As a result of this occurrence, the Bureau of Air Safety
Investigation is investigating perceived safety deficiencies
involving helicopter performance, pilot licensing and experience
requirements.
Any recommendation issued as a result of this deficiency
analysis will be published in the Bureau's Quarterly Safety
Deficiency Report.
- The pilot was inexperienced.
- The density altitude and relative humidity were high.
- The wind conditions were gusty.
- There was no documented data or guidance available to the pilot
to assist him in assessing the expected performance of the
helicopter during the takeoff. - The pilot did not adequately plan the takeoff to account for
the weather conditions and helicopter landing site
characteristics. - The pilot used an inappropriate takeoff technique.
- The helicopter was probably at or close to maximum all up
weight and had inadequate performance to complete the takeoff in
nil wind. - The weather conditions had changed since the first takeoff and
did not assist the helicopter during the second takeoff.
The helicopter weighed close to its maximum permissible all up
weight. The pilot reported that the power required to hover the
helicopter in ground effect was about 23 inches manifold air
pressure, which was close to the placarded limit. The flight manual
data also indicated that the helicopter had insufficient power to
hover out of ground effect in nil wind. The reported high power
being used to achieve an in ground effect hover associated with the
high density altitude conditions and the available flight manual
performance data, indicated that the helicopter's engine was
unlikely to have been capable of providing appreciably more power
than that already being used.
The reported site information indicated that the helicopter
would have needed to achieve a climb profile of at least three
degrees. However, the available performance data indicated that
there was unlikely to have been sufficient power available to
depart from the in ground effect hover and achieve the required
climb profile in nil wind. The helicopter's performance would have
been adversely affected by the high relative humidity, which had
the effect of further increasing the already high density altitude.
Had the pilot consulted the flight manual or conducted a power
check prior to landing on the pad, he may have realised that there
was unlikely to have been sufficient power available to attempt the
departure, or at least he could have planned the departure with a
rejected takeoff in mind.
Neither the helicopter's flight manual, nor operator's
operations manual provided climb performance data or guidance on
expected power requirements for the helicopter to depart the hover
and transition into forward climbing flight. Although the Civil
Aviation Orders specify minimum performance requirements for
aeroplanes, there are no similar requirements for helicopters. With
no regulatory requirement for climb performance information to be
provided by either the helicopter's manufacturer or the operator,
the pilot had no documented guidance on the helicopter's expected
performance in forward climbing flight. While it would have been
prudent for the pilot to conduct a power check before commencing
operations into or out of the helicopter landing site, there was no
guidance provided by either the operator or helicopter manufacturer
on required power margins. Therefore, a power check may have been
of relevance to a pilot with experience in R22 limited power
operations. However, the accident pilot's experience was not
extensive, with a total flying time of about 173 hours. While he
had accumulated 36 flying hours during the month prior to the
accident he had only flown about 50 hours during the previous 16
months. It appears incongruous that, in accordance with the
regulations and orders, the pilot had sufficient experience to
transport passengers but insufficient flying experience to
undertake mustering operations. While there was no documentary
evidence detailing the pilot's initial training, there appeared to
be some gaps in his knowledge with regard to operating the R22
helicopter close to its limits. The limited amount of flying he
conducted in the 15 months between completing his course and
joining the helicopter's operator may have also been a factor. He
appeared to have been ill prepared to operate the helicopter in the
high density altitude conditions of Northern Australia.
Although the task of carrying passengers from the station was
not authorised by the helicopter's operator, the pilot reported
that he was advised that the on-site experienced pilot was "in
charge". The helicopter's operator was unaware of the requirement
to conduct passenger flights, and in using the term "in charge" in
relation to the on-site pilot, probably contributed to the pilot's
belief that the on-site pilot was a nominated person who could
authorise all flights. If the operator had been aware of the
passenger flights, then more appropriate supervision of the pilot
may have been provided. There appeared to have been a
misunderstanding between the operator and the on-site pilot as
regards to the use of the helicopter.
