Altitude deviation.

Attributes
ACN	307700
Time
Date	199506
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 7700 msl bound upper : 8000
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	307700
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Incident occurred under ord approach control. Autoplt on -- first officer flying. 8000 ft assigned altitude. Aircraft at 8400 ft and descending at 1500 FPM. Approach ordered left turn, slow 250 KTS to 210 KTS. Maneuver was initiated with 25 degree bank, then slats extended. Altitude capture was annunciated on FMA. Autoplt trim light came on at 8000 ft. Aircraft continued descent to approximately 7850 ft when captain ordered corrective action. First officer promptly initiated manual control climb autoplt off. Stopped descent at 7700 ft and climbed back to 8000 ft in approximately 15 seconds. ATC notified us to check altitude and reply was at 7800 ft and correcting to 8000 ft. Autoplt may have been at fault. Autoplt was normal after incident. The combination of bank, high gross weight, idle power, and slats extending exceeded autoplt trim capabilities even though all inputs were procedurally correct. I believe the prompt response by crew prevented more serious deviation. Ord TRACON was contacted by telephone and stated that they had no problem with incident. Crew was debriefed accordingly.

Original NASA ASRS Text

Title: ALTDEV.

Narrative: INCIDENT OCCURRED UNDER ORD APCH CTL. AUTOPLT ON -- FO FLYING. 8000 FT ASSIGNED ALT. ACFT AT 8400 FT AND DSNDING AT 1500 FPM. APCH ORDERED L TURN, SLOW 250 KTS TO 210 KTS. MANEUVER WAS INITIATED WITH 25 DEG BANK, THEN SLATS EXTENDED. ALT CAPTURE WAS ANNUNCIATED ON FMA. AUTOPLT TRIM LIGHT CAME ON AT 8000 FT. ACFT CONTINUED DSCNT TO APPROX 7850 FT WHEN CAPT ORDERED CORRECTIVE ACTION. FO PROMPTLY INITIATED MANUAL CTL CLB AUTOPLT OFF. STOPPED DSCNT AT 7700 FT AND CLBED BACK TO 8000 FT IN APPROX 15 SECONDS. ATC NOTIFIED US TO CHK ALT AND REPLY WAS AT 7800 FT AND CORRECTING TO 8000 FT. AUTOPLT MAY HAVE BEEN AT FAULT. AUTOPLT WAS NORMAL AFTER INCIDENT. THE COMBINATION OF BANK, HIGH GROSS WT, IDLE PWR, AND SLATS EXTENDING EXCEEDED AUTOPLT TRIM CAPABILITIES EVEN THOUGH ALL INPUTS WERE PROCEDURALLY CORRECT. I BELIEVE THE PROMPT RESPONSE BY CREW PREVENTED MORE SERIOUS DEV. ORD TRACON WAS CONTACTED BY TELEPHONE AND STATED THAT THEY HAD NO PROB WITH INCIDENT. CREW WAS DEBRIEFED ACCORDINGLY.

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.