RV-12
Flight Crew Private
Flight Crew Last 90 Days 35; Flight Crew Total 700; Flight Crew Type 550
Situational Awareness
ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action
Airspace Structure; Human Factors; Procedure
Was on a VFR flight plan flight using ATC services. I cruised at 7;500 feet for the flight and began my descent [as I approached my] destination. I was under control of Whidbey (NAS) Approach. I was outside their Class C; but under their control.I was descending at 500 FPM; later 600 FPM; when 500 would not take me down to pattern altitude prior to reaching [my destination]. My glass panel display shows the location of arriving at selected altitude. The weather was VFR; but in heavy smoke; no clouds. The vertical visibility was limited; maybe 3-5 miles slant range; horizontal visibility was unknown; but very poor. The airport AWOS was reporting 8 miles and clear skies.While descending through 4;100 feet; the Whidbey Controller told me to maintain VFR at or above 4;500. I told him I had already passed 4;500 and was approaching 4;000 feet. He didn't reply; so I advised I was climbing back up to 4;500 feet. At that point another Controller came on frequency (an instructor? NUW seems to have many ATC trainees). He advised me to 'descend immediately; there was an immediate traffic conflict with another aircraft at 4;000 feet.'I disconnected the autopilot; pulled the throttle and pushed the nose over. I then leveled off at about 2;500 feet and resumed navigating to the airport. Because of the poor visibility; the Controller asked that I 'remain with him'; (they normally terminate radar coverage about their Class C boundary) and gave me radar vectors to the airport. I became visual with a landmark and was able to track it until I spotted the airport and entered a left crosswind for Runway XX. I then cancelled radar services and landed normally.On analysis of my data downloaded after the flight; I found I had pitched 20 degrees nose down; reached over 4;000 FPM rate of descent; and hit 145 knots IAS; 158 knots TAS (Vne for my airplane is 136 knots TAS.) The vertical acceleration went from +1.0 to +0.5 to +1.5 over a 7 second period. It had been running in the range of +0.8 to +1.1
The pilot of a VANS RV reported that ATC alerted him to an immediate traffic conflict with another aircraft.