Safety alert advises multi-engine pilots when to feather prop if one engine loses power

The NTSB has released a safety alert, SA-091, along with a companion video on YouTube, warning general aviation pilots of multiengine piston airplanes about an issue few are familiar with: When confronted with loss of power in one engine, it’s crucial to promptly feather the affected engine’s propeller before its speed falls below the range where start locks engage.

“This critical threshold is typically 1000–800 rpm, but varies by make and model,” NTSB officials said, noting, “some manufacturers include this number in their propeller owner’s manual, while others do not.”

Once the propeller’s speed drops below the range at which start locks engage, feathering is not possible.

“The resulting windmilling and parasitic drag are almost invariably followed by loss of control with fatal consequences,” NTSB officials said.

Agency officials noted that this guidance is not just applicable to total loss of engine power (LOEP) scenarios.

“In fact, it’s perhaps even more relevant for partial LOEP situations, where the danger is that much more pernicious,” they noted.