Narrative:

Preflight was normal up to point where captain tested lights. Upon light test we discovered that the RAT green 'press' light would not illuminate. I called line maintenance and entered discrepancy into ACARS system. Within 5 mins mechanic arrived to troubleshoot. Captain and first officer remained in seats and continued preflight. Neither captain nor first officer touched the RAT switch. Mechanic pulled 1 circuit breaker on overhead panel and then attempted to remove the RAT switch/light. It was removed and inspected and mechanic determined that a new assembly would have to be installed. He reinserted the old assembly; and we noted the amber 'unlocked' light was on in the RAT switch; plus had an EICAS RAT deployed message. We expressed concern to the mechanic about inadvertent RAT deployment and also contacted maintenance control via dispatch to see if there were any additional steps to follow to prevent inadvertent RAT deployment. Maintenance control indicated there were 3 more circuit breakers to pull. Shortly after that another mechanic came to the cockpit and indicated that the RAT had already deployed. Despite being about 20 mins before scheduled pushback and having ramp personnel loading cargo in the aircraft; there were fortunately no people in the vicinity of the RAT when it inadvertently deployed. A new RAT switch assembly was found at the hangar and brought over for installation. The RAT was then restowed; and the flight departed about 1 hour late. Supplemental information from acn 790809: I asked the mechanic to be certain someone cleared the area for fear of an inadvertent deployment of RAT. He stopped and called down to be sure of this; but much later when the part arrived; he reinserted the (5IN) module; and this activated the unlock function...the RAT deployed. I would recommend that anytime the RAT is not functioning properly that someone be stationed near it; or at least have barriers set up to alert any ground crew from inadvertently stepping into the deployment path. I am of the impression that the gravity of the situation was not fully appreciated; and would further suggest a review of the danger of this element of the aircraft. I would commend the mechanic on his attempt to mitigate the time of delay; but am afraid this also led to a less than safe outcome.

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Original NASA ASRS Text

Title: A B777'S RAT WAS INADVERTENTLY DEPLOYED DURING GND MAINTENANCE BECAUSE OF INCORRECT PROCEDURES. NO MONITOR WAS NEAR THE RAT AREA TO CLR RAMP PERSONNEL.

Narrative: PREFLT WAS NORMAL UP TO POINT WHERE CAPT TESTED LIGHTS. UPON LIGHT TEST WE DISCOVERED THAT THE RAT GREEN 'PRESS' LIGHT WOULD NOT ILLUMINATE. I CALLED LINE MAINT AND ENTERED DISCREPANCY INTO ACARS SYS. WITHIN 5 MINS MECH ARRIVED TO TROUBLESHOOT. CAPT AND FO REMAINED IN SEATS AND CONTINUED PREFLT. NEITHER CAPT NOR FO TOUCHED THE RAT SWITCH. MECH PULLED 1 CIRCUIT BREAKER ON OVERHEAD PANEL AND THEN ATTEMPTED TO REMOVE THE RAT SWITCH/LIGHT. IT WAS REMOVED AND INSPECTED AND MECH DETERMINED THAT A NEW ASSEMBLY WOULD HAVE TO BE INSTALLED. HE REINSERTED THE OLD ASSEMBLY; AND WE NOTED THE AMBER 'UNLOCKED' LIGHT WAS ON IN THE RAT SWITCH; PLUS HAD AN EICAS RAT DEPLOYED MESSAGE. WE EXPRESSED CONCERN TO THE MECH ABOUT INADVERTENT RAT DEPLOYMENT AND ALSO CONTACTED MAINT CTL VIA DISPATCH TO SEE IF THERE WERE ANY ADDITIONAL STEPS TO FOLLOW TO PREVENT INADVERTENT RAT DEPLOYMENT. MAINT CTL INDICATED THERE WERE 3 MORE CIRCUIT BREAKERS TO PULL. SHORTLY AFTER THAT ANOTHER MECH CAME TO THE COCKPIT AND INDICATED THAT THE RAT HAD ALREADY DEPLOYED. DESPITE BEING ABOUT 20 MINS BEFORE SCHEDULED PUSHBACK AND HAVING RAMP PERSONNEL LOADING CARGO IN THE ACFT; THERE WERE FORTUNATELY NO PEOPLE IN THE VICINITY OF THE RAT WHEN IT INADVERTENTLY DEPLOYED. A NEW RAT SWITCH ASSEMBLY WAS FOUND AT THE HANGAR AND BROUGHT OVER FOR INSTALLATION. THE RAT WAS THEN RESTOWED; AND THE FLT DEPARTED ABOUT 1 HR LATE. SUPPLEMENTAL INFO FROM ACN 790809: I ASKED THE MECH TO BE CERTAIN SOMEONE CLRED THE AREA FOR FEAR OF AN INADVERTENT DEPLOYMENT OF RAT. HE STOPPED AND CALLED DOWN TO BE SURE OF THIS; BUT MUCH LATER WHEN THE PART ARRIVED; HE REINSERTED THE (5IN) MODULE; AND THIS ACTIVATED THE UNLOCK FUNCTION...THE RAT DEPLOYED. I WOULD RECOMMEND THAT ANYTIME THE RAT IS NOT FUNCTIONING PROPERLY THAT SOMEONE BE STATIONED NEAR IT; OR AT LEAST HAVE BARRIERS SET UP TO ALERT ANY GND CREW FROM INADVERTENTLY STEPPING INTO THE DEPLOYMENT PATH. I AM OF THE IMPRESSION THAT THE GRAVITY OF THE SITUATION WAS NOT FULLY APPRECIATED; AND WOULD FURTHER SUGGEST A REVIEW OF THE DANGER OF THIS ELEMENT OF THE ACFT. I WOULD COMMEND THE MECH ON HIS ATTEMPT TO MITIGATE THE TIME OF DELAY; BUT AM AFRAID THIS ALSO LED TO A LESS THAN SAFE OUTCOME.

Data retrieved from NASA's ASRS site as of May 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.