Safety Advisory Notice

Detecting an unsecured canopy prior to take-off could prevent in-flight control issues resulting in injury or aircraft damage.

What happened

On 14 October 2014, a Van’s Aircraft Inc. (Van’s) RV-6A departed Moorabbin Airport, Victoria on a local flight. Shortly after reaching 2,900 ft, the aircraft descended rapidly and a witness reported observing objects falling from the aircraft. The aircraft collided with the ground next to a house 8 km south of Moorabbin. The pilot was fatally injured and the aircraft was destroyed. Members of the public found a number of items away from the accident site that belonged to the pilot.

Tip-up canopy open

(Source: Supplied)

Why did it happen

The liberation of the items from the aircraft’s interior indicated that the tip-up (forward-hinged) canopy likely opened in‑flight. While the ATSB was unable to determine how the canopy opened and the effect on aircraft control, there were indications the pilot was attempting to respond to the situation. However, for reasons undetermined, recovery did not occur before the impact with the ground. The ATSB found that, in a number of Van’s models, the in-flight opening of a tip-up canopy may potentially result in a significant pitch down tendency that may affect aircraft control.

Safety advisory notice

: The consequences when an aircraft canopy opens in-flight, including on other than Van’s aircraft types, can vary from being relatively benign to significant, such as a sudden pitch down. In any event, in the first instance, pilots should expect an element of startle and distraction. The detection of an unsecured canopy prior to take-off could prevent in-flight control issues resulting in injury or aircraft damage. The ATSB advises pilots to be vigilant and to confirm the security of their aircraft’s canopy prior to take-off.

Check the security of your canopy

The in-flight opening of canopies in a number of Van’s aircraft models highlights the varying consequences in the case of such occurrences. The result can vary from being relatively benign to significant. While this investigation focused on Van’s aircraft, the implications are applicable to all aircraft fitted with a canopy, in particular, a tip-up canopy. Such occurrences serve as a reminder for pilots to check the security of their aircraft’s canopy prior to take‑off. Additional measures, such as the incorporation of a specific pre-flight checklist item, and/or the installation of a canopy-open warning device, have the potential to assist pilots detect an unintentionally-open canopy.

The ATSB encourages pilots who experience a canopy opening in-flight to notify the aircraft manufacturer and, in the case of difficulty controlling their aircraft, the ATSB in accordance with the reporting requirements of the Transport Safety Investigation Act 2003. This will allow for a greater understanding of the safety implications of these types of occurrences.

Read more about this ATSB investigation: AO-2014-164

Safety issue: Potential adverse effects of a tip-up canopy opening in-flight

What happened

In the early hours of 14 July 2015, the offshore support vessel (OSV) Skandi Pacific was loading cargo from an oil rig about 165 km off Australia’s north-west coast. As the weather deteriorated, cargo operations were stopped and the OSV moved a short distance from the rig. Two crewmembers then began securing the cargo on the vessel’s aft deck.

While securing the cargo, the crewmembers slackened the securing chain they had used to secure the containers on the starboard side to better secure the entire stow. Shortly after, two large waves came over Skandi Pacific’s open stern, shifting the unsecured containers forward. One crewmember was trapped between the moving containers, chains and a skip and suffered fatal crush injuries.

Skandi Pacific's aft deck

Source: DOF Management

Why did it happen

The deteriorating weather conditions had resulted in the cargo operations being stopped. After the crewmembers had lashed the cargo they found two mini-containers forward were not properly secured. To secure the containers, they decided to use a secondary chain, by securing it to the crash barrier then to the primary chain. When tightened, this chain would bring the primary chain in tight against the mini-containers. Their plan required slackening the primary chain to secure the secondary.
However, the sequence of working exposed them to high risk if water was shipped on Skandi Pacific’s aft deck. The crewmember attempting to fasten a securing chain forward of the two unsecured mini-containers was in a position of danger when waves came over the vessel’s open stern.

