SF34, Moruya NSW Australia, 2015
SF34, Moruya NSW Australia, 2015
On 9 January 2015, a Saab 340B encountered a flock of medium-sized birds soon after decelerating through 80 knots during its landing roll at Moruya. A subsequent flight crew inspection in accordance with the prevailing operator procedures concluded that the aircraft could continue in service but after completion of the next flight, a propeller blade tip was found to be missing. The Investigation concluded that the blade failure was a result of the earlier bird impact and found that airline procedures allowing pilots to determine continued airworthiness after a significant birdstrike had unknowingly been invalid.
On 9 January 2015, a Saab 340B (VH-OLM) being operated by Regional Express on a scheduled domestic passenger flight from Sydney to Moruya had just touched down on runway 18 at its destination in day VMC and was decelerating during its landing roll when it encountered a flock of medium-sized birds and hit several of them. Having not detected any consequent damage on inspection during the subsequent turn round, the crew continued their next scheduled sector to Merimbula where damage to one of the propeller blades was noticed and the aircraft was grounded.
A Serious Incident Investigation was carried out by the Australian Transport Safety Bureau (ATSB) and relevant data was obtained from the aircraft FDR. It was noted that the Captain had 6,999 hours total flying experience which included 4,264 hours on type and that the First Officer had 5,399 hours total flying experience which included 4,235 hours on type.
It was established that shortly after the Captain had taken over as PF from the First Officer as the aircraft passed 80 knots after touchdown following an uneventful straight in visual approach to runway 18, a large flock of medium-sized birds identified as Galahs had taken off from the grass on the west side of the runway and flown eastwards at a low height over the runway. Anticipating a birdstrike, the Captain had increased braking and selected reverse pitch propeller on both engines and then, just prior to an unavoidable impact with some of the birds about halfway down the runway, had re-selected Idle.
Having tested the ice protection system before the engines were shut down, the crew advised airport personnel who subsequently recovered around ten bird carcases from the runway. The aircraft was initially inspected externally by the First Officer in accordance with the Operator’s post-birdstrike procedures and he reported finding “clear evidence of multiple bird strikes to the right side of the fuselage and to the right engine and propeller in the form of blood staining and bird carcass debris”. One of the left engine propeller blades was also found to be blood-stained with white powder marks, considered consistent with a birdstrike. No evidence of ingestion into the engines or physical damage to the aircraft or propeller blades was found during this inspection. The Captain and the First Officer reported that they had subsequently carried out a detailed visual examination of the birdstrike-affected propeller blades which included rotating them “so that the forward and aft blade surfaces could be inspected for cracking, buckling, chips, dents or deformation along each affected blade’s leading edge”. After finding no damage, the Captain had contacted the Regional Express for further technical advice and subsequently received clearance to continue with the remainder of the flight schedule. His actions were in accordance with relevant Regional Express procedures.
The crew then operated the aircraft from Moruya to Merimbula where, on opening the forward left door after engine shutdown, the First Officer had “observed that the tip of one of the left propeller blades had detached” (see the illustration below) and the aircraft was withdrawn from service. No damage to the aircraft structure which could be attributed to the loss of the blade tip was found.
A further detailed examination of the aircraft found that most bird remains were on the right side of the fuselage behind the forward right door which was consistent with birds having contacted the lower half of the right propeller disc. There were small pieces of debris on both engine nacelles but no evidence that any had entered either engine. All of the right propeller blades showed evidence of bird impact but only the single damaged blade on the left propeller had any evidence of bird contact. FDR data for the flight from Moruya to Merimbula was examined and found not to provide any evidence as to when the missing left propeller blade tip had separated.
It was noted that the propeller blades were of composite construction. The damaged blade had been installed as a new item in 2000 and had undergone routine inspections and, during overhaul of the propeller in 2011, ultrasonic NDT and there was no record of any impact to this blade prior to the observed birdstrike. The propeller manufacturer concluded that the damage was consistent with that likely in the event of a bird or other hard object impact. It also considered that the buckling of the leading edge erosion strip was likely to have been caused by impact rather than being attributable to subsequent aerodynamic loading and that kinking of this strip “would most likely have been present at the time the blade was inspected at Moruya after the strike”.
