Narrative:

Aircraft was not de-iced in cvg prior to departure. Pre-takeoff control checks were normal. Aircraft encountered visible moisture with a ram air temperature of less than 10 degrees C during most of the climb to FL370. The crew operated the engine anti-ice system. Aircraft was in VMC on top of all cloud layers at FL370. While at cruise at FL370, the crew noticed periodic small altitude deviations of +/- 10 ft with the autoplt engaged in VNAV mode. A check of the sat revealed the temperature fluctuating between -62 and -63 degrees C, however, the period of the altitude oscillations did not match the period of the temperature changes. The altitude deviations began to increase in amplitude. Crew observed the ap trim light on the FMA and a constantly moving trim indicator on the pedestal. The trim indicator movement bracketed an approximately trim setting of zero. As the autoplt was correcting from an excursion of approximately 100 ft, the captain (PF) manually disconnected the autoplt. PF noted that the elevator feel was very stiff and almost unresponsive to input. Before PF could exert enough press on the control column to reverse the upward trend of the aircraft's nose, an altitude deviation of approximately +250 ft occurred. When the PF attempted to adjust the aircraft pitch so as to affect a level-off at FL370, the same stiffness and unresponsive feel as when the yoke was pushed forward was noted when the PF pulled aft on the control column. The PF was unable to raise the aircraft nose before the aircraft descended again below FL370. At captain's direction, the first officer (PNF) requested and received a clearance from ATC to descend to FL330. During this descent, the PF successfully employed the primary trim switches on the yoke to assist with pitch control. Also during this descent, the captain established a 2000 FPM rate of descent and turned control of the aircraft over to the first officer. The captain directed him to shallow the descent to 1000 FPM. At this time, the first officer confirmed the stiffness and unresponsiveness of the controls. The captain took control of the aircraft again. The captain evaluated potential divert fields. Based on the elevator feel, a requirement for a substantial length of runway was established. ZZZ was chosen as a divert field because of its proximity to the aircraft and the length of the available runways. The captain directed the first officer to declare an emergency, and announce our intention to divert to ZZZ because of our flight control problems. ATC queried us as to whether or not we would be able to maintain altitude. PNF responded in the affirmative. We turned towards ZZZ and initiated a gradual descent, complying with ATC instructions. Current WX at ZZZ was evaluated and found to be satisfactory. Crew requested that emergency equipment be made available at ZZZ. At the transition from mach to indicated airspeed, PF conducted the descent at 280 KIAS. As the aircraft descended and slowed, the elevator feel became more responsive. Approach and landing were conducted without further incident. Callback conversation with reporter revealed the following information: reporter stated that he received no information from the company as to the cause of the elevator problem. Reporter advised that there was no indication of an elevator control problem on pre-takeoff check or during the climb, but that the elevator was slow to respond and felt stiffer than normal after the autoplt was disengaged. Reporter stated that the elevator controls regained normal feel and responsiveness by the time the aircraft was slowed for approach. Reporter stated that he has not encountered this problem prior to , or after this incident. Follow up conversation with reporter on revealed the following information: reporter stated that the only thing that he has heard from his company was that sometimes nothing is found by the maintenance department in the case of incidents such as he reported. Reporter stated that he assumed this was the case with the control problem he reported and that he has had no further contact with the company regarding the matter.

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Original NASA ASRS Text

Title: MD88 ABNORMAL ELEVATOR CTL RESPONSE.

