Loss of control

The pilot reported he had commenced a take-off roll on runway 08, after completing pre-take-off checks and receiving a take-off clearance. At a speed of about 40 knots, as he pushed forward on the control column to raise the tail, his seat slid fully aft on the seat rails. Although his feet could no longer reach the rudder pedals to maintain directional control, he was able to close the throttle and abandon the take-off.

The aircraft subsequently ground looped to the left, collapsing the right landing gear, before coming to rest on the side of the runway.

The student pilot with approximately 50 hours experience was undertaking conversion onto a single-seat, higher performance glider.

About one week before the accident flight, the club flying instructor flew with the pilot in a two-seater training aircraft.  During the take-off, the launch cable broke, and the pilot executed a recovery using the correct technique. The flight continued without incident and the flying instructor assessed that the pilot was fully qualified for the conversion onto the higher performance glider.

The accident flight was his second on the type, the first lasting 26 minutes.

The glider was winch launched and was observed climbing in a steep attitude from the start of the climb.  At approximately 100 ft, the glider initially began a turn to the right but then commenced turning to the left.  The nose dropped and the glider was observed to enter a spin before impacting the ground at a steep angle.  Witnesses, experienced glider pilots, observed that immediately before descent the aircraft appeared to be losing speed.

Examination of the wreckage found no deficiencies with the glider, its structure or systems.  Witnesses examining the wreckage on site found the elevator trimmed so as to give the glider maximum nose-up pitch.

Examination of the elevator trim mechanism failed to find any deficiency with the system which would have accounted for the nose-up trim setting. Additionally, analysis of the effect of the impact on the trim mechanism indicated that the impact would have had a tendency to move it into a nose-down trim setting.  The reason for the nose-up elevator trim setting could not be determined.

Findings

1. The pilot lost control of the glider.
2. The glider entered a spin and impacted the ground.
3. There was no indication of any fault in the winch launch of the glider.
4. No pre-existing glider defect contributing to the accident was identified.
5. The elevator trim was found in the full nose-up position.

The aircraft was engaged in a crop spraying operation, and during a procedure turn to the right, with a light downwind component, the pilot allowed the aircraft's airspeed to deteriorate, resulting in a stall.

He was able to partially recover the aircraft close to ground level, but the landing gear wheels became entangled in the crop, causing the aircraft to descend further and contact the top of a drain bank.

Using full power, the pilot attempted to fly away, but the aircraft was unable to clear a line of trees at the perimeter of the paddock which it flew into and came to rest inverted on the ground below.

The pilot reported that during the landing roll the right brake failed, and the aircraft ground looped to the left. The right landing gear separated, rupturing fuel lines. The aircraft ignited when it came to rest and was totally destroyed.

An emotionally disturbed young woman was allowed to board the aircraft as the sole passenger for the 25-minute flight. At top of climb, the passenger attacked the pilot and made an attempt to exit through the pilot's side window. In the process, she disturbed the aircraft and engine controls. The aircraft descended out of control from 4,500 ft and after pushing the passenger out of the cockpit, the pilot regained control by 3,000 ft. After being threatened by the pilot, the passenger remained subdued for some time. However, approaching Bundaberg, she again became agitated and harassed the pilot. The aircraft landed safely.

Resort staff allowed the passenger to board the aircraft unescorted despite the availability of suitable staff. The passenger had been "playing up" all weekend had caused problems at the resort.

The pilot said that he had intended to fly practice circuits in the tailwheel aircraft. During the landing roll of his first circuit, he lost directional control at about 25 to 30 knots indicated airspeed. After yawing first left then right, the aircraft entered a ground loop to the left at about 20 to 25 knots. The right-wing tip and right tail plane made contact with the ground.

The aircraft was taxied back to the hangar.

The passenger, who was an experienced instructor but was on board as a passenger, indicated that the pilot had made inappropriate control inputs following touchdown. This led directly to a loss of control. An intercommunication system was not fitted in this aircraft.

The student helicopter pilot elected to conduct an unsupervised hover practice at Casey Airfield.  His total helicopter experience was 27 hours dual and seven hours solo, all in his privately owned Rotorway EXEC 90.  The terrain over which the helicopter was hovering was level ground covered by grass about half a metre high.  The wind was calm and visibility excellent.  The pilot advised that while trying to land, the front of the right skid touched the ground first and the helicopter rolled over onto its side.  Damage sustained by the helicopter was consistent with a rollover accident.  The rollover probably occurred as the helicopter drifted sideways with the landing skids in the grass.

During wreckage inspection of VH-COC it was discovered that the collective scissor link block was off its mount and that the nuts had been pulled off the two 3/16 bolts which attach the block to its mount.  There was concern that had the block pulled free before impact, loss of collective control would have occurred, probably resulting in sudden flat pitch on both main rotor blades.  Such loss of control in the hover probably would have caused the helicopter to be slammed onto the ground with more resultant damage than occurred in this rollover accident.

Another wrecked Rotorway EXEC 90, VH-YCP, was examined for comparison. Its scissor link block was still attached but score marks and fretting under the bolt heads were evidence that the block had not been securely attached to the airframe mount.  Similar evidence of fretting was subsequently found on VH-COC.  On both helicopters the airframe mounts were not flat surfaces. Also, both mounts were coated with paint which could be detrimental to a close tolerance fit.  In contrast, the base of the scissor link block was a machined flat surface.  When one end of the block was attached with a bolt, the other end of the block was proud of the steel mounting plate by 0.020 inches.

