What happened
Following engine start, the pilot attempted to release the collective friction lock on an Enstrom F28. The pilot used both hands to perform this action. Upon releasing the lock, the collective unexpectedly moved to the full up position, causing the aircraft to roll to the left about its longitudinal axis.
The pilot had been relying on an undocumented modification, consisting of a collective hold-down chain, to keep the collective secure. The pilot reported receiving no guidance regarding the proper use of this specific hold-down device.
The investigation
Investigators determined that according to the aircraft manufacturer, there are no approved collective hold-down devices for this model other than the installed friction lock. While the Enstrom F28 'before takeoff' checklist instructs pilots to keep their hand on the collective and maintain a down position when the lock is disengaged, the presence of the undocumented chain modification influenced the pilot's actions during the release of the friction lock.