<< >> NASA ASRS Report 696056, May 2006

MD80 flight crew has the autoflt system (autoplt; autothrottles) malfunction at cruise and aircraft departs altitude.

Attributes
ACN	696056
Time
Date	200605
Local Time Of Day	0601 To 1200
Place
Locale Reference	intersection : maxxo
State Reference	NM
Altitude	msl bound lower : 34700 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab.artcc tower : zzz.tower
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	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	696056
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	696055
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

Had climbed to FL350 and just received clearance nearing gup VOR to go direct to txo VOR. Shortly after that at about 1.5 hours of flight; the aircraft was engaged to autoplt #1 in altitude hold; and began a descent and the autothrottles rolled back to the low limit. The autoplt was disengaged and then the autothrottles and the aircraft was recovered to level flight at FL350. The aircraft had lost 300-500 ft during this uncommanded descent. No call was received from ATC. The autoplt was re-engaged and altitude hold on the #1 system tried and worked ok. The #2 autoplt and altitude hold were selected and the flight continued in rvsm airspace. Aircraft was reported to maintenance and logbook entry made. The aircraft had a similar maintenance entry for autoplt #1 that had been cleared.

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Original NASA ASRS Text

Title: MD80 FLT CREW HAS THE AUTOFLT SYS (AUTOPLT; AUTOTHROTTLES) MALFUNCTION AT CRUISE AND ACFT DEPARTS ALT.

Narrative: HAD CLBED TO FL350 AND JUST RECEIVED CLRNC NEARING GUP VOR TO GO DIRECT TO TXO VOR. SHORTLY AFTER THAT AT ABOUT 1.5 HRS OF FLT; THE ACFT WAS ENGAGED TO AUTOPLT #1 IN ALT HOLD; AND BEGAN A DSCNT AND THE AUTOTHROTTLES ROLLED BACK TO THE LOW LIMIT. THE AUTOPLT WAS DISENGAGED AND THEN THE AUTOTHROTTLES AND THE ACFT WAS RECOVERED TO LEVEL FLT AT FL350. THE ACFT HAD LOST 300-500 FT DURING THIS UNCOMMANDED DSCNT. NO CALL WAS RECEIVED FROM ATC. THE AUTOPLT WAS RE-ENGAGED AND ALT HOLD ON THE #1 SYS TRIED AND WORKED OK. THE #2 AUTOPLT AND ALT HOLD WERE SELECTED AND THE FLT CONTINUED IN RVSM AIRSPACE. ACFT WAS RPTED TO MAINT AND LOGBOOK ENTRY MADE. THE ACFT HAD A SIMILAR MAINT ENTRY FOR AUTOPLT #1 THAT HAD BEEN CLRED.

Data retrieved from NASA's ASRS site as of January 2009 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.