The Australian Transport Safety Bureau (ATSB) found that vessel’s managers had not adequately assessed the risks associated with shipping seas over the vessel’s stern while securing cargo on this type of vessel (the OSV had an open stern). Further, there were no clearly defined limits for excessive water on deck that necessitated stopping operations, leaving individuals to make difficult, and necessarily subjective, decisions about whether or not to stop work.

The ATSB investigation also identified that the vessel’s safety management system procedures did not contain clearly defined weather limits for working or securing cargo in adverse weather.

Safety advisory notice

: The Australian Transport Safety Bureau advises the masters, owners and operators of all offshore support vessels to ensure that the risks associated with working on the aft deck of vessels with open sterns are adequately assessed.

Read more about this ATSB investigation: Fatality on board Skandi Pacific, off the Pilbara coast, Western Australia on 14 July 2015.

Safety Advisory Notice

To Beechcraft Baron operators

Beechcraft Baron heater fuel supply line inspection

The ATSB is encouraging Baron operators to inspect the heater fuel supply line and nearby wiring in the aircraft cockpit to reduce the risk of an in-flight fire.

What happened

At approximately 0835 on the morning of 16 April 2022, the pilot of a Beechcraft B58 Baron registered VH-NPT commenced an approach to Runway 12 at the East Kimberley Regional Airport near Kununurra. Upon selection of the landing gear to the down position the pilot reported multiple unusual indications, the gear failed to extend and smoke started to emerge from forward of the pilots side circuit breaker panel. By the time the pilot had declared a PAN, flame was emerging from the same location as the smoke. The pilot expended the aircraft’s fire extinguisher but the fire returned. Smoke and flame continued to effect the pilot until the aircraft collided with terrain where it was consumed by a significant post impact fire. The pilot sustained serious injuries and the single passenger onboard was fatally injured.

Related Occurrence

During the initial phase of the investigation the ATSB identified a similar occurrence that had been investigated in 2014 (

). The investigation of the in-flight cockpit fire found that electrical wiring had chaffed through the heater fuel supply line causing it to arc and burn a hole in the fuel line. This provided an ignition source and accelerant for the fire.

Why did it happen

Both the heater fuel line and the aircraft wiring of NPT were consumed by the post impact fire, and an examination was not possible. However, the location, initiation and severity of the fire is similar to the incident detailed in AO‑2014‑040. As such, while the specific circumstances of the fire initiation and acceleration remain under investigation, in the interest of transport safety, the ATSB has issued this safety advisory notice.

Manufacturer Response

In response to the advanced release of this ATSB SAN the manufacturer advised that there is a potential for chafing of wiring across several Beechcraft models including the Baron. Model Communiqué 116 references wire chafing reports in the Beechcraft Bonanza but the communiqué states that the protection of wires from chafing damage is applicable to all Beechcraft models.

Safety advisory notice

AO-2022-026-SAN-001: The ATSB encourages operators of Beechcraft Baron aircraft to conduct a detailed inspection of the heater fuel supply line and wiring in its vicinity. The examination should focus specifically on the area below the pilot’s circuit breaker panel and areas forward of this under the instrument panel. Any identified issues should be reported to CASA (via the defect reporting system) and the manufacturer.

The ATSB encourages Baron operators to review the Electrical Wire Chafing Protection section in Model Communiqué 116 (See attachment A) put out by Beechcraft in June of 2008, which is applicable to all Beechcraft models.

The ATSB further encourages operators to review the anti-chafing provisions within the relevant aircraft maintenance manual (see 20-04-00-001 – Electrical Wiring – Description and Operation) to ensure serviceability of anti-chafing materials and replace or fit, as necessary. Specific consideration should be given to wiring in the vicinity of lines carrying flammable liquids.

ATSB comment

The ATSB notes similarities in several Beechcraft models, that utilise fuel lines running through the cockpit. While a review of ATSB data does not support the broadening of the SAN to include other aircraft models,  chafe protection should be applied to wiring as per the manufacturers' requirements and particular care should be taken when wiring is in the proximity of lines carrying flammable liquids.

