Accident at Miami, Florida, 19 Dec 2005 (G-73T)

Accident narrative

On December 19, 2005, about 1439 eastern standard time, a Grumman Turbo Mallard (G-73T) amphibious airplane, N2969, operated by Flying Boat, Inc., doing business as Chalk’s Ocean Airways flight 101, crashed into a shipping channel adjacent to the Port of Miami, Florida. The airplane's right wing separated during flight shortly after takeoff from the Miami Seaplane Base. All 20 people aboard were killed, and the airplane was destroyed by impact forces.

### The flight

Flight 101 was a regularly scheduled passenger flight to Bimini, Bahamas, operating under visual flight rules in visual meteorological conditions. There were 2 flight crewmembers and 18 passengers on board, including three lap-held infants.

The captain, age 37, had accumulated 2,820 hours of total flying time, including 1,630 hours in the G-73T. She also served as the company's director of safety. The first officer, age 34, had accumulated 1,420 hours of total flying time, with 71 hours in the G-73T.

The accident airplane was manufactured by Grumman Aircraft Engineering Corporation in May 1947 as a G-73 model equipped with radial piston engines. In July 1981, Chalk's Ocean Airways modified it to a G-73T model by replacing the piston engines with turbopropeller engines in accordance with a supplemental type certificate. At the time of the accident, the airplane had accumulated 31,226 total flight hours and 39,743 total cycles.

### The sequence of events

The flight crew flew the airplane from Fort Lauderdale to the Miami Seaplane Base earlier that afternoon, landing about 1321. The airplane departed on the accident flight about 1438.

About one minute later, the airplane crashed into the water. Witnesses reported that the airplane's right wing separated from the rest of the airplane in flight, that smoke or fire came from the wing or a fireball in the sky, and that the airplane subsequently descended into the water. About one-half of the witnesses reported hearing an explosion associated with the wing separation.

Most of the wreckage was located in about 30 feet of water. The U.S. Coast Guard launched a helicopter about 7 minutes after receiving notification and began recovery efforts 6 minutes afterward.

### What the investigation found

The airplane was equipped with a cockpit voice recorder, but the audio was unintelligible. Testing revealed a failure of the electronic circuit card for the erase head, resulting in the tape being recorded over multiple times without being erased. The airplane was not equipped with a flight data recorder, nor was it required to be. An explosives examination found no evidence of explosives.

**Wreckage and structural failure** The investigation found that the center wing box structures were fractured where the wing intersected the fuselage at right wing station 34, allowing the right wing to separate. The right wing fuel tank was breached, and fire damage was evident on the right wing and on fuselage and empennage skins aft of the right wing. The left wing showed no evidence of fire damage.

Detailed examination of the right wing revealed preexisting fatigue fractures and cracks in the rear Z-stringer, lower skin, and rear spar lower spar cap. The Board's analysis revealed that the right rear Z-stringer likely fractured first, with fatigue initiating at a slosh hole. After the stringer fractured, the lower skin developed a fatigue crack that grew to about 16 inches in length. Finally, fatigue cracks initiated in the rear spar lower spar cap from a double-drilled hole, and the spar cap fractured in overstress. The Board concluded that this multiple-element fatigue damage reduced the residual strength capability of the wing structure and caused the fatigue failure of the wing during normal flight operations.

The left wing also exhibited fatigue fracture features in the rear Z-stringer, middle Z-stringer, front spar lower spar cap, and lower skin near left wing station 34.

**Maintenance program deficiencies** The Board found that the Chalk's Ocean Airways maintenance program was ineffective in identifying and correcting longstanding structural problems. The skin crack under the right wing intersected three stop drill holes, indicating that the crack had been detected by maintenance personnel on at least three occasions. One external and three internal doublers had been applied to the area, but the company's maintenance records contained no entry for this major repair. The Board concluded this repair was ineffective because it did not restore the load-carrying capability of the skin and did not address the underlying fractured Z-stringer. Fasteners for the doubler were inserted through hard green sealant around a fuel sump drain instead of skin material.

Flight logs from July and September 2005 documented numerous fuel leak discrepancies in the right wing root and dry bay areas. Maintenance records indicated these were corrected by removing existing sealant and applying new sealant. The Board concluded that the repetitive fuel leaks were indicators of structural damage inside the right wing, and that the company's evaluation of the recurring leaks was inadequate.

The investigation noted maintenance-related problems with other airplanes in the company's fleet. In August 2005, a designated engineering representative inspected another company G-73T after reports of fuel leaks and found a 22-inch crack in the right wing lower skin and corroded stringers. The Board concluded that, based on the repetitive fuel leaks on the accident airplane and the structural damage found on the other airplane, Chalk's Ocean Airways should have performed a comprehensive inspection of the wing structures in its fleet.

Interviews with pilots revealed concerns about the maintenance of company airplanes. One former captain stated he resigned because of maintenance concerns, writing in a letter to the company that delayed and ignored maintenance had caused an alarming trend.

**FAA oversight and certification** The FAA principal maintenance inspector was responsible for overseeing the company's maintenance program. The inspector conducted an aging aircraft inspection in October 2005, but the paperwork did not include the undocumented major repair to the right wing lower skin. The inspector also did not attend the July and September 2005 company meetings where the fuel leaks were discussed. The Board concluded that the FAA's procedures for maintenance program oversight, when applied to commercial operators of aircraft with limited manufacturer or engineering support, were insufficient to ensure the adequacy of the structural airworthiness plans.

The Board also reviewed the airplane's certification. When the supplemental type certificate to install turbopropeller engines was applied for in 1968, the FAA allowed the applicant to use the airplane's original 1940s certification basis. This required a static strength analysis but no fatigue analysis. The Board concluded the FAA missed an opportunity to recertify the airplane with a fatigue analysis, which likely would have included a determination of a safe operating life and inspection requirements that could have prevented the accident.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "the in-flight failure and separation of the right wing during normal flight, which resulted from (1) the failure of the Chalk’s Ocean Airways maintenance program to identify and properly repair fatigue cracks in the right wing and (2) the failure of the Federal Aviation Administration to detect and correct deficiencies in the company’s maintenance program."