A Squirrel AS 350B helicopter, and a Jetranger 206B helicopter, were conducting scenic flights in the Sydney area on the afternoon of the occurrence. These flights usually passed over Middle Harbour but, because runway 25 was in use, they were cleared to track in company via the less familiar St Peters route. The Squirrel, being the faster of the two aircraft, flew in the lead.

Nearing the end of the flight, both aircraft were asked to hold for ten minutes at Rose Bay. Both pilots later said that they became concerned because it was almost at the end of daylight, and neither helicopter was certificated to undertake commercial night operations. After holding for about seven minutes the tower cleared both aircraft to track to Sydney Airport via St Peters and requested the pilots to expedite their return.

Whilst tracking inbound, the Jetranger began to fall behind the lead helicopter. The pilot of the Jetranger did not advise the tower, nor the pilot of the Squirrel, that he had fallen behind. As he approached to cross runway 25, the pilot of the Jetranger observed a fixed wing aircraft on final for that runway and slowed his helicopter because of wake turbulence concerns. The tower, on hearing the Squirrel report on the ground at Helipad H1 on the southern side of runway 25, assumed that the Jetranger was also about to land. At the same time a Sikorsky S-76A helicopter was inbound from the Harbour Bridge for Helipad H4, on the northern side of runway 25. A short time later the pilot of the Sikorsky reported that a Jetranger had passed in front of him from right to left, within a distance of about 150 ft, near Helipad H4.

All three pilots subsequently reported on the difficulties of sighting other aircraft against the city lights. Although the pilot of the Squirrel was aware of the proximity of the Sikorsky, the pilot of the Jetranger was not. Nor was the Sikorsky pilot aware of the proximity of the other two helicopters. The aerodrome controller did not see the Jetranger against the background of aircraft and city lights and was consequently unaware of the potential traffic confliction.

The pilot reported that he started the pre-landing checks as he joined the circuit and not on the downwind leg which is where he would normally start them. He selected full flap earlier than normal on the base leg and checked the throttle was at idle because the aircraft was not descending as quickly as he expected. He could not work out why. At no stage did the landing gear warning horn sound. After he flared the aircraft for the landing the propeller began to strike the runway, and the aircraft settled onto its fuselage. It slid to a stop to one side of the runway. The pilot indicated that he had forgotten to select the gear down prior to landing and had not noticed the lack of gear indications during his checks.

The pilot further advised that the gear warning horn had been reported as unserviceable on previous flights and although he had been told that it had been repaired it was apparently still unserviceable.

One factor often identified during inadvertent wheels-up accidents is the interruption of the pre-landing checks, usually because they have been started too early and the pilot is not ready to extend the gear when he gets to that item on the list. Universally recommended practice is to restart the checks from the beginning if they have been interrupted for any reason. The pilot in this accident reported that he had started his checks early and had stopped at the gear item.

The student pilot, operating under the remote supervision of an instructor had been conducting circuits in his own aircraft. Whilst conducting a glide approach, the pilot noticed that the aircraft was at a lower altitude than desirable and decided to delay extending the landing gear until late on the approach. The aircraft subsequently landed with the landing gear retracted.

According to the pilot and his instructor the 'gear unsafe' warning horn was not working at the time of the accident, nor had it worked during the endorsement. An engineer had told them that it was a permissible unserviceability. This information was subsequently found to have been incorrect.

The pilot reported that he had selected the landing gear down, and first stage of flap while on the downwind leg of the circuit but did not confirm the gear position during the pre-landing check either by observing the gear down lights or a visual check of the gear position through the window.

Full flap was selected on short final, and power reduced during the flare with the aircraft settling on the runway in a wheels up landing.

An investigation failed to find any problems with the landing gear or its system, and the pilot subsequently admitted that he had forgotten to lower the gear. The gear unsafe warning horn did not activate as the pilot had used a considerable amount of engine power throughout the final approach.

Witnesses reported that after the aircraft came to a stop the landing gear appeared to be partially extended, and the gear lever was in the down position. This gives the appearance that the pilot had realised his mistake too late and attempted to extend the gear just prior to touchdown.

The aircraft was being used to conduct parachuting operations from Hamilton Island. On this flight, an instructor was to carry out a tandem jump and another parachutist was to make a solo jump.

