|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||0601 To 1200|
|Locale Reference||airport : zzz.airport|
|Altitude||msl single value : 28000|
|Controlling Facilities||artcc : zzz.artcc|
|Operator||common carrier : air carrier|
|Make Model Name||MD-80 Series (DC-9-80) Undifferentiated or Other Model|
|Operating Under FAR Part||Part 121|
|Flight Phase||cruise : level|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Anomaly||aircraft equipment problem : less severe|
|Independent Detector||other flight crewa|
|Resolutory Action||flight crew : overcame equipment problem|
Flight Crew Human Performance
Upon departure; autothrottle would not engage. Manually set power and continued takeoff. WX essentially cavu. Airborne; autoplt would also not engage. I was PF. Flew RNAV departure manually so as to troubleshoot outside of the terminal area. After center handoff and above 10000 ft; attempted to swap DFGS to #2 and had same result -- no autothrottle or autoplt. Continued climb. WX en route and at destination was VFR; so we advised ATC that we were going to stay out of rvsm airspace and we began troubleshooting after leveloff at FL280 (assigned). I xferred control to first officer and referenced QRH. The only procedure we have ever had or used for resetting the DFGS(south) is to cycle the 3 circuit breakers C17; C18; and C19 to reset the DFGS switching (it has worked in past per previous references). When I pulled C17 we had what felt like a full (restr travel) scale rudder deflection -- extreme yaw; and first officer had almost full opposite roll to counteract the aircraft roll from the rudder input. I immediately reset C17 and the yaw instantly ceased. I contacted maintenance. The first suggestion was to do exactly what I had done. When I told him about the yaw; he said that it was a known problem and that the autoplt was going into the test mode and severe rudder oscillations could occur. Needless to say; we abandoned that avenue of troubleshooting. I had maintenance put on alert and we hand flew the flight to its completion. Once on ground with passenger disembarked; we killed all power to the aircraft and re-powered all system. Both DFGS's reset and we regained use of autothrottle; autoplt. The problem is the potential for a sudden and unexpected rudder hard-over if either C17 is pulled or (and I don't know; but can assume) pops (the resulting loss of power would create the same scenario). Maintenance told me that this has happened before and yet in over 20 yrs of flying this aircraft; I had never heard of it. I suspect further research needs to be done and either a caution or warning needs to accompany the procedure not to pull the DFGS system switch circuit breakers if this is a possible result. Loss of control or a structural problem could result depending on airspeed/altitude/flight conditions. I spoke with chief pilot at the end of the work day and advised him of the anomaly. Callback conversation with reporter revealed the following information: it was determined after the event that this circuit breaker (C17) affects yaw damper operation in addition to DFGS switching and causes the rudder to deflect to the yaw damper limit of 2 degrees. The reporter has many years of experience on the MD80; and this procedure was carried over from his early training on the aircraft. Needless to say; it will not be used as an airborne procedure in the future. In the event that this circuit breaker popped on its own; normal QRH procedures would have led to turning of the yaw damper allowing the rudder to center.
Original NASA ASRS Text
Title: MD80 FLT CREW INDUCES RUDDER DEFLECTION AT FL280 ATTEMPTING TO RESET DFGS BY PULLING CIRCUIT BREAKERS.
