Narrative:

Initial startup was normal. After clearance and taxi instructions received; experienced slight odor in the cabin attendant; which we thought was exhaust through the open window. During pretkof engine checks noticed signs of smoke from under the console. Switched off all electrical equipment other than 1 radio and notified ground control of our problem requesting taxi back to parking. The smoke increased and having reported this to ground control I shut down the aircraft on the taxiway. Subsequent examination revealed a faulty gear system pump. Callback conversation with reporter revealed the following information: reporter stated this aircraft has a retractable gear that uses a dc power gear system pump. Normally; when the selector switch is positioned to 'on;' the gear pump provides hydraulic pressure and relays will open at a predetermined time and disconnect dc power to the pump. However; in this case; according to maintenance; the selector switch relays shorted to continuous 'on.' this caused the pump to overheat and started smoking. Reporter also stated; this was not a little smoke; but rather a substantial cloud that engulfed the cockpit. With the pump selector switch shorted to 'on' and the pump running continuously on dc power; with no way to shut the pump off; he had to shut all power down. Reporter added; he does not know if this gear pump selector switch has been a problem in the past for this type aircraft.

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Original NASA ASRS Text

Title: A CESSNA-210 CENTURION PILOT DURING PRE-TAKEOFF ENGINE CHECKS; NOTICED SIGNS OF SMOKE FROM UNDER THE INSTRUMENT CONSOLE.

Narrative: INITIAL STARTUP WAS NORMAL. AFTER CLRNC AND TAXI INSTRUCTIONS RECEIVED; EXPERIENCED SLIGHT ODOR IN THE CAB; WHICH WE THOUGHT WAS EXHAUST THROUGH THE OPEN WINDOW. DURING PRETKOF ENG CHKS NOTICED SIGNS OF SMOKE FROM UNDER THE CONSOLE. SWITCHED OFF ALL ELECTRICAL EQUIP OTHER THAN 1 RADIO AND NOTIFIED GND CTL OF OUR PROB REQUESTING TAXI BACK TO PARKING. THE SMOKE INCREASED AND HAVING RPTED THIS TO GND CTL I SHUT DOWN THE ACFT ON THE TXWY. SUBSEQUENT EXAM REVEALED A FAULTY GEAR SYS PUMP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THIS ACFT HAS A RETRACTABLE GEAR THAT USES A DC POWER GEAR SYSTEM PUMP. NORMALLY; WHEN THE SELECTOR SWITCH IS POSITIONED TO 'ON;' THE GEAR PUMP PROVIDES HYD PRESSURE AND RELAYS WILL OPEN AT A PREDETERMINED TIME AND DISCONNECT DC POWER TO THE PUMP. HOWEVER; IN THIS CASE; ACCORDING TO MAINT; THE SELECTOR SWITCH RELAYS SHORTED TO CONTINUOUS 'ON.' THIS CAUSED THE PUMP TO OVERHEAT AND STARTED SMOKING. REPORTER ALSO STATED; THIS WAS NOT A LITTLE SMOKE; BUT RATHER A SUBSTANTIAL CLOUD THAT ENGULFED THE COCKPIT. WITH THE PUMP SELECTOR SWITCH SHORTED TO 'ON' AND THE PUMP RUNNING CONTINUOUSLY ON DC POWER; WITH NO WAY TO SHUT THE PUMP OFF; HE HAD TO SHUT ALL POWER DOWN. REPORTER ADDED; HE DOES NOT KNOW IF THIS GEAR PUMP SELECTOR SWITCH HAS BEEN A PROBLEM IN THE PAST FOR THIS TYPE ACFT.

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.