Narrative: ACFT WAS NOT DE-ICED IN CVG PRIOR TO DEP. PRE-TKOF CTL CHECKS WERE NORMAL. ACFT ENCOUNTERED VISIBLE MOISTURE WITH A RAM AIR TEMP OF LESS THAN 10 DEGS C DURING MOST OF THE CLB TO FL370. THE CREW OPERATED THE ENG ANTI-ICE SYS. ACFT WAS IN VMC ON TOP OF ALL CLOUD LAYERS AT FL370. WHILE AT CRUISE AT FL370, THE CREW NOTICED PERIODIC SMALL ALTITUDE DEVIATIONS OF +/- 10 FT WITH THE AUTOPLT ENGAGED IN VNAV MODE. A CHECK OF THE SAT REVEALED THE TEMP FLUCTUATING BTWN -62 AND -63 DEGS C, HOWEVER, THE PERIOD OF THE ALT OSCILLATIONS DID NOT MATCH THE PERIOD OF THE TEMP CHANGES. THE ALT DEVIATIONS BEGAN TO INCREASE IN AMPLITUDE. CREW OBSERVED THE AP TRIM LIGHT ON THE FMA AND A CONSTANTLY MOVING TRIM INDICATOR ON THE PEDESTAL. THE TRIM INDICATOR MOVEMENT BRACKETED AN APPROX TRIM SETTING OF ZERO. AS THE AUTOPLT WAS CORRECTING FROM AN EXCURSION OF APPROX 100 FT, THE CAPT (PF) MANUALLY DISCONNECTED THE AUTOPLT. PF NOTED THAT THE ELEVATOR FEEL WAS VERY STIFF AND ALMOST UNRESPONSIVE TO INPUT. BEFORE PF COULD EXERT ENOUGH PRESS ON THE CTL COLUMN TO REVERSE THE UPWARD TREND OF THE ACFT'S NOSE, AN ALT DEVIATION OF APPROX +250 FT OCCURRED. WHEN THE PF ATTEMPTED TO ADJUST THE ACFT PITCH SO AS TO AFFECT A LEVEL-OFF AT FL370, THE SAME STIFFNESS AND UNRESPONSIVE FEEL AS WHEN THE YOKE WAS PUSHED FORWARD WAS NOTED WHEN THE PF PULLED AFT ON THE CTL COLUMN. THE PF WAS UNABLE TO RAISE THE ACFT NOSE BEFORE THE ACFT DSNDED AGAIN BELOW FL370. AT CAPT'S DIRECTION, THE FO (PNF) REQUESTED AND RECEIVED A CLRNC FROM ATC TO DSND TO FL330. DURING THIS DSCNT, THE PF SUCCESSFULLY EMPLOYED THE PRIMARY TRIM SWITCHES ON THE YOKE TO ASSIST WITH PITCH CTL. ALSO DURING THIS DSCNT, THE CAPT ESTABLISHED A 2000 FPM RATE OF DSCNT AND TURNED CTL OF THE ACFT OVER TO THE FO. THE CAPT DIRECTED HIM TO SHALLOW THE DSCNT TO 1000 FPM. AT THIS TIME, THE FO CONFIRMED THE STIFFNESS AND UNRESPONSIVENESS OF THE CTLS. THE CAPT TOOK CTL OF THE ACFT AGAIN. THE CAPT EVALUATED POTENTIAL DIVERT FIELDS. BASED ON THE ELEVATOR FEEL, A REQUIREMENT FOR A SUBSTANTIAL LENGTH OF RWY WAS ESTABLISHED. ZZZ WAS CHOSEN AS A DIVERT FIELD BECAUSE OF ITS PROXIMITY TO THE ACFT AND THE LENGTH OF THE AVAILABLE RWYS. THE CAPT DIRECTED THE FO TO DECLARE AN EMER, AND ANNOUNCE OUR INTENTION TO DIVERT TO ZZZ BECAUSE OF OUR FLT CTL PROBLEMS. ATC QUERIED US AS TO WHETHER OR NOT WE WOULD BE ABLE TO MAINTAIN ALT. PNF RESPONDED IN THE AFFIRMATIVE. WE TURNED TOWARDS ZZZ AND INITIATED A GRADUAL DSCNT, COMPLYING WITH ATC INSTRUCTIONS. CURRENT WX AT ZZZ WAS EVALUATED AND FOUND TO BE SATISFACTORY. CREW REQUESTED THAT EMER EQUIP BE MADE AVAILABLE AT ZZZ. AT THE TRANSITION FROM MACH TO INDICATED AIRSPEED, PF CONDUCTED THE DSCNT AT 280 KIAS. AS THE ACFT DSNDED AND SLOWED, THE ELEVATOR FEEL BECAME MORE RESPONSIVE. APCH AND LNDG WERE CONDUCTED WITHOUT FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE RECEIVED NO INFO FROM THE COMPANY AS TO THE CAUSE OF THE ELEVATOR PROB. RPTR ADVISED THAT THERE WAS NO INDICATION OF AN ELEVATOR CTL PROB ON PRE-TKOF CHK OR DURING THE CLB, BUT THAT THE ELEVATOR WAS SLOW TO RESPOND AND FELT STIFFER THAN NORMAL AFTER THE AUTOPLT WAS DISENGAGED. RPTR STATED THAT THE ELEVATOR CTLS REGAINED NORMAL FEEL AND RESPONSIVENESS BY THE TIME THE ACFT WAS SLOWED FOR APCH. RPTR STATED THAT HE HAS NOT ENCOUNTERED THIS PROB PRIOR TO , OR AFTER THIS INCIDENT. FOLLOW UP CONVERSATION WITH RPTR ON REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ONLY THING THAT HE HAS HEARD FROM HIS COMPANY WAS THAT SOMETIMES NOTHING IS FOUND BY THE MAINT DEPT IN THE CASE OF INCIDENTS SUCH AS HE RPTED. RPTR STATED THAT HE ASSUMED THIS WAS THE CASE WITH THE CTL PROB HE RPTED AND THAT HE HAS HAD NO FURTHER CONTACT WITH THE COMPANY REGARDING THE MATTER.

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.