ACCORDING TO THE SURVIVING PASSENGER (THE PLT'S 15 YR OLD SON), THEY SAW SOME SKIERS AFTER CROSSING OVER A MOUNTAIN PASS. HE STATED THAT AS THEY TURNED, HIS FATHER SAID, 'LET'S BUZZ THEM.' HE REPORTED THAT THEY TURNED SHARPLY, 'SORT OF DOVE DOWN TO BUZZ THEM,' THEN THAT WAS ALL HE COULD REMEMBER. ACCORDING TO ONE OF THE SKIERS THAT WAS FAMILIAR WITH T-28 ACFT, THEY HEARD & SAW THE T-28 CROSS ROLLINS PASS AT APRX 300 TO 350 FT AGL. AS THE ACFT PASSED, THEY WAVED AT IT & THEN THE PLT RESPONDED (THEY BELIEVED) BY ROCKING HIS WINGS. SOON AFTER THAT, THE ACFT WENT INTO A STEEP LEFT BANK AS IF TO TURN BACK TOWARD THEM. THE WITNESS REPORTED THAT THE ACFT WAS TURNING AT A CONSTANT ALTITUDE, WHEN THE NOSE SUDDENLY DROPPED. THE PLT LEVELED THE WINGS & THE ACFT STARTED A DIVE, THEN DISAPPEARED FROM HIS VIEW, BEHIND A RIDGE. HE HEARD POPPING SOUNDS THAT HE THOUGHT SOUNDED LIKE A T-28 HAVING HAD THE THROTTLE MOVED RAPIDLY. AN INVESTIGATION REVEALED THE ACFT HAD COLLIDED WITH TREES & CRASHED. NO PREIMPACT/MECHANICAL FAILURES FOUND.