Area of concern in an exemplar Baron B58 showing the location of the fuel line and wiring looms. Inspection should encompass any areas along the fuel line where it may contact wiring looms.

Source: Operator

Read more about this ATSB investigation: Collision with terrain involving Beechcraft Baron 58, VH-NPT, near Kununurra Airport, Western Australia, 16 April 2022

Safety Advisory Notice

To aerobatic pilots and instructors

All aircraft types do not spin and recover in the same way. Know your aeroplane type, what recovery techniques will work and what recovery techniques will not work.

What happened

On 23 June 2021, while conducting spin entry and recovery training from 5,800 ft above ground level, the Cessna A150M Aerobat did not fully recover from a spin to the left before impacting terrain.

Factors uncovered during the investigation

The aerobatics instructor was experienced in conducting spins, primarily in the Pitts Special aircraft type. However, it was likely that they had no experience in spinning a Cessna A150 Aerobat or any similar variant.

The instructor’s theoretical spin training provided to the aerobatic student pilot (and another student at the same time) did not include instruction on the recovery technique as prescribed in the Aerobat pilot’s operating handbook (POH). Further, the ATSB established that it was likely the instructor intended to practice 2 spin recovery techniques (Mueller/Beggs and PARE). The technique broadly known as the Mueller/Beggs recovery method, has been shown to not recover a Cessna A150 Aerobat established in a spin to the left. However, the PARE method was similar to Aerobat POH method, with less emphasis on the brisk full forward movement of the control yoke.

Safety advisory notice

: The ATSB strongly encourages all aerobatic pilots and aerobatic flight instructors to be aware:

• the Mueller/Beggs method of spin recovery does not recover all aircraft types from a spin
• the Mueller/Beggs spin recovery method limitations should be emphasised during spin theory training
• the Mueller/Beggs method of spin recovery will not recover a Cessna A150 Aerobat or similar variants from a spin in some circumstances
• they should review the pilot’s operating handbook of the aircraft type that they intend to operate for the recommended spin recovery technique
• prior to doing spins in any model aircraft, pilots should obtain instruction and or advice in spins from an instructor who is fully qualified and current in spinning that model.

Read more about this ATSB investigation: Investigation: AO-2021-025 - Collision with terrain involving Cessna A150M, VH-CYO 5 km west-south-west of Peachester, Queensland, on 23 June 2021

Safety Advisory Notice

To operators and maintainers of UH-1H helicopters

Loss of drive to the main rotor system

What happened

On 14 February 2022, the pilot of a Garlick Helicopters UH-1H was providing aerial firefighting support to combat the ‘Labrina’ bushfire that had developed north of Launceston, Tasmania. That afternoon, the pilot was tasked to firebomb a localised hot-spot that had developed within the fireground. Witnesses both on the ground, and within a nearby helicopter, observed the early release of the water load from the underslung bucket, before the UH-1H commenced a left turn and descended toward nearby open terrain. The helicopter was then observed to slow and enter a hover, then rapidly yaw, before descending and impacting terrain. The pilot was fatally injured, and the helicopter was destroyed.

Why did it happen

The ATSB’s on-site examination of the wreckage found anomalies with the helicopter’s main drive shaft, identified as a KAflex and manufactured in the United States by Kamatics Corporation (Kamatics), that transmits engine power to the transmission. The shaft was found to have fragmented during the accident sequence, with 4 of the flex-frame attaching hardware (nuts, bolts, and their washers) and portions of the flexible frame elements unable to be accounted at the accident site. The ATSB subsequently commenced a detailed technical examination of the KAflex shaft assembly and importantly, severe frictional and wear damage was identified to have occurred to one portion of the shaft. The results of that work was presented to Kamatics and the Civil Aviation Safety Authority (CASA).

While the ATSB’s investigation of this accident and further technical examination of the KAflex shaft remain ongoing, the manufacturer advised that the presence of the frictional damage was evidence that the shaft had entered fail-safe mode during operation. The frictional damage was consistent with other KAflex shafts that had entered fail-safe mode following the release of flex-frame attaching hardware, or, when one of the flexible frame elements had fractured during operation.

