The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence. The report presented below was prepared principally from information supplied to the Bureau.
REPORTED INFORMATION
At 1139 eastern standard time on 2 February 2005, the crew of a Fairchild Industries Incorporated SA227 aircraft, registered VH-MYI, landed at Julia Creek aerodrome on a scheduled regular public transport service from Richmond, Queensland. At that time the runway was not available due to aerodrome line marking works, which had been notified in a notice to airmen (NOTAM) issued on 26 January 2005. There was no equipment or personnel on the runway at the time the aircraft landed.
The pilot in command (PIC) had read the NOTAM prior to commencement of his duty, but he only noticed that the line marking works were in progress and not that the runway was not available. The copilot did not read the NOTAMs prior to departure, nor was he required to by the company operations manual.
The aerodrome operator had issued a method of working plan (MOWP), YJLC Number 2, 18 October 2004 that detailed the works to be undertaken, the expected dates and the NOTAMs to be issued for the various stages. The runway was only to be closed for resurfacing during Stage 1 of the MOWP. There were to be no operational restrictions on use of the aerodrome during line marking, which was to be undertaken during Stage 2.
The Civil Aviation Safety Authority (CASA) Manual of Standards Part 139-Aerodromes Chapter 10, paragraph 10.10.2.8 stated that an:
operator must not close the aerodrome to aircraft operations due to aerodrome works, unless a NOTAM giving notice of the closure has been issued not less than 14 days before the closure takes place.
The NOTAM issued for the line marking was not in accordance with that requirement, or Stage 2 of the MOWP.
The operator of the Fairchild has amended the operations manual for all aircraft types to require both pilots to read NOTAMs prior to departure.
The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence. The report presented below was prepared principally from information supplied to the Bureau.
REPORTED INFORMATION
At 2020 Eastern Summer Time on 20 February 2005, a Boeing Company 767-338ER aircraft, registered VH-OGO was being operated on a scheduled passenger service between Sydney and Melbourne. The copilot reported feeling unwell during cruise and was physically ill during descent through FL 200. A flight attendant was called to the flight deck to assist and the flight continued under the control of the pilot in command with the copilot assuming a monitoring role for the remainder of the flight.
After a 2-day recovery period and having discussed his illness with the company medical practitioner, the copilot was declared fit and returned to duty.
Following the landing at Adelaide on the previous flight, the flight crew inadvertently engaged the 'B' system autopilot in the control wheel steering mode. This inadvertent selection occurred when the 'B' system flight director switch was being moved to the OFF position while the crew were carrying out the 'taxi in' normal procedure. The inadvertent engagement of the autopilot was not detected by the crew.
With an autopilot engaged in the control wheel steering mode, the stabiliser trim wheel would have moved in response to forward or rearward movement of the control column. This movement of the trim wheel and the sounding of the autopilot warning horn during engine shutdown apparently led the crew to assume that there was a fault in the stabiliser trim system.
The next flight was the occurrence flight, which was operated by a different crew. During the climb, the crew noticed the stabiliser trim wheel moving opposite to the direction of the control column movement and they concluded that the apparent fault had recurred in the stabiliser trim system. As a result, the crew performed the non-normal procedure for a runaway stabiliser trim when the trim wheel movement was due to normal activation of the speed trim system.
Factaul Information
On 17 February 2005, a Boeing Company 737-838 aircraft, registered VH-VXN, with seven crew and 150 passengers, was being operated on a scheduled passenger flight from Adelaide, SA to Sydney, NSW. The crew reported that, as the aircraft was climbing through flight level (FL) 180 (18,000 ft), they noticed the stabiliser trim wheel moving opposite to the direction of the control column (elevator) movement.
The pilot in command was the handling pilot for the sector and was manually flying the aircraft when the movement was observed. The crew considered that the trim movement was uncommanded and consequently completed the non-normal procedure for a runaway stabiliser. As the non-normal checklist did not contain the words 'Plan to land at the nearest available airport', the crew levelled the aircraft at FL270 and continued the flight to Sydney.
Following the occurrence, a built in test equipment check was carried out on the flight control system and no faults were found. The two flight control computers were subsequently removed from the aircraft and tested at the operator's avionics workshop with no faults being found in either unit.
