Failure of the autopilot stab trim system to correct airspeed deviations in turbulence contributed t...

Narrative:

Departed on part 121 flight and received a moderately choppy ride starting at about 16;000 ft. The autopilot was on and aircraft speed approached barber pole (uncommanded). Went to override; intending to slow aircraft to 280 KTS (per fom procedure for chop). As we continued to climb the aircraft trim motor was not responding to the autopilot inputs. The aircraft pitched up and slowed twenty-five knots below commanded speed and moving towards minimum clean speed. Amber autopiot trim light illuminated on FMA indicating the horizontal stab was out of trim. I attempted using the altitude long trim to assist the autopilot trim motor; but was unable to correct speed and marginally aided in lowering the pitch. Approaching assigned altitude of FL230 @ 2500FPM; I disconnected autopilot and leveled off manually and regained speed. Unfortunately; the captain and I neglected the climb check at 18;000 ft and as a result failed to set our altimeters to 29.92. We were queried by ATC and advised to check our altimeters. Although I do not believed separation was lost; we were 200 ft above our assigned altitude when queried. ATC did not advise us to phone or notify us of any loss of separation. The autopilot trim motor issue was a contributing factor to this deviation as was our distraction; as a crew; by missing the mandated climb checklist. I was focused on our airspeed; insuring that we did not stall; but simply overlooked the altimeter change. The MD88 does seem to have an issue with adequate trim authority during autopilot use; especially in the instance of configuration or speed changes near leveling off. However I've not found the instance that we encountered to be a typical of most of our MD88 fleet.

Original NASA ASRS Text

Title: Failure of the autopilot stab trim system to correct airspeed deviations in turbulence contributed to a MD88 flight crew's failure to reset their altimeters to QNE passing through FL180.

Narrative: Departed on Part 121 flight and received a moderately choppy ride starting at about 16;000 FT. The autopilot was on and aircraft speed approached barber pole (uncommanded). Went to override; intending to slow aircraft to 280 KTS (per FOM procedure for chop). As we continued to climb the aircraft trim motor was not responding to the autopilot inputs. The aircraft pitched up and slowed twenty-five knots below commanded speed and moving towards minimum clean speed. Amber autopiot trim light illuminated on FMA indicating the Horizontal Stab was out of trim. I attempted using the ALT LONG TRIM to assist the autopilot trim motor; but was unable to correct speed and marginally aided in lowering the pitch. Approaching assigned altitude of FL230 @ 2500FPM; I disconnected autopilot and leveled off manually and regained speed. Unfortunately; the Captain and I neglected the climb check at 18;000 FT and as a result failed to set our altimeters to 29.92. We were queried by ATC and advised to check our altimeters. Although I do not believed separation was lost; we were 200 FT above our assigned altitude when queried. ATC did not advise us to phone or notify us of any loss of separation. The autopilot trim motor issue was a contributing factor to this deviation as was our distraction; as a crew; by missing the mandated Climb Checklist. I was focused on our airspeed; insuring that we did not stall; but simply overlooked the altimeter change. The MD88 does seem to have an issue with adequate trim authority during autopilot use; especially in the instance of configuration or speed changes near leveling off. However I've not found the instance that we encountered to be a typical of most of our MD88 fleet.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	834731
Time
Date	200905
Local Time Of Day	1201-1800
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Horizontal Stabilizer Trim
Person 1
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 220 Flight Crew Total 5000 Flight Crew Type 1000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Speed All Types Inflight Event / Encounter Weather / Turbulence

Failure of the autopilot stab trim system to correct airspeed deviations in turbulence contributed to a MD88 flight crew's failure to reset their altimeters to qne passing through FL180.