Kamatics further advised that, although the fail-safe feature is intended to allow for uninterrupted drive for up to 30 minutes of helicopter operation, if a flex-frame attachment bolt were to release, the time before complete shaft failure may be significantly reduced. Reports from other UH-1H accidents involving a partial KAflex shaft failure identified that the off-centre operation and corresponding imbalance can produce sudden loud noises, vibrations, and control difficulties for the pilot.

Kamatics also stated that, while the United States Federal Aviation Administration airworthiness directive AD 2021‑26‑16 became effective on 25 February 2022 for the inspection and potential replacement of KAflex shafts installed in UH-1H helicopters, some concern remains for shafts identifed in the serial number ranged 0635 and below. The manufacturer is uncertain of the configuration status of this serial number range, whereby these shafts may be fitted with legacy flex-frame attachment hardware that can exhibit signs of deterioration, increasing the potential for shaft failure.

While the specific circumstances of this accident are still under investigation, the ATSB has issued the following safety advisory notice to advise UH-1H operators and maintainers of the potential safety concern.

Safety advisory notice

: KAflex main drive shaft failure

The ATSB advises operators of UH-1H helicopters to note the preliminary details of this accident, the content of AD 2021‑26‑16 and CASA Airworthiness Bulletin AWB 63-004, and to look for the presence of:

• corrosion
• fretting
• frame cracking
• missing or damaged flex-frame attaching hardware

during all inspections of the KAflex drive shaft. Any identified defects should be notified to the Civil Aviation Safety Authority and the ATSB.

Additionally, operators should be aware of Kamatics concern of a certain serial number range of shafts for the UH‑1H helicopter that may be fitted with legacy flex-frame attachment hardware. Kamatics (chris.prain@kaman.com) should be contacted if a shaft in the affected serial number range (0635 and below) is identified.

Fragmented KAflex from the accident helicopter, source ATSB

Read more about this ATSB investigation: Drive shaft failure and loss of control involving Garlick Helicopters UH-1H, VH-UHX, 36 km north of Launceston, Tasmania, on 14 February 2022

Safety Advisory Notice

To manufacturers and operators of larger air transport aeroplanes

Delayed flight crew responses can lead to hazardous high-speed rejected take-offs or flight with unreliable airspeed indications.

What happened

On the night of 18 July 2018, an Airbus A330 commenced take-off from Brisbane, Queensland with covers left on the aircraft’s three pitot probes (airspeed sensors). The primary flight displays showed red speed flags in place of the airspeed indication early in the take‑off, and either speed flags or unrealistically low airspeeds for the remainder of the flight. The standby airspeed display was also invalid throughout the flight.

The flight crew did not see or respond to the speed flags until the aircraft’s speed was too high for a safe rejection of the take-off. The take-off was continued and the aircraft returned to Brisbane.

Source: Airbus 

Why did it happen  

Surprise, uncertainty, time pressure, and ineffective communication between the two pilots during the take-off probably led to stress and high cognitive workload. Numerous take-offs have been continued, or rejected at high speed, with single or multiple airspeed anomalies. Flight crews who continued generally turned back.

The ATSB found that flight crews were not detecting unreliable airspeed early enough in the take-off, or if they did, other factors prevented or delayed a decision to reject the take-off. This is probably because:

• aircraft alerts related to unreliable airspeed were either not available during take-off, or were not prominent enough to gain both the flight crew’s attention in a manner that the presence and importance of the problem were both immediately apparent                                                                                                                         
• there was limited guidance provided to flight crews to aid in the detection and decision-making processes in response to unreliable airspeed indications.

These concerns are very likely to be relevant to many aircraft types.

