NAVION RANGEMASTER PLT HAD THE PLT SEAT SLIP BACK AFTER ENG START AND LOST ACFT CTL. IT HIT A PARKED ACFT; TRAILER; AND A BUILDING.

Narrative

MR X IS THE GENTLEMAN WHO WAS SELLING THE PLANE -- I WAS BUYING. THE ACFT HAD BEEN RECENTLY RUN AND WAS STILL HOT. MR X REMINDED ME THAT IT WOULD BE A 'HOT START' WHICH HE HAD GONE OVER WITH IN DETAIL THE EVENING BEFORE. I ENTERED THE ACFT AND MOVED THE SEAT FORWARD. I ADJUSTED THE SEAT AND THOUGHT THAT IT LATCHED. I HAD THE PROP CTL FULLY FORWARD; THE THROTTLE FULLY FORWARD AND THE MIXTURE FULLY AFT OR FULL LEAN. I PUT THE BATTERY AND GENERATOR SWITCHES ON; ACTIVATED THE FUEL PUMP; CHKED FUEL PRESSURE AND CRANKED THE ENG. IT DID NOT START. AFTER ANOTHER ATTEMPT OR TWO; THE ENG STARTED. AS I MOVED THE MIXTURE FORWARD (TO FULL RICH) AND THE ENG GAINED RPM; THE ACFT STRAINED SLIGHTLY AGAINST THE BRAKES. WHILE I WAS IN THE PROCESS OF PULLING THE THROTTLE AFT (IDLE) AND APPLYING ADDITIONAL FOOT PRESSURE TO THE BRAKES; THE SEAT SUDDENLY SLID AFT. THE ACFT BEGAN ROLLING FORWARD AND I WAS IN A POS WHERE I COULD NOT REACH THE FOOT PEDALS OR ANY OF THE ENG CTLS. I TRIED PULLING MYSELF FORWARD IN AN ATTEMPT TO APPLY ADDITIONAL BRAKE PRESSURE AND TO GRASP THE THROTTLE CTL AND OR THE MIXTURE CTL. I KEPT TRYING TO GRAB THE THROTTLE AND OR MIXTURE BUT COULD NOT GET SUFFICIENT PURCHASE. I COULD NOT REACH THE BRAKES. THE PLANE CONTINUED FORWARD EVENTUALLY COMING TO REST AGAINST A TRAILER AND A BUILDING. I LEARNED LATER THAT THE R TIP TANK HAD MADE CONTACT WITH THE R WING OF PARKED PIPER CHEROKEE.