Narrative:

Jammed stabilizer. After arriving at aircraft, the first officer completed the initial checks, including both primary and alternate trim checks. I set the initial center of gravity and trim settings and noted that the primary trim was operation. After taxiing we were number 3 for departure behind an air carrier B757. I requested and took a 2 minute delay behind that aircraft. The first officer hand flew the takeoff and departure without the autoplt engaged through 10000 ft without incident. While lowering the nose to accelerate and climb at approximately 300 KTS, the first officer noted the primary trim inoperative and asked me to check my switches. I confirmed that my switches and the suitcase handles were also inoperative and told him to level at 13000 ft and slow the aircraft. I advised departure control we had a problem and needed to stop the climb and check the system and would advise. While I was reaching for the flight manual checklist, the first officer slowed the aircraft to approximately 270 KTS. The first officer then advised me that the trim was working again. I told him that it might have been some dirt on a contact and we decided to continue. Because the trim system regained function, I then advised ATC that we would continue. ATC issued a climb clearance and turn for an on course heading. As the first officer applied power, accelerated and initiated a climb, he said the trim quit working again. At that time, I determined that the aircraft was experiencing a flight control problem possibly in the trim system and decided to rtn to ZZZ. I told the first officer that he had the aircraft and I advised ATC that we had a flight control problem and were declaring an emergency and needed vectors to return for landing. After making a PA and advising the flight attendants of the situation, I started a jammed stabilizer checklist. As instructed by the checklist, I checked the alternate trim system, which worked in the forward position but not in the aft position. And then did not work at all. I checked with the first officer to see how the aircraft felt. He could tell it was out of trim but stated that he could handle it. I noted that he had good control of the aircraft. Based on that observation I decided he would continue to fly the aircraft without interruption. I took the radios and checklist and the workload became heavy for me. ATC had frequent radio calls for heading, altitude, speed, and frequency changes. That interrupted my work. While I was complying with the checklist the first officer was able to regain primary trim but only for a few seconds. In addition, when I checked the primary, neither it nor the alternate was working. At one point while I was running the jammed stabilizer checklist, the first officer engaged the autoplt. It immediately tripped off and we felt the flight bump and saw a flashing red autoplt light. This occurred at about the same time during the checklist procedure that states if the alternate trim is inoperative do not engage the autoplt. I advised the first officer not to use the autoplt. At this point I stopped running the jammed stabilizer checklist and advised ATC that we needed about 5 or 10 minutes to complete our work and would be ready to land. I then ran the before landing checklist and set out slat/flap landing bugs. I discussed this with the first officer noting that we did not have the full jammed stabilizer situation: the aircraft was flying and although we had some control pressures, the flying was manageable. We discussed the flap settings for landing. I was considering 40 degree flaps but the first officer wanted 28 degree because he had excellent control I agreed to 28 degree flaps for landing. I decided however, that if after selecting landing flaps the control pressures were too great, we would go back into the jammed stabilizer checklist and reset our bugs accordingly. We agreed on this and if no adverse pressure was encountered the approach would be hand flow by the first officer as a normal flap 28 degree approach to landing. I then went back into the jammed stabilizer checklist to check the circuit breakers for both trims while the first officer requested slats extended and slowed to approximately 210 KTS. The first officer then said the aircraft seemed to be in trim for 210 KTS. We noted this and advised ATC that we were ready for vectors for the approach. While vectoring, ATC asked if we had the airport and wanted to give us a visual. I decided negative on the visual and stated we wanted vectors to final. After line up with final and on localizer/GS, gear and flaps set for landing, descending through 1500 ft AGL, I asked the first officer how it felt. He said it was nose heavy but it was manageable. Deciding that continuing the approach with a manageable aircraft rather than undertaking further trim attempts that may have uncertain results, I advised against any further trimming. Noting that we were stable we continued for a normal landing. I set medium automatic brakes which we had briefed earlier. I noted that his selected speed was reference plus five KTS. I decided to increase the speed up 5 KTS to reference plus 10 or 12. He agreed and we continued to a normal landing. I would like to note several items that may need to be reconsidered with reference to the jammed stabilizer checklist. First, contrary to the checklist, continued flying with one trim system inoperative is inadvisable and may be risky. For example, if the stabilizer is not jammed and one of the trim system inoperative, the checklist advises continued flight. I do not think this is prudent. If the only remaining operable system fails, an avoidable situation becomes a critical situation. Second, there is nothing in our checklists that specifically addresses trim failure. I believe that a trim failure checklist should be included in the flight manual and should advise landing the aircraft if either system has failed. Finally, to prevent the pilot from incorrectly assuming that the alternate trim system has failed, I would recommend including a note in all checklists that calls for checking the alternate trim to hold the alternate trim switches 5 to 7 seconds for confirmation of operation. Because the alternate trim motor operates at a much slower rate than the primary trim motor, the slower response time may be interpreted as a failure when in fact the system is operating. It should be noted that during my emergency situation I was aware of this requirement and held the switch for a sufficient amount of time. However, a note in the checklist would ensure that this requirement is fulfilled.