Narrative: UPON DEP; AUTOTHROTTLE WOULD NOT ENGAGE. MANUALLY SET PWR AND CONTINUED TKOF. WX ESSENTIALLY CAVU. AIRBORNE; AUTOPLT WOULD ALSO NOT ENGAGE. I WAS PF. FLEW RNAV DEP MANUALLY SO AS TO TROUBLESHOOT OUTSIDE OF THE TERMINAL AREA. AFTER CTR HDOF AND ABOVE 10000 FT; ATTEMPTED TO SWAP DFGS TO #2 AND HAD SAME RESULT -- NO AUTOTHROTTLE OR AUTOPLT. CONTINUED CLB. WX ENRTE AND AT DEST WAS VFR; SO WE ADVISED ATC THAT WE WERE GOING TO STAY OUT OF RVSM AIRSPACE AND WE BEGAN TROUBLESHOOTING AFTER LEVELOFF AT FL280 (ASSIGNED). I XFERRED CTL TO FO AND REFED QRH. THE ONLY PROC WE HAVE EVER HAD OR USED FOR RESETTING THE DFGS(S) IS TO CYCLE THE 3 CIRCUIT BREAKERS C17; C18; AND C19 TO RESET THE DFGS SWITCHING (IT HAS WORKED IN PAST PER PREVIOUS REFS). WHEN I PULLED C17 WE HAD WHAT FELT LIKE A FULL (RESTR TRAVEL) SCALE RUDDER DEFLECTION -- EXTREME YAW; AND FO HAD ALMOST FULL OPPOSITE ROLL TO COUNTERACT THE ACFT ROLL FROM THE RUDDER INPUT. I IMMEDIATELY RESET C17 AND THE YAW INSTANTLY CEASED. I CONTACTED MAINT. THE FIRST SUGGESTION WAS TO DO EXACTLY WHAT I HAD DONE. WHEN I TOLD HIM ABOUT THE YAW; HE SAID THAT IT WAS A KNOWN PROB AND THAT THE AUTOPLT WAS GOING INTO THE TEST MODE AND SEVERE RUDDER OSCILLATIONS COULD OCCUR. NEEDLESS TO SAY; WE ABANDONED THAT AVENUE OF TROUBLESHOOTING. I HAD MAINT PUT ON ALERT AND WE HAND FLEW THE FLT TO ITS COMPLETION. ONCE ON GND WITH PAX DISEMBARKED; WE KILLED ALL PWR TO THE ACFT AND RE-POWERED ALL SYS. BOTH DFGS'S RESET AND WE REGAINED USE OF AUTOTHROTTLE; AUTOPLT. THE PROB IS THE POTENTIAL FOR A SUDDEN AND UNEXPECTED RUDDER HARD-OVER IF EITHER C17 IS PULLED OR (AND I DON'T KNOW; BUT CAN ASSUME) POPS (THE RESULTING LOSS OF PWR WOULD CREATE THE SAME SCENARIO). MAINT TOLD ME THAT THIS HAS HAPPENED BEFORE AND YET IN OVER 20 YRS OF FLYING THIS ACFT; I HAD NEVER HEARD OF IT. I SUSPECT FURTHER RESEARCH NEEDS TO BE DONE AND EITHER A CAUTION OR WARNING NEEDS TO ACCOMPANY THE PROC NOT TO PULL THE DFGS SYS SWITCH CIRCUIT BREAKERS IF THIS IS A POSSIBLE RESULT. LOSS OF CTL OR A STRUCTURAL PROB COULD RESULT DEPENDING ON AIRSPD/ALT/FLT CONDITIONS. I SPOKE WITH CHIEF PLT AT THE END OF THE WORK DAY AND ADVISED HIM OF THE ANOMALY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: IT WAS DETERMINED AFTER THE EVENT THAT THIS CIRCUIT BREAKER (C17) AFFECTS YAW DAMPER OPERATION IN ADDITION TO DFGS SWITCHING AND CAUSES THE RUDDER TO DEFLECT TO THE YAW DAMPER LIMIT OF 2 DEGREES. THE REPORTER HAS MANY YEARS OF EXPERIENCE ON THE MD80; AND THIS PROCEDURE WAS CARRIED OVER FROM HIS EARLY TRAINING ON THE ACFT. NEEDLESS TO SAY; IT WILL NOT BE USED AS AN AIRBORNE PROCEDURE IN THE FUTURE. IN THE EVENT THAT THIS CIRCUIT BREAKER POPPED ON ITS OWN; NORMAL QRH PROCEDURES WOULD HAVE LED TO TURNING OF THE YAW DAMPER ALLOWING THE RUDDER TO CENTER.
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.