Previous flight
A different flight crew operated the aircraft on the preceding flight to Adelaide. That crew reported uncommanded stabiliser trim wheel movement while the aircraft was being taxied to the terminal, after landing at Adelaide. The crew also reported that when the aircraft was shutdown, the autopilot warning horn sounded. They did not notice any autoflight flight director system status annunciations on their respective Electronic Attitude Director Indicator (EADI), nor did they observe the illumination of the autopilot disengage indicator lights on the pilot and copilot instrument panels when the warning horn sounded. The operator's engineering personnel were advised about the apparent uncommanded movement of trim. A built-in test equipment check was subsequently carried out prior to the flight to Sydney but no fault was detected in the flight control system.
Stabiliser trim
The horizontal stabiliser is positioned by the main electric trim motor and is controlled through either of the stabiliser trim switches on each pilot's control column, or by the autopilot trim servo motor. The stabiliser may also be positioned by manually rotating the stabiliser trim wheels located on the control stand between the two pilots.
Pitch control of the aircraft includes a speed trim system. This system is used to improve flight handling characteristics during operations with low gross weight, rearward centre of gravity and high thrust when the autopilot is not engaged. The system provides positive speed stability characteristics to the pilot by adjusting the control column force so that the pilot must provide a significant amount of 'pull' force to reduce airspeed, or a significant amount of 'push' force to increase airspeed. The system trims the stabiliser in the direction calculated to provide the pilot positive speed stability characteristics. Since pilots typically attempt to trim control column force to zero and the speed trim system attempts to trim to positive stick force, the speed trim system operation may be opposite to the direction the pilot is trimming.
Autopilot flight director system
The autopilot flight director system is a dual system consisting of two individual flight control computers and a single mode control panel. The two flight control computers are identified as 'A' and 'B'. For autopilot operation, the computers send control commands to their respective pitch and roll hydraulic servos, which operate the flight controls through two separate hydraulic systems. For flight director operation, each computer positions the flight director command bars on the respective EADI located on the instrument panel for each pilot.
Either autopilot can be engaged in command mode or control wheel steering mode by pushing the appropriate engage switch on the mode control panel, which is located on the glare shield in front of each pilot (Figure 1).
If the autopilot flight director system is engaged in control wheel steering mode, the following system status annunciations will appear above the attitude indications on each pilot's EADI:
FD
(the flight director is ON and the autopilot is either OFF or engaged in control wheel steering mode)
CWS P
(the autopilot is engaged in control wheel steering pitch mode)
CWS R
(the autopilot is engaged in control wheel steering roll mode)
Flight data recorder information
Following the occurrence, data from the aircraft's flight data recorder (FDR) was downloaded and analysed by the aircraft manufacturer and the Australian Transport Safety Bureau (ATSB). The data indicated that during the previous flight the autopilot was engaged after landing at Adelaide. The autopilot was engaged by pushing the control wheel steering mode autopilot engage switch for the 'B' autopilot flight director system. The autopilot engagement occurred when the 'B' system flight director switch was selected to the OFF position while the aircraft was taxiing to the terminal. The flight director switches are usually selected to the OFF position by the crew while carrying out the 'taxi in' normal procedures when the aircraft has vacated the runway after landing.
The 'B' system flight director switch and the control wheel steering engage switch are in close proximity to each other on the glare shield mode control panel, above the centre instrument panel (Figure 1).
The data showed that various up and down trim movements were commanded by the autoflight flight director system following engagement of the control wheel steering mode after landing at Adelaide. The data also showed that the 'B' autopilot flight director system remained engaged when the FDR recording ended for that flight. The aircraft manufacturer advised that 'it is expected that it [the autopilot] disengaged later on (with warning horn) when additional power switching or configuration changes occurred.' The aircraft operator advised that the autopilot would have disengaged when the engines were shutdown and the electrical power source to the autoflight flight director system transferred from the engine driven generators to the auxiliary power unit driven generator.
The aircraft manufacturer also advised that, from their review of the FDR data, 'no trim anomalies could be seen on the following climb out [the occurrence flight]'.
Summary
On 17 February 2005, a Boeing Company 737-838 aircraft, registered VH-VXN, with seven crew and 150 passengers, was being operated on a scheduled passenger flight from Adelaide, SA to Sydney, NSW. The crew reported that, as the aircraft was climbing through flight level (FL) 180 (18,000 ft), they noticed the stabiliser trim wheel moving opposite to the direction of the control column (elevator) movement.
The pilot in command was the handling pilot for the sector and was manually flying the aircraft when the movement was observed. The crew considered that the trim movement was uncommanded and consequently completed the non-normal procedure for a runaway stabiliser. As the non-normal checklist did not contain the words 'Plan to land at the nearest available airport', the crew levelled the aircraft at FL270 and continued the flight to Sydney.
