Collision with terrain

What happened

On 8 November 2019, a Robinson R44 helicopter was conducting sling load operations about 10 NM north-east of Jabiru, Northern Territory. On the first lift of the day at approximately 1430 Central Standard Time, the pilot attached a load estimated to be about 120 kilograms to the helicopter by a 30-foot sling. In the prevailing windless conditions, the pilot lifted into a high hover, began to lift the load off the ground, and continued to climb until the load was clear of the surrounding trees. Once established in the hover, at approximately 80-100 feet AGL, the pilot observed all the engine gauges to be in the normal range and the helicopter appeared to be operating normally.

As the pilot commenced the translation into forward flight over a treed area, the rotor RPM began to decay and the low rotor RPM warning horn sounded. The pilot unsuccessfully attempted to regain rotor RPM by lowering the collective^[1] and increasing the throttle. In an attempt to alleviate the situation by reducing the weight on the helicopter, the pilot released the slung load. This action did not assist with the recovery of rotor RPM and the aircraft continued to descend into the trees before colliding with the ground.

Figure 1: Area of operations and wreckage

Source: Operator

Operator’s investigation

The operator has conducted an investigation into the circumstances surrounding this accident.

The investigation revealed that in the hot and humid operating conditions, a contributing factor to the accident was the pilot over-pitching during the sling load operation. The over-pitching was to such a degree that it made successful recovery in the circumstances unlikely. The operator’s investigation also stated the pilot’s decision to depart the pick-up location over a treed area when clearer areas were available also restricted the options available once the helicopter started to descend.

Over-pitching

The International Civil Aviation Organization (ICAO) manual of aircraft accident and incident investigation, chapter 15: Helicopter investigation, described over-pitching as a phenomena that happens when collective pitch is increased to a point where the main rotor blade angle of attack creates so much drag that all available engine power cannot maintain or restore normal operation rotor speed. At low rotor speed, the rotor blades bend upwards and drag increases. The high inflow angles and rotor drag quickly decay main rotor speed, which may decrease to the point where the main rotor blades stall.

Hover performance

Hover performance is essentially a product of engine power available and engine power required. The main factors affecting engine power required in a hover are helicopter weight, density of air and proximity to the ground (ground effect).

To maintain a steady high hover, lift a sling load or climb, the helicopter requires more main rotor thrust to act as lift, which in turn requires more engine power.

As air density decreases with an increase in altitude, temperature, and to a lesser degree humidity a normally aspirated engine produces less power. Additionally, if the same amount of rotor thrust is needed, the rotor blades need a higher angle of attack, which creates more drag and generates a requirement for more engine power.

When a helicopter is hovering within about one rotor diameter^[2] of the ground, the performance of the main rotor is affected by ground effect. A helicopter hovering in-ground-effect requires less engine power to hover than a helicopter hovering out-of-ground-effect.

Safety action

As a result of this occurrence, the operator has advised the ATSB that they are taking the following safety actions:

The operator will produce a report for all company pilots to fully explain the circumstances surrounding this accident to further educate and train pilots of the considerations when undertaking similar operations. To increase the safety of company operations, this further training will concentrate on decision-making, helicopter performance and weather effects, over pitching and using available terrain features when approaching and departing from unprepared landing sites.

Safety message

This accident serves as a reminder that when operating helicopters from unprepared landing sites, pilots should consider the approach and departure routes available in conjunction with operational constraints, weather (particularly wind), performance available and possible emergency recovery. Time spent considering and confirming the fundamental factors of decision-making, helicopter performance and limitations and the consideration of actions in an emergency may help prevent injury to crew and damage to, or loss of, an aircraft.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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1. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity.
2. The Robinson R44 main rotor diameter is 33 feet.

What happened

On 22 September at about 0700 Eastern Standard Time, a Kavanagh E-240 balloon was operating a charter flight over Melbourne, Victoria with a pilot and 10 passengers on board.

