N106CP

On March 31, 1998, about 0900 eastern standard time, a Southwest Florida Aviation SW204, N106CP, registered to Colony Services, Inc., operating as a 14 CFR Part 137 agricultural aerial application flight, experienced engine surging while lifting off a flatbed trailer in a citrus grove near Indiantown, Florida. The helicopter crashed on a canal bank and was substantially damaged. Visual meteorological conditions prevailed and no flight plan was filed. The commercial-rated pilot was not injured. The flight was originating at the time of the accident.

The pilot stated that as he lifted off the trailer, having taken on fuel, (650 pounds, total) and 100 gallons of rinse water, (835 pounds) subsequent to a spray mission, the engine suddenly started to lose power. The helicopter settled back onto the platform and bent the landing skids. The engine regained power and the pilot maneuvered the helicopter backward off the trailer where he experienced another power loss and started settling into a citrus tree. The engine regained power a third time, the pilot maneuvered the helicopter toward a clear area when the engine sustained a total failure causing an inflight collision with the bank of an irrigation canal.

Statements from each of the two ground crewmen, in the form of sworn affidavits taken by a law firm and sent to the company's FAA Principle Maintenance Inspector, revealed that due to a faulty quantity gage, the ground crew overfilled the helicopter's chemical tank to overflowing with rinse water while it was on the platform at idle power, and the ground crew was in the process of acquiring a drain hose to remedy the mistake when the pilot waved them off and attempted a liftoff. The statement added, "When he tried to take off the engine kind of choked down real bad because he didn't have enough power." Their individual affidavits also state that the pilot added canal water to the fuel system, postcrash, and threatened them to secrecy.

According to Colony Services, Inc., the maximum gross liftoff weight of N106CP was 8,500 pounds and is substantiated by the type certificate data sheets for the SW204 helicopter. The company stated that the empty weight of N106CP was 5762 pounds, and that its chemical tank capacity was 250 gallons. The density altitude at the time and location of the accident was 1,360 feet. Total liftoff weight of the helicopter plus fuel onboard as stated by the pilot plus chemical tank load as stated by the ground crew would have been about 8669 pounds or about 169 pounds over weight.

Subsequent tear-down inspection of the Lycoming turbine engine, model T53-L-11D, serial number LE-11597, with FAA oversight, was conducted at the Allied-Signal Product Safety and Integrity Investigation Laboratory, Phoenix, Arizona, on May 20, 1998. Inspection revealed the following; (1) power turbine nozzle retention bolts were not properly tab-locked, (2) four of these retention bolts had backed out and were found lying in the 1st power turbine, (PT) nozzle outer flange/scroll, (3) severe pitting/erosion was present on the forward face of the PT rotor disk, (4) the PT rotor shaft was fractured through 360 degrees just forward of the rotor disk, (5) of the 62 PT rotor blades, 33 were fractured at or near the blade platform and 29 were fractured near the midspan or the tip, (6) the fuel regulator filter element was found to be saturated with water and iron rust. Material analysis conclusions were that the specimen PT blades had features associated with a tensile overload fracture, no defects were observed on the fracture surfaces, and no evidence of fatigue was noted. (See enclosed report, Tear Down Report of One Model T53-L-11D Turboshaft Engine Serial Number LE-11597).

The fuel regulator and power turbine governor computer assembly were inspected and functionally tested at an FAA certified repair station, Tucson, Arizona, on August 20, 1998, with NTSB and FAA oversight. The inspection report states, "Based upon the results of bench test and corrosion of the computer assembly, it can be concluded the erratic operation of the fuel regulator was caused by the corrosion. The corrosion can be attributed to the water found in the fuel control unit." (See enclosed report, NTSB Investigation: MIA98LA114, Subject: Fuel Regulator and Power Turbine Governor and enclosed FAA report, Functional Overhaul Flow Test).