Safety advisory notice

The Australian Transport Safety Bureau encourages all manufacturers and operators of larger air transport aeroplanes to consider what types of unreliable airspeed events can occur, how the information is presented to flight crews, and what responses are the safest in different phases of the take-off and in a range of potential situations. Aircraft alerting systems, flight crew procedures, and flight crew training should be designed to provide sufficient assurance that flight crews become aware of and understand how to appropriately respond to unreliable airspeed on take-off in a timely manner.

Read more about this ATSB investigation: Airspeed indication failure on take-off involving Airbus A330, 9M-MTK, Brisbane Airport, Queensland, on 18 July 2018

Safety Advisory Notice

To helicopter pilots and operators

A correctly fitted and secured flight helmet can significantly reduce injuries and save lives in the event of a serious incident or accident. But a helmet is only fully effective if it is fitted correctly, retained securely on the wearer’s head, and maintained in accordance with the manufacturer’s instructions.

Source: ATSB

What happened

On 31 July 2020, the pilot of a Robinson R44 helicopter was conducting aerial spraying along a property fence line. During the fifth spray load, as the helicopter descended from above trees to recommence spraying, it struck a powerline about 5 metres above the ground. The helicopter subsequently collided with terrain resulting in substantial damage. The pilot sustained fatal injuries.

Survivability

The pilot was not adequately restrained by the seat belt’s shoulder sash resulting in the pilot’s head impacting on the left side of the helicopter. This resulted in non-survivable head injuries.

The pilot was wearing a helmet during the initial impact. While it could not be determined if the accident impact forces were survivable, the helmet may not have been fully effective as it came off during the accident sequence.

There was also no evidence that the helmet had been maintained or serviced, including after it had likely been worn in a previous accident. 

Helmet regulations and standards

For all pilots conducting low-level operations, a helmet is an essential component of personal protective equipment required to be worn under work, health and safety guidelines. Wearing a helmet is not mandated by the Civil Aviation Safety Authority, and there is no Australian Standard for flight helmets. However, many commercially available helmets meet or exceed military and US and European civilian standards, some of which are designed specifically for helicopter operations.

To work as designed, a helmet must be adjusted to fit the head and the chin strap must be fastened securely. The helmet must be serviced regularly, routinely inspected for damage, and replaced immediately if it has sustained a major impact.

Safety advisory notice

: The ATSB strongly encourages all pilots conducting low-level operations to wear a flight helmet, ensuring that it is:

• fit for purpose
• custom fitted to the pilot’s head
• properly secured by using the chin strap
• maintained in accordance with the manufacturer’s recommendations.

Read more about the ATSB’s investigation: Wirestrike and collision with terrain involving Robinson R44, VH-HNF, 69 km south-east of Hay Airport (Steam Plains), New South Wales, on 31 July 2020

Safety Advisory Notice

To owners and maintainers of Stolp Acroduster SA-700/750 aircraft

Stolp Acroduster upper-wing attachment point, eye bolt fatigue cracking resulted in an in-flight break-up.

What happened

On 18 August 2021, an amateur-built Stolp Acroduster II SA-750, registered VH-YEL, departed Caboolture Airfield, Queensland, Australia for an aerobatic flight, with the pilot being the sole occupant. A short time later the aircraft sustained an in-flight break-up. The aircraft was destroyed and the pilot was fatally injured.

Why did it happen

The centre section of the upper wing was located away from the main aircraft wreckage. Technical examination of the cabane struts from the centre section confirmed that there was fatigue cracking on the fracture surfaces of the eye bolts that had been fitted in the upper-wing forward position on the left and right cabane struts. The fatigue cracking had initiated in the thread root of each eye bolt at its termination into the cabane strut.

Stolp Acroduster II SA-750 showing centre wing forward attachment points locations

Source: Supplied, annotated by the ATSB

The right eye bolt had sustained fatigue cracking through about 90 per cent of the cross-section, and the left eye bolt had sustained about 40 per cent fatigue cracking through its cross-section. From the preliminary examination findings, it is indicative that fatigue cracking and then fracture of the eye bolts has led to structural instability of the centre-wing section and a consequential in-flight break-up of the upper-wing structure.