While landing at a reserve, the pilot deployed the handling line to ground crew. The pilot then determined that the balloon was unable to land in the available space and instructed the ground crew to let go of the handling line in order to manoeuvre to a different landing site.

The balloon continued the descent and the basket subsequently made contact with the roof of a house. The balloon then landed in the original landing site with the assistance of the ground crew utilising the handling line, which was still attached to the basket. The pilot and passengers were uninjured.

Pilot comments

The pilot stated that the main contributing factor to the occurrence was the use of the handling line in an attempt to guide the balloon into the landing site. Although this is common practice, during this particular landing the pilot ran out of sufficient space in the landing site.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On 12 September 2019, a Robinson R44 II helicopter landed at Parachilna, South Australia to unload passengers after conducting a scenic flight in the Wilpena Pound area. The landing area was a raised disused railway platform that the pilot had used previously as it allowed the tail rotor to be maintained well clear of any possible obstacles.

At approximately 1540 Central Standard Time, after the passengers were unloaded and had moved away from the helicopter, the pilot commenced the lift into the hover. As the helicopter became light on the skids, the helicopter‘s nose pitched up and it began to roll to the left. The tail rotor impacted the ground and the main rotor struck the tail boom (Figure 1 Insert A).

After securing the helicopter, the pilot determined that a section of steel on the edge of the platform had dislodged and caught on the rear of the left hand skid (Figure 1 Insert B). This resulted in the unanticipated pitch and roll during the take-off sequence.

Figure 1: Accident site showing aircraft and platform

Source: Aircraft operator

Safety action

As a result of this occurrence, the aircraft operator advised the ATSB that they ceased operations to the landing site. The operator advised that operations may recommence in the location after the necessary maintenance has been completed on the platform and a site inspection is carried out to confirm the suitability and safety for future operations. They will also ensure that periodic inspections are performed at any helicopter landing sites to ensure ongoing safe operations.

Safety message

The assessment of suitability and safety of helicopter landing sites does not end after the initial reconnaissance or even after operating from the site for a period of time. Pilots must be aware of all potential hazards to operations, particularly in the critical phases of flight such as lifting to the hover, taxiing and commencing take-off.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On 11 June 2019, a Cessna 150M departed Lismore, New South Wales to conduct a training flight. There was an instructor and a student on board.

The student was conducting a practice glide approach to runway 15 at Lismore when the aircraft’s approach profile became too low. The instructor took over control of the aircraft to correct the profile, however, was unable to do so in time resulting in the wheel spat colliding with the airport’s perimeter fence. The aircraft sustained minor damage.

Safety message

During training flights, instructors need to be vigilant and prepared to take over control of the aircraft at short notice. When conducting practice glide approaches, correct speed and approach profile need to be maintained, as power is not used. If the approach is too low and intervention is delayed, there is an increased risk of the aircraft colliding with obstacles.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On 21 December 2018, the pilot, and sole occupant of the Ayres Corporation S2R departed Dalby, Queensland to conduct aerial agriculture spraying.

During initial climb, at about 200 ft above ground level, the aircraft did not respond to control inputs to climb further. The pilot turned right to avoid hitting obstructions but found the aircraft was not performing in the way he expected. The pilot attempted to climb by increasing the throttle to maximum and lowering the nose of the aircraft to increase airspeed, but the aircraft was unable to maintain height.

As the aircraft’s airspeed decreased, the pilot experienced wallowing^[1]. The pilot attempted to drop the chemical load to lighten the aircraft’s weight, but the aircraft did not respond. The pilot then lowered the nose of the aircraft to conduct a forced landing. The aircraft entered a stall and subsequently impacted a row of trees resulting in substantial damage and minor injuries to the pilot.

Figure 1: Ayres Corporation S2R post-accident

Source: Chief Pilot

Safety message

This accident highlights the importance of monitoring and checking instruments during flight, to ensure aircraft speed and performance is maintained. As aircraft speed reduces and approaches Vmca^[2], low speed controllability of the aircraft becomes very difficult. Pilots and operators are also reminded of the need to ensure that the aircraft’s weight is within limits and maximum take-off weight to ensure the on-going safety of the aircraft and operations.

