NTSB: Wing broke off in-flight before deadly plane crash in Snohomish County

The National Transportation Safety Board (NTSB) has recovered the wreckage of a plane that crashed in Snohomish on Friday, killing all four passengers aboard.

NTSB officials say the Cessna 208B airplane's right wing separated in flight and landed about 200 yards from the main crash site, in an agricultural field near Harvey Airfield. The cause of the wing separation has not yet been determined.

The wreckage has been brought to a secure facility for reconstruction, where investigators hope to learn more about what happened to the plane.

FOX 13 learned that the crew on-board were working for Raisbeck Engineering, a Tukwila-based aircraft supply company.

Raisbeck has been working on a modification that could be attached to the plane, but company president Hal Chrisman stressed that they had not changed anything on the plane before the test flight on Friday. Instead, Chrisman said that Friday's test flight would have been used to establish a "baseline aircraft performance" before they modified the plane.

Veteran airline pilot and online aviation commentator Juan Browne told FOX 13 News that the crash raises a number of questions that the NTSB and FAA will have to answer during an investigation. 

One thing that stood out to Browne is the type of aircraft that crashed – he noted that he doesn't know of any reports of a Cessna 208B Grand Caravan EX breaking apart in mid-air. 

"What were they doing that they managed to pull the wings off it?" asked Browne. "I'm not sure why they're testing it to this degree. Why are they testing it this hard just to get a baseline – or was it a maneuver performed incorrectly, and they accidentally overstressed the air frame?"

In a release to FOX 13 News, Raisbeck noted the two test pilots that were on-board had thousands of hours of flight experience between them. A flight test director and an instrumentation engineer were also on-board.

PREVIOUS COVERAGE: Snohomish County plane crash: 4 killed in crash were pilots, engineers testing aircraft

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Officials say a preliminary report is expected to finish in two to three weeks, and the full investigation should finish in one to two years.