Narrative:

Inbound on gilmore 3 arrival to mem at 8000 ft MSL, straight and level in cavu conditions, calm (smooth) air. Was at 10 mi in trail behind A320, which was descending from above after it joined the arrival ahead of us from a turn. At approximately 20 mi from mem VOR, we encountered rapid chop, followed by a left roll, which the autoplt was unable to correct. At approximately 20 degree left bank, I disengaged the autoplt and hand flew the aircraft at 20 degrees left bank, and pitched the aircraft to approximately 5 degrees nose down to fly out of the wake. We exited the wake at approximately 7700 ft and 30 degrees left of course. We advised ATC immediately and received deviation clearance. We attempted to rejoin the arrival and encountered a second wake roll event, again at 8000 ft level on the arrival. This time we immediately executed a descending left turn to heading 090 degrees and 7500 ft, which I held until I felt comfortably distant from the wake. Again, we advised ATC. As soon as practical, we returned to 8000 ft and paralleled the arrival course, awaiting further instruction from ATC. We kept ATC advised at all times. Separation was never less than 10 NM. Aircraft roll did not exceed 40 degree bank. Pitch did not exceed +/-5 degrees. I feel that the vague response, made in a casual manner, by ATC when first advised of a wake encounter deviation ('roger, deviate as necessary') could be made more explicit. For instance, 'roger, cleared to deviate, heading and altitude as necessary.' followed with, after a sufficient time to allow maneuvering, 'report able to return to previous altitude (course, etc).' this phraseology should be standard with ATC to allow crews to immediately feel comfortable to maneuver as necessary, especially in IMC. The mem controller seemed unconcerned with our position and status, perhaps due to the clear WX and lack of other traffic in our proximity. The advice to 'lower the nose' in such encounters proved extremely effective in controling the aircraft. We would have certainly upset (inverted) had we attempted to maintain altitude and heading. Each encounter was preceded by a rapid-frequency, continuous light chop prior to roll for approximately 2-3 seconds.

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Original NASA ASRS Text

Title: CAPT OF AN LTT TURBOPROP WAS CAUGHT BY WAKE TURB FROM A PREVIOUS TURBOJET ACR ACFT WHILE ON A STAR ARR TO MEM AT 8000 FT. HAPPENED TWICE UNTIL THE RPTR MAINTAINED AN OFFSET PARALLEL COURSE AND WAITED FURTHER INSTRUCTIONS FROM APCH CTL.

Narrative: INBOUND ON GILMORE 3 ARR TO MEM AT 8000 FT MSL, STRAIGHT AND LEVEL IN CAVU CONDITIONS, CALM (SMOOTH) AIR. WAS AT 10 MI IN TRAIL BEHIND A320, WHICH WAS DSNDING FROM ABOVE AFTER IT JOINED THE ARR AHEAD OF US FROM A TURN. AT APPROX 20 MI FROM MEM VOR, WE ENCOUNTERED RAPID CHOP, FOLLOWED BY A L ROLL, WHICH THE AUTOPLT WAS UNABLE TO CORRECT. AT APPROX 20 DEG L BANK, I DISENGAGED THE AUTOPLT AND HAND FLEW THE ACFT AT 20 DEGS L BANK, AND PITCHED THE ACFT TO APPROX 5 DEGS NOSE DOWN TO FLY OUT OF THE WAKE. WE EXITED THE WAKE AT APPROX 7700 FT AND 30 DEGS L OF COURSE. WE ADVISED ATC IMMEDIATELY AND RECEIVED DEV CLRNC. WE ATTEMPTED TO REJOIN THE ARR AND ENCOUNTERED A SECOND WAKE ROLL EVENT, AGAIN AT 8000 FT LEVEL ON THE ARR. THIS TIME WE IMMEDIATELY EXECUTED A DSNDING L TURN TO HDG 090 DEGS AND 7500 FT, WHICH I HELD UNTIL I FELT COMFORTABLY DISTANT FROM THE WAKE. AGAIN, WE ADVISED ATC. AS SOON AS PRACTICAL, WE RETURNED TO 8000 FT AND PARALLELED THE ARR COURSE, AWAITING FURTHER INSTRUCTION FROM ATC. WE KEPT ATC ADVISED AT ALL TIMES. SEPARATION WAS NEVER LESS THAN 10 NM. ACFT ROLL DID NOT EXCEED 40 DEG BANK. PITCH DID NOT EXCEED +/-5 DEGS. I FEEL THAT THE VAGUE RESPONSE, MADE IN A CASUAL MANNER, BY ATC WHEN FIRST ADVISED OF A WAKE ENCOUNTER DEV ('ROGER, DEVIATE AS NECESSARY') COULD BE MADE MORE EXPLICIT. FOR INSTANCE, 'ROGER, CLRED TO DEVIATE, HDG AND ALT AS NECESSARY.' FOLLOWED WITH, AFTER A SUFFICIENT TIME TO ALLOW MANEUVERING, 'RPT ABLE TO RETURN TO PREVIOUS ALT (COURSE, ETC).' THIS PHRASEOLOGY SHOULD BE STANDARD WITH ATC TO ALLOW CREWS TO IMMEDIATELY FEEL COMFORTABLE TO MANEUVER AS NECESSARY, ESPECIALLY IN IMC. THE MEM CTLR SEEMED UNCONCERNED WITH OUR POS AND STATUS, PERHAPS DUE TO THE CLR WX AND LACK OF OTHER TFC IN OUR PROX. THE ADVICE TO 'LOWER THE NOSE' IN SUCH ENCOUNTERS PROVED EXTREMELY EFFECTIVE IN CTLING THE ACFT. WE WOULD HAVE CERTAINLY UPSET (INVERTED) HAD WE ATTEMPTED TO MAINTAIN ALT AND HDG. EACH ENCOUNTER WAS PRECEDED BY A RAPID-FREQ, CONTINUOUS LIGHT CHOP PRIOR TO ROLL FOR APPROX 2-3 SECONDS.

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.