The instructor and student were practising engine out landings, to touchdown, on a grassed area of the airport. On the accident approach, ground speed had been reduced to below five knots before the aircraft touched down. As the aircraft slid along on its skids they dug into the soft ground and the helicopter pitched forward until the main rotor blades struck the ground. The helicopter then rolled onto its right side.

The instructor was aware of the soft ground and was monitoring the approach carefully. Because the ground speed was low, the instructor was not expecting any problems with the landing and, as a result, he had insufficient time to take corrective action before the main rotor blades struck the ground.

The aircraft stalled and touched down heavily following an approach for a landing.

The student pilot was practicing a glide approach under the supervision of the instructor. The student misjudged the flare for landing and the aircraft ballooned to a height of about 25ft above the runway. The instructor applied some power as he told the student to lower the nose. The student was slow to react, and the airspeed reduced rapidly. The instructor took the controls, lowered the nose and applied full power but he was unable to prevent the aircraft from stalling and landing heavily.

Crew

In later discussion, the pilot in command stated that he was attempting to comply with the request from Canberra Approach to maintain a maximum speed descent. He believed that the aircraft would pass the 20 NM range circle indicated by the aircrafts Distance Measuring Equipment (DME), above 6,000 ft which was the lower limit of controlled airspace at that distance. He thought that it had done so as the aircrafts DME indicated 17 NM from Canberra when GPWS warning was received. The first officer, who was the handling pilot during the incident, stated that he checked the DME reading when the warning was received. At 17 DME, the lower limit of controlled airspace was 5,000 ft.

Flight data recorder information

The flight data recorder (FDR) data confirmed that the aircraft was descending through 6,000 ft when the GPWS activated. FDR data also confirmed the GPWS warnings and the 300 ft climb.

Recorded values of latitude and longitude revealed that the GPWS warnings were activated as the aircraft overflew Bulls Head, spot height 4,482 ft, approximately 20 NM on the 240-degree radial from Canberra VOR. The data confirmed that a valid Mode 2A Excessive Terrain Closure GPWS warning had occurred, and the crew had taken the appropriate actions to remove the aircraft from the GPWS activation envelope.

The FDR data showed the aircraft on descent at an airspeed of approximately 315 Kt on a heading of 078 degrees magnetic when the GPWS warning occurred. Recorded radar altimeter data indicated showed rates of closure with terrain in excess of 9,000 feet per minute (fpm). The radar altitude reduced from 2,658 to 2,044 ft in a three-second period.

ANALYSIS

GPWS parameters

The GPWS will give a Mode 2A warning if the aircraft is flying with less than 25 degrees of flap and there is an excessive rate of closure with rising terrain. If the airspeed exceeds 250 kts, the upper boundary of the radio altitude envelope is 2,450 ft with a rate of closure of 5,105 fpm and the lower boundary is 50 ft with a rate of closure of 2,063 fpm for a "TERRAIN, TERRAIN" warning. Within this envelope is the envelope triggering the "WHOOP WHOOP PULL UP..." warning.

The combination of the aircrafts rate of descent and the rising terrain on the western side of the Bulls Head resulted in a rate of closure in excess of 9,000 fpm and a radar altitude of 2,044 ft which was within the GPWS inner operating envelope.

Pilot’s intentions and results

The pilot’s intentions were to maintain the maximum speed during descent and to pass the 20 DME range circle just above 6,000 ft, continuing descent to 5,000 ft when inside the 20 DME circle. Both radar and FDR data revealed that the aircraft descended below 6,000 ft beyond the 20 DME circle and thus operated outside controlled airspace (OCTA) for a short time.

An aircraft operating at an altitude which is the published lower limit of controlled airspace is operating OCTA. Another aircraft, about which the air traffic services held no information, could have been operating OCTA at the altitude reached by the B737.

As both pilots reported that the aircrafts DME indicated 17 NM from Canberra when the GPWS warning was received, the DME equipment may have been faulty.

SIGNIFICANT FACTORS

1. While the pilot was attempting to maintain a maximum speed descent for air traffic control sequencing purposes, the aircraft descended below the lower limit of controlled airspace.
2. The combination of the aircrafts rate of descent and rising terrain placed the aircraft within the GPWS warning envelope.

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.

At 0349.34, the pilot of VH-EXC reported to Flight Service (FS) that he was over St Helens at 7000 feet, commencing descent and advised he would report again by 0410 or on missed approach.  His intention was to make a practice NDB approach.  In response FS advised him that there was no IFR traffic.

At 0357.00, the pilot of VH-HFD reported that he had departed St Helens at 57, was tracking 243 degrees (from the NDB) and was on climb to 8000 feet. (VH-HFD was running 20 minutes early on flight planned estimate for departure St Helens).   FS asked him if he had copied VH-EXC (as traffic) to which he replied negative.  FS then advised VH-HFD that VH-EXC was in the St Helens area for an NDB approach.  The two pilots then made contact with each other. By this time VH-HFD had left 5000 feet on climb and VH-EXC was at 2000 feet, tracking outbound in the NDB approach. Conditions were IMC and it was apparent that the two aircraft had gone through each other's levels, possibly in close proximity.

From timings on the transcript and information provided by the pilots, it was calculated that VH-HFD would have commenced its take-off roll at about 0352. Engines would have been started two to three minutes prior to then at about 0349.  The pilot of VH-HFD said that he made taxy broadcasts on both the FS and Common Traffic Advisory Frequency (CTAF).  Both aircraft were dual VHF equipped, and both pilots said they were monitoring both CTAF and FS frequencies.  The pilot of VH-EXC did not hear either of the taxy calls reportedly made by the pilot of VH-HFD.  The pilot of VH-HFD did not hear the call made by the pilot of VH-EXC on arrival over St Helens at 7000 feet.  On timings, it is possible that that broadcast was made prior to the pilot of VH-HFD commencing a listening watch on the two frequencies.

