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.
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.
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.
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 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.
|Date:||01 March 1998||Investigation status:||Completed|
|Time:||1406 hours CSuT|
|Location:||Mt Gambier, Aero.|
|State:||South Australia||Occurrence type:||Collision with terrain|
|Release date:||04 July 2000||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||Fatal|
|Aircraft manufacturer||Air Tractor Inc|
|Type of operation||Private|
|Damage to aircraft||Destroyed|
|Departure point||Mt Gambier, SA|
|Departure time||1400 hours CSuT|
|Destination||Mt Gambier, SA|
|Role||Class of licence||Hours on type||Hours total|