The National Transportation Safety Board said a Trapper Creek plane crash last summer that killed a father flying over his daughter's wedding reception happened when the pilot flew into trees during a low pass.
In a Tuesday update on the July 19 crash that killed 54-year-old Michael Zagula, the board said its probable cause was "the pilot's failure to maintain clearance from trees while intentionally maneuvering close to the ground." Witnesses had seen Zagula's Cessna U206G making "treetop-level" passes over the forested area where the reception took place, at speeds of 100 to 120 knots -- about 115 to 140 mph.
"The airplane made two successful passes over the group, and, on the third pass, the airplane entered a right turn and initiated a climb just before impacting the top of a spruce tree," investigators wrote. "The climb continued briefly before the airplane rolled inverted and descended through the trees to ground impact."
Mat-Su Borough first responders traveled to the crash site near Petersville Road on four-wheelers, following initial reports at about 7 p.m. on July 19. Zagula's body was subsequently taken to the State Medical Examiner Office.
The final report on the accident's probable cause also noted that drugs were present in the pilot's system but stopped short of declaring them a factor.
The report said an NTSB toxicology examination performed on Zagula, the Cessna's pilot and sole occupant, had identified "likely impairing levels of tetrahydrocannabinol (THC) and low levels of diazepam" in his blood. THC is the active component of marijuana, while diazepam is an anti-anxiety drug originally sold as Valium.
When investigators examined the Cessna's airframe and engine, the report said, they found "no mechanical malfunctions or anomalies that would have precluded normal operation."
NTSB investigator Brice Banning, who conducted the Trapper Creek investigation, said Tuesday that the drug findings from the toxicology examination weren't listed in the crash's probable cause because they couldn't be positively linked to it.
"After death, there's a redistribution of drugs in the body that makes analysis very difficult, and we were unable to determine if it played a role," Banning said. "It was something we were concerned at and we looked at very thoroughly -- but we were just unable to determine if it was a factor."
Alaskans legalized the recreational use of marijuana in a 2014 vote.
The NTSB investigation of the crash that killed Zagula is one of several last year depicted by the Smithsonian Channel show "Alaska Aircrash Investigations." Investigators with the board have said that further information on crashes depicted in the show will be released ahead of the relevant episodes' air dates.
The "Alaska Aircrash Investigations" episode covering the Trapper Creek crash is set to air Sunday at 8 p.m. Alaska time.