The ATSB has been advised by Mampaey Offshore Industries that: The locking device of the type in question has been sold by [Mampaey Offshore Industries] since the early 1960’s, and 11,288 hooks have been sold with this feature. There has never been a reported case of a pin accidently failing into the locking slot.
With almost any mechanical device which is switched between two positions by hand, it would be possible to find the point of balance between those two positions, so that any slight movement could move it one way or the other. This applies even to an electrical switch. The locking device in this case had a clear locked position and a clear unlocked position. It is difficult to imagine why it would be placed in a position of fine balance between these points. Whether the locking device were on top of the hook, or under the hook the same issue would apply. If the locking device were under the hook, gravity would still be a factor, although in reverse. Such a locking device could fall out of its slot, thereby unlocking the hook, just as easily as the present locking device could fall into the slot. It could be just as dangerous for a hook to become unintentionally unlocked, as to become unintentionally locked. Placing the locking device under the hook would make it harder to access, harder to see and harder to reach. [Mampaey Offshore Industries] has designed and is now selling an alternative device... However, this was not introduced in relation to any safety concern.
It was introduced for the sole reason that it is easier to operate when being used with thickly gloved hands, and can even be operated by foot. It is known as the “Alaska” locking device, as it can be used in arctic circumstances, where the operators are using thick gloves.