An MD80 on approach at 5000 ft descended below assigned altitude in a turn due to autoplt pitch chan...

Attributes
ACN	464998
Time
Date	200003
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : pit.airport
State Reference	PA
Altitude	msl bound lower : 4400 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pit.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : holding
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : atp pilot : cfi pilot : commercial pilot : instrument pilot : private
Experience	flight time last 90 days : 50 flight time total : 4000 flight time type : 50
ASRS Report	464998
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude maintenance problem : non compliance with mel maintenance problem : improper maintenance non adherence : published procedure non adherence : far
Independent Detector	other controllera other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude
Consequence	other
Factors
Maintenance	contributing factor : manuals contributing factor : schedule pressure performance deficiency : logbook entry performance deficiency : testing performance deficiency : repair performance deficiency : non compliance with legal requirements
Supplementary
Problem Areas	Maintenance Human Performance Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

We lost altitude when autoplt would not hold altitude. Autoplt trim was MEL'ed inoperative. It was my first time flying with this MEL. I selected 30 degrees bank 'selector switch.' the autoplt commanded a 30 degree bank and then let the nose drop. Autoplt did have altitude capture annunciated. ATC gave us a large intercept angle to the approach and the aircraft rolled to the 30 degree bank immediately. With autoplt trim inoperative it could not maintain altitude. We had been manually trimming aircraft for climbs/dscnts (every time we would disconnect autoplt). Initially we lost 300 ft then 300 ft to recover. It caught me by surprise. I was busy reviewing approach plate confign, etc. Callback conversation with reporter revealed the following information: the reporter stated he only had 50 yrs experience on this airplane when this incident occurred. The reporter said the autoplt trim coupler was deferred as inoperative and manual trim was used the entire flight when needed and the autoplt was re-engaged after trimming. The reporter stated when approach control requested hold 5000 ft and a right turn to 270 degrees a turn with 30 degree bank angle was started with the autoplt. The reporter said while in the turn he was distraction looking for traffic when the nose dropped and 300 ft was lost and another 300 ft to regain control. The reporter said the autoplt made no nose up input while in the turn.

Original NASA ASRS Text

Title: AN MD80 ON APCH AT 5000 FT DSNDED BELOW ASSIGNED ALT IN A TURN DUE TO AUTOPLT PITCH CHANNEL MALFUNCTION.

Narrative: WE LOST ALT WHEN AUTOPLT WOULD NOT HOLD ALT. AUTOPLT TRIM WAS MEL'ED INOP. IT WAS MY FIRST TIME FLYING WITH THIS MEL. I SELECTED 30 DEGS BANK 'SELECTOR SWITCH.' THE AUTOPLT COMMANDED A 30 DEG BANK AND THEN LET THE NOSE DROP. AUTOPLT DID HAVE ALT CAPTURE ANNUNCIATED. ATC GAVE US A LARGE INTERCEPT ANGLE TO THE APCH AND THE ACFT ROLLED TO THE 30 DEG BANK IMMEDIATELY. WITH AUTOPLT TRIM INOP IT COULD NOT MAINTAIN ALT. WE HAD BEEN MANUALLY TRIMMING ACFT FOR CLBS/DSCNTS (EVERY TIME WE WOULD DISCONNECT AUTOPLT). INITIALLY WE LOST 300 FT THEN 300 FT TO RECOVER. IT CAUGHT ME BY SURPRISE. I WAS BUSY REVIEWING APCH PLATE CONFIGN, ETC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE ONLY HAD 50 YRS EXPERIENCE ON THIS AIRPLANE WHEN THIS INCIDENT OCCURRED. THE RPTR SAID THE AUTOPLT TRIM COUPLER WAS DEFERRED AS INOP AND MANUAL TRIM WAS USED THE ENTIRE FLT WHEN NEEDED AND THE AUTOPLT WAS RE-ENGAGED AFTER TRIMMING. THE RPTR STATED WHEN APCH CTL REQUESTED HOLD 5000 FT AND A R TURN TO 270 DEGS A TURN WITH 30 DEG BANK ANGLE WAS STARTED WITH THE AUTOPLT. THE RPTR SAID WHILE IN THE TURN HE WAS DISTR LOOKING FOR TFC WHEN THE NOSE DROPPED AND 300 FT WAS LOST AND ANOTHER 300 FT TO REGAIN CTL. THE RPTR SAID THE AUTOPLT MADE NO NOSE UP INPUT WHILE IN THE TURN.

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.

An MD80 on approach at 5000 ft descended below assigned altitude in a turn due to autoplt pitch channel malfunction.