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.
|Date:||30 November 2003||Investigation status:||Completed|
|Time:||0830 hours ESuT|
|State:||New South Wales||Occurrence type:||Propeller/rotor malfunction|
|Release date:||16 December 2004||Occurrence class:||Technical|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||de Havilland Canada|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Minor|
|Departure point||Sydney, NSW|
|Departure time||0830 hours ESuT|