Preliminary Report: Wing separated on chalk's mallard

 - September 26, 2006, 9:02 AM

Grumman G-73T Turbo Mallard, Miami Beach, Fla., Dec. 19, 2005–The right wing separated from a Chalk’s Turbo Mallard as it was taking off from Chalk’s Watson Island seaplane base. It plunged into the ocean, and all 20 people on board–18 passengers and two crewmembers–died. A witness said he heard a loud noise, then saw the wing fall off before the amphibious airplane fell into the water in flames. Frakes Aviation of Cleburne, Texas, had converted the amphibious aircraft with Pratt & Whitney Canada PT6 turboprops.

Chalk’s voluntarily grounded the remaining four Mallards in its fleet, and on December 30 the FAA issued an emergency Airworthiness Directive requiring extensive, detailed inspection and repair of any cracks or corrosion on all piston- and turboprop-powered Mallards. Some 40 Mallards are in operation, although Chalk’s is the only commercial operation reported.

NTSB engineers and metallurgists found that the right wing had separated at the inboard section, at the wing/fuselage juncture. The signatures are consistent with fatigue fractures, the NTSB said, although it has not released a probable cause for the accident. The AD noted fatigue cracking of the wing spar, skin cracking and a broken z-stringer. The accident Mallard was manufactured by Grumman in 1947 and had logged 31,000 total flight hours and 39,000 total flight cycles. In Chalk’s service, it was operated in a saltwater environment.

No audible sound was found on the cockpit voice recorder; the airplane had no flight data recorder. The Mallard, on a flight to Bimini, the Bahamas, is registered to Seaplane Adventures of Greenwich, Conn. This accident is the first for Chalk’s to involve passenger fatalities.