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Original NASA ASRS Text

Title: MD80 CREW HAD BOTH STABILIZER TRIM SYS BECOME INOP.

Narrative: JAMMED STABILIZER. AFTER ARRIVING AT ACFT, THE FO COMPLETED THE INITIAL CHECKS, INCLUDING BOTH PRIMARY AND ALTERNATE TRIM CHECKS. I SET THE INITIAL CENTER OF GRAVITY AND TRIM SETTINGS AND NOTED THAT THE PRIMARY TRIM WAS OP. AFTER TAXIING WE WERE NUMBER 3 FOR DEP BEHIND AN ACR B757. I REQUESTED AND TOOK A 2 MINUTE DELAY BEHIND THAT ACFT. THE FO HAND FLEW THE TKOF AND DEP WITHOUT THE AUTOPLT ENGAGED THROUGH 10000 FT WITHOUT INCIDENT. WHILE LOWERING THE NOSE TO ACCELERATE AND CLB AT APPROX 300 KTS, THE FO NOTED THE PRIMARY TRIM INOP AND ASKED ME TO CHECK MY SWITCHES. I CONFIRMED THAT MY SWITCHES AND THE SUITCASE HANDLES WERE ALSO INOP AND TOLD HIM TO LEVEL AT 13000 FT AND SLOW THE ACFT. I ADVISED DEP CTL WE HAD A PROB AND NEEDED TO STOP THE CLB AND CHECK THE SYS AND WOULD ADVISE. WHILE I WAS REACHING FOR THE FLT MANUAL CHECKLIST, THE FO SLOWED THE ACFT TO APPROX 270 KTS. THE FO THEN ADVISED ME THAT THE TRIM WAS WORKING AGAIN. I TOLD HIM THAT IT MIGHT HAVE BEEN SOME DIRT ON A CONTACT AND WE DECIDED TO CONTINUE. BECAUSE THE TRIM SYS REGAINED FUNCTION, I THEN ADVISED ATC THAT WE WOULD CONTINUE. ATC ISSUED A CLB CLRNC AND TURN FOR AN ON COURSE HDG. AS THE FO APPLIED PWR, ACCELERATED AND INITIATED A CLB, HE SAID THE TRIM QUIT WORKING AGAIN. AT THAT TIME, I DETERMINED THAT THE ACFT WAS EXPERIENCING A FLT CTL PROB POSSIBLY IN THE TRIM SYS AND DECIDED TO RTN TO ZZZ. I TOLD THE FO THAT HE HAD THE ACFT AND I ADVISED ATC THAT WE HAD A FLT CTL PROB AND WERE DECLARING AN EMER AND NEEDED VECTORS TO RETURN FOR LNDG. AFTER MAKING A PA AND ADVISING THE FLT ATTENDANTS OF THE SIT, I STARTED A JAMMED STABILIZER CHECKLIST. AS INSTRUCTED BY THE CHECKLIST, I CHECKED THE ALTERNATE TRIM SYS, WHICH WORKED IN THE FORWARD POS BUT NOT IN THE AFT POS. AND THEN DID NOT WORK AT ALL. I CHECKED WITH THE FO TO SEE HOW THE ACFT FELT. HE COULD TELL IT WAS OUT OF TRIM BUT STATED THAT HE COULD HANDLE IT. I NOTED THAT HE HAD GOOD CTL OF THE ACFT. BASED ON THAT OBSERVATION I DECIDED HE WOULD CONTINUE TO FLY THE ACFT WITHOUT INTERRUPTION. I TOOK THE RADIOS AND CHECKLIST AND THE WORKLOAD BECAME HVY FOR ME. ATC HAD FREQUENT RADIO CALLS FOR HDG, ALT, SPD, AND FREQ CHANGES. THAT INTERRUPTED MY WORK. WHILE I WAS COMPLYING WITH THE CHECKLIST THE FO WAS ABLE TO REGAIN PRIMARY TRIM BUT ONLY FOR A FEW SECONDS. IN ADDITION, WHEN I CHECKED THE PRIMARY, NEITHER IT NOR THE ALTERNATE WAS WORKING. AT ONE POINT WHILE I WAS RUNNING THE JAMMED STABILIZER CHECKLIST, THE FO ENGAGED THE AUTOPLT. IT IMMEDIATELY TRIPPED OFF AND WE FELT THE FLT BUMP AND SAW A FLASHING RED AUTOPLT LIGHT. THIS OCCURRED AT ABOUT THE SAME TIME DURING THE CHECKLIST PROC THAT STATES IF THE ALTERNATE TRIM IS INOP DO NOT ENGAGE THE AUTOPLT. I ADVISED THE FO NOT TO USE THE AUTOPLT. AT THIS POINT I STOPPED RUNNING THE JAMMED STABILIZER CHECKLIST AND ADVISED ATC THAT WE NEEDED ABOUT 5 OR 10 MINUTES TO COMPLETE OUR WORK AND WOULD BE READY TO LAND. I THEN RAN THE BEFORE LNDG CHECKLIST AND SET OUT SLAT/FLAP LNDG