Following the occurrence, a built-in test equipment check was carried out on the flight control system and no faults were found. The two flight control computers were subsequently removed from the aircraft and tested at the operator's avionics workshop with no faults being found in either unit.
On 15 February 2005, a de Havilland Canada DHC-8-102 (Dash 8) aircraft, registered VH-TNX, was being operated on a scheduled passenger service from Hamilton Island to Cairns, Qld. The aircraft was in instrument meteorological conditions with significant turbulence reported by the pilot in command, who was the pilot flying (PF).
During the climb from Hamilton Island, the PF engaged the autopilot while manoeuvring to intercept the outbound track. During a right turn at 2,624 ft above mean sea level, the Enhanced Ground Proximity Warning System (EGPWS) bank angle advisory activated. That advisory was in the form of an aural alert to the flight crew of 'BANK ANGLE, BANK ANGLE' when a roll angle of 35 degrees was exceeded, and the aircraft was greater than 156 feet above ground level.
Recorded flight data indicated that, while the aircraft was being manually flown, the angle of right bank was increasing as the autopilot was engaged. The angle of bank momentarily reached a maximum of 34.9 degrees, which activated the EGPWS. The PF briefly disengaged and re-engaged the autopilot a number of times during the manoeuvring. That included disengaging the autopilot during a subsequent left turn that was required to make good the outbound track, before re-engaging the autopilot for the remainder of the flight.
A post-flight engineering inspection found no fault with the aircraft's number one Attitude Heading Reference System (AHRS) or with the flight guidance computer system (FGC1). However, as a precautionary measure, these systems were replaced.
Occurrence summary
Investigation number
200500654
Occurrence date
15/02/2005
Location
Hamilton Island, Aero.
State
Queensland
Report release date
31/07/2007
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Mode of transport
Aviation
Aviation occurrence category
E/GPWS warning
Occurrence class
Incident
Highest injury level
None
Aircraft details
Manufacturer
De Havilland Canada/De Havilland Aircraft of Canada
Occurrence investigations commenced from 1 July 2003 are initially categorised as category 4 unless agreed by the ATSB Executive to be above this level at the outset. As detailed in Section 21 (2) of the TSI Act 2003, the Executive Director is empowered to discontinue an investigation at any time. Section 21 (3) of the TSI Act 2003 requires the Executive Director to publish a statement setting out the reasons for discontinuing an investigation (commenced from 1 July 2003) within 28 days of discontinuing the investigation. To obtain a copy of the Brief Print Public for Discontinued Investigations prior to 1 July 2003.
Factaul Information
Information was provided to the ATSB indicating that the crew of
a foreign registered Boeing 747 cargo aircraft conducted an
emergency landing at Adelaide aerodrome on the morning of 9
February 2005, during the curfew period. Emergency services were
placed on local standby and the aircraft landed at 0438 CSuT. The
information included claims that the emergency was fuel
related.
The ATSB commenced a category 4 investigation to determine if
safety was compromised. Following a comprehensive assessment of
available information, including air traffic control communications
recordings, no safety issues were found to have been involved. When
the aircraft landed, it contained fuel sufficient for about 100
minutes flight.
Status: Downgraded the occurrence to category 5
and investigation discontinued.
Examination of failed thrust bearings from a Teledyne Continental Motors GTSIO520M engine
Factual Information
1.1 Examination brief
The Australian Transport Safety Bureau (ATSB) was requested by officers from the Civil Aviation Safety Authority (CASA) to conduct an examination and analysis of several damaged thrust bearing elements from the propeller drive shaft of a Teledyne Continental Motors model GTSIO520M aircraft engine (serial number 810712). Information received indicated that the bearings and accompanying propeller shaft were removed from service during maintenance activities; the discovered damage prompting the aircraft operator to submit a defect report / service difficulty report (SDR) to CASA. A second similar instance of bearing failure and shaft damage was also reported, having occurred on a similar engine (serial number 239168R) approximately one month previously.
The assessment of bearing compliance with the manufacturer's specifications or the direct applicability of the particular bearing part to the engine within which they were installed was not within the scope of the investigation.
1.2 Items received
The ATSB received the full set of thrust bearing elements and the propeller shaft from engine serial number (ESN) 810712 (figure 1). The propeller shaft from the earlier occurrence was also provided (figure 2), however the associated thrust bearing set was not available.
Figure 1. Propeller shaft and thrust bearings from engine serial number 810712.
Figure 2. Propeller shaft from engine serial number 239168R.
