Narrative:

Upon trying to level off at 5000 ft MSL, I told the captain that was I unable to hold the nose of the aircraft down. Exerting full forward pressure on control yoke, the captain tried his primary pitch control to no avail and then the secondary. Neither had an effect on the controls. After another attempt on the secondary trim the captain was able to reduce the nose trim from 8 units up to 6 units up. Still full force was needed to keep the nose down. Captain then took control of the aircraft, I declared an emergency and requested an immediate return to the airport. After receiving vectors for runway 22L at ord, captain called for flaps 9 degrees then gear, flaps 22 degrees, then flaps 95 degrees on schedule. As the airload on the aircraft was reduced more control was gained. At approximately xa:30 we landed without incident on runway 22L. As far as I know, both primary pitch control switches, the secondary pitch control system and the horizontal stabilizer control unit (hscu) are being replaced. I believe at touchdown, we had somewhere around 5 units of nose up trim.callback conversation with reporter revealed the following information: the reporter stated neither primary nor secondary stabilizer trim operated to correct nose up condition. The reporter said this airplane is new and was reported having stabilizer trim problems in the nose down direction two days prior to this event. The reporter said the corrective action taken in that event is unknown. The reporter stated on the ground maintenance could duplicate the report and replaced the primary and secondary actuators and a horizontal stabilizer control unit with no success. The reporter said the jack screw assembly with gearbox was replaced with two more actuators and the actuators were found burned out. The reporter stated a third set of actuators was replaced with the same result and only a fourth set of primary and secondary actuators corrected the problem. The reporter said to his knowledge there have been no other stabilizer problems on the fleet other than this airplane. The reporter said the circuit breakers were checked and found not tripped.supplemental information from acn 464061: departed ord runway 22L, first officer was flying. As we approached 5000 ft he stated that he was having trouble getting the nose down. I tried to trim it from 8 degrees nose up with my primary pitch trim and was unsuccessful. I then tried the secondary pitch trim and was also unsuccessful on the first few attempts. After some trying I was able to get it down to 6 degrees nose up with the secondary pitch trim. At that time I took control of the aircraft and we declared an emergency. I reduced thrust and as we approached 200 KTS I asked for flaps 9 degrees. Then gear and flaps 22 degrees, as we slowed and the aerodynamic load decreased, the aircraft became more controllable. On approach I was able to get the trim to around 4 degrees or so. The data recorder will probably give more information on that. We landed flaps 45 degrees with no problem and taxied in. Takeoff weight was 39471 pounds so we did not make an overweight landing. Pulled cvr circuit breaker prior to leaving aircraft.callback conversation with reporter revealed the following information: after landing the crew reported that all trim functions returned to normal. The aircraft was removed from service by the air carrier and remained grounded for over three days. During troubleshooting, three separate primary horizontal stabilizer control units and three separate secondary horizontal stabilizer control units were used in order to find units which would operate successfully with each other. The reporter questions the aircraft design which allows no direct control of something as critical as aircraft pitch trim. The captain has heard of other similar problems with the aircraft. The crews pulled and reset various aircraft circuit breakers to restore the trim system. This procedure is not authorized.

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Original NASA ASRS Text

Title: AN EMBRAER 145 AT LEVELOFF AT 5000 FT DECLARED AN EMER AND DIVERTED DUE TO UNABLE TO TRIM THE ACFT NOSE DOWN CAUSED BY STABILIZER TRIM ACTUATORS' FAILURE.