The pilot involved in this accident was required to make important decisions in a short period of time, including where to land and how to manage the remaining altitude. Pre-flight self-briefing is an important tool in reinforcing planned emergency actions.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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1. Wallowing - Uncommanded motion about all three axes of an aircraft occurring simultaneously.
2. Vmca - Minimum control speed in the take-off configuration minimum control speed.

What happened

On 8 September 2018, at 0700 Central Standard Time, a Da-Jiang Innovations (DJI) Inspire 2 remotely piloted aircraft (RPA) was conducting a test flight above Fort Hill Wharf, Northern Territory.

During the test flight, the operator flew the RPA near a cruise ship. The RPA lost signal and the operator initiated the return-to-home procedure. During this procedure, at a height of 120 feet above ground level, the RPA deviated from the return-to-home path and collided with the ship, resulting in the aircraft being destroyed.

The pilot speculated that the ship caused interference with the datalink signal, resulting in the RPA deviating off course and subsequently colliding with the ship.

Safety message

This incident highlights the importance of ensuring that while operating RPAs, a sufficient distance is maintained from vehicles, ships, buildings and people at all times. The Civil Aviation Safety Authority has published an extensive amount of information on flying drones/remotely piloted aircraft in Australia.

Further information about flying your RPA safely can be found on the ATSB website, under the news item: Know your drone and the rules to fly safely.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On 20 November 2018, a Yamaha RMAX remotely piloted aircraft (RPA) was conducting an air work flight in a paddock near Muswellbrook, New South Wales. A ground support officer and navigator/spotter aided the RPA pilot.

The pilot climbed the RPA to provide ample clearance above trees and put the RPA into a hover. The pilot then moved to position himself better for the area of operation. The pilot unknowingly stepped over an electric fence. He received an electric shock, dropping the controller as a result. In the process of dropping the controller, the throttle moved to full negative. The pilot quickly picked up the controller and increased the throttle. The RPA’s descent reduced as a result but not enough to avoid contacting trees. The RPA subsequently collided with the ground resulting in substantial damage. The pilot and support personnel positioned at a safe distance from the accident were not injured.

Safety action

As a result of this occurrence, the operator has made changes to the way electrical fencing is identified and labelled. Crews will also carry an electric fence testing meter to be used at relevant sites.

Safety message

Electric fences along with other distractions and trip hazards need consideration when operating an RPA. Any operation that requires the operator to reposition themselves while operating an RPA increases the risk of trip hazards.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On the morning of 8 September 2018, a Bell 206B helicopter departed a caravan park on a private flight with a pilot and three passengers on board. Approximately 30 minutes into the flight, the pilot conducted an orbit around a cleared area intended for landing and completed his landing checks. During late downwind, the pilot reports that the helicopter experienced an uncommanded yaw to the right. To counteract the yaw, the pilot applied left pedal, however the helicopter continued to yaw to the right and subsequently began an uncontrolled descent into trees. As the helicopter entered the trees, the pilot rolled off the throttle and pulled on the collective^[1] and the helicopter contacted the ground, resulting in the tail rotor severing. The main rotor also sustained damage from contact with the trees. The pilot and passengers exited the helicopter without injury.

At the time of the accident, the pilot reports that gusty, variable winds were encountered which may have caused a loss of tail rotor effectiveness (LTE),^[2] contributing to the accident.

Safety message

There are various factors that can contribute to a loss of tail rotor effectiveness. The NTSB Safety Alert, Loss of Tail Rotor Effectiveness in Helicopters identifies these factors and the subsequent risks associated with LTE.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

__________

1. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity.
2. In helicopters, loss of tail rotor effectiveness (LTE), or unanticipated yaw, is an uncommanded rapid yaw that does not subside on its own accord.