In view of the failure of the pilot inspection at Moruya to detect any signs of bird strike damage given the likelihood that some evidence of propeller blade impact was likely to have been overlooked, the Investigation reviewed the applicable Regional Express procedures. These stated that an External Inspection (Crew Change) as specified in the FCOM must be carried out and noted that “generally, blood and/or feathers are noticeable in the impact area of a bird strike”. They also stated that “if the inspection does not reveal the existence of a defect or damage and there was no effect on the aircraft’s performance following the event, the aircraft may continue to operate”. However, the External Inspection referenced in the FCOM was found to contain only two propeller-related items, namely the inspection of the propeller assembly for oil or grease leakage from the hub assembly and inspection of the propeller de-icer boots. It was noted that the FCOM procedures for a post flight inspection included the item “Propellers - including freedom of rotation and each blade front and back for obvious damage”. It was accepted that it was not possible to know if an engineering inspection at Moruya would have detected any deformation to the leading edge erosion strip of the propeller blade which had subsequently shed its tip but it was considered that if an appropriately qualified person had examined the multiple propeller blade bird impacts, “they may have sought further advice from the propeller manufacturer” in accordance with the PMM procedure requiring this "if there is doubt concerning secondary impact damage”.
It was established that under Regional Express aircraft maintenance procedures, birdstrike inspection procedures were supposed to be “derived from” the AMM for airframe inspections and the propeller manufacturer’s Component Maintenance Manual (CMM) and an aircraft specific Propeller Maintenance Manual (PMM) for propeller inspections. The applicable CMM was found to contain a general statement to the effect that “qualified personnel and good engineering practice” must be used for all procedures and standard practices contained in it. The PMM was found to contain a specific sub section covering inspection of propellers after a birdstrike or other impact which included the following:
- Propellers which have had, or are thought to have had a bird strike or other impact must be examined immediately.
- Refer to propeller blade damage limits for allowable damage limits and repairs. Refer to CMM 61-10-39 Check. If the damage is within the allowable limits the propeller can stay in service.
- If the damage is more than the allowable limits, but within the repair limits, a ferry flight may be allowed. The operator should write a ferry flight request on a concession form and send it to Dowty Propellers. Refer to Service Letter E340.
The CMM also contained a sub section on Impact Damage which was applicable to birdstrikes but the ATSB considered that its content was ambiguous as “it was not readily apparent from the procedures whether the bird contact alone would constitute damage” and according to the propeller manufacturer, the presence of feathers and dust marks (a visual indicator) even if there are no signs of visible damage, “may require further investigation”.
It was found that in 2011, Regional Express had sought approval from the Civil Aviation Safety Authority (CASA) for their flight crew to carry out birdstrike inspections of aircraft. After a period of consultations and receipt of guidance on the matter, the airline had developed and submitted for approval a draft flight crew birdstrike inspection procedure. Following some minor changes, this procedure had been approved and incorporated into the Regional Express Policy and Procedures Manual in April 2012. However, following the event under investigation, the airline had advised the ATSB that it had “misinterpreted” the guidance provided by CASA in that when it developed the procedure, it had relied solely on the AMM and had “inadvertently not considered the propeller manufacturer’s PMM and the birdstrike inspection procedure it contained”.
In respect of the wildlife hazard at Moruya, a certified but uncontrolled airport close to the coastline, it was noted that it had a corresponding risk management programme which was assessed as adequate. Although the presence of birds at Moruya Airport was frequent and significant enough to warrant an ‘additional information note’ in the AIP advising that a bird hazard existed, birdstrike rates at Moruya were found to be “considerably lower than those at other regional aerodromes”. More generally, a review of the ATSB occurrence database for the period 1977 to 2014 did not find any other blade failures or in-flight blade tip failures for the propeller type involved in this event which could be attributable to bird impact.
The formally-documented Findings of the Investigation included identification of one Contributory Factor as “the impact from multiple galahs (which) almost certainly reduced the structural integrity of a propeller blade, resulting in the separation of its tip during the subsequent flight”. The Findings also included the identification of one ‘Factor that increased Risk’ as “permitting flight crew to carry out post bird strike inspections was outside the approval of the regulator and propeller manufacturer and reduced the likelihood of identifying serviceability issues”.
Safety Action taken by Regional Express as a result of the investigated occurrence whilst the Investigation was in progress was recorded as the issue of new guidance on birdstrike inspections which introduced an explicit requirement that “If there is any evidence of impact (blood/feathers/dust) on the propellers following (a) wildlife strike the aircraft must not depart until an engineering inspection is complete”.
The Final Report was released on 14 December 2017. No Safety Recommendations were made.