Aviation safety investigations & reports

Rotor RPM decay and hard landing involving Robinson R44, VH-HGX, 5 km south of Ayers Rock Airport, Northern Territory, on 17 January 2018

Investigation number:
AO-2018-006
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

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What happened

In the evening of 17 January 2018, a Professional Helicopter Services Robinson R44 helicopter, registered VH-HGX, departed the Yulara Town helipad, Northern Territory, for a 15-minute scenic flight with the pilot and three passengers onboard. Shortly after take-off, the rotor RPM began to decay and the low rotor RPM warning activated. The rotor RPM continued to decay to a level from which the pilot could not recover. The pilot attempted a forced landing, but was unable to arrest the rate of descent, resulting in a hard landing. The pilot and two passengers were seriously injured, and the remaining passenger experienced minor injuries. The helicopter was substantially damaged.

What the ATSB found

The ATSB found that the take-off was conducted at a high density altitude[1] at near maximum weight. Therefore, a high engine manifold pressure (MAP) would be expected for the take-off. However, passenger video evidence indicated the rotor RPM (revolutions per minute) decay started at a relatively low MAP, and that the MAP increased slowly as the RPM steadily decayed. The ATSB found that the engine was producing the published rated take‑off power earlier on the day of the accident and that the pilot had flown the same departure with a full load of passengers on three previous flights. The rotor RPM decay was consistent with the low observed MAP. As such, the ATSB concluded the helicopter's rotor RPM steadily decayed due to a likely limited opening of the engine throttle during take-off. Fine-tuning of the engine throttle is controlled automatically by the engine governor, but it can be manually overridden by the pilot. The reason for the limited opening of the throttle could not be determined.

Following activation of the low rotor RPM warning, the pilot initially did not apply full throttle (for at least 5 seconds), and the helicopter maintained a positive rate of climb. At the time, the pilot was conducting the departure procedure low over the tree tops with an early left turn, which required visual attention outside of the helicopter for the majority of time. As a result, it was likely that the pilot had no spare attentional capacity at this time to immediately comprehend and respond to the deteriorating situation. In consideration of the potential power margin available at the time, if the pilot had applied full throttle in the first 5 seconds, and then lowered the collective lever sufficiently to prevent the helicopter from climbing, the low rotor RPM was likely recoverable.

The helicopter continued flight for about another 90 seconds, during which it climbed to about 200 ft at a low airspeed. This resulted in the rotor RPM decaying further to a level from which the pilot could not recover (likely below 80 per cent).

The ATSB further established that the pilot had inadvertently adopted a practice of conducting the rotors running turn-around (for passenger transfers) with the governor switched off. This was not in accordance with the Robinson Helicopter Company R44 checklist requirement for the governor to remain on from start until shut-down, nor the operator’s procedure for the governor to be selected on for the engine run-up. Although the pilot reported that the governor was selected on and checked before lift-off, this practice increased the risk of an inoperative governor not being detected before take-off.

The operator used individual passenger weights for their loading calculations, which was considered best practice. However, it was found that the operator’s passenger scales were not calibrated and were under‑reading the actual occupant weights. This resulted in the helicopter operating at a higher weight than planned, but less than the maximum weight. While the operating weight was within the published limits, the under-reading scales increased the risk of their helicopters not achieving their take-off performance.

The ATSB also found that the Robinson Helicopter Company’s R44 pilot operating handbook emergency procedure for low rotor RPM recovery did not include reference to the minimum power airspeed. Knowledge of this as a subsequent consideration to the immediate actions could assist pilots in the recovery from this safety-critical condition.

What has been done as a result

The operator temporarily suspended their tourist flights at their Uluru Base (including the Yulara Town helipad). Their chief pilot then conducted check flights with the local base pilots to ensure they could safely resume operations. In addition, the operator completed an audit of the helipad and updated their helicopter landing site register in accordance with the latest recommendations from the Civil Aviation Safety Authority (2014), and introduced a calibration schedule for their passenger scales.

The ATSB have issued a safety recommendation to the Robinson Helicopter Company to review the R44 pilot's operating handbook low rotor RPM recovery procedure for consideration to include a reference to the minimum power airspeed (Vy) for pilot awareness. Robinson reported that this will be reviewed by their engineering staff for possible revision to the pilot operating handbook.

Safety message

The intent behind checklist actions is not always apparent when learning procedures. Pilots should ensure they understand the purpose behind all checklist items, and if any doubt exists, seek clarification to reduce the likelihood of misunderstanding the requirements.

Low rotor RPM may develop in various flight conditions, but it is the low airspeed-low height condition, which is most likely to result in an accident. Helicopter pilots should ensure they are familiar with the power curve, the associated airspeeds for their particular helicopter, and be prepared to respond immediately to a low RPM warning.

Robinson Helicopter Company reported that pilots of their piston-engine helicopters should roll on throttle while lowering the collective lever, as per the low RPM recovery procedure, so that the throttle remains open. There is an overtravel spring in the throttle linkage that may, or may not, compress during the recovery. Pilots should not be concerned if the spring is, or is not, compressed, they should continue to roll the throttle on and lower the collective lever until the RPM is recovered.

In addition, the Robinson Helicopter Company website provides training videos for higher risk flight conditions that have resulted in fatal accidents. They include several presentations on energy management, tailored specifically for Robinson helicopter pilots, which could be beneficial to pilots during their initial training, upgrades and flight reviews.

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  1. Density altitude is pressure altitude corrected for non-standard temperature. Pressure altitude is the altitude corrected for non-standard atmospheric pressure.
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The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Additional details

Sources and submissions

Safety Issues

Go to AO-2018-006-SI-01 - Go to AO-2018-006-SI-02 -

Passenger scales

Professional Helicopter Services did not have a calibration schedule for their passenger scales, which were under-reading. This increased the risk of their helicopters not achieving their expected take-off performance.

Safety issue details
Issue number: AO-2018-006-SI-01
Status: Closed – Adequately addressed

Pilot’s operating handbook

The Robinson R44 pilot’s operating handbook low rotor RPM recovery procedure did not include reference to the minimum power airspeed for the helicopter as a consideration, which may assist a pilot to recover from a low rotor RPM condition.

Safety issue details
Issue number: AO-2018-006-SI-02
Status: Open – Safety action pending
General details
Date: 17 January 2018   Investigation status: Completed  
Time: 1830 CST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 5 km South of Ayers Rock Airport   Investigation phase: Final report: Dissemination  
State: Northern Territory   Occurrence type: Control issues  
Release date: 07 October 2020   Occurrence category: Accident  
Report status: Final   Highest injury level: Serious  

Aircraft details

Aircraft details
Aircraft manufacturer Robinson Helicopter Co  
Aircraft model R44  
Aircraft registration VH-HGX  
Serial number 0762  
Operator Professional Helicopter Services  
Type of operation Charter  
Sector Helicopter  
Damage to aircraft Substantial  
Departure point Ayres Rock, Northern Territory  
Destination Ayres Rock, Northern Territory  
Last update 07 October 2020