According to an Airforce spokesman: " The personnel doing the testing was two experienced pilots.Performing a test program.
Probably a translation from Aftenbladet newspaper.
Han forteller at to erfarne flygere var om bord i maskinen da den veltet. Fire personer oppholdt seg på utsiden.
Actually I believe a "Flygere" could also be construed as Airman or Aircrew. It is common in Norway for mechanics to do ground run on helicopters since pilots are rather expensive to call out there for startups. Ground resonance is a possibility then.
Any native Norwegian speaker care to comment?