As installed, the thrust bearings comprised two sets of semicircular opposing plates, located against flange elements at the rear of the propeller shaft (figure 3 ). The rear bearings, carrying the primary propeller thrust loads, had sustained extensive mechanical and thermal damage, whereas the forward bearings showed little evidence of abnormal service and were visibly sound (figures 4, 5). The undamaged (forward) bearing set carried the rear surface identification '646260 G'. Damage to the rear bearings prevented the recognition of any similar markings on those items.
Figure 4. Contact (bearing) surfaces of thrust bearings as-received.
Figure 5. Rear (backing) surfaces of thrust bearings as-received.
The thrust bearings were understood to be of tri-metal construction, comprising a surface layer of lead-tin babbit, over a copper-lead intermediate layer on a steel backing. The SDR document indicated the bearing set had operated for 433.4 hours since new installation (TSN).
1.1 Examination findings
1.1.1 Rear thrust bearings
Close visual examination of the set of failed bearings (attachments A - D) showed heavy scoring, gross disruption and partial loss of the bearing alloy from the bearing running (contact) surfaces (figure 6). Partial melting of the surface alloys and other evidence of elevated temperatures was prevalent, as was the blackening and discolouration of the surfaces where alloy loss had occurred. The rear (back) faces of the bearings also showed blackening and the accumulation of melted alloy (figure 7). The lubrication channels on one bearing were partially filled with transferred material that had been melted and dislodged from adjacent areas.
Figures 6 and 7. Low-power microscopic view of a damaged area on the contact and backing surfaces of a damaged thrust bearing.
In isolated regions, the bearing alloy had completely separated from the steel backing, with the affected areas characterised by exposure of the comparatively flat, featureless interfacial surfaces (figure 8).
Figure 8. Area on a damaged bearing showing complete separation of the bearing alloy from the steel backing.
Several metallographic sections taken transversely through one bearing confirmed the basic tri-metal construction, with the intermediate layer presenting as a coarse intermittent network of lead within a copper alloy matrix. In numerous areas, the lead network had interconnected, creating filled fissures (figure 9), the larger of such broaching the external surface. Evidence of lead migration to the steel backing interface was observed at and adjacent to the areas of alloy separation, creating a continuous lead boundary layer approximately 5-10 m thick.
Figure 9. Cross-sectional microstructure of a damage bearing, showing the agglomeration of lead (dark phase) within the copper bearing alloy and along the backing interface. Unetched.
Scanning electron microscopy of the prepared sections confirmed the metallographic observations, with back-scattered electron imaging (figure 10) and x-ray dot mapping (figure 11) graphically illustrating the lead agglomeration and migration to the backing interface.
Figure 10. SEM image of the metallographic section, illustrating the lead migration.
Figure 11. SEM X-ray map confirming the lead migration (green phase) within the copper alloy (red phase) and at the steel (blue phase) interface.
1.2.1 Forward thrust bearings
In contrast with the rear elements, the forward bearings presented in an essentially undamaged condition (figure 12), with very little evidence of metal-to-metal surface contact and no evidence of thermal distress, overheating or physical degradation. The rear surfaces were not fretted or rubbed to any significant extent and showed no indication of improper seating, movement or miss-installation.
Several metallographic sections, taken in a similar sense to those from the rear bearings, presented a similar general microstructure, with the intermediary alloy layer showing a distinct as-cast (dendritic) distribution of lead within the copper alloy matrix (figure 13). No evidence of fissuring or lead migration to the backing interface was observed within the cross-sections studied.
Typical thicknesses of the bearing component layers and backing were established by measurement under the SEM, i.e. Surface Pb-Sn babbit: 7 - 10 m (0.007 - 0.010 mm) Intermediate Cu-Pb alloy: 715 - 725 m (0.715 - 0.725 mm) Steel backing: 1,650 m (1.65 mm)
Figure 12. Undamaged running surfaces of the forward bearing set.
Figure 13. Metallographic cross-section through an undamaged bearing - no lead migration to the alloy interface.
1.2.2 Propeller shafts
Both propeller shafts showed distinct discolouration and evidence of localised heating in a band around the back face of the rear thrust flange (figure 14). Similar discolouration was also noted in a band around the rearmost ends of the reduction gear teeth (figure 15), however the tooth contact surfaces themselves showed no evidence of distress, uneven wear or excessive localised friction.
The inside (bearing) surfaces of the rear shaft flanges (those working against the failed bearing elements) showed heavy wear and circumferential scoring around the contact path (figure 16). In contrast, the opposite flange faces (figure 17) showed little if any physical manifestation of service - abnormal or otherwise.
