What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) N118AT was on an IFR flight cruising at an assigned altitude of 12,000 feet en route to the north Las Vegas air terminal when la center issued to traffic advisory at 12 o'clock, 2 miles, opposite direction 1,000 feet below. Several seconds later, center queried N118AT about its altitude because of an altitude alert issued by the ATC automation. N118AT replied he was fighting a little turbulence, but was back level at 12,000 feet. Ntap shows the airplane descended 400 feet below it assigned altitude resulting in a loss of separation from opposite direction traffic at 11,000 feet. This was a brief and limited excursion from the assigned altitude. It appears the pilot may have been distracted looking from traffic below just after the traffic advisory and allowed the aircraft to descend. He was also dealing with turbulence. However, it appears that the turbulence experienced was not severe enough to exceed the pilot's or aircraft's capability of maintaining altitude, but we cannot prove this to be the case. With more careful attention, the pilot probably could have employed flight control inputs to compensate for turbulence and maintain the assigned altitude. I contacted the pilot by phone 8/7 & 8/8/2008 and counseled him.
As the FAA filed it
(-23) N118AT WAS ON AN IFR FLIGHT CRUISING AT AN ASSIGNED ALTITUDE OF 12,000 FEET EN ROUTE TO THE NORTH LAS VEGAS AIR TERMINAL WHEN LA CENTER ISSUED TO TRAFFIC ADVISORY AT 12 O'CLOCK, 2 MILES, OPPOSITE DIRECTION 1,000 FEET BELOW. SEVERAL SECONDS LATER, CENTER QUERIED N118AT ABOUT ITS ALTITUDE BECAUSE OF AN ALTITUDE ALERT ISSUED BY THE ATC AUTOMATION. N118AT REPLIED HE WAS FIGHTING A LITTLE TURBULENCE, BUT WAS BACK LEVEL AT 12,000 FEET. NTAP SHOWS THE AIRPLANE DESCENDED 400 FEET BELOW IT ASSIGNED ALTITUDE RESULTING IN A LOSS OF SEPARATION FROM OPPOSITE DIRECTION TRAFFIC AT 11,000 FEET. THIS WAS A BRIEF AND LIMITED EXCURSION FROM THE ASSIGNED ALTITUDE. IT APPEARS THE PILOT MAY HAVE BEEN DISTRACTED LOOKING FROM TRAFFIC BELOW JUST AFTER THE TRAFFIC ADVISORY AND ALLOWED THE AIRCRAFT TO DESCEND. HE WAS ALSO DEALING WITH TURBULENCE. HOWEVER, IT APPEARS THAT THE TURBULENCE EXPERIENCED WAS NOT SEVERE ENOUGH TO EXCEED THE PILOT'S OR AIRCRAFT'S CAPABILITY OF MAINTAINING ALTITUDE, BUT WE CANNOT PROVE THIS TO BE THE CASE. WITH MORE CAREFUL ATTENTION, THE PILOT PROBABLY COULD HAVE EMPLOYED FLIGHT CONTROL INPUTS TO COMPENSATE FOR TURBULENCE AND MAINTAIN THE ASSIGNED ALTITUDE. I CONTACTED THE PILOT BY PHONE 8/7 & 8/8/2008 AND COUNSELED HIM.