A B777-222 reported a wake turbulence encounter on base leg behind a B747-400 at egll.

Attributes
ACN	859485
Time
Date	200911
Local Time Of Day	0601-1200
Place
Locale Reference	EGLL.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	B747-400
Flight Phase	Final Approach
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 80 Flight Crew Total 6000 Flight Crew Type 500
Events
Anomaly	Inflight Event / Encounter Wake Vortex Encounter

Narrative:

Wake vortex encounter while being vectored for the approach to runway 27L at egll. Ceiling was 100 broken; 1000 meters visibility; so we planned for a CAT III autoland. In clear; smooth air at FL050; while on base; we were vectored 4.5 miles behind a B747-400 that was landing on 27R. With the autopilot on; in a right 25 degree bank turn; the roll rate accelerated; and we went to about 35 degrees right bank. The first officer wanted me to disconnect the autopilot; which I was ready to do; but the autopilot was correcting for the bank excursion and it did remain engaged. We did report the wake encounter to ATC; and they asked if we were going to file a wake vortex encounter report. We said we were not. Although this was a significant encounter; it was at what I would define as the boundary of acceptable encounters.

Original NASA ASRS Text

Title: A B777-222 reported a wake turbulence encounter on base leg behind a B747-400 at EGLL.

Narrative: Wake vortex encounter while being vectored for the approach to Runway 27L at EGLL. Ceiling was 100 broken; 1000 meters visibility; so we planned for a CAT III autoland. In clear; smooth air at FL050; while on base; we were vectored 4.5 miles behind a B747-400 that was landing on 27R. With the autopilot on; in a right 25 degree bank turn; the roll rate accelerated; and we went to about 35 degrees right bank. The First Officer wanted me to disconnect the autopilot; which I was ready to do; but the autopilot was correcting for the bank excursion and it did remain engaged. We did report the wake encounter to ATC; and they asked if we were going to file a wake vortex encounter report. We said we were not. Although this was a significant encounter; it was at what I would define as the boundary of acceptable encounters.

Data retrieved from NASA's ASRS site as of April 2012 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.