It was discovered that the Civil Aviation Authority (CAA) had required the collective scissor link attachment bracket, originally supplied by the manufacturer, to be replaced by the block of aluminium.  A bracket might flex enough during installation to achieve a flush fit with the mounting plate, whereas the aluminium block was inflexible.

Further inspection of Rotorway helicopters discovered that there was no airframe down stop for the collective lever in the cockpit and that the mechanical advantage between the collective lever and the scissor link was 24 to 1. Pushing down on the collective lever placed the two 3/16 bolts in tension.  Several 3/16 aircraft bolts were tested in tension to destruction. On average the nuts pulled off the bolts at 2714 ft/lbs.  In training, particularly during practise autorotations, it is normal for the pilot (occasionally for both the pilot under instruction plus the instructor) to push down on the collective to ensure flat pitch.  The combination of bolts under tension and the non flush fit of the blocks on VH-COC and VH-YCP had caused the blocks to move/work in the past and in time could have caused the bolts to fail.

Significant Factors

The following factors were considered relevant to the development of the accident:

1. The student pilot conducted an unauthorised solo flight.
2. The pilot probably inadvertently allowed the landing skids to drag through long grass as the helicopter drifted sideways in the hover.

Safety Action

The CAA was immediately informed of the Bureau's findings and concern about the attachment of the collective scissor link block to the airframe.  A CAA Airworthiness Surveyor inspected VH-YCP. The Australian agent for the Rotorway kit helicopter was advised verbally of the findings.  The CAA approved Australian Rotorway EXEC 90 test pilot, and the CAA test pilot were advised of the findings as soon as possible.

Since this accident there has been a Rotorway EXEC 90 incident in which cyclic control became marginal in flight, resulting in a very unsafe condition. This incident exposed that the aircraft type did not comply with the flight characteristics requirements for an amateur built helicopter in Australia.  It was found that the friction and adjustment of the slider ball (uniball) was temperature sensitive and had caused binding of the cyclic control system. The instructions provided by the manufacturer to address cyclic binding were not acceptable to the CAA.

The CAA was not made aware of the potential cyclic problem during the application for the amateur built aircraft approval process.  Accordingly, the CAA has withdrawn Permits to Fly, and a Certificate of Airworthiness will not be issued for any helicopter of this type until the matter of the cyclic control is resolved.

Witnesses reported seeing the helicopter land in the corner of a fenced paddock. A short time later the helicopter took off again but after climbing to about three metres above the ground, it began rotating and gyrating erratically, contacting the ground a number of times. It came to rest in an upright position but with the tail boom severed and damage to the main rotor assembly and gear box.

The pilot reported that he had recently recovered from a viral complaint which was characterised by severe coughing bouts but had been free of these symptoms for a few weeks. As he flew over the area of the accident, however, he had experienced the incipient stages of a coughing fit, so he landed the helicopter, shut the engine down, and walked around for a short time until the symptoms disappeared. He then reboarded the helicopter to continue the flight but shortly after lift-off was overcome by a severe coughing fit. This caused him to partially lose control of the helicopter, and it contacted either the fence or the ground.

The helicopter was tracking coastal at about 500 feet AMSL when the pilot saw a crocodile on a riverbank and commenced a descent to enable photographs to be taken. He made a right turn to position the helicopter into wind while descending to a height of about 100 feet and decelerating to 10-20 knots.

As the helicopter came out of the turn the pilot applied normal up collective control and left anti-torque pedal to regain level flight which was immediately accompanied by a severe vibration. The helicopter began to rotate rapidly to the right and the pilot applied full left pedal, but with no response, the feel on the pedals being as if they were detached from the tail rotor system.

The pilot lowered the collective and applied forward cyclic in an attempt to control the rotation and vibration. Although the rotation rate slowed, the helicopter rotated through another 2-3 turns and descended to about 30 feet above the sea. The pilot realising that he would be unable to effect a successful recovery, landed the helicopter in the water with a forward speed of about 10-20 knots in a tail low attitude while still rotating to the right.

The helicopter rolled inverted and floated upside down for 3-4 minutes. All occupants evacuated the helicopter and swam ashore. The helicopter sank, but after a while it resurfaced then floated out to sea on the tide and was recovered the next day. The tail boom was found to have been severed behind the horizontal stabiliser, the vertical fin, tail rotor gearbox and tail rotor being lost in the sea.

Subsequent investigation revealed that the tail rotor drive forward short shaft had failed due to torsional overload. The severed tail boom, when matched to a serviceable helicopter of the same type, showed that the damage and impact marks were found to align with the tail rotor blades. The tail rotor drive long shaft had only slight impact damage and had uncoupled intact off the splines at the tail rotor gearbox, indicating that a main rotor blade impact had not caused the tail boom to fail.

The tail boom was severed by a direct strike from a tail rotor blade under power, which then caused the tail rotor drive short shaft to fail under load. It was not possible to determine the reason why the tail rotor blade struck the tail boom.