B737-300 crew expressed concern about wake turbulence following a B747 in IMC for runway 24R in lax ...

Attributes
ACN	511351
Time
Date	200105
Day	Thu
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : sct.tracon
State Reference	CA
Altitude	msl single value : 4000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 75 flight time total : 12000 flight time type : 7000
ASRS Report	511351
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	inflight encounter : wake turbulence inflight encounter : weather
Independent Detector	aircraft equipment other aircraft equipment : fmc wind readout other flight crewa other flight crewb
Resolutory Action	controller : issued advisory flight crew : took precautionary avoidance action
Consequence	other
Supplementary
Problem Areas	ATC Human Performance FAA
Primary Problem	ATC Human Performance
Situations
ATC Facility	procedure or policy : sct.tracon

Narrative:

The flight was arriving in lax. The WX was overcast at the airport, but VMC on final. The controller slowed us to 170 KTS and announced we would be following a B747. We had the traffic pointed out to us as he turned from downwind to final in front of us. Approach gave us a speed reduction to 150 KTS while still on a long final (approximately 16 mi). Realizing the B747 was configured and slow, I was concerned that he would be producing a strong jet wash. If I'm slow, I would be at a less than ideal speed to counter his vortices since I would be configured. I requested s-turns to the north for spacing instead of the speed adjustment, which was denied. The controller's options were to slow or receive a breakout and resequence. I considered flying high on the ILS GS, but since there was a 10 KT tailwind, I was concerned I'd have to 'unspool' on short final as I broke out of the overcast. I did not want to be slow, low, unspooled and then encounter jet wash. I am uncomfortable being placed behind a heavy with minimum required spacing and having the controllers using minimum speeds to effect this required distance. The required statement issued by ATC to 'use caution, following a heavy' seems a bit useless and ineffective when it would appear my only option at this point was a 'breakout.' I would consider 5 mi behind a heavy adequate as long as I can maintain 170 KTS.

Original NASA ASRS Text

Title: B737-300 CREW EXPRESSED CONCERN ABOUT WAKE TURB FOLLOWING A B747 IN IMC FOR RWY 24R IN LAX CLASS B AIRSPACE.

Narrative: THE FLT WAS ARRIVING IN LAX. THE WX WAS OVCST AT THE ARPT, BUT VMC ON FINAL. THE CTLR SLOWED US TO 170 KTS AND ANNOUNCED WE WOULD BE FOLLOWING A B747. WE HAD THE TFC POINTED OUT TO US AS HE TURNED FROM DOWNWIND TO FINAL IN FRONT OF US. APCH GAVE US A SPD REDUCTION TO 150 KTS WHILE STILL ON A LONG FINAL (APPROX 16 MI). REALIZING THE B747 WAS CONFIGURED AND SLOW, I WAS CONCERNED THAT HE WOULD BE PRODUCING A STRONG JET WASH. IF I'M SLOW, I WOULD BE AT A LESS THAN IDEAL SPD TO COUNTER HIS VORTICES SINCE I WOULD BE CONFIGURED. I REQUESTED S-TURNS TO THE N FOR SPACING INSTEAD OF THE SPD ADJUSTMENT, WHICH WAS DENIED. THE CTLR'S OPTIONS WERE TO SLOW OR RECEIVE A BREAKOUT AND RESEQUENCE. I CONSIDERED FLYING HIGH ON THE ILS GS, BUT SINCE THERE WAS A 10 KT TAILWIND, I WAS CONCERNED I'D HAVE TO 'UNSPOOL' ON SHORT FINAL AS I BROKE OUT OF THE OVCST. I DID NOT WANT TO BE SLOW, LOW, UNSPOOLED AND THEN ENCOUNTER JET WASH. I AM UNCOMFORTABLE BEING PLACED BEHIND A HVY WITH MINIMUM REQUIRED SPACING AND HAVING THE CTLRS USING MINIMUM SPDS TO EFFECT THIS REQUIRED DISTANCE. THE REQUIRED STATEMENT ISSUED BY ATC TO 'USE CAUTION, FOLLOWING A HVY' SEEMS A BIT USELESS AND INEFFECTIVE WHEN IT WOULD APPEAR MY ONLY OPTION AT THIS POINT WAS A 'BREAKOUT.' I WOULD CONSIDER 5 MI BEHIND A HVY ADEQUATE AS LONG AS I CAN MAINTAIN 170 KTS.

Data retrieved from NASA's ASRS site as of July 2007 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.

B737-300 crew expressed concern about wake turbulence following a B747 in IMC for runway 24R in lax class B airspace.