Narrative:

I was flying just slightly below a benign looking undercast and forward visibility was about 3 miles in haze. I suddenly encountered a severe downdraft. Normal cruise IAS in this aircraft is about 115 to 118 knots (at that altitude). I increased engine power to max and raised the pitch attitude to the point that my IAS decreased to 65 knots and was unable to arrest the decent. I lost about 600 feet during this event. The ARTCC frequency was busy and in the few seconds that transpired during the loss of altitude; I was unable to tell the controller what was happening. Plus; aircraft control demanded my full attention.due to an ads-B traffic display that I have installed in my aircraft; I know that there was IFR traffic at my 12 to 11 o'clock position at 7;000 MSL that I did not have in sight. At some point; very early in this event; knowing that IFR separation had been lost and separation was decreasing rapidly; I started a right turn (without controller direction) to 300 degrees to at least increase the lateral separation from that traffic. (The ads-B traffic display did not show any traffic behind me). At this point (probably; about 30 seconds after this event started); the center controller asked what was going on. After my brief explanation; the controller then assigned my flight; 6;000 MSL and soon after I was given a left turn; back on course.I offered to make a phone call to the ARTCC after landing to explain the event further; but the controller indicated that a phone call was unnecessary.

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Original NASA ASRS Text

Title: Glasair pilot reported encountering a severe downdraft enroute. This pushed him down 600 feet creating an airborne conflict which he deviated his track 30 degrees to avoid.

Narrative: I was flying just slightly below a benign looking undercast and forward visibility was about 3 miles in haze. I suddenly encountered a severe downdraft. Normal cruise IAS in this aircraft is about 115 to 118 knots (at that altitude). I increased engine power to max and raised the pitch attitude to the point that my IAS decreased to 65 knots and was unable to arrest the decent. I lost about 600 feet during this event. The ARTCC frequency was busy and in the few seconds that transpired during the loss of altitude; I was unable to tell the controller what was happening. Plus; aircraft control demanded my full attention.Due to an ADS-B traffic display that I have installed in my aircraft; I know that there was IFR traffic at my 12 to 11 o'clock position at 7;000 MSL that I did not have in sight. At some point; very early in this event; knowing that IFR separation had been lost and separation was decreasing rapidly; I started a right turn (without Controller direction) to 300 degrees to at least increase the lateral separation from that traffic. (The ADS-B traffic display did not show any traffic behind me). At this point (probably; about 30 seconds after this event started); the Center Controller asked what was going on. After my brief explanation; the Controller then assigned my flight; 6;000 MSL and soon after I was given a left turn; back on course.I offered to make a phone call to the ARTCC after landing to explain the event further; but the Controller indicated that a phone call was unnecessary.

Data retrieved from NASA's ASRS site 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.