Retractable gear aircraft have gone with holding the gear up by hydraulics only (Pipers typically - no up-locks) or with latching systems - i.e. Commanders, Glasair RG's have used no up-locks on their smaller aircraft whereas the larger Glasair III's use an up-lock system. Both designs have worked fine. Because there was more g-loaded leverage pulling out the larger Glasair III gear, an up-lock system was employed.
In the design phase of the 3400 amphibs the issue was debated and an up-lock system was engineered.
An inquiry was put out into the float community regarding the issue. Concerns surfaced regarding the high danger in a float plane where one gear is stuck in the up position and the other has come down.Figuring that a hydraulic line will break under a high pressure condition, which could happen if an up-lock gets hung up, the pilot has no way of moving the gear and he is in a difficult position with possibly one gear down and the other locked up. He can't land on the water and landing on the land will be very interesting. We were made aware of a fellow in British Columbia who destroyed his aircraft upon landing as a result of this condition.
It was felt that with the great mechanical advantage of the Aerocet 3400 main gear ram, we could eliminate the high pressure need in the system and that the ram could hold the main gear up even under a 15 G load - hence no up-locks.
We could also eliminate complexity for manufacture and maintenance over the life of the float. If both main gear come out, a ground landing is required, but a successful landing could be made without the nose gear deployed and the mains down and locked. It is not practical to default the main gear to an up position because the spring power would be too heavy.
Slide tracks may be used on the main gear to achieve an up-lock. The issue with slide tracks is that they can get debris in them, causing a potential jam. Again, if a hydraulic line breaks, there is no assurance where the main gear is positioned.
Takeoff is not possible when there is a hydraulic line failure on the water. We include an easily accessible back up hydraulic hand pump on all installations if the electric pump fails. A broken hydraulic line necessitates fixing.
If one wants to trust his up-locks to keep the gear secure and go from water to water then this would be an advantage to having up-locks.
Again, our position is that we didn't want the complexity, maintenance, and a possible one gear up, one gear down condition from up-locks. Either system will get the job done until you have a problem and we chose to go in this direction for the 3400's.
With so many amphibs out there now without issue, we feel confident about the direction taken.