There were about 130 Acroduster SA-700/750 aircraft that were completed. The accident aircraft was first flown in the US in 1981, where it was registered N97177. It was exported to Australia in 2007, and registered as VH-YEL. It has accumulated about 717 flight hours at the time of the accident.

Right forward cabane strut showing fractured eye bolt

Source: ATSB

Additional information

This aircraft type has had previous instances of cracking in the same area of the cabane strut upper-wing attachment eye bolts, through the threaded sections. The location of fatigue cracking in the forward upper-wing attachment eye bolts makes identifying fatigue crack during visual inspections difficult and in some cases impossible without removing the eye bolts from the cabane strut. The aircraft type does not have a specific detailed scheduled inspection of the eye bolts to ensure their ongoing airworthness. It also does not have a time-life replacement of the eye bolts at set periods.

Due to the location of the fatigue cracking through a primary structual support to the upper wing, the ATSB is concerned for the ongoing airworthiness of the Stolp Acroduster aircraft.

Safety advisory notice

:

The Australian Transport Safety Bureau advises all owners, operators and maintainers of Stolp Acroduster SA‑700/750 aircraft to consider the safety implications of the initial findings of this investigation regarding the fatigue cracking on forward cabane strut upper wing attachment eye bolts, and take action where considered appropriate to ensure that their aircraft remain airworthy.

Read more about this ATSB investigation: In-flight break-up, Stolp Acroduster II SA-750, VH-YEL, 16 km north-east of Caboolture airfield, Queensland, on 18 August 2021

Safety Advisory Notice

To R44 helicopter operators

Fatigue cracking in an R44 helicopter clutch shaft resulted in the total loss of drive to the main rotor system while airborne.

What happened

On the morning of 22 December 2020, the pilot of a Robinson R44 helicopter was conducting aerial agricultural spray operations on a property 13 km south‑east of Clare Valley Aerodrome, South Australia. After completing numerous spray runs throughout the morning, the pilot was preparing to land the helicopter adjacent to a loading vehicle for replenishment of chemical product by a ground crewman when a loud bang emanated from the rear of the helicopter.

The pilot reported that, following the noise, the helicopter descended rapidly and there was significant resistance from the flight controls. The helicopter collided heavily with the loading vehicle, coming to rest on its side. The pilot and crewman were uninjured. The operator’s preliminary on-site assessment of the substantially damaged helicopter identified that a mechanical disruption had occurred to the drive system. 

Fractured clutch shaft yoke 

Source ATSB

Why did it happen

The ATSB’s preliminary metallurgical examination of the drive train components identified that the clutch shaft forward yoke had fractured. The fracture occurred at a bolt hole on the yoke lug that connected with the forward flex plate (Figure 1) and was due to the development of fatigue cracking that progressed almost entirely through the yoke cross‑section.

Figure 1: Main gearbox forward flex plate and yoke assemblies

Source: Robinson Helicopter Company illustrated parts catalogue, annotated by the ATSB 

The fracture resulted in the loss of engine drive to the main rotor system. Corrosion product and fretting damage were identified in the vicinity of the bolt hole adjacent to the fatigue fracture surfaces.

The airworthiness of the yoke is not limited to a total time in service (no life-limit) and it is required to be inspected at every 100-hour, or annual, inspection. The opportunity to conduct a detailed examination of the yoke contact surfaces for defects is generally limited to those occasions when the bolts are removed and the yoke is separated from the forward flex plate. That is only scheduled to occur during 12 year/2,200 hour overhaul inspections.

A general visual inspection of the assembled clutch shaft yoke during the 100‑hour (or annual) inspection may not easily identify defects such as corrosion, fretting and/or cracking.

While the specific circumstances that led to the fatigue crack on the accident helicopter are still under investigation, the ATSB has issued the following safety advisory notice to advise R44 operators of a potential safety concern.

Safety advisory notice

: The ATSB advises operators of R44 helicopters to note the preliminary finding of this accident and to look for the presence of corrosion, fretting or cracking, which may not be visually obvious, during all inspections of the clutch shaft yoke. Any identified defects should be notified to both the ATSB and the Civil Aviation Safety Authority.

