Canadian authorities have formally mandated the retrofit of a lock-out system on Bombardier Dash 8 turboprops to prevent inadvertent in-flight selection of power settings below flight-idle.
The modification requires installation of new electrical circuits to stop pilots from placing the throttle levers into the beta-range, which can cause propeller overspeed and damage the engine.
While a warning horn was developed to alert pilots, Transport Canada says the system design does not prevent selection of the beta-range during flight.
Bombardier has issued a service bulletin to install a beta lock-out system on the Dash 8-100, -200 and -300. Transport Canada is mandating the installation and given operators three years or 6,000h flight time to carry out the work.