Originally Posted by
MX Trainer
Many aircraft have an interlock system installed that will not allow you to physically move the Power Lever below the flight idle gate on landing unless certain conditions are met. One of those conditions on some aircraft is the Propeller Control must be fully forward at the 100% position.
Thanks.
I remember that the Twin Otter had the interlock but not the King Air and beech 99. Never understood why.
The interlock system was a potential trap for the unwary and could lead to an accident. On the Twin Otter, full forward on the prop levers was actually considered to be 96% selection with no reverse capability available(due to the interlock) unless a prop lever position above 91% was selected.
Many captains didn't want the prop levers selected forward until touchdown to avoid excessive noise. Twice, it happened to me where, there was some sort of a hangup between the power levers and the prop levers due to reverse being attempted while the prop levers were still being moved forward. This meant no reverse available.
I was lucky....in both cases we were on long runways. But many of our flights were to extremely short offstrip locations where you needed max reverse.
We had one accident out on the ocean ice where they could not get reverse and damaged the aircraft. The pilots swore that they props had been selected forward for landing and maybe they were, but no mechanical or electrical malfunction could be found. I believe there is a friction selector but I don't know whether it was tight or loose for the prop levers in that accident.
So perhaps the props were selected forward but moved slightly aft by themselves prior to reverse selection on touchdown. There is not very much propeller lever travel between 91 and 96%.
Bottom line, after these experiences, when landing offstrip, I would have props selected full forward and have my hand giving positive forward pressure on both prop levers on touchdown, always, even if the captain said not to move them forward until touchdown. Never had another problem after that.