Aviation safety issues and actions

Dash 8 propeller system design

Issue number: AO-2011-159-SI-01
Who it affects: The aircraft operator
Issue owner: Bombardier Aerospace
Transport function: Aviation: Other
Background: Investigation Report AO-2011-159
Issue release date: 25 February 2013
Current issue status: Adequately addressed
Issue status justification:

The aircraft manufacturer has released a service bulletin to fit a Beta Lockout System to all Dash 8 100, 200 and 300 series aircraft, that service bulletin was mandated by the Canadian aviation regulator Transport Canada.

Safety issue description

A significant number of DHC-8-100, -200 and -300 series aircraft did not have a means of preventing inadvertent or intentional movement of power levers below the flight idle gate in flight, or a means to prevent such movement resulting in a loss of propeller speed control.

Proactive Action

Action number: AO-2011-159-NSA-037
Action organisation: Bombardier Aerospace
Date: 25 February 2013
Action status: Closed

On 19 June 2012 the manufacturer issued an All Operator Message No. 994, which stated that:

Despite incorporation of the beta warning horn modification, incidents continue to occur in which the power levers are selected aft of the flight idle gate, into the beta range during flight.

As a result, Transport Canada has indicated their intention to issue an Airworthiness Directive to mandate incorporation of a beta lockout modification for all aircraft that do not already have one installed. Bombardier has conducted an internal review of the existing engineering for the FAA approved installation and will be revising the engineering to cover all aircraft configurations in service and to introduce modification kits.

On 13 September 2012 the manufacturer issued Service Bulletin (SB) 8-11-115, which recommended the fitment of a warning placard in the cockpit that stated:

Positioning of the power levers below the flight idle stop during flight is prohibited. Such positioning may lead to loss of airplane control, or may result in an engine overspeed condition and consequent loss of engine power.

That SB was mandated by Transport Canada AD CF-2012-33 for fitment within 60 months or 400 flight hours whichever comes first.



On 15 May 2013 the manufacturer issued a service bulletin to fit the Beta Lockout System to all Dash 8 100, 200 and 300 series aircraft.

On 19 June 2013 the Canadian aircraft regulator (Transport Canada) issued an Airworthiness Directive which mandated the aircraft manufactures Beta Lockout System service bulletin within 3 years or 6000 flight hours.

ATSB comment:

The ATSB is satisfied that the manufacturer’s beta lockout system service bulletin, when mandated by Transport Canada and implemented, will address the propeller system design issue.


Last update 12 February 2014