Gap In Training And Awareness For Partial Engine Failures

The NTSB recently issued a Safety Alert for pilots of piston twin-engine aircraft that identifies an apparent gap in training and awareness for situations when there is a partial power loss in one engine. Current training primarily addresses only total engine failures.

The agency notes that partial power loss is often mismanaged, accompanied by a higher probability of loss of control. The problem is that manually feathering props are equipped with start locks to prevent the blades from feathering during a normal shutdown procedure. This ensures that the next startup is made easier with the prop blades at a low pitch blade angle.

The start lock disengages when the prop is spinning above a certain rpm. However, if the propeller drops below the critical rpm during flight, such as during a partial power loss, the start lock can re-engage and prevent the pilot from feathering the prop, leading to a dangerous increase in drag with a subsequent potential loss of control. The only way to disengage the lock is to increase rpm which may not be possible with a partial loss of engine power.

The specific start lock engagement speed varies among various propeller makes and models, so the NTSB Safety Alert urges pilots to become familiar with the start lock engagement speed for their particular propeller and to train and practice partial power losses to know when to feather the prop before the rpm drops below that speed.

The Safety Alert states: “It is imperative, therefore, to feather the propeller before the rpm decreases below the start lock engagement speed. Delayed propeller feathering in partial loss of engine power scenarios can dangerously result in drag, compromising control and safety."

Read the full Safety Alert at the link below.

FMI:  www.ntsb.gov/