A B747-400 encounters wake turbulence following an A340 4.5 miles ahead on an ILS.

Attributes
ACN	811031
Time
Date	200811
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : vhhh.airport
State Reference	FO
Altitude	msl single value : 1500
Aircraft 1
Controlling Facilities	tower : frg.tower
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 07l
Route In Use	approach : instrument precision
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : vhhh.tower
Make Model Name	A340
Flight Phase	descent : approach
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 16000 flight time type : 2500
ASRS Report	811031
Events
Anomaly	inflight encounter : wake turbulence
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment
Supplementary
Problem Areas	Environmental Factor ATC Human Performance
Primary Problem	Ambiguous

Narrative:

We intercepted the runway 7L final at about 6 miles and shortly thereafter encountered at least 2 instances of strong wake turbulence from the preceding A340 4.5 NM ahead of us. It took 3/4 aileron and corresponding rudder to keep the aircraft under control. Even still; the aircraft banked significantly. We informed ATC but they claimed that we had 'legal' separation. This is the second time in 2 weeks that I have encountered wake turbulence on approach to hkg.

Original NASA ASRS Text

Title: A B747-400 ENCOUNTERS WAKE TURBULENCE FOLLOWING AN A340 4.5 MILES AHEAD ON AN ILS.

Narrative: WE INTERCEPTED THE RWY 7L FINAL AT ABOUT 6 MILES AND SHORTLY THEREAFTER ENCOUNTERED AT LEAST 2 INSTANCES OF STRONG WAKE TURBULENCE FROM THE PRECEDING A340 4.5 NM AHEAD OF US. IT TOOK 3/4 AILERON AND CORRESPONDING RUDDER TO KEEP THE ACFT UNDER CONTROL. EVEN STILL; THE ACFT BANKED SIGNIFICANTLY. WE INFORMED ATC BUT THEY CLAIMED THAT WE HAD 'LEGAL' SEPARATION. THIS IS THE SECOND TIME IN 2 WEEKS THAT I HAVE ENCOUNTERED WAKE TURBULENCE ON APPROACH TO HKG.

Data retrieved from NASA's ASRS site as of May 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.