In-flight wake turbulence encounter.

Attributes
ACN	295119
Time
Date	199501
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pxr airport : phx
State Reference	AZ
Altitude	msl bound lower : 12000 msl bound upper : 13800
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Gulfstream IV
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : zab
Flight Plan	IFR
Aircraft 2
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	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 7900 flight time type : 1900
ASRS Report	295119
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : undershoot altitude deviation : crossing restriction not met inflight encounter other non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

En route from dallas to phx, ZAB had our G-4 and a B-757, both en route to phx. We were approximately 4000 ft above the B-757 jet at the time we would normally begin descent. ZAB hi sector anticipated the situation well and sent the B-757 on direct routing toward the tonto intersection and started us both descending incrementally. When we had separation, we were given a notice to 'expect tonto at 12000 ft and a 280 KT speed restr.' the B-757 was given the 'expect...' notice as well, and we were both switched to the lower altitude sector controller, who cleared us both to cross tonto at 12000 ft. A third aircraft, a king air, was between ourselves and the B-757 at a lower altitude, descending to 11000 ft, per the STAR. I am certain we had 7-8 mi in-trail separation from the B-757, and since separation criteria were met, we were not told the type aircraft. It also appeared we were above the B-757 in our descent angle. We hit the wake turbulence at about 13800 ft, rolling the G-4 violently through approximately 60 degrees of bank. I immediately pulled up elevator and popped right out of the vortex, but was in no hurry to descend again. We crossed tonto intersection at about 14000 ft. I believe this was a fluke occurrence. Winds were not particularly strong out of the west. There is a topographic upslope in that area which might account for the vortex not settling as usual and the possibility that the B-757 may have had to shallow its descent angle to meet the 250 KT restr at tonto intersection, but enough to contribute to the vortex being at a higher altitude than anticipated. Believe me, I will give those guys all the room they need and take all factors into consideration for wake turbulence avoidance. Recommend b- 757 be classed formally as a 'heavy.' callback conversation with reporter revealed the following information: reporter participated in wake turbulence structured callback study. Reporter was hurried due to impending flight and only added that he believes more spacing is required between B-757 aircraft and they should be reclassified as a heavy.

Original NASA ASRS Text

Title: INFLT WAKE TURB ENCOUNTER.

Narrative: ENRTE FROM DALLAS TO PHX, ZAB HAD OUR G-4 AND A B-757, BOTH ENRTE TO PHX. WE WERE APPROX 4000 FT ABOVE THE B-757 JET AT THE TIME WE WOULD NORMALLY BEGIN DSCNT. ZAB HI SECTOR ANTICIPATED THE SIT WELL AND SENT THE B-757 ON DIRECT ROUTING TOWARD THE TONTO INTXN AND STARTED US BOTH DSNDING INCREMENTALLY. WHEN WE HAD SEPARATION, WE WERE GIVEN A NOTICE TO 'EXPECT TONTO AT 12000 FT AND A 280 KT SPD RESTR.' THE B-757 WAS GIVEN THE 'EXPECT...' NOTICE AS WELL, AND WE WERE BOTH SWITCHED TO THE LOWER ALT SECTOR CTLR, WHO CLRED US BOTH TO CROSS TONTO AT 12000 FT. A THIRD ACFT, A KING AIR, WAS BTWN OURSELVES AND THE B-757 AT A LOWER ALT, DSNDING TO 11000 FT, PER THE STAR. I AM CERTAIN WE HAD 7-8 MI IN-TRAIL SEPARATION FROM THE B-757, AND SINCE SEPARATION CRITERIA WERE MET, WE WERE NOT TOLD THE TYPE ACFT. IT ALSO APPEARED WE WERE ABOVE THE B-757 IN OUR DSCNT ANGLE. WE HIT THE WAKE TURB AT ABOUT 13800 FT, ROLLING THE G-4 VIOLENTLY THROUGH APPROX 60 DEGS OF BANK. I IMMEDIATELY PULLED UP ELEVATOR AND POPPED RIGHT OUT OF THE VORTEX, BUT WAS IN NO HURRY TO DSND AGAIN. WE CROSSED TONTO INTXN AT ABOUT 14000 FT. I BELIEVE THIS WAS A FLUKE OCCURRENCE. WINDS WERE NOT PARTICULARLY STRONG OUT OF THE W. THERE IS A TOPOGRAPHIC UPSLOPE IN THAT AREA WHICH MIGHT ACCOUNT FOR THE VORTEX NOT SETTLING AS USUAL AND THE POSSIBILITY THAT THE B-757 MAY HAVE HAD TO SHALLOW ITS DSCNT ANGLE TO MEET THE 250 KT RESTR AT TONTO INTXN, BUT ENOUGH TO CONTRIBUTE TO THE VORTEX BEING AT A HIGHER ALT THAN ANTICIPATED. BELIEVE ME, I WILL GIVE THOSE GUYS ALL THE ROOM THEY NEED AND TAKE ALL FACTORS INTO CONSIDERATION FOR WAKE TURB AVOIDANCE. RECOMMEND B- 757 BE CLASSED FORMALLY AS A 'HVY.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN WAKE TURB STRUCTURED CALLBACK STUDY. RPTR WAS HURRIED DUE TO IMPENDING FLT AND ONLY ADDED THAT HE BELIEVES MORE SPACING IS REQUIRED BTWN B-757 ACFT AND THEY SHOULD BE RECLASSIFIED AS A HVY.

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.