What happened

On 2 June 2018 the pilot and a passenger departed a station west of Alice Springs, Northern Territory, in a Robinson R22 helicopter for a routine property inspection.

At approximately 1215 Central Standard Time, the pilot conducted a landing at a bore site and the passenger exited the helicopter. The pilot then also exited the helicopter with the engine still running. Shortly after exiting and moving away from the helicopter, the pilot heard the engine power up and began to run towards the helicopter. The helicopter then began to move and the pilot stopped moving towards it.

The helicopter was observed to move backwards and the tail rotor dug into the ground, flipping the helicopter onto its side resulting in substantial damage.

Pilot comments

The pilot reported that during maintenance the previous day, the collective was adjusted to loosen the friction. Before exiting the helicopter, the pilot tightened the cyclic, ensured the collective was down, and the friction nut tightened. The pilot suspects that the friction has loosened, causing the collective to rise and the helicopter to power up.

Safety message

Leaving engines running without a pilot in a control seat presents a significant hazard to the helicopter and persons on the ground. The aircraft manufacturer includes a warning against such practice in the aircraft flight manual, Safety Notice SN-17, Never exit helicopter with engine running.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

What happened

On 12 Jul 2018, at about 1000 Eastern Standard Time, the pilot of a Robinson R44 helicopter took off with one passenger on board to conduct a few circuits^[1] at Lethbridge Airport, Victoria, prior to departing the airport for a private flight.

The pilot conducted two circuits and on the third circuit, set up for an autorotation^[2] to demonstrate to the passenger the rate of descent during the manoeuvre. The pilot selected a landing point 1/3 down the runway and established the helicopter at 70 kt, 600 ft above ground level (AGL). The pilot then partially rolled off the throttle to reduce the motor RPM and lowered the collective^[3] to enter autorotation. The pilot was explaining the autorotation to the passenger when the low rotor RPM horn and light came on followed by a significant wobble and shake of the helicopter. The pilot checked the rotor RPM and it was about 70 per cent. The pilot initiated recovery by increasing collective and winding the throttle back on. This made little difference and at 300 ft, the pilot pitched the nose of the helicopter forward to increase RPM. Just prior to impact with the ground the pilot flared the helicopter and pulled full collective, however there was little rotor RPM left.

The pilot called for the passenger to brace and the helicopter landed somewhat level. As it skidded forward, the helicopter rolled to the left side and came to a stop. The helicopter was destroyed and the passenger sustained serious injuries.

Figure 1: R44 wreckage at Lethbridge Airport, Victoria 

Source: Owner

Safety message

Practice of emergency recovery techniques such as autorotations should not be conducted with passengers on board. These carry an inherently elevated degree of risk. Additionally, passengers increase a pilot’s workload and can cause distractions. When conducting an autorotation; attitude, airspeed and rotor RPM should be the focus of the pilot’s attention. Practice autorotations are a dynamic manoeuver, increasing the potential to mishandle the helicopter. Two serious conditions associated with a mishandled autorotation are low rotor RPM stall and vortex ring state.

Safety Notice SN-10 on the Robinson Helicopter Company website states that, ‘No matter what causes the low rotor RPM, the pilot must first roll on throttle and lower the collective simultaneously to recover the RPM before investigating the problem.’

Safety Notice SN-24 Low RPM Rotor Stall can be Fatal and Safety Notice SN-22 Vortex Ring State Catches Many Pilots by Surprise, both detail recovery actions that require the collective to be lowered as part of the initial recovery actions.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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1. Circuit: The circuit is an orderly pattern that involves the pilot making approaches to a landing area, touching down and then applying power to take off again.
2. Autorotation: Autorotation is a condition of descending flight where, following engine failure or deliberate disengagement, the rotor blades are driven solely by aerodynamic forces resulting from rate of descent airflow through the rotor. The rate of descent is determined mainly by airspeed.
3. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity.