The plane was passing through an area of turbulence and may have been affected by wind-shear or lightning storm causing an electrical failure. Now this is all pre-conjecture, and all that's left of the plane...
"천둥이나 번개 때문에 전자기기가 망가진 것일 수도 있으나 이것은 전부 추측에 불과합니다"