A crew reports wake turbulence encounter near hln at FL340 from crossing B747 at FL350.

Attributes
ACN	709794
Time
Date	200609
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : hln.vortac
State Reference	MT
Altitude	msl single value : 34000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc.artcc artcc : zla.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute airway : j9.airway
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zlc.artcc
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	709794
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	inflight encounter : wake turbulence
Independent Detector	other flight crewa
Resolutory Action	none taken : insufficient time
Supplementary
Problem Areas	Airspace Structure ATC Human Performance Aircraft
Primary Problem	Airspace Structure

Narrative:

While cruising at FL340 observed crossing traffic at FL350. The traffic was approximately 10 miles ahead as observed on the TCAS. A few minutes later my aircraft encountered a sharp jolt of moderate intensity. I inquired with ATC what type of aircraft had crossed our path. ZLC said a boeing 747 1000 ft up. I told the controller that we had encountered moderate turbulence from the B747 and would have appreciated some notification of an impending traffic call especially a heavy. I also asked that the controller make a report per my event. At the time of the encounter; the air was smooth and the seat belt sign was turned off. After my report to ATC; I contacted my flight crew to ascertain if anyone had been injured and made a PA announcement to my passenger explaining what had occurred. Had this turbulence been associated along the longitudinal axis rather than the lateral axis; the outcome could have been much worse. It is my opinion that wake turn separation needs to be developed for cruise flight.

Original NASA ASRS Text

Title: A CREW RPTS WAKE TURB ENCOUNTER NEAR HLN AT FL340 FROM CROSSING B747 AT FL350.

Narrative: WHILE CRUISING AT FL340 OBSERVED CROSSING TFC AT FL350. THE TFC WAS APPROX 10 MILES AHEAD AS OBSERVED ON THE TCAS. A FEW MINUTES LATER MY ACFT ENCOUNTERED A SHARP JOLT OF MODERATE INTENSITY. I INQUIRED WITH ATC WHAT TYPE OF ACFT HAD CROSSED OUR PATH. ZLC SAID A BOEING 747 1000 FT UP. I TOLD THE CTLR THAT WE HAD ENCOUNTERED MODERATE TURB FROM THE B747 AND WOULD HAVE APPRECIATED SOME NOTIFICATION OF AN IMPENDING TFC CALL ESPECIALLY A HVY. I ALSO ASKED THAT THE CTLR MAKE A RPT PER MY EVENT. AT THE TIME OF THE ENCOUNTER; THE AIR WAS SMOOTH AND THE SEAT BELT SIGN WAS TURNED OFF. AFTER MY RPT TO ATC; I CONTACTED MY FLT CREW TO ASCERTAIN IF ANYONE HAD BEEN INJURED AND MADE A PA ANNOUNCEMENT TO MY PAX EXPLAINING WHAT HAD OCCURRED. HAD THIS TURB BEEN ASSOCIATED ALONG THE LONGITUDINAL AXIS RATHER THAN THE LATERAL AXIS; THE OUTCOME COULD HAVE BEEN MUCH WORSE. IT IS MY OPINION THAT WAKE TURN SEPARATION NEEDS TO BE DEVELOPED FOR CRUISE FLT.

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