Investigation number
200304918
Occurrence date
Location
Sydney, Aero.
Report release date
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Aviation occurrence type
Propeller/rotor malfunction
Occurrence category
Incident
Highest injury level
None

Sequence of events

On 30 November 2003, a de Havilland Canada DHC-8 (Dash 8)
aircraft, registered VH-TQA, departed Sydney, NSW, on a scheduled
passenger flight to Albury, NSW. Shortly after takeoff, a passenger
reported damage to the lower area of the window on the left side of
the aircraft, at row five. After confirming the damage, the flight
crew returned the aircraft to Sydney, where an inspection revealed
that a propeller blade collar had separated from one of the blades
of the left propeller (refer figure 1). A small piece of the
separated collar, with one attaching bolt and nut, was subsequently
retrieved adjacent to the departure runway (refer figure 2).

An engineering examination of the left propeller revealed that a
blade collar had separated from one propeller blade. As one other
propeller blade sustained damage from the collar separation, both
were sent to an overhaul facility in New Zealand for examination
under the supervision of the New Zealand Transport Accident
Investigation Commission (TAIC).

In December 2002, a major inspection was completed on the
propeller blade from which the collar had separated. In June 2003,
it had undergone a trailing edge repair, due to impact damage. The
blade collar was bonded to the blade root with sealant compound
RTV-157, and the collar halves were also fastened by two connecting
bolts, nuts and associated washers. The single recovered bolt, nut
and washers were found intact with no apparent damage.

An examination of the sealant compound on the recovered section
of the collar revealed that the sealant used was the correct type
and specification and within its time and life expiration dates. A
detailed examination of the recovered collar piece at the ATSB
revealed that the collar displayed no gross manufacturing defects,
but that the bonded joint gap was large and that no effective
bonding had occurred on the mating surface. There was also evidence
of sealant compound having been applied as a thin layer at a
previous time. This film of sealant was partially covered by black
paint.

A small sample of recovered RTV157 sealant was sent to a
specialist laboratory for examination and comparison with a known
reference sample. That examination indicated that the sealant
recovered from the failed propeller blade cuff had been
contaminated with a black substance giving it a different
appearance from the supplied reference sample. The failed RTV 157
also contained a significant proportion of an extractable
ester-based chemical that was not detected in the reference
compound.

A review of the laboratory findings by the propeller
manufacturer, relating to the RTV 157 compound, indicated that
there were a number of potential sources of sealant contamination
during assembly, installation, and operation of the propeller.
However, there was not enough evidence to indicate the source of
the observed contamination.

Subsequent to this occurrence, on 28 October 2004 a collar
separated from the propeller of another of the operator's Dash 8
aircraft. In this instance, the collar did not impact the aircraft
and was noticed missing during a subsequent pre-flight inspection.
That collar had also been bonded with RTV-157 sealant.

As the entire blade collar was not recovered, a full assessment
of the collar failure was not possible and factors relating to the
assembly geometry of the collar could not be assessed.

As a result of the occurrence, the aircraft operator immediately
initiated an inspection program of all similar propeller blade
collars. That inspection revealed that five other aircraft had at
least one loose propeller blade collar. All affected propeller
blade collars were immediately repaired.

Subsequent to the initial fleet inspection, the operator
initiated a repetitive inspection regime, requiring a visual
inspection for condition and security of all propeller blade
collars. Additionally, the operator issued an instruction to all
propeller workshops servicing their propellers, requiring that all
propeller blade collars are to be bonded using an approved
alternate bonding compound, PR 1826.

Aircraft Details
Departure point
Sydney, NSW
Destination
Albury, NSW
Model
DHC-8
Serial number
365
Registration
VH-TQA
Operation type
Air Transport High Capacity
Damage
Minor
Manufacturer
De Havilland Canada
Departure time
0830 hours ESuT