Loss of control

The pilot reported that he and his 13 year old son were going for a short flight from Maryborough airport. All necessary preflight checks were carried out and sufficient fuel was on board for the intended flight. After take-off from runway 17 at between 100 and 200 ft the engine stopped completely. Witnesses saw the aircraft enter a left turn at a low height. The aircraft then appeared to stall and hit the ground inverted. The landing gear was in the retracted position.

The pilot stated that the engine failed because the magneto switches were bumped to the off position. Both switches are mounted close together in the centre of the instrument panel with other switches below them. The pilot stated that he was told in hospital that his son was waving to a person on the ground and had bumped the magneto switches off.

The pilot reported that he was giving another pilot instruction for the purpose of endorsement on type. A few seconds into the landing roll the left wing lifted, and the aircraft veered sharply left towards the runway edge. Both the instructor and the student applied opposite rudder resulting in the aircraft turning quickly right. This was followed by a series of sharp turns left and right down the runway until the aircraft eventually entered a ground loop to the left before coming to a halt.

The pilot reported that during take-off with a full load, and 15 knots of crosswind, he lost directional control and ground-looped the aircraft about one third of the way along the strip. The right gear collapsed, and the right wing was damaged when it contacted the ground.

Boeing B737-476, VH-TJK, was being radar vectored onto the Sydney 16R localiser from the right, to follow a B747-438 already established on the localiser. The pilot in command was flying the aircraft with autopilot "A" engaged, heading mode selected, and VOR/localiser capture mode armed. The aircraft turned onto the localiser, descending through an altitude of 2,500 ft, some 2.3 dots below the glideslope, about 10 NM from the landing threshold. As the B737 began to intercept the localiser track, maintaining an airspeed of about 218 kts, the bank angle was progressively increased to 29.5 degrees before the aircraft abruptly rolled further to the right. This uncommanded event coincided with initiation of trailing edge flap and leading edge slat extension from the stowed position. The aircraft reached a maximum bank angle of 62.9 degrees before the roll was stopped, and the wings levelled by the handling pilot. A missed approach was carried out, after which the aircraft was landed normally without further incident. At the time of the occurrence the surface wind was 210 degrees at 10-15 kts, with scattered cloud at 1,800 ft and light rain in the area.

VH-TJK immediately underwent an extensive ground inspection program, followed by a flight test, in accordance with recommendations from the manufacturer. No defects were found which could have contributed to the occurrence.

An examination was carried out of recorded radar data, and of information derived from the flight data recorders of

VH-TJK and the preceding B747. It was found that the B747 had intercepted the 16R localiser at an altitude of 3,000 ft, approximately 11 NM from the landing threshold. The aircraft maintained 3,000 ft until intercepting the glideslope at about 9.5 NM and carried out what appeared to be a normal ILS approach to runway 16R. There was no reported turbulence.

VH-TJK intercepted the localiser at about 10 NM from the landing threshold, some 500 ft lower and about 115 seconds later than the B747 had been at the same lateral position. Recorded wind data from the inertial reference systems of both aircraft indicated the wind direction varied between 155 and 165 degrees, at a velocity of 25-35 kts. As the localiser track is 155 degrees, this meant there would have been little or no lateral displacement of any wake vortices produced by the B747.

Research has shown that for a typical jet transport aircraft, the wake descends behind the generating aircraft at approximately 300-500 ft/min for about 30 seconds. The descent rate decreases and eventually approaches zero at

500-900 ft below the flight path. The decay process of the wake is complex and is strongly influenced by atmospheric conditions (Boeing Airliner/Jan.-Mar. 1995). UK CAA wake turbulence studies have also shown that B747 and B757 aircraft produce higher Category A incident rates than other aircraft, where Category A incidents correspond to the development of uncommanded roll angles 30 degrees or greater to following affected aircraft. The same studies showed that aircraft with the highest incident rates of encountering wake turbulence behind B747 and B757 aircraft were BAC-111, B737 and DC9 types.

CAA wake turbulence radar separation standards are described in the Australian Manual of Air Traffic Services and are based on three categories determined from the maximum certified take-off mass of the aircraft. B747 aircraft are categorised as heavy, while B737 aircraft fall into the medium category. The standard, which is based on distance, shall be applied when an aircraft is crossing behind, or operating within 0.5 NM laterally of another aircraft's flight path at the same level or less than 1,000 ft below. In this case, a medium behind a heavy required a minimum separation of 5 NM. Examination of the recorded radar data showed that the separation between VH-TJK and VH-OJC was approximately 5 NM at the time of the occurrence.

The recorded trailing edge flap and leading edge slat data for VH-TJK indicated that the uncommanded roll occurred whilst the devices were extending from their fully stowed positions. It was not possible to determine from the recorded data whether this was responsible for the uncommanded roll or contributed to its severity. However, ground inspections and subsequent flight testing did not reveal any defect in the operation of those systems.

It is therefore considered that the onset of the uncommanded roll resulted from an encounter with wake turbulence generated by the preceding B747.

Significant Factors

1. Atmospheric conditions were conducive to the slow decay of wingtip vortices generated by the preceding B747.
2. VH-TJK intercepted the localiser some 500 ft below the altitude of the preceding B747.
3. The maximum longitudinal spacing between VH-TJK and the precedingB747 was 5 NM.

The student pilot was conducting a series of stop and go landings. On the fourth approach, Tower instructed the pilot to carry out a touch and go landing due to a following RPT aircraft. The aircraft bounced on landing and the pilot lost directional control. During the subsequent ground loop, the propeller and right-wing tip struck the ground.

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.