Narrative: UPON TRYING TO LEVEL OFF AT 5000 FT MSL, I TOLD THE CAPT THAT WAS I UNABLE TO HOLD THE NOSE OF THE ACFT DOWN. EXERTING FULL FORWARD PRESSURE ON CTL YOKE, THE CAPT TRIED HIS PRIMARY PITCH CTL TO NO AVAIL AND THEN THE SECONDARY. NEITHER HAD AN EFFECT ON THE CTLS. AFTER ANOTHER ATTEMPT ON THE SECONDARY TRIM THE CAPT WAS ABLE TO REDUCE THE NOSE TRIM FROM 8 UNITS UP TO 6 UNITS UP. STILL FULL FORCE WAS NEEDED TO KEEP THE NOSE DOWN. CAPT THEN TOOK CTL OF THE ACFT, I DECLARED AN EMER AND REQUESTED AN IMMEDIATE RETURN TO THE ARPT. AFTER RECEIVING VECTORS FOR RWY 22L AT ORD, CAPT CALLED FOR FLAPS 9 DEGS THEN GEAR, FLAPS 22 DEGS, THEN FLAPS 95 DEGS ON SCHEDULE. AS THE AIRLOAD ON THE ACFT WAS REDUCED MORE CTL WAS GAINED. AT APPROX XA:30 WE LANDED WITHOUT INCIDENT ON RWY 22L. AS FAR AS I KNOW, BOTH PRIMARY PITCH CTL SWITCHES, THE SECONDARY PITCH CTL SYS AND THE HORIZONTAL STABILIZER CTL UNIT (HSCU) ARE BEING REPLACED. I BELIEVE AT TOUCHDOWN, WE HAD SOMEWHERE AROUND 5 UNITS OF NOSE UP TRIM.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED NEITHER PRIMARY NOR SECONDARY STABILIZER TRIM OPERATED TO CORRECT NOSE UP CONDITION. THE RPTR SAID THIS AIRPLANE IS NEW AND WAS RPTED HAVING STABILIZER TRIM PROBS IN THE NOSE DOWN DIRECTION TWO DAYS PRIOR TO THIS EVENT. THE RPTR SAID THE CORRECTIVE ACTION TAKEN IN THAT EVENT IS UNKNOWN. THE RPTR STATED ON THE GND MAINT COULD DUPLICATE THE RPT AND REPLACED THE PRIMARY AND SECONDARY ACTUATORS AND A HORIZONTAL STABILIZER CTL UNIT WITH NO SUCCESS. THE RPTR SAID THE JACK SCREW ASSEMBLY WITH GEARBOX WAS REPLACED WITH TWO MORE ACTUATORS AND THE ACTUATORS WERE FOUND BURNED OUT. THE RPTR STATED A THIRD SET OF ACTUATORS WAS REPLACED WITH THE SAME RESULT AND ONLY A FOURTH SET OF PRIMARY AND SECONDARY ACTUATORS CORRECTED THE PROB. THE RPTR SAID TO HIS KNOWLEDGE THERE HAVE BEEN NO OTHER STABILIZER PROBS ON THE FLEET OTHER THAN THIS AIRPLANE. THE RPTR SAID THE CIRCUIT BREAKERS WERE CHECKED AND FOUND NOT TRIPPED.SUPPLEMENTAL INFO FROM ACN 464061: DEPARTED ORD RWY 22L, FO WAS FLYING. AS WE APCHED 5000 FT HE STATED THAT HE WAS HAVING TROUBLE GETTING THE NOSE DOWN. I TRIED TO TRIM IT FROM 8 DEGS NOSE UP WITH MY PRIMARY PITCH TRIM AND WAS UNSUCCESSFUL. I THEN TRIED THE SECONDARY PITCH TRIM AND WAS ALSO UNSUCCESSFUL ON THE FIRST FEW ATTEMPTS. AFTER SOME TRYING I WAS ABLE TO GET IT DOWN TO 6 DEGS NOSE UP WITH THE SECONDARY PITCH TRIM. AT THAT TIME I TOOK CTL OF THE ACFT AND WE DECLARED AN EMER. I REDUCED THRUST AND AS WE APCHED 200 KTS I ASKED FOR FLAPS 9 DEGS. THEN GEAR AND FLAPS 22 DEGS, AS WE SLOWED AND THE AERODYNAMIC LOAD DECREASED, THE ACFT BECAME MORE CONTROLLABLE. ON APCH I WAS ABLE TO GET THE TRIM TO AROUND 4 DEGS OR SO. THE DATA RECORDER WILL PROBABLY GIVE MORE INFO ON THAT. WE LANDED FLAPS 45 DEGS WITH NO PROB AND TAXIED IN. TKOF WEIGHT WAS 39471 POUNDS SO WE DID NOT MAKE AN OVERWEIGHT LNDG. PULLED CVR CIRCUIT BREAKER PRIOR TO LEAVING ACFT.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: AFTER LNDG THE CREW RPTED THAT ALL TRIM FUNCTIONS RETURNED TO NORMAL. THE ACFT WAS REMOVED FROM SVC BY THE ACR AND REMAINED GROUNDED FOR OVER THREE DAYS. DURING TROUBLESHOOTING, THREE SEPARATE PRIMARY HORIZONTAL STAB CTL UNITS AND THREE SEPARATE SECONDARY HORIZONTAL STAB CTL UNITS WERE USED IN ORDER TO FIND UNITS WHICH WOULD OPERATE SUCCESSFULLY WITH EACH OTHER. THE RPTR QUESTIONS THE ACFT DESIGN WHICH ALLOWS NO DIRECT CTL OF SOMETHING AS CRITICAL AS ACFT PITCH TRIM. THE CAPT HAS HEARD OF OTHER SIMILAR PROBS WITH THE ACFT. THE CREWS PULLED AND RESET VARIOUS ACFT CIRCUIT BREAKERS TO RESTORE THE TRIM SYS. THIS PROC IS NOT AUTHORIZED.

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.