On arrival over St Helens at 7000 feet, VH-EXC entered the holding pattern to lose altitude.  The outbound leg of the NDB approach was commenced at 4500 feet probably at about 0355.  The outbound track is 107 degrees.  The pilot of VH-HFD departed from runway 08 at about 0352 and maintained runway heading until reaching 2000 feet where he made a right turn to track back to the NDB while continuing to climb.  It is obvious from these timings that the two aircraft passed in close proximity both vertically and laterally while in cloud and on close to reciprocal tracks.

Significant Factors

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

Neither pilot heard advisory broadcasts made by the other pilot.  It is possible that the pilot of VH-HFD may not have commenced a listening watch at the time the pilot of VH-EXC made his call on arrival over St Helens but the pilot of VH-EXC should have heard the calls from VH-HFD.

Melbourne FS cannot receive calls made on the ground at St Helens so were not aware that VH-HFD was taxying and were therefore unable to pass traffic information to VH-EXC.  In addition, VH-HFD was running 20 minutes early on flight plan so FS could not pass traffic information in anticipation of a planned departure time.

The pilot of VH-HFD did not establish contact with Melbourne FS as soon as possible after becoming airborne. Instead, he waited until he had climbed to 5000 feet and established the aircraft on the departure track.  This denied both FS and the pilot of VH-EXC the opportunity to become aware of the whereabouts of VH-HFD.

The amphibian aircraft landed on relatively smooth water in a lagoon. As soon as the floats touched the water the aircraft slewed to the left, nosed into the water, and turned over. The aircraft came to rest upside down in about three feet of water. The occupants evacuated the aircraft within half a minute, and the pilot activated an emergency beacon. A helicopter responding to the emergency arrived at the scene at about 0940.

Visual inspection of the aircraft after the accident revealed that the left main gear was extended. The pilot stated that he had the correct gear-up indications before landing. An inspection of the aircraft did not reveal any reason for the extended left main gear.

One passenger received minor injuries when fuel affected skin on her legs whilst standing in fuel contaminated sea water.

The pilot taxied out for take-off on strip 36. Run up and pre-take-off checks were normal. Full power was applied for take-off and the aircraft accelerated. However, by two thirds to three quarters of the 1000 metre length the aircraft was not airborne. The pilot applied back pressure on the control column and lifted off. The airspeed then decreased so the pilot lowered the nose. The left wing dropped, and the aircraft descended, striking the ground nose down and overturning.

The pilot had inadvertently taken off in strong gusty downwind conditions.

Significant Factors

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

1. The pilot did not pay adequate attention to ascertaining the direction of the wind.

2. The pilot attempted a take-off in strong downwind conditions.

A Boeing 747 had just landed on runway 19 and was in the process of vacating the runway. At the same time, a King Air aircraft was given a clearance to cross the runway at taxiway "M".

The pilot of a Beech 99 requested a take-off clearance from the intersection of runway 19 and taxiway A4. The ADC (aerodrome controller) assessed that both the B747 and King Air would be clear of the runway in time and issued a take-off clearance to the Beech 99. As that aircraft entered the runway, and commenced the take-off run, the crew observed the King Air about to cross the runway. They rejected the take off and queried the take-off clearance. The ADC saw no safety risk and recleared the aircraft for take off.

The ADC was probably surprised to a minor extent about the rolling take-off, however he judged that there were no safety implications in allowing the take off to continue. The distance between taxiway A4 and taxiway "M" was 1410 metres.

The aircraft did not accelerate normally during the take-off roll. The pilot elected to reject the take-off but the aircraft overran the end of the runway. During the overrun, the nosewheel was torn off.

The pilot reported that post-accident inspection indicated the strip surface was softer than expected. This retarded the aircraft's acceleration.

The pilot reported that on commencing descent at 50 nautical miles from Cairns, engine power was reduced to 3,000 pounds of torque. At approximately 40 nautical miles a further reduction was made to 2,700 pounds. When the next reduction was made at 30 nautical miles the left engine did not respond to throttle movement and remained at 2,700 pounds. Right hand engine response was normal. The crew considered shutting down the left engine, but with weather and terrain circumstances taken into account, it was decided to leave the engine going. After arrival in the circuit area, speed was reduced, and movement of the power lever was checked. The torque on the left engine had then reduced to approximately 2,400 pounds. After selection of landing gear and flap, propellor revolutions per minute were reduced to 1,400, and a normal approach profile was maintained. After selection of maximum propellor revolutions per minute, engine torque reduced to approximately 2,000 pounds, and as a normal profile could be maintained, it was decided not to shut the left engine down. Power was reduced on the right engine to maintain profile on the approach.

After touchdown on the damp runway, the power levers were retarded by the pilot and the aircraft immediately swung to the right. Corrective action was taken with flight controls and brakes. Directional control was regained and as the aircraft decelerated the crew became aware that the right main tyre had blown. The aircraft was stopped on the runway and rescue and fire services attended the aircraft.

Investigation revealed that the left engine power control cambox had jammed and this had prevented the power lever from transmitting movement to the fuel control unit via a teleflex cable. The cam mechanism appears to have been sticking due to inadequate lubrication, and hardened grease. The power lever could still be moved due to the flexibility in the Teleflex cable.