- The aircraft speed rapidly reduced during an unusually steep
climb. - The flaps extended beyond 10 degrees during the climb.
- Control of the aircraft was lost at a height from which
recovery was not possible.
Video evidence indicated that the approach to the water drop was
normal, although the airspeed approaching the target area was about
10 kts higher than the maximum recommended in the AFM for load
release. The aircraft nose would have suddenly pitched-up during
the release of the load and there was no evidence of any
significant elevator input to counteract the change in nose
attitude.
Although the pilot had only logged 7.6 hours operating aircraft
equipped with the Fire Retardant Dispersal System, he was
sufficiently experienced on the aircraft type to appreciate the
magnitude of pitching moment likely to be encountered. Insufficient
forward elevator had been applied during the release of the load to
counter the tendency of the aircraft nose to pitch upwards.
There was no evidence to indicate that a mechanical defect or
medical incapacitation had contributed to the lack of elevator
input during the load release and subsequent climb. It was possible
that the pilot had intended to climb the aircraft steeply after
releasing the load in an attempt to increase the visual impact of
the display, which was consistent with comments attributed to the
pilot about his stated intention to put on a good display. The
observed yawing and rolling to the left during the climb may have
been an attempt by the pilot to turn the aircraft for another pass
of the crowd.
The extension of flap during the climb would have created a
significant amount of additional drag. Consequently, for the
aircraft to reach a height of 450 ft with the amount of flap being
applied, it was likely that the engine was operating at a high
power setting and the propeller producing a significant amount of
thrust and resultant torque.
It was not possible to determine whether the extension of flap
beyond 10 degrees during the climb was intentional. The extension
of the flaps probably reduced the likelihood of the manoeuvre being
safely completed. Although the extension of flap during the climb
may have caused the aircraft nose to pitch-up further than the
pilot had originally anticipated, there was no evidence that the
pilot had made an elevator input to reduce the steepness of the
climb.
The ailerons would have become less effective as the airspeed of
the aircraft reduced during the climb. The low airspeed combined
with the apparent turning manoeuvre, reduced aileron effectiveness
and high torque being produced by the propeller probably
contributed to the aircraft's roll inverted and entry to the
incipient inverted spin. Once the aircraft had entered the spin, it
was unlikely that there was sufficient height available for the
pilot to effect a recovery.
The pilot of the Air Tractor 802A (AT-802A) was scheduled to
demonstrate the fire-fighting capabilities of the aircraft at the
Mount Gambier airshow. After becoming airborne the pilot positioned
the aircraft for the first pass of the crowd. This pass was made at
a height of approximately 100 ft in a north easterly direction and
overhead the runway that was being used as the display axis for the
airshow.
The pilot then confirmed by radio to the airshow coordinator
that he was starting his "drop run". The aircraft was observed to
fly in a gentle descent towards the designated target area, and at
a height of about 40 ft the load release commenced at, or close to,
the maximum rate. During the load release the nose of the aircraft
pitched up and the aircraft entered a climb. On completion of the
load release the aircraft nose continued to pitch up and the climb
angle increased.
The aircraft climbed straight ahead for a short distance before
commencing to yaw and roll to the left. The bank angle increased to
a maximum of about 90 degrees while the nose attitude dropped to
almost the horizontal. At a height of about 450 ft and while at
very low airspeed, the aircraft rolled inverted and entered the
incipient stages of an inverted spin. Recovery to controlled flight
was not achieved and the aircraft impacted the ground inverted, in
a wings level attitude at a nose-down angle of approximately 45
degrees.
The aircraft caught fire immediately after it struck the ground.
The fire was fed by aviation turbine fuel from the ruptured fuel
tanks and was quickly brought under control by local fire fighting
services which had been on stand-by at the aerodrome. The pilot
sustained fatal injuries. Impact forces and the ensuing fire
destroyed the aircraft.
Wreckage and impact information
Fire had affected the forward fuselage, consumed most of the
right wing and the inboard portion of the left wing. The left wing
flap was at an almost fully extended position and the right wing
flap was destroyed by fire. Examination of the wreckage did not
reveal any mechanical defect that may have contributed to the loss
of control.
An examination of the aircraft's propeller revealed that the
blades remaining within the propeller hub were in an approximate
coarse pitch setting. One of the blades had dislodged from the hub
on impact with the ground and an adjacent blade had fractured in
close proximity to the hub.
The engine and propeller were dispatched overseas to the engine
manufacturer for further examination. Examination of the engine
revealed no evidence of pre-impact distress or operational
dysfunction. The engine damage was consistent with it producing
high power at impact.
The engine manufacturer subsequently reported that they could
find no record of receiving the propeller. Despite additional
inquiries, the propeller could not be located and consequently it
was not possible to conduct a detailed examination of this
component. Therefore it was not possible to establish if the
propeller blade angle observed at the accident site was due to
impact forces, a result of a malfunction, or because of a control
input by the pilot.
Pilot information
The pilot in command was appropriately licensed and qualified to
undertake the flight. He held a valid Commercial Pilot Licence and
Grade 1 Agricultural Rating and had accumulated a total of
approximately 11,354 hours aeronautical experience, including 182.5
hours logged in AT-802A type aircraft. The pilot was experienced in
airborne fire-fighting operations and was professionally employed
in that capacity.