As the aircraft was climbing to altitude the pilot parachute on the instructor's rig opened. The pilot parachute was drawn out of the aircraft and the instructor managed to exit the aircraft and deploy his main parachute. He made a successful water landing. The solo parachutist jumped from the aircraft to render any necessary assistance to the instructor. The parachutist who was to jump in tandem with the instructor remained in the aircraft which was landed successfully at Hamilton Island.

Subsequent inspection of the aircraft found that the right stabiliser and elevator were bent upward, and the elevator horn balance torn off. 

The reason for the inadvertent deployment of the pilot parachute is unknown.

FACTUAL INFORMATION

Sequence of events

The crew reported that the flight had been normal and that the subsequent approach, which was flown by the co-pilot, was stable. The touchdown on runway 16R was smooth. The anti-skid and auto-spoiler systems were armed prior to touchdown. However, the ground spoilers did not automatically deploy but were manually raised by the pilot in command when the aircraft was about 150 metres beyond the touchdown point.

Coincident with the raising of the ground spoilers, the crew became aware of a thumping noise from the rear of the aircraft, and of the right wing beginning to drop. The aircraft deviated about 8 metres to the right of the runway centreline and was brought to a stop at the intersection of runways 16R and 07.

The aerodrome controller activated the crash alarm after observing excessive smoke from the right main landing gear and the shredding of the tyres. The airport RFFS attended the aircraft and confirmed that there was no fire and that the brakes were cold. The only heat present had been generated by the failed tyres. The engines were shut down and the APU was started to maintain the aircraft electrical system. After the pilot in command had confirmed that personnel were available to ensure their safety, the passengers were disembarked via the rear airstair.

On-site investigation

Inspection of the tyres and the tyre markings on the runway indicated that neither right main gear wheel rotated at touchdown. The right tyres produced heavy rubber skid marks from the touchdown point for about 120 metres, until the inboard tyre failed. The outboard tyre then failed about 20 metres further on. The aircraft travelled about 700 metres from the touchdown point. The complete tread section of the right inboard tyre had separated from the casing at some time subsequent to its failure.

Flaying tyre material had detached the landing gear outer door and damaged a trailing edge flap and flap fairing. Prior to touchdown the crew had not been aware of any abnormal technical indications. The wind was from 140 degrees, at 10 to 15 knots, gusting to 20 knots, and the runway was dry.

The aircraft was fitted with auto brakes. However, they were not used for this landing, as the operator's procedure when landing on runways such as 16R at Sydney was to use reverse thrust until the aircraft speed had reduced to below 60 knots. Normal braking would then be used.

Initial inspection of the right landing gear and braking system established that the wheels were able to rotate freely and that the fusible plugs in the wheels remained intact. Both failed tyres appeared to have been in serviceable condition prior to the landing. The inner tyre had accumulated 37 landings, while the outer tyre had accumulated four landings. The brake assemblies appeared to be serviceable.

Engineering examination

Subsequent detailed inspection of the aircraft systems found that with the anti-skid system activated and the right brake applied, the right inboard mainwheel locked. The fault was traced to switch No 480, which was found to be defective, and its mounting twisted. The switch was designed to provide locked wheel protection signalling for the anti-skid system, to ensure full brake release of the inboard pair of wheels at touchdown. The signal is cancelled when wheel speed of 60 mph is sensed, and the anti-skid system is then activated.

Locked wheel protection for the outboard wheel pair is provided by the landing gear accessory unit which is switched by the squat switch on the left main gear. This unit could not be faulted on ground test. Complete testing of the anti-skid system in accordance with the maintenance manual and recommendations from the manufacturer failed to detect any reason for lockup of the outboard brake. The failure of switch No 480 is consistent with inadequate lubrication of the control cable mechanism which activates the switch. Lack of lubrication can cause binding which may lead to disruption of the control. Similar problems with this mechanism have been reported by another operator.

Testing of the auto-spoiler system did not detect any defects. The system, when armed, will automatically deploy at touchdown when wheel rotational speed of 60 mph is sensed by a wheel on each landing gear, or after a time interval of 4 seconds after the squat switch on the left gear is sensed in ground mode. Although both wheels on the right landing gear were locked, the auto-spoilers would have deployed 4 seconds after ground mode was sensed, had the pilot not manually selected them.

The aircraft maintenance manual recommended replacement of the brake metering valve when tyre scuffing was evident. Consequently, the right brake metering valve was changed as a precaution. However, apart from this recommendation, the reason for the outboard tyre failure was not determined. Flight recorder information

The aircraft was fitted with a Sundstrand Universal Flight Data Recorder. Twelve parameters were recorded, including vertical and horizontal acceleration, pitch and roll attitude, magnetic heading, airspeed and engine pressure ratios.

