- Nov 25, 2001
- Total Time
Anyone have any experience with this?
A few years back, Colgan pancaked a 1900 by inadvertantly lifting the levers over the gate in the flare. At that time, the props were off the governors so that is why they could go into beta.
Marko Ramius said:Well Pratt did a better job on the 1900 engine than on the EMB-120 "ATF". For an overspeed to occur three governers would have to fail completely. The primary and secondary governors essentially work on the same principles that you see in pistons-using flyweights to move a valve that admits oil into or releases it from the hub. Should both of those fail, a fuel topping governor takes over limiting RPM to I believe 106% of that selected by the prop lever. It basically changes the bleed air input to the fuel control unit causing it to reduce fuel flow to the engine and subsequently slow the prop. Under certain situations this can cause the engine to fail, but that's a different story.
Well, you pretty much described the system on the 120. We have a primary and secondary governor as well as p3 fuel topping to the HMU. The governors limit up to 103% and the fuel topping limits up to 109%.
Despite all 3 of these safeties, there have still been several overspeeds. The early ones were due to destruction of the transfer tube that sends the control input from the governor to the hub. Without it, the governors are useless.
Several others were due to crews lifting the gates and shifting to Beta. Locks were installed to prevent this in flight.
As recently as the last 6 months, ASA had a catastrophic overspeed which the crew managed to get on the ground through heroic airmanship. The prop reached 160%Np before the engine came apart. It was outside the marker on final at a very mountainous airport. Neither Embraer, the airline or the FAA have been able to figure this one out yet.
So don't say it's impossible. Be ready...