Propeller Warning Issued Before Governor’s Crash

Six weeks before South Dakota Gov. George S. Mickelson was killed in the crash of a twin-engine plane, the federal government’s transportation safety agency warned aviation regulators the propellers used on that aircraft--and thousands of others--could cause a “catastrophic accident.”

The National Transportation Safety Board’s March 4 letter was the third in seven months pressuring the Federal Aviation Administration to order inspections of the suspect propellers. The letter called the FAA’s inaction an “unacceptable response.”

Mickelson’s plane crashed April 19 near Dubuque, Iowa, after the pilot reported engine trouble. All eight people on board were killed.

Safety board investigators found a crack on the mountings that connected a missing propeller blade to the state-owned, twin-engine plane. The aircraft used four-bladed propellers manufactured by Hartzell Propeller Inc., of Piqua, Ohio. An estimated 6,000 propellers of that model are in use on commuter and corporate aircraft.

The Iowa crash resembled a 1991 incident over Utica, N.Y., in which a propeller blade separated in flight and pierced the fuselage of a similar Mitsubishi MU-2, officials say. That plane landed safely, but the safety board last August urged that all similar propellers be checked for possible cracks.

The board repeated the recommendation to the FAA in January when it did not act.

The cracking inside the propeller hub was linked to scratches that probably occurred in manufacturing, the board said in the Aug. 13 letter.

The FAA, in a Jan. 4 reply, said the Utica incident did not warrant a mass inspection of the propellers. The 3,000-hour inspections recommended by Hartzell should be sufficient, the FAA said.

Hartzell Propeller could not determine why the hub cracked in the 1991 incident, said Jim Brown, the company chairman.

“In our judgment it was an unexplained, extremely rare incident,” Brown said Tuesday.