Narrative:

Was holding at runway 1 for an IFR release. An mlt was cleared for VFR touch and go and to remain in pattern. The mlt did a low approach and then continued on around his pattern. After the low approach an small aircraft on base was cleared to land. Approximately 2-3 mins had passed and I was cleared for takeoff. I took my time departing to allow extra time for the wake turbulence--although winds were reported about 350/5, they appeared calm. After takeoff I cleaned up and climbed about 20 KTS faster than normal. I made a slight left turn. Going through about 1200' I had just lowered the nose slightly because I thought I had cleared the crosswind path of the mlt. About that time the aircraft started a smooth slow roll to left. I first started scanning for an engine failure or asymmetric flap. At that time the aircraft felt like it was trying to pitch up. I applied nose down pressure and then heard the engines cavitate and we pitched down rather abruptly. The aircraft then felt solid, so I throttled back and gradually pulled up and resumed the climb. The incident shook up some of the passenger, so I explained to them what I thought happened and that we would return to the airport. I notified the company before landing and they had a second aircraft prepared. I switched planes and then took the passenger onto anc. My aircraft was properly inspected and returned to service later. In all my flying and my frequent interaction with large and heavy aircraft, this is truly the first time that I have even encountered a large wake. In what I've read before and after this encounter, I feel that there is so much emphasis on dealing with wake turbulence in the first 3 mins and little on the dangers after that when in fact under certain conditions a dangerous wake could continue for much, much longer.

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Original NASA ASRS Text

Title: ACFT ENCOUNTERED WAKE TURBULENCE RESULTING IN MOMENTARY LOSS OF ALT.

Narrative: WAS HOLDING AT RWY 1 FOR AN IFR RELEASE. AN MLT WAS CLRED FOR VFR TOUCH AND GO AND TO REMAIN IN PATTERN. THE MLT DID A LOW APCH AND THEN CONTINUED ON AROUND HIS PATTERN. AFTER THE LOW APCH AN SMA ON BASE WAS CLRED TO LAND. APPROX 2-3 MINS HAD PASSED AND I WAS CLRED FOR TKOF. I TOOK MY TIME DEPARTING TO ALLOW EXTRA TIME FOR THE WAKE TURB--ALTHOUGH WINDS WERE RPTED ABOUT 350/5, THEY APPEARED CALM. AFTER TKOF I CLEANED UP AND CLBED ABOUT 20 KTS FASTER THAN NORMAL. I MADE A SLIGHT LEFT TURN. GOING THROUGH ABOUT 1200' I HAD JUST LOWERED THE NOSE SLIGHTLY BECAUSE I THOUGHT I HAD CLRED THE XWIND PATH OF THE MLT. ABOUT THAT TIME THE ACFT STARTED A SMOOTH SLOW ROLL TO LEFT. I FIRST STARTED SCANNING FOR AN ENG FAILURE OR ASYMMETRIC FLAP. AT THAT TIME THE ACFT FELT LIKE IT WAS TRYING TO PITCH UP. I APPLIED NOSE DOWN PRESSURE AND THEN HEARD THE ENGS CAVITATE AND WE PITCHED DOWN RATHER ABRUPTLY. THE ACFT THEN FELT SOLID, SO I THROTTLED BACK AND GRADUALLY PULLED UP AND RESUMED THE CLB. THE INCIDENT SHOOK UP SOME OF THE PAX, SO I EXPLAINED TO THEM WHAT I THOUGHT HAPPENED AND THAT WE WOULD RETURN TO THE ARPT. I NOTIFIED THE COMPANY BEFORE LNDG AND THEY HAD A SECOND ACFT PREPARED. I SWITCHED PLANES AND THEN TOOK THE PAX ONTO ANC. MY ACFT WAS PROPERLY INSPECTED AND RETURNED TO SVC LATER. IN ALL MY FLYING AND MY FREQUENT INTERACTION WITH LARGE AND HVY ACFT, THIS IS TRULY THE FIRST TIME THAT I HAVE EVEN ENCOUNTERED A LARGE WAKE. IN WHAT I'VE READ BEFORE AND AFTER THIS ENCOUNTER, I FEEL THAT THERE IS SO MUCH EMPHASIS ON DEALING WITH WAKE TURB IN THE FIRST 3 MINS AND LITTLE ON THE DANGERS AFTER THAT WHEN IN FACT UNDER CERTAIN CONDITIONS A DANGEROUS WAKE COULD CONTINUE FOR MUCH, MUCH LONGER.

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