|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1201 To 1800|
|Locale Reference||airport : mzt|
|Altitude||agl bound lower : 0|
agl bound upper : 0
|Controlling Facilities||tower : ryy|
|Operator||common carrier : air carrier|
|Make Model Name||Commercial Fixed Wing|
|Operating Under FAR Part||Part 121|
|Flight Phase||ground : preflight|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
|Experience||flight time last 90 days : 200|
flight time total : 20000
flight time type : 5000
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Qualification||pilot : commercial|
pilot : instrument
|Anomaly||aircraft equipment problem : less severe|
other anomaly other
|Independent Detector||other other : unspecified cockpit|
|Resolutory Action||flight crew : overcame equipment problem|
|Air Traffic Incident||other|
On ramp in mzt, mexico, first officer and I noticed autoplt switch on forward panel came 'on' uncommanded. We turned switch off only to have it come on again. Control wheel did rapid movement and was indeed locked onto autoplt as we were unable to move control wheel. We attempted to disconnect autoplt with control wheel button. Autoplt would stay off as long as button was depressed. Once button was released, autoplt came back on. Unable to disconnect autoplt except through circuit breakers to autoplt and flight guidance system. Callback conversation with reporter revealed the following information: reporter stated that their company technical representative from mcdonnell douglas said what he described could not have happened. After the technical representative was briefed by technicians, he said maybe it could happen. However, after they placed the defective autoplt control box into another aircraft, he finally became a believer. Analysis revealed that the coil in the autoplt's control box had shorted out locking the system on, even though the circuit breaker was popped open. The reporter was advised by the technical representative that if they would have been airborne, the control wheel would not have locked up, but could have been overridden.
Original NASA ASRS Text
Title: THE AUTOPLT CAME ON WITHOUT BEING TURNED ON BY THE FLC. THE AUTOPLT COULD NOT BE TURNED OFF IN THE NORMAL MANNER BUT ONLY WITH THE CIRCUIT BREAKER.
Narrative: ON RAMP IN MZT, MEXICO, FO AND I NOTICED AUTOPLT SWITCH ON FORWARD PANEL CAME 'ON' UNCOMMANDED. WE TURNED SWITCH OFF ONLY TO HAVE IT COME ON AGAIN. CTL WHEEL DID RAPID MOVEMENT AND WAS INDEED LOCKED ONTO AUTOPLT AS WE WERE UNABLE TO MOVE CTL WHEEL. WE ATTEMPTED TO DISCONNECT AUTOPLT WITH CTL WHEEL BUTTON. AUTOPLT WOULD STAY OFF AS LONG AS BUTTON WAS DEPRESSED. ONCE BUTTON WAS RELEASED, AUTOPLT CAME BACK ON. UNABLE TO DISCONNECT AUTOPLT EXCEPT THROUGH CIRCUIT BREAKERS TO AUTOPLT AND FLT GUIDANCE SYS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THEIR COMPANY TECHNICAL REPRESENTATIVE FROM MCDONNELL DOUGLAS SAID WHAT HE DESCRIBED COULD NOT HAVE HAPPENED. AFTER THE TECHNICAL REPRESENTATIVE WAS BRIEFED BY TECHNICIANS, HE SAID MAYBE IT COULD HAPPEN. HOWEVER, AFTER THEY PLACED THE DEFECTIVE AUTOPLT CTL BOX INTO ANOTHER ACFT, HE FINALLY BECAME A BELIEVER. ANALYSIS REVEALED THAT THE COIL IN THE AUTOPLT'S CTL BOX HAD SHORTED OUT LOCKING THE SYS ON, EVEN THOUGH THE CIRCUIT BREAKER WAS POPPED OPEN. THE RPTR WAS ADVISED BY THE TECHNICAL REPRESENTATIVE THAT IF THEY WOULD HAVE BEEN AIRBORNE, THE CTL WHEEL WOULD NOT HAVE LOCKED UP, BUT COULD HAVE BEEN OVERRIDDEN.
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.