The ATSB has released its final report on a loss of control incident involving a Robinson R44 that landed heavily in a dam in Victoria in April.
On April 30 2011, the owner-pilot of a Robinson Helicopter Co. R44 helicopter, registered VH-ETT, was conducting a local flight from a private property near Kilmore Gap, Victoria.
During low-level manoeuvring at low speed around a dam, the pilot lost directional control and landed heavily in the water. The helicopter was seriously damaged, with the pilot and passenger sustaining only minor injuries.
The investigation found that the helicopter was probably serviceable and that the loss of directional control was likely to be a result of a loss of tail rotor effectiveness.
The emergency locator transmitter (ELT) activated on impact and prompted an effective search and rescue (SAR) response through a broadcast on the 121.5 MHz frequency. However, the 406 MHz transmission that was monitored by the SAR agency did not trigger an alert or provide identification information. As a result, there was no assurance of an immediate and effective response from the SAR agency.
The investigation found that the ELT could be programmed with identification information either directly or (if fitted) by input from a component (dongle) in the ELT wiring connector. In this occurrence, the ELT had been inadvertently reprogrammed with incorrect information from the dongle.
A minor safety issue was identified in that there were only subtle cues to distinguish programmable dongles from the standard-type wiring connector. There was also variability in the conduct of post-installation ELT testing.
Sequence of events
At 1020, the pilot departed Moorabbin Airport to a private property located near Kilmore, Victoria to position for a series of local flights. The pilot completed three flights of about 10 minutes duration in succession without any problem.
On the fourth and last intended local flight, with one passenger on board, the pilot conducted a circuit and brought the helicopter to a hover on the airstrip. The pilot then turned the helicopter to the north and proceeded at low speed and low level to make a right circuit around a nearby dam to inspect recently completed earthworks.
The pilot had turned around the dam and was turning onto a southerly heading when he realised that the helicopter was not straightening up as intended. He suspected a loss of tail rotor effectiveness (LTE) and lowered the helicopter’s nose in an attempt to increase airspeed and, consequently, the aerodynamic effectiveness of the helicopter’s tail.
The R44 did not respond to the control inputs and the right turn continued. In an effort to avoid hitting the uneven ground around the dam, the pilot raised the collective control, which had the deleterious effect of increasing the rate of rotation of the helicopter. By now, the pilot was unable to maintain effective external reference and decided to put the helicopter down wherever it was at the time.
The pilot lowered the collective rapidly and heard a splash as the helicopter descended into the water of the dam. The engine stopped immediately and the main rotor blades hit the water and/or mud. The helicopter became partially submerged before the pilot and passenger exited the helicopter and made their way to the bank of the dam. The pilot and passenger sustained minor injuries and the helicopter was seriously damaged. The pilot estimated that the accident occurred at 1305.
Pilots of a number of overflying aircraft detected the helicopter’s emergency locator transmitter (ELT) transmission on frequency 121.5 MHz during routine monitoring and advised air traffic control (ATC). In turn, ATC notified the rescue coordination centre (RCC) at 1331. At 1352, the RCC tasked the crew of a search and rescue helicopter to respond. The crew homed in on the 121.5 MHz ELT signal and arrived at the accident site at 1415.
The next day, the helicopter was recovered from the dam. The tail rotor system was inspected by the helicopter owner-pilot, with no sign of any defect or anomaly existing before the accident. The pilot and passenger reported that there were no warning lights or sounds of a horn before or during the event, and no apparent precursors to the loss of directional control.
Meteorological information
The area forecast that was obtained by the pilot prior to departing Moorabbin indicated that the low-level wind would be from the north at 10 kts. The pilot reported that the surface wind at the property varied between nil and 10 kts and was generally from a northerly direction.
Pilot information
The pilot held a Commercial Pilot (Helicopter) Licence that was issued on September 28 2009 and an R44 endorsement. All of the pilot’s helicopter flight time of 152 hours was conducted in R44 helicopters. The pilot also held a Commercial Pilot (Aeroplane) Licence with about 2600 hours total aeroplane flying time.
Helicopter information
The helicopter was manufactured in the US in 2008 and was imported to Australia as a new aircraft. Since that time it had been operated for about 200 hours with about 30 hours since the last 100-hour/annual maintenance inspection. There were no reports or record of any helicopter defects. The pilot calculated that the helicopter’s weight was 158 kg below the maximum gross weight and that the centre of gravity was within limits.
Loss of tail rotor effectiveness
The thrust generated by the tail rotor of a helicopter counteracts the torque reaction produced by the rotation of the main rotor blades. Pilot control of tail rotor blade pitch allows variation in the tail rotor thrust and provides directional control. In helicopters with a single main rotor that rotates counter-clockwise (as in the R44), any loss of tail rotor effectiveness (LTE) results in an uncommanded yaw to the right (nose to the right).
In simple terms, that yaw is a product of proportionally less tail rotor thrust (relative to main rotor torque) resulting primarily from disruption to the airflow over the tail rotor. Factors that increase the risk of the onset LTE are:
• high all-up weight
• out of ground effect hover
• low forward airspeed (less than 30 kts)
• high power settings
• a wind direction from the left or rear of the helicopter
• turns to the right.
The recommended recovery technique is to simultaneously apply full left pedal and to move the cyclic forward to increase speed. If altitude permits, power should be reduced. If a pilot’s response to the onset of LTE is incorrect or slow, the yaw rate may rapidly increase to a point where recovery is not possible.
LTE has been identified as a contributing factor in a number of previous helicopter accidents and incidents in Australia.
Analysis
Given the apparent absence of any helicopter unserviceability prior to the pilot’s loss of directional control, the accident was probably related to the pilot’s handling of the helicopter in the local environmental conditions.
The helicopter was being operated at slow speed and out of ground effect, probably with a crosswind from the left, when the pilot was ready to make a right turn to return to the airstrip. In those conditions, the helicopter was susceptible to loss of tail rotor effectiveness (LTE) and the ensuing behaviour of the helicopter was symptomatic of deepening LTE.
This accident highlights the insidious nature of LTE and the difficulty in recovering from it at low altitude. The action by the pilot in putting the helicopter down when he did probably reduced the severity of the outcome.
Findings
From the evidence available, the following findings are made. They should not be read as apportioning blame or liability to any particular organisation or individual.
Contributing safety factor
• During low-level manoeuvring at low airspeed, the pilot lost directional control of the helicopter and landed heavily, probably as a result of loss of tail rotor effectiveness.
Other safety factors
• The emergency locator transmitter activated on impact, but the 406 MHz transmission was in test protocol, which did not provide assurance of an immediate response from the search and rescue (SAR) agency and prevented SAR agency access to the aircraft and owner details that could have enhanced the effectiveness of the SAR response.
• There were only subtle cues to the optional fitment of programming dongles in aircraft and variability in the conduct of post-installation testing, increasing the risk of inadvertent and undetected emergency locator transmitter reprogramming and a less effective search and rescue response.
In response to this incident, on June 6 CASA published Airworthiness Bulletin 25-018 to
alert maintenance organisations to the risk of programming dongles
transferring potentially invalid details to the memory of ELTs.
Robinson Helicopter Co. advised that they were introducing measures to
increase awareness of programming dongles in their new helicopters.
(Photo courtesy of the helicopter owner-pilot).