The Civil Aviation Safety Authority (CASA) had issued the pilot
with a class one medical certificate. The CASA Acting Director of
Aviation Medicine reviewed the pilot's medical history file
together with the pathologist's report of the post-mortem
examination. He reported that it was unlikely there was a direct
medical factor involved in the apparent loss of aircraft
control.
The pilot had previously completed demonstration flights of the
AT-802 aircraft. One of the owners of the aircraft reported that he
had spoken to the pilot about flying at the airshow a few days
before the accident. They discussed some aspects of this type of
event, in particular the potential for a pilot to impulsively
initiate an impromptu routine. The aircraft owner reported that the
pilot said that this was not going to be a problem and appeared
quite subdued about his participation in the event.
A number of people reported that they had spoken to the pilot on
the day of the accident. He had given the impression that he
intended putting on a "good display" and that he thought a
high-speed load release would look spectacular. The pilot
reportedly also commented about the high standard of some of the
other display routines and that he would "pull something out of the
box" to impress the crowd. Aircraft information
The AT-802A had a five blade constant-speed propeller that was
powered by a PT-6 turbine engine. The accident aircraft was
specifically equipped to conduct airborne fire-fighting operations
and was fitted with a computer controlled Fire Retardant Dispersal
System. The system had the capacity to deliver high volumes of
water through a pair of hydraulically operated, computer controlled
doors at the base of the hopper at rates well in excess of
conventional delivery systems. The pilot used a control panel in
the cockpit to select the ground coverage rate and the quantity of
hopper contents to be delivered. The hopper capacity was 3,104
litres.
The pilot had logged approximately 7.6 hours flying aircraft
that were equipped with this type of dispersal system. The
investigation could not determine the number of times the pilot had
used the system or the types of delivery he had made.
The AT-802A wing was equipped with fowler type flaps, which
extended to a maximum setting of 30 degrees. The approved Aircraft
Flight Manual (AFM) recommended that during fire control operations
the flaps be set to 10 degrees for approach and load release and
that flaps may be used as an aid in turning when extended to a
maximum of 8 degrees.
Extending the flaps beyond 10 degrees resulted in a significant
amount of additional drag and flap extensions greater than 10
degrees was normally used only for landing. The flaps could be
selected by the pilot to any position between 0 and 30 degrees
using a switch, mounted just below the throttle quadrant, or by a
toggle switch mounted on the control stick. Experienced AT-802A
pilots reported that it was possible to inadvertently extend the
flaps by unintentionally activating the switch mounted on the
control stick. Extending the wing flaps resulted in a conventional
nose-up pitching moment.
The AT-802A type aircraft was certified by the US Federal
Aviation Administration as an aircraft for "special purpose
operations". Flight-testing during the certification process
assessed the aircraft as being compliant with the Federal Aviation
Regulations (FAR) which required an aircraft to demonstrate
satisfactory aerodynamic stalling characteristics. Because low
altitude agricultural type operations were considered to
significantly reduce the probability of recovery from a spin, the
aircraft's compliance with the FAR relating to satisfactory spin
recovery characteristics was not required to be assessed.
The AFM for the AT-802A prohibited acrobatic flight manoeuvres,
including spins. The manual also noted that during fire control
operations the load release should be conducted at an airspeed
between 109 and 113 kts and recommended that 10 degrees of flap be
used to approach the target area and for the load release. In
addition, the AFM advised pilots to "be aware that during the load
release there will be a sudden pitch-up of the nose of the
aircraft" and to "begin forward motion on the control stick as soon
as the drop button has been activated".
Pilots experienced on the AT-802A reported that the intensity of
the pitching moment depended on the aircraft's speed and the rate
at which the hopper was emptied. The most significant pitching
moment occurred when the full hopper contents were released at the
maximum rate, at an airspeed exceeding 125 kts. It was also
reported that a pilot experienced on the AT-802A should be able to
anticipate the intensity of the nose pitch and accordingly, could
be expected to safely control the climb profile of the
aircraft.
Weather conditions
The weather conditions at the time of the accident were
generally fine with a light to moderate south easterly wind. The
temperature was about 23 degrees C and there was scattered cloud at
3,000 ft. The prevailing weather conditions were not considered to
have been a factor in the accident.
Video & photographic information
Analysis of video and photographic evidence revealed that the
aircraft approached the designated target area with about 10
degrees of flap extended and at an airspeed of about 125 kts. The
elevator remained approximately in a neutral position during the
release of the load and the aircraft nose commenced to pitch up,
reaching an angle of approximately 45 degrees on completion of the
delivery. The wing flaps extended to at least 25 degrees during the
first part of the climb with the elevator remaining close to a
neutral position. The climb angle then progressively steepened to
about 70 degrees. Pilots experienced on the AT-802A assessed the
initial delivery of water and foam to be normal, however the
subsequent aircraft climb profile was abnormally steep.
After the aircraft had rolled inverted, it adopted an almost
flat attitude, consistent with the incipient stages of an inverted
spin. Movement of the elevator control was evident during the
initial stages of the spin, however due to the resolution of the
video recordings, it was not possible to conclusively assess any
other movements of the control surfaces.