Don't waist to much time about what a STOL aircraft is and what not. The fact is, the Dash 7 can be considered "safe enough" to meet commercial OPS requirement in Courchevel, while the Dash 8 can't. Let me explain why:
Any commercial operation needs to meet the required take off performance. This includes:
- All engine go
- Accelerate Stop (Accelerate to decision speed, loose an engine and come to a stop on the remaining part of the runway)
- Accelerate Go (Accelerate to decision speed, loose and engine and continue your take off safely)
Any take off has to be aborted, if "VMC G" (Minimum Control Speed Ground) is not met. Otherwise it will leave the runway and crash. It for sure can't be rotated either, before Minimum Control Air is reached, otherwise you lift off and crash right away. Here we come to the big problem for any Multi Engine Take Off in Courchevel. Due to the slope, the Take Off can't be aborted, once initiated. So, Accelerate Stop you can forget for any aircraft taking off in Courchevel. This for the very simple reason, once the aircraft comes in the slope, there will be no way to bring it to a stop. It has to lift off or will crash at the end of the runway.
All engine go would probably be met also for the Dash 8. As the Dash 7 was successfully operated in Courchevel for years, I think we do not need to debate if it meets or not
Accelerate Go on the Dash 7 isn't a big issue, as the aircraft will lift off in Courchevel anyhow on the 3 remaining engines (more details at the end). The Dash 8 on the other hand has the big problem, that between a certain speed and Minimum Control Speed Ground, it ends up uncontrollable but the take off could not be aborted either.
The Dash 7 had a Minimum Control Speed Ground Issue in Couchevel as well. The thing was, that loosing one of the outboard engines below a certain speed would not allow to keep the aircraft straight. So Tyrolean developed a procedure which was finally accepted by the authorities and allowed them to fly safely for years in and out of Courchevel.
Their procedure was to bring both inboard engines to take off power, but the outboard ones only to a reduced setting, allowing them still to keep straight if one of them was lost. At Minimum Control Speed Ground, the assisting pilot had then to advance the two outboard throttles as well to take off power. So in fact, they started their take off roll in Courchevel with a partially reduced power setting, which was brought up during the roll.
Tyrolean demonstrate here that even unconventional procedures can give a safe and successful operation, if it is adapted seriously and the crews well trained for.