AL 2000-05
12 September 2000
Tail Rotor Blades
There have been several recent incidents where parts of the tail rotor blade have separated. These tail rotor blades are listed under different part numbers and are interchangeable for the Bell 205, 212 and 412.
The first incident occurred to a Bell 412 when approximately 14 inches of the outboard end of the blade separated during flight. This created an imbalance condition which was so severe that the tail rotor assembly and tail rotor gearbox separated from the rotorcraft. This particular failure resulted from a stress fracture that was caused by corrosion on the inside of the blade skin.
A second incident occurred to a Bell 205A-1 in forward flight at 70 knots at 300 feet AGL. The blade tip closure separated from the tail rotor blade (TSN 2678 hours) assembly. The pilot then felt a severe vibration in the tail rotor but maintained directional control during the immediate landing. Subsequent inspection revealed that the tip closure had separated completely, leaving the honeycomb inner structure totally exposed. This condition created the severe vibration because of tail rotor blade imbalance. The 90-degree gearbox, tail rotor assembly and pitch change assembly were changed as a precautionary measure.
A third incident occurred to a Bell 212 while carrying out power recovery autorotations during pilot training. The pilot was just beginning to practice another autorotation when a loud bang was heard followed by a severe vibration. An emergency landing was carried out. Inspection revealed that the 90-degree gearbox and complete tail rotor assembly had separated from the rotorcraft. When the missing parts were found, it was discovered that the tip weight and end cap of one of the tail rotor blades were missing. Further examination revealed that the tip block had not been properly bonded to the blade. The secondary attachment, countersunk screws, had also failed because the holes had been drilled slightly oversize which allowed the screws to free-fall through the leading edge skin.
In addition to these three incidents, numerous Service Difficulty Reports (SDR) have been submitted on tail rotor blade problems. The majority of these reports list defects such as blade skin debonding, filler missing, skin lifted, separation, material being thrown off and delamination.
Bell Helicopter Textron Incorporated is assisting in the investigations of these incidents. Until a root cause can be determined and appropriate corrective action defined, Transport Canada urges pilots, operators and maintenance personnel to be especially diligent in the inspections of these parts.
Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada.
For further information, contact a Transport Canada Centre, or call Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone (613) 952-4358, facsimile (613) 996-9178, or e-mail caldweb@tc.gc.ca.
For Director, National Aircraft Certification
B. Goyaniuk
Chief, Continuing Airworthiness