B727 crew has trim malfunction which causes aircraft to lose altitude in rvsm airspace.

Attributes
ACN	719659
Time
Date	200612
Local Time Of Day	0001 To 0600
Place
Locale Reference	navaid : psb.vortac
State Reference	PA
Altitude	msl single value : 31000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	B727-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 8000 flight time type : 1700
ASRS Report	719659
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial
Experience	flight time last 90 days : 50 flight time total : 12800 flight time type : 400
ASRS Report	719658
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

While in cruise flight in rvsm airspace; autoplt began trimming nose down and started slow descent. When autoplt was disconnected; aircraft pitched down and approximately 300 ft altitude loss occurred. Notified ATC of autoplt problem and requested departure from rvsm airspace. ATC cleared us to FL270. Remainder of flight uneventful.supplemental information from reporter acn 719658: autoplt was disconnected and manually returned to FL310. Heavy control forces were necessary to overcome during maneuver.callback conversation with reporter acn 719659 revealed the following information: the reporter stated the cruise trim motor was not disengaging at the moment trim inputs ceased; causing the trim to coast past the desired set point. This characteristic became rather cumbersome during approach. The crew decided to hand fly the aircraft and make manual trim inputs via the trim wheel. This still did not work well but after a little practice; they were able to fly an approach to a normal landing. The cruise trim motor problem was discovered by maintenance during troubleshooting.

Original NASA ASRS Text

Title: B727 CREW HAS TRIM MALFUNCTION WHICH CAUSES ACFT TO LOSE ALT IN RVSM AIRSPACE.

Narrative: WHILE IN CRUISE FLT IN RVSM AIRSPACE; AUTOPLT BEGAN TRIMMING NOSE DOWN AND STARTED SLOW DSCNT. WHEN AUTOPLT WAS DISCONNECTED; ACFT PITCHED DOWN AND APPROX 300 FT ALT LOSS OCCURRED. NOTIFIED ATC OF AUTOPLT PROB AND REQUESTED DEP FROM RVSM AIRSPACE. ATC CLRED US TO FL270. REMAINDER OF FLT UNEVENTFUL.SUPPLEMENTAL INFO FROM RPTR ACN 719658: AUTOPLT WAS DISCONNECTED AND MANUALLY RETURNED TO FL310. HVY CTL FORCES WERE NECESSARY TO OVERCOME DURING MANEUVER.CALLBACK CONVERSATION WITH RPTR ACN 719659 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CRUISE TRIM MOTOR WAS NOT DISENGAGING AT THE MOMENT TRIM INPUTS CEASED; CAUSING THE TRIM TO COAST PAST THE DESIRED SET POINT. THIS CHARACTERISTIC BECAME RATHER CUMBERSOME DURING APCH. THE CREW DECIDED TO HAND FLY THE ACFT AND MAKE MANUAL TRIM INPUTS VIA THE TRIM WHEEL. THIS STILL DID NOT WORK WELL BUT AFTER A LITTLE PRACTICE; THEY WERE ABLE TO FLY AN APCH TO A NORMAL LNDG. THE CRUISE TRIM MOTOR PROB WAS DISCOVERED BY MAINT DURING TROUBLESHOOTING.

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.