B757 wake turbulence separation behind B747.

Attributes
ACN	328568
Time
Date	199602
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lax
State Reference	CA
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : takeoff ground : holding
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : takeoff
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	328568
Person 2
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Our flight was cleared to position and hold behind a B747-400, to expect immediate departure, we responded, 'we'll need 2 mins.' tower controller asked us to taxi down runway to first exit to get back in line. We arrived in line behind another B747-400. Note, it took 3 mins to get a plane airborne after we cleared. We were again cleared to position to expect immediate. We again requested 2 mins. Tower said, 'I can only give you 1 1/2 min, I can't do 2 mins.' we asked his initials, he declined, however, we sat in position for 4 mins, and created an unsafe situation. This action cost my company 8 mins. Concerned passenger created an unsafe situation, and it was not unrealistic of the crew to request this separation. 2 distinct factors were involved. We were restr to 2000 ft which could have created an encounter. If an engine failed on takeoff we may also have encountered wake vortex or turbulence. The extraordinary climb performance of the B757 cannot be used as a reason to disregard this dangerous threat.

Original NASA ASRS Text

Title: B757 WAKE TURB SEPARATION BEHIND B747.

Narrative: OUR FLT WAS CLRED TO POS AND HOLD BEHIND A B747-400, TO EXPECT IMMEDIATE DEP, WE RESPONDED, 'WE'LL NEED 2 MINS.' TWR CTLR ASKED US TO TAXI DOWN RWY TO FIRST EXIT TO GET BACK IN LINE. WE ARRIVED IN LINE BEHIND ANOTHER B747-400. NOTE, IT TOOK 3 MINS TO GET A PLANE AIRBORNE AFTER WE CLRED. WE WERE AGAIN CLRED TO POS TO EXPECT IMMEDIATE. WE AGAIN REQUESTED 2 MINS. TWR SAID, 'I CAN ONLY GIVE YOU 1 1/2 MIN, I CAN'T DO 2 MINS.' WE ASKED HIS INITIALS, HE DECLINED, HOWEVER, WE SAT IN POS FOR 4 MINS, AND CREATED AN UNSAFE SIT. THIS ACTION COST MY COMPANY 8 MINS. CONCERNED PAX CREATED AN UNSAFE SIT, AND IT WAS NOT UNREALISTIC OF THE CREW TO REQUEST THIS SEPARATION. 2 DISTINCT FACTORS WERE INVOLVED. WE WERE RESTR TO 2000 FT WHICH COULD HAVE CREATED AN ENCOUNTER. IF AN ENG FAILED ON TKOF WE MAY ALSO HAVE ENCOUNTERED WAKE VORTEX OR TURB. THE EXTRAORDINARY CLB PERFORMANCE OF THE B757 CANNOT BE USED AS A REASON TO DISREGARD THIS DANGEROUS THREAT.

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.