Figure 14. Discolouration of the rear thrust flange surface typifying the localised overheating.
Figure 15. Discolouration (similar to figure 12) evident on the ends of the reduction gear teeth.
Figure 16. Appearance and extent of scoring and wear sustained by the propeller shaft rear thrust flange contact surface.
Figure 17. Forward thrust flange (opposite that shown above), presenting in sound condition.
Analysis
Damage to the propeller shaft thrust bearing assembly was limited to the rear bearings and shaft flanges, those being the components carrying the primary propeller thrust loads when under power. The forward bearings and shaft flanges were undamaged and showed no indication of anomalous service.
The rear propeller shaft thrust bearings from ESN 810712 had failed as a result of gross localised overheating. The local discolouration of the shaft flanges and adjacent surfaces and the partial melting and microstructural changes within the bearing alloy attested to the excursion in temperatures to a level well above the normal component operating range. The physical loss of sections of bearing alloy from the backing material was a direct manifestation of the overheating, with the elevated temperatures causing the lower melting point lead alloy to agglomerate and migrate to the steel interface, where it weakened the normal bond and allowed the break-up and separation of the bearing material. There was no evidence of a deficiency within the construction or make-up of the bearings examined, nor was there any evidence that the bearings had been improperly installed.
In a general sense, the overheating of bearings results from the generation of frictional heating at a rate greater than the assembly and environment is able to conduct it away. Heating, from surface and lubricant frictional effects, is a function of numerous interrelated factors including:
bearing operating (transmitted) loads
clearances
lubricant properties
lubricant quantities and flow rates
relative surface speeds
surface conditions and finishes
bearing materials
The investigation was not able to directly identify which of the identified factors were contributory to the failures sustained, however it is suggested that issues relating to the initial bearing clearances, lubricant and operating (thrust) loads would be the most likely in terms of the general nature and function of the assembly.
Conclusions
The following conclusions, in terms of the bearing failures, were drawn from the examination of the supplied components:
The bearings from ESN 810712 had failed as a result of gross, localised frictional overheating, resulting in the physical and microstructural degradation of the bearing alloy.
There was no evidence that a manufacturing defect, material anomaly or other deficiency within the bearing components themselves had contributed to the failure.
There was no evidence found to suggest that the bearings had been improperly installed.
The investigation was not able to directly identify the proximate cause/s of bearing failure, however it is suggested that initial bearing clearances, lubrication and loading were most likely in terms of the nature of the failure and the general function of the assembly.
Summary
The Australian Transport Safety Bureau (ATSB) was requested by the Civil Aviation Safety Authority (CASA) to conduct an examination and analysis of several damaged thrust bearing elements from the propeller drive shaft of a Teledyne Continental Motors model GTSIO520M aircraft engine (serial number 810712). Information received indicated that the bearings and accompanying propeller shaft were removed from service during maintenance activities; the discovered damage prompting the aircraft operator to submit a defect report / service difficulty report (SDR) to CASA. A second similar instance of bearing failure and shaft damage was also reported, having occurred on a similar engine (serial number 239168R) approximately one month previously.
The assessment of bearing compliance with the manufacturer's specifications or the direct applicability of the particular bearing part to the engine within which they were installed was not within the scope of the investigation.
On 2 February 2005, a de Havilland Canada DHC-8-315 (Dash 8) aircraft, registered VH-TQE, was being operated on a scheduled passenger service between Sydney and Tamworth, NSW, at flight level 160. At 150 km south-east of Tamworth the aircraft's cabin rapidly depressurised. That was followed by the failure of navigation aids and the illumination of warning and caution lights on the aircraft's caption panel 1. The pilot in command declared an emergency and conducted a rapid descent to 10,000 ft. Aerodrome emergency services at Tamworth were activated and the aircraft landed without incident.
The airline commenced an investigation into the circumstances of the incident. The problem was isolated to the number-one starter-generator unit. It was determined that the output of the direct current generator had decreased to the extent that systems connected to the left main electrical bus dropped off line. The under-voltage condition resulted in multiple failures, including the release of the pressurisation outflow valve and the loss of all navigation aids except the number-two automatic direction finding indicator. The release of the pressurisation outflow valve depressurised the aircraft. There was no low voltage warning associated with those systems.