The pilot reported that he had not experienced any problems
during the first takeoff from the site. He reported the wind as
being gusty, averaging 15 kts and that there were thunderstorms in
the area. With evidence indicating that there was probably little
power available to depart the hover and achieve the required
departure angle in nil wind, it was likely that the helicopter's
performance was assisted during the previous takeoff by the wind
conditions existing at the time. This may have lulled the pilot
into a belief that the helicopter had sufficient power to attempt
further takeoffs.
During the accident takeoff, the helicopter's main rotor RPM
decreased. No evidence of a mechanical fault was subsequently
found. The pilot reported that the wind was gusty and the humidity
was high and increasing as storms built-up in the area. It was
possible that the relative humidity had increased sufficiently to
decrease the main and tail rotor performance or decrease the amount
of power available from the engine. Alternatively, or in
combination with the high relative humidity, the wind may have
changed direction or lost strength during the accident takeoff. In
either case, the pilot would have had to increase the collective
pitch to maintain the departure profile. This may have resulted in
the power required to drive the helicopter's rotor system exceeding
the power available from the engine. As a result, the main rotor
RPM drooped which reduced the lift being produced by the main rotor
and the helicopter descended to the ground. Because the pilot had
conducted the departure without considering the possible
requirement to reject the takeoff, the area into which the
helicopter descended was unsuitable for landing.
CONCLUSIONS
Findings
While the pilot was conducting the takeoff from Fossil Downs
Station, the environmental conditions may have changed such that
the power required to maintain the helicopter's departure profile
exceeded the power available from the engine. As a result, the main
rotor RPM decayed and the helicopter descended onto the ground. The
pilot had not adequately assessed the power needed to conduct the
takeoff and had used an inappropriate takeoff technique for the
environmental conditions and helicopter weight. There was a
misunderstanding between the operator and the customer as to the
use of the helicopter. The pilot inadvertently believed he was
authorised in accordance with the company operations manual to
conduct the passenger flights. The helicopter's operator was
unaware that the passenger flights were being conducted.
The Robinson R22 helicopter was sent to Fossil Downs Station by
the operator to conduct a small mustering assignment. As the
operator's pilot was relatively inexperienced and not qualified to
conduct mustering operations, the helicopter was fitted with dual
controls so that an experienced and qualified pilot who was on-site
could conduct the flying while the operator's pilot occupied the
other seat. However, after the aircraft arrived at the station, the
on-site pilot requested that the operator's pilot transport two
passengers from the station to Fitzroy Crossing. Although the
operator's pilot had insufficient hours to conduct mustering, he
held a commercial pilot's licence and was qualified to carry
passengers.
The pilot transported the first passenger from the helicopter
landing site without incident. However during the second departure,
at about 15 ft and just as the helicopter was achieving
translational lift, it sank back towards the ground. When the pilot
increased the collective pitch in an attempt to regain the required
departure profile, the low rotor RPM warning horn sounded and the
rate of descent increased. The pilot reported that he checked that
the throttle was fully open but the main rotor RPM continued to
decay. The helicopter landed heavily and the main rotor blades
clipped a tree. The pilot reported that as soon as it landed, he
shut the engine down. The helicopter was extensively damaged but
neither occupant was injured. The pilot reported that he flew the
second flight's takeoff into wind along a similar path to that
flown during the previous passenger flight.
The maintenance organisation that repaired the helicopter
reported that no mechanical fault was found that would have
contributed to the accident. The accident was not subject to an
on-site investigation by the Bureau of Air Safety
Investigation.
Weather conditions
The pilot reported that the ambient temperature was about 37
degrees Celsius. He also reported that the humidity was high and
increasing as storms were developing in the area. The wind was
averaging about 15 kts from the south-east and gusting. The density
altitude at the site, without factoring the relative humidity, was
calculated to be about 3,000 ft.
The helicopter landing site
The pilot reported that he was using a southerly departure from
the site to align with the general wind direction. The pilot
reported that in the southerly direction, the helicopter landing
site had an available length of about 50 to 60 m from the departure
point with about 3 m high bushes at the departure end. There was
also a small fence running east to west about 40 m from the
departure point.
Helicopter performance
The helicopter weighed close to its maximum all up weight of 622
kgs. The helicopter's flight manual indicated that the calculated
maximum weight to hover out of ground effect in nil wind, was about
605 kgs. The pilot did not consult the helicopter's flight manual
for likely power requirements and power availability; nor did he
conduct a power check prior to arriving at the helicopter landing
site in order to ascertain the actual power available. While the
Robinson R22 Flight Manual provided hover performance data, it did
not contain performance data related to the expected climb
performance of the helicopter during takeoff, or in forward flight.
