A B747-400 captain experienced unusual trim requirements during the climbout. A review of the flight...

Narrative:

During climb I felt the aircraft needed more trim inputs than usual. At level off I decided to check the maintenance display page for flight controls to make sure the trim settings and spoiler positions were normal. That is when I discovered that the aileron wheel input showed 29.4 units of aileron wheel to the right. Maintenance control and dispatch were consulted. The flight deck crewmembers; dispatch; and maintenance agreed that the safest thing to do was to return to our departure airport. Fuel was dumped enroute and we made an uneventful landing at about 626;000 pounds. Fuel jettison began at XA30Z at FL320 [and] fuel jettison terminated at XB15Z at FL230.

Original NASA ASRS Text

Title: A B747-400 Captain experienced unusual trim requirements during the climbout. A review of the Flight Control EICAS display page revealed the existence of 29.4 units of right aileron trim. After dumping fuel the flight returned to their departure airport for maintenance.

Narrative: During climb I felt the aircraft needed more trim inputs than usual. At level off I decided to check the maintenance display page for flight controls to make sure the trim settings and spoiler positions were normal. That is when I discovered that the aileron wheel input showed 29.4 units of aileron wheel to the right. Maintenance Control and Dispatch were consulted. The flight deck crewmembers; Dispatch; and Maintenance agreed that the safest thing to do was to return to our departure airport. Fuel was dumped enroute and we made an uneventful landing at about 626;000 LBS. Fuel jettison began at XA30Z at FL320 [and] fuel jettison terminated at XB15Z at FL230.

Data retrieved from NASA's ASRS site as of July 2013 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	988663
Time
Date	201201
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZZ.ARTCC
State Reference	FO
Aircraft 1
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Aileron Trim System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 160 Flight Crew Total 22500 Flight Crew Type 8700
Events
Anomaly	Aircraft Equipment Problem Critical

A B747-400 captain experienced unusual trim requirements during the climbout. A review of the flight control EICAS display page revealed the existence of 29.4 units of right aileron trim. After dumping fuel the flight returned to their departure airport for maintenance.