 The mechanism that alerts pilots that they are selecting beta range had been the subject of previous investigations and it was found that a manufacturer-approved service centre had a history of releasing defective parts back to operators.Following a number of previous incidents of inadvertent selection of Ground Beta range on Dash 8 aircraft, that resulted in serious damage to engines, the U.S. Federal Aviation Administration mandated that an additional safeguard was required to be fitted to aircraft operated by U.S. airlines.This system, called a Beta Lockout, was developed by the manufacturer and completely prevents inadvertent selection of Ground Beta range while airborne at high speeds, but operators outside the U.S. were not notified or required to fit the modification.