The operator's operations manual did not provide guidance regarding
power margins. There was no requirement under the existing
regulations for information or guidance related to required power
margins for departure or climb performance to be provided by either
the helicopter's manufacturer or operator.
The pilot reported that the power setting required to hover the
helicopter in ground effect was about 23 inches manifold air
pressure, which was approximately the placarded limit manifold air
pressure of 23.5 inches. The pilot could not recall the power
indication during the accident takeoff.
Ambient wind conditions can have significant and differing
effects on a tail rotor equipped helicopter's performance. Engine
power is delivered to a transmission system, which drives the main
and tail rotors The power required to drive the transmission system
is determined primarily by the amount of drag being produced by the
rotors and the power available is determined by the power output of
the engine(s). The difference between the power available and power
required is known as the power margin. If the power required to
drive transmission exceeds the amount of power available from the
engine, then the main and tail rotor speed will decay, or droop.
When the speed of the main rotor droops significantly, the main
rotor loses lift and the helicopter descends. Wind blowing over a
main rotor provides translational lift that can significantly
reduce the power required to drive the helicopter's transmission
system. Wind may also assist a helicopter to maintain heading,
which also reduces the load demand on the transmission and
therefore reduces the power required to drive the transmission.
Conversely, a wind from an adverse direction may increase the load
demand on the transmission and, in turn, the power required from
the engine. Therefore, the wind may cause a net effect which,
depending on its strength and direction, will reduce or increase
the power required for a tail rotor equipped helicopter to maintain
flight.
The density of air is affected by a number of factors including
its moisture content. Relative humidity is the ratio of the amount
of moisture in the air to the amount it is capable of absorbing at
a given temperature. The greatest decrease in air density (increase
in density altitude) due to moisture content will be at a high
temperature. In general, as the density altitude increases,
helicopter rotor and piston engine performance decrease. The
performance data provided in the R22 helicopter's flight manual is
only valid for nil-wind conditions and does not account for the
adverse effects of high relative humidity.
Although the Civil Aviation Orders (CAOs) specify minimum
performance requirements for single and multi-engine aeroplanes,
there are no minimum performance criteria specified for
helicopters.
Pilot Experience
The pilot had about 173 hours flying experience, of which about
83 hours were in command. All his flying experience had been gained
on the Robinson R22 helicopter. Prior to joining the operator, he
had flown about 14 hours during the 15 months since gaining his
commercial (helicopter) pilot's licence in September 1997. He had
been employed by the operator for less than one month and had
accumulated just over 36 flying hours in that time. His initial
training was conducted at several helicopter training schools in
Queensland and he reported that during the training, he had not
experienced the helicopter being close to limits of power or
practiced rejected departures and had not previously experienced
main rotor RPM droop. He also reported that at the time of the
accident, he was unaware of how to recover from a low rotor RPM
condition. There were no available records related to his initial
flying training, however, the pilot reported that he considered the
training to be adequate. The operator conducted a proficiency check
on the pilot about three weeks prior to the accident. The pilot's
performance during the check was rated as satisfactory. About a
month after the accident, the pilot attended a Robinson Safety
Course where he flew with an experienced R22 helicopter instructor.
The instructor reported that the pilot demonstrated an
inappropriate takeoff technique and that he required remedial
instruction.
The Civil Aviation Orders impose a minimum requirement of 100
hrs as pilot-in-command before a pilot may conduct mustering
operations. The Civil Aviation Regulations specify that a pilot may
obtain a commercial (helicopter) pilot's licence, under certain
circumstances, after a minimum total of 105 flying hours of which
at least 35 hours are as pilot-in-command.
The company's operations manual required pilots to obtain
authorisation from the Chief Pilot or a person nominated by the
Chief Pilot before conducting any flights. The pilot reported that
the Chief Pilot told him that the on-site pilot was "in charge".
When he was requested to conduct the passenger flights, the pilot
believed that the on-site pilot had the appropriate authority.