Analysis of the recorded information confirmed that all parameters relevant to this occurrence were normal. The information indicated that a minor heading correction to the right was made immediately before touchdown.

Additional information

About two weeks after the aircraft had been returned to service, with the same flight crew and the co-pilot again handling the controls, the right outboard tyre failed during landing. The evidence indicated that there had not been wheel rotation at touchdown, and the tyre had skidded for about 120 metres before failure. Engineering inspection found that the landing gear lever UP switch No 781, which controls both inner and outer wheel pairs via the anti-skid system, was intermittently inoperative. The area in which the switch was located had been treated with a water dispersant type spray lubricant. This substance appeared to have adversely affected the operation of the switch.

The switch was changed, and the entire system then tested normally. The aircraft was returned to service, and no further incidents have been reported.

ANALYSIS

The initial occurrence was caused by the failure of the locked wheel protection circuitry for both the inboard and the outboard wheel pairs. Consequently, pressure applied to the right brakes during touchdown would have locked both right wheels.

The protection circuitry became inoperative when switch No 480 failed and an intermittent fault developed in switch No 781.

With the auto brakes disarmed, the brakes can only be applied by manual pressure on the brake pedal. It is possible that the handling pilot inadvertently applied right brake pressure when making the slight heading change which occurred immediately prior to touchdown.

The complete loss of the tread from the right inboard tyre may indicate that some rotation of the wheel occurred after the tyre failed.

The circumstances in which the right outer wheel was locked at touchdown when the second incident occurred, could not be fully substantiated. However, the section of switch No 781 which controls the locked wheel protection for the outboard wheel pair had malfunctioned.

CONCLUSIONS

Findings

1. Switch No 480 failed.
2. Switch No 781 malfunctioned intermittently.
3. There was no indication of a problem prior to the touchdown.
4. Immediately before touchdown there was a slight heading correction to the right.
5. The touchdown was smooth.
6. Neither right main landing gear wheel rotated at touchdown.

Significant factors

1. The main wheels' anti-lock systems protection did not function.
2. The right brakes may have been inadvertently applied at touchdown.

The Boeing 737 was tracking towards Sydney at about 250 kts, descending through 6000 ft, following a Boeing 747, when the crew of the 737 reported that they suddenly encountered wake turbulence. The aircraft abruptly rolled about 30 degrees to the left before the handling pilot was able to return the aircraft to straight and level. The crew advised ATC that they required greater separation from the 747.

No passengers were injured, however the purser cut her arm, and the second senior flight attendant grazed her knee, when they fell during the occurrence.

Subsequent investigation revealed that the 737 was 5.8 NM behind and 600 ft below the 747 at the time of the occurrence. The 737 had rolled 38.1 degrees to the left before the roll was stopped. The minimum longitudinal separation standard required for wake turbulence avoidance was 5 NM.

Circumstances

On the afternoon of the accident, the chief pilot was to undergo a 'check pilot' approval flight for company aircraft with a Civil Aviation Safety Authority Flight Operations Inspector (FOI). The chief pilot was initially required to demonstrate his competence to fly from the right seat of the company's De Havilland Beaver, including both into-wind and crosswind circuits. Following the completion of this demonstration, the chief pilot was to hand over control of the aircraft to the FOI. The FOI was to fly the aircraft under the supervision of the chief pilot.

The FOI was endorsed on the Beaver with a total time on type of three hours including one hour as pilot-in-command.

Weather information for the flights had been obtained by Affix. There was a light northerly breeze at approximately 10 kts. In the area where crosswind circuits were to be conducted, the crosswind strength was approximately 8 kts with gusts of up to an additional 5 kts. Surface conditions on the lake at the time of the accident were described as a 'moderate ripple'.

The chief pilot completed a number of circuits. The FOI was satisfied with this aspect of the approval flight. Control of the aircraft was then handed over to the FOI.

The FOI reported that the into-wind circuits he had flown had been uneventful, including a practice forced landing. The chief pilot added that, although the landing technique had been satisfactory, the landing nose attitude had been a little lower than would be considered ideal. He had discussed this with the FOI during these circuits.

The FOI then requested to fly a crosswind landing and take-off. A short discussion followed in which the FOI mentioned that most of his training on 'floats' had been carried out in 'light' wind conditions.

