As the pilot of the Brasilia was applying takeoff power, a
nickel leading edge erosion strip separated from one of the left
propeller blades. The strip then bounced off the tarmac under the
aircraft and struck the right propeller blades. The engines were
shutdown and all passengers disembarked safely.
The propeller blades had completed a total of 17,161 hours in
service. The last repair work including the fitment of the nickel
sheath protective strips took place approximately 2,100 hours prior
to the incident.
The erosion strip was recovered and was forwarded for specialist
metallurgical examination. This examination confirmed that the
erosion strip had separated due to loss of adhesion at the adhesive
to sheath interface.
The propeller blade and the failed portions of the nickel sheath
were returned to the manufactuer for detailed examination including
investigation of the procedures used to perform the nickel sheath
replacement. It was found that the sheath had been bonded using an
approved adhesive AF111. Inspection of the nickel sheath showed
that the surface had been prepared correctly prior to the adhesive
being applied. Examination of the blade and nickel sheath showed
the cause of the separation to be cracking of the sheath-to-blade
bond joint. Spectrum analysis of the adhesive showed the presence
of silicone.
The investigation determined that this contamination was
introduced during the bonding process. Review of the process showed
that an adhesive tape containing silicone had been used, and this
is considered to be the most likely cause of the introduction of
silicone.
The propeller manufacturer has reviewed its procedures
associated with this process. Improvements have been identified,
and are being incorporated into the manufacturer's Component
Maintenance Manuals.