BUGS. I DISCUSSED THIS WITH THE FO NOTING THAT WE DID NOT HAVE THE FULL JAMMED STABILIZER SIT: THE ACFT WAS FLYING AND ALTHOUGH WE HAD SOME CTL PRESSURES, THE FLYING WAS MANAGEABLE. WE DISCUSSED THE FLAP SETTINGS FOR LNDG. I WAS CONSIDERING 40 DEG FLAPS BUT THE FO WANTED 28 DEG BECAUSE HE HAD EXCELLENT CTL I AGREED TO 28 DEG FLAPS FOR LNDG. I DECIDED HOWEVER, THAT IF AFTER SELECTING LNDG FLAPS THE CTL PRESSURES WERE TOO GREAT, WE WOULD GO BACK INTO THE JAMMED STABILIZER CHECKLIST AND RESET OUR BUGS ACCORDINGLY. WE AGREED ON THIS AND IF NO ADVERSE PRESSURE WAS ENCOUNTERED THE APCH WOULD BE HAND FLOW BY THE FO AS A NORMAL FLAP 28 DEG APCH TO LNDG. I THEN WENT BACK INTO THE JAMMED STABILIZER CHECKLIST TO CHECK THE CIRCUIT BREAKERS FOR BOTH TRIMS WHILE THE FO REQUESTED SLATS EXTENDED AND SLOWED TO APPROX 210 KTS. THE FO THEN SAID THE ACFT SEEMED TO BE IN TRIM FOR 210 KTS. WE NOTED THIS AND ADVISED ATC THAT WE WERE READY FOR VECTORS FOR THE APCH. WHILE VECTORING, ATC ASKED IF WE HAD THE ARPT AND WANTED TO GIVE US A VISUAL. I DECIDED NEGATIVE ON THE VISUAL AND STATED WE WANTED VECTORS TO FINAL. AFTER LINE UP WITH FINAL AND ON LOC/GS, GEAR AND FLAPS SET FOR LNDG, DESCENDING THROUGH 1500 FT AGL, I ASKED THE FO HOW IT FELT. HE SAID IT WAS NOSE HVY BUT IT WAS MANAGEABLE. DECIDING THAT CONTINUING THE APCH WITH A MANAGEABLE ACFT RATHER THAN UNDERTAKING FURTHER TRIM ATTEMPTS THAT MAY HAVE UNCERTAIN RESULTS, I ADVISED AGAINST ANY FURTHER TRIMMING. NOTING THAT WE WERE STABLE WE CONTINUED FOR A NORMAL LNDG. I SET MEDIUM AUTO BRAKES WHICH WE HAD BRIEFED EARLIER. I NOTED THAT HIS SELECTED SPD WAS REF PLUS FIVE KTS. I DECIDED TO INCREASE THE SPD UP 5 KTS TO REFERENCE PLUS 10 OR 12. HE AGREED AND WE CONTINUED TO A NORMAL LNDG. I WOULD LIKE TO NOTE SEVERAL ITEMS THAT MAY NEED TO BE RECONSIDERED WITH REFERENCE TO THE JAMMED STABILIZER CHECKLIST. FIRST, CONTRARY TO THE CHECKLIST, CONTINUED FLYING WITH ONE TRIM SYS INOP IS INADVISABLE AND MAY BE RISKY. FOR EXAMPLE, IF THE STABILIZER IS NOT JAMMED AND ONE OF THE TRIM SYS INOP, THE CHECKLIST ADVISES CONTINUED FLT. I DO NOT THINK THIS IS PRUDENT. IF THE ONLY REMAINING OPERABLE SYS FAILS, AN AVOIDABLE SIT BECOMES A CRITICAL SIT. SECOND, THERE IS NOTHING IN OUR CHECKLISTS THAT SPECIFICALLY ADDRESSES TRIM FAILURE. I BELIEVE THAT A TRIM FAILURE CHECKLIST SHOULD BE INCLUDED IN THE FLT MANUAL AND SHOULD ADVISE LNDG THE ACFT IF EITHER SYS HAS FAILED. FINALLY, TO PREVENT THE PLT FROM INCORRECTLY ASSUMING THAT THE ALTERNATE TRIM SYS HAS FAILED, I WOULD RECOMMEND INCLUDING A NOTE IN ALL CHECKLISTS THAT CALLS FOR CHECKING THE ALTERNATE TRIM TO HOLD THE ALTERNATE TRIM SWITCHES 5 TO 7 SECONDS FOR CONFIRMATION OF OP. BECAUSE THE ALTERNATE TRIM MOTOR OPERATES AT A MUCH SLOWER RATE THAN THE PRIMARY TRIM MOTOR, THE SLOWER RESPONSE TIME MAY BE INTERPRETED AS A FAILURE WHEN IN FACT THE SYS IS OPERATING. IT SHOULD BE NOTED THAT DURING MY EMER SIT I WAS AWARE OF THIS REQUIREMENT AND HELD THE SWITCH FOR A SUFFICIENT AMOUNT OF TIME. HOWEVER, A NOTE IN THE CHECKLIST WOULD ENSURE THAT THIS REQUIREMENT IS FULFILLED.

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.