The FOI stated that, as he manoeuvred the aircraft for the crosswind approach and landing, the crosswind was still from the right, but it had moderated a little from earlier observations.

As directed by the chief pilot, the FOI adopted a level nose attitude when the aircraft was close to the water and placed the right wing down to stop the 'drift'. At this time the power was reduced. The right float touched the water first, as expected for a crosswind landing, but the aircraft then 'skipped' slightly.  The second time it touched down the float dug into the water and the aircraft yawed to the right.  At this point, the FOI stated that he applied full left rudder to counteract the yaw. The chief pilot also stated that he took hold of the control column and applied full backpressure to assist with the recovery actions of the FOI.

The aircraft did not respond to these corrective measures.  It proceeded to lurch violently left in what was described as a cart-wheeling motion.

The aircraft came to rest, right side up, facing the opposite direction to that of the intended landing, and with the right wing down approximately 20-30 degrees.

The aircraft rapidly filled with water from the right side. The FOI attempted to open his door on the left side, but it appeared to be jammed by a float, as were all four doors. The chief pilot tried to assist the FOI but without success. While the FOI climbed into the rear seat to attempt to open the rear left door, the chief pilot attempted to exit from the window of the left front door. The FOI used a paddle to assist in opening his door but without results. As the aircraft started to sink the float moved away from the cabin area sufficiently to allow the FOI to evacuate through the left rear door. The chief pilot pulled himself through the left front window as the fuselage was starting to submerge.

The two pilots clung to the aircraft floats to await rescue. Both pilots sustained minor cuts and bruises.

The aircraft sustained major structural damage. Both wings were torn from the wing roots. It was later recovered from the lake.

Analysis

The chief pilot was experienced on the aircraft type but, considering he was in the process of an approval flight at the time of the accident, his experience as a 'check pilot' was limited.

The chief pilot stated that he felt the FOI was using a satisfactory technique to land the aircraft, albeit with a slightly 'flat' nose attitude. He was sufficiently confident in the FOI's ability to safely fly the aircraft that he did not feel it necessary to have his hands placed close to the control column. He pointed out, however, on this landing, the aircraft seemed to 'settle' at a greater rate than he had expected. He considered that, when the Beaver first touched down and 'skipped', the FOI was capable of recovering without assistance. It was not until the aircraft 'dug in' on the second touchdown that he felt it necessary to assist. In retrospect, the chief pilot thought that this action was a little too late to affect the recovery.

The FOI had limited experience in float plane operations. It had been some time since his 'type' endorsement on the Beaver had been completed. He also stated that his flights in the Beaver had all been conducted in 'light' wind conditions. The crosswind on the day of the accident was considered to be greater than he had previously experienced.

Findings

1. The FOI had limited experience in float plane operations.
2. The FOI had limited experience on the aircraft type in crosswind conditions.
3. The chief pilot had limited experience as a check pilot.
4. The FOI lost directional control of the aircraft during a crosswind landing.
5. Both pilots experienced difficulty evacuating the aircraft.

The pilot reported that the aircraft was landed off a normal full flap approach. The strip slopped down from the touchdown point. After lowering the nosewheel the pilot applied the brakes; however, they did not work, and the aircraft's speed did not reduce. He shouted to the passengers to brace themselves and, as the end of the strip was approaching rapidly, he attempted to steer the aircraft into a fence to bring it to a stop. There was insufficient room to complete a go-around. Shortly after turning the aircraft towards the fence the brakes operated, locking the main wheels. The pilot was unable to establish any further directional control, and the aircraft collided with a tree.

A post-accident inspection of the braking system did not disclose any reason for the brake problem.

The pilot was ferrying the aircraft to Killara Station for the owner. He had checked the condition of the strip prior to departure and was advised to land on a road near the homestead as the main strip was unserviceable.

The pilot reported that on arrival he made two low approaches to confirm that the road was suitable and then made a third approach for the landing. There was no windsock visible; however, a windmill indicated that the wind was a crosswind from the right. At about 25 ft on final approach the aircraft started to drift away from the centreline of the road. The pilot was unhappy with the approach and decided to go-around. He opened the throttle; however, before the engine could respond the aircraft descended rapidly and landed heavily on the edge of the road. The aircraft ran off the road into trees, the nosewheel dug in and it overturned.

It was reported that there were no unusual atmospheric conditions present at the time of the accident. It is probable that the sudden descent occurred because the pilot inadvertently allowed the airspeed to reduce to the stall speed during the attempted go-around.