AND SO DID NOT SEND RESPOND.

Data retrieved from NASA's ASRS site as of January 2009 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.