Narrative:

I just scared the bleep out of myself. I am a past member of an E120 propeller overspd committee. One of the opinions of that committee was that experienced pilots (in the E120) would not unknowingly move the power levers below flight idle in-flight. I have just changed my opinion. It is well known and agreed that moving the lower levers below flight idle in-flight will cause an immediate propeller overspd. If not corrected within 1-2 seconds it will lead to destruction of the power section. This is an extremely serious event. As such, a flight idle interlock solenoid system has been retrofitted into all E120's. There is also an airworthiness directive for the pilots to check this system's circuit breakers daily. Now for the incident that scared me. We were on 10 mi final to sfo runway 28R. We were on normal descent profile. I was a little fast (maybe 10 KTS) so I reduced power to flight idle, and unconsciously pulled up on the power lever flight idle releases. As soon as I did it, I realized what my hands were doing and pushed the power levers forward. The power levers moved above flight idle with an audible click. Once in the gate I checked the circuit breakers and tested the system. It worked. I was surprised to find it allowed the power levers to move fractionally below flight idle. There have been numerous problems (hence the daily circuit breaker check airworthiness directive) with the flight idle solenoid interlocks. A more positive flight idle gating system is needed. The only thing standing between me and disaster today was my quick realization of what I'd done and a temperamental interlock system. And I'm much more cognizant of the danger than the average line pilot. Callback conversation with reporter revealed the following information: the reporter felt the catastrophic consequences of a propeller runaway/engine destruction called for greater design protection than currently exists. Because of the customary use of the reverse on landing roll and during taxiing and because of the comfortable position associated with the fingers around release lever it would easily be foreseeable that a pilot would inadvertently move the reverse lock lever at idle while in-flight as a result of reflexive muscle memory. If the flight interlock were failed the propeller would run away. Embraer mechanics do checks that require pulling the air/ground sensor circuit breaker. With that circuit breaker pulled the flight interlock circuit breaker may pop. There is a procedure to check that circuit breaker through a viewing window. Even so, in the last 1000 hours the reporter has experienced 3 interlock system failures. The reporter was not sure of the scenarios that cause the flight interlock circuit breaker to pop or the reasons the flight interlock solenoid would fail, but, all too often the protection is not working.

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Original NASA ASRS Text

Title: RPTR INADVERTENTLY ACTUATED PROP FLT IDLE INTERLOCK SYS.

Narrative: I JUST SCARED THE BLEEP OUT OF MYSELF. I AM A PAST MEMBER OF AN E120 PROP OVERSPD COMMITTEE. ONE OF THE OPINIONS OF THAT COMMITTEE WAS THAT EXPERIENCED PLTS (IN THE E120) WOULD NOT UNKNOWINGLY MOVE THE PWR LEVERS BELOW FLT IDLE INFLT. I HAVE JUST CHANGED MY OPINION. IT IS WELL KNOWN AND AGREED THAT MOVING THE LOWER LEVERS BELOW FLT IDLE INFLT WILL CAUSE AN IMMEDIATE PROP OVERSPD. IF NOT CORRECTED WITHIN 1-2 SECONDS IT WILL LEAD TO DESTRUCTION OF THE PWR SECTION. THIS IS AN EXTREMELY SERIOUS EVENT. AS SUCH, A FLT IDLE INTERLOCK SOLENOID SYS HAS BEEN RETROFITTED INTO ALL E120'S. THERE IS ALSO AN AIRWORTHINESS DIRECTIVE FOR THE PLTS TO CHK THIS SYS'S CIRCUIT BREAKERS DAILY. NOW FOR THE INCIDENT THAT SCARED ME. WE WERE ON 10 MI FINAL TO SFO RWY 28R. WE WERE ON NORMAL DSCNT PROFILE. I WAS A LITTLE FAST (MAYBE 10 KTS) SO I REDUCED PWR TO FLT IDLE, AND UNCONSCIOUSLY PULLED UP ON THE PWR LEVER FLT IDLE RELEASES. AS SOON AS I DID IT, I REALIZED WHAT MY HANDS WERE DOING AND PUSHED THE PWR LEVERS FORWARD. THE PWR LEVERS MOVED ABOVE FLT IDLE WITH AN AUDIBLE CLICK. ONCE IN THE GATE I CHKED THE CIRCUIT BREAKERS AND TESTED THE SYS. IT WORKED. I WAS SURPRISED TO FIND IT ALLOWED THE PWR LEVERS TO MOVE FRACTIONALLY BELOW FLT IDLE. THERE HAVE BEEN NUMEROUS PROBS (HENCE THE DAILY CIRCUIT BREAKER CHK AIRWORTHINESS DIRECTIVE) WITH THE FLT IDLE SOLENOID INTERLOCKS. A MORE POSITIVE FLT IDLE GATING SYS IS NEEDED. THE ONLY THING STANDING BTWN ME AND DISASTER TODAY WAS MY QUICK REALIZATION OF WHAT I'D DONE AND A TEMPERAMENTAL INTERLOCK SYS. AND I'M MUCH MORE COGNIZANT OF THE DANGER THAN THE AVERAGE LINE PLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FELT THE CATASTROPHIC CONSEQUENCES OF A PROP RUNAWAY/ENG DESTRUCTION CALLED FOR GREATER DESIGN PROTECTION THAN CURRENTLY EXISTS. BECAUSE OF THE CUSTOMARY USE OF THE REVERSE ON LNDG ROLL AND DURING TAXIING AND BECAUSE OF THE COMFORTABLE POS ASSOCIATED WITH THE FINGERS AROUND RELEASE LEVER IT WOULD EASILY BE FORESEEABLE THAT A PLT WOULD INADVERTENTLY MOVE THE REVERSE LOCK LEVER AT IDLE WHILE INFLT AS A RESULT OF REFLEXIVE MUSCLE MEMORY. IF THE FLT INTERLOCK WERE FAILED THE PROP WOULD RUN AWAY. EMBRAER MECHS DO CHKS THAT REQUIRE PULLING THE AIR/GND SENSOR CIRCUIT BREAKER. WITH THAT CIRCUIT BREAKER PULLED THE FLT INTERLOCK CIRCUIT BREAKER MAY POP. THERE IS A PROC TO CHK THAT CIRCUIT BREAKER THROUGH A VIEWING WINDOW. EVEN SO, IN THE LAST 1000 HRS THE RPTR HAS EXPERIENCED 3 INTERLOCK SYS FAILURES. THE RPTR WAS NOT SURE OF THE SCENARIOS THAT CAUSE THE FLT INTERLOCK CIRCUIT BREAKER TO POP OR THE REASONS THE FLT INTERLOCK SOLENOID WOULD FAIL, BUT, ALL TOO OFTEN THE PROTECTION IS NOT WORKING.

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.