Read more about this ATSB investigation: Loss of control and collision with terrain involving Robinson R44 II, VH-HOB, near Clare, South Australia, on 22 December 2020

Safety Advisory Notice

Yakovlev Aircraft Factories Yak-52 owners and maintainers

Elevator bellcranks manufactured from aluminium alloy, fitted to Yakovlev Aircraft Factories Yak-52 aircraft, are known to crack. Periodic inspections are important for detecting the presence of fatigue cracking early and ultimately preventing the failure of the component in-flight.

What happened

On 5 June 2019, the pilot and passenger of a Yakovlev Aircraft Factories Yak-52 aircraft, departed Southport airfield, Queensland, for a private aerobatic flight. During the flight, the aircraft collided with water near South Stradbroke Island. The occupants were fatally injured, and the aircraft was destroyed.

What increased risk

During the wreckage examination, the ATSB identified two small cracks at the change in section of the elevator bellcrank. The location was coincident with that identified in previously published airworthiness directives^[1] and the manufacturer’s airworthiness data. Further examination confirmed at least one was a pre-existing fatigue crack (Figure 1). Although this crack did not contribute to the accident, if not detected, cracking in this area could result in failure of the bellcrank and a subsequent loss of aircraft control.

Elevator bellcrank and mass balance removed from VH-PAE

The aircraft had flown about 35 hours since the bellcrank was last inspected. In Australia, the Australian Warbirds Association Limited^[2] Yak-52 maintenance schedule specified bellcrank inspections to be carried out in accordance with the United Kingdom Civil Aviation Authority issued Mandatory Permit Directive (MPD 2000-004, issued in 2000), which required:

• a dye penetrant inspection of the elevator bellcrank every 100 flying hours or 12 months, and
• if cracks were detected, no further flight was permitted until replacement.

However, a review of the available Yak-52 maintenance documentation identified a difference in the requirements for inspecting the bellcrank. In 2009, the Yakovlev Design Bureau in Russia, issued an amendment to the scheduled maintenance program, which required a dye penetrant inspection of the elevator bellcrank every 25 ± 5 flying hours. Further, as a result of a fatal Yak-52 accident in 2010, where the elevator bellcrank had failed in-flight, the manufacturer directed that all aluminium alloy bellcranks be replaced with steel. A service bulletin issued on 12 July 2012, 121-BD (121-БД), required the bellcranks to be replaced no later than December 2012.

The airworthiness requirements for Yak-52 aircraft are determined independently in countries outside Russia and have remained relatively unchanged since 2000. While significant, the 2009 changes made to the Yakovlev Design Bureau’s scheduled maintenance program and their actions in response to the accident in 2010 had not been incorporated into maintenance schedules in Australia, nor was there a requirement to do so. Common to both, however, is the importance of detecting cracks and the removal of these bellcranks from service.

Figure 1: Elevator bellcrank cracks observed on VH-PAE

Source: ATSB

Safety advisory notice

Given the known fatigue cracking and potential failure of Yakovlev Aircraft Factories Yak 52 elevator bellcranks manufactured from aluminium alloy, the ATSB reminds maintainers and operators of the importance of dye penetrant inspections to remove defective bellcranks from service. The ATSB would also like to ensure that operators and maintainers of Yak 52 aircraft are aware that Russia, the aircraft’s state of design, increased the inspection frequency for the bellcranks to 25 ± 5 flying hours. Further, aluminium alloy bellcranks are no longer approved for use on Yak-52s operating in Russia.

Read more about this ATSB investigation: AO-2019-027

__________

1. CAI-TSD-007/2000 (Lithuania), MPD 2000-004 (United Kingdom), and DCA/YAK/5 (New Zealand).
2. Australian Warbirds Association Limited (AWAL) is a self-administering recreational aviation organisation providing oversight of warbird, ex-military and replica aircraft.