Functional testing of the generator found an open circuit within the number-one shunt coil. A broken wire was found at approximately 28 turns on the 100-turn coil. The broken wire would have caused the voltage output of the generator to fall to a residual level, typically of 2 or 3 volts. The wire could have been damaged either during manufacture or routine maintenance. A conclusive determination could not be made due to the condition of the wire.
The starter-generator had operated for 3,947 flight hours prior to the failure. It was last overhauled on 4 September 2004 and failed 920 flight hours later.
The caption panel on the flight deck contains a series of caution and warning advisory lights designed to alert the flight crew to an abnormal condition.
-
ATSB Comment:
It is likely that the failure of multiple systems in the aircraft alerted the flight crew to a possible electrical problem. However, their initial response in dealing with the cabin depressurisation event and associated checklist items would have distracted them from attempts to locate the source of the problem. The subsequent failure of other systems would also have required specific checklist responses. These actions, when combined with the need to follow navigation and air traffic control requirements, as well as the absence of an under-voltage warning system, minimised opportunities for the crew to identify the problem.
Occurrence summary
Investigation number
200500395
Occurrence date
02/02/2005
Location
41km E Scone
State
New South Wales
Report release date
24/03/2006
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Mode of transport
Aviation
Occurrence class
Incident
Highest injury level
None
Aircraft details
Manufacturer
De Havilland Canada/De Havilland Aircraft of Canada
On 25 January 2006, the operator advised the Australian Transport Safety Bureau that:
The training department has developed a New Technologies training segment effective 18 January 2006. That training includes the use of the Head-up Guidance System (HGS) on the Boeing 737 which will enhance situational awareness during take-off and landing.
Analysis
The operator’s 737 manual provided information on the handling techniques to maintain tail clearance margins during take-off, including take-off in gusty and crosswind conditions.
While the pilot in command (PIC) needed to react quickly and precisely to manage roll in the gusty crosswind conditions, a more measured input of pitch control was required during the aircraft’s rotation to maintain the allowable tail clearance margin. The almost doubling of the average pitch rate of rotation during the take-off indicates that the PIC exceeded the recommended rate. It is possible that the PIC used a similar style of control input for pitch that he was using to manage roll.
This occurrence highlights the fact that during a take-off manoeuvre, tail clearance margins can reduce to the point where a tail strike will probably occur if the recommended rotation rate is exceeded.
Factual Information
On 1 February 2005, a Boeing Company 737-838 (737) was being operated on a scheduled passenger service from Sydney, NSW, to Darwin, NT with two pilots, five cabin crew and 151 passengers. The pilot in command (PIC) was the pilot flying for the take-off. At 1931 Eastern Daylight-saving Time, during lift-off from runway 34 Left (34L), in gusty crosswind conditions, the PIC and co-pilot felt the aircraft's tail strike the runway. They queried the rear cabin crew, who confirmed that there was an unusual noise during the aircraft's rotation. The pilots performed the 737 Quick Reference Handbook (QRH) Non-Normal Checklist for tail strike on take-off. Following completion of the checklist, the PIC elected to return to Sydney for an overweight landing.
An engineering inspection confirmed that the aircraft had sustained a tail strike during the takeoff. A crushable cartridge, fitted to minimise damage to the aircraft during a tail strike, was damaged and required replacement. There was also minor wear to the tailskid shoe. A structural inspection of the tail section and an overweight landing check were completed and the aircraft was found to be serviceable.
The Sydney Airport automatic terminal information service (ATIS) provided meteorological and operational information for pilots of arriving and departing aircraft by means of a continuous and repetitive radio broadcast. The information broadcast at the time advised that runway 07 was in use, the wind direction was 030 degrees M at a speed of 20 kts and gusting to 30 kts. The maximum crosswind was 18 kts [for aircraft operating on runway 07]. Those conditions would have resulted in a crosswind of 16 kts to 23 kts for runway 34L.
The Bureau of Meteorology provided a report of the weather conditions at 1930 as recorded by the automatic weather station at Sydney Airport. The report indicated that there was a north-easterly wind (from 050 degrees T), with a speed of 25 kts and gusting to 35 kts. That resulted in a right crosswind of 22 kts (mean) and up to 31 kts during a gust, for aircraft operating on runway 34L.
The aircraft's weight and balance sheet provided to the pilots by the operator showed that the planned take-off weight was 75,689 kg1. That resulted in a calculated take-off decision speed (V1) of 150 kts indicated airspeed2 (IAS), a rotation speed (Vr) of 151 kts IAS and a take-off safety speed (V2) of 156 kts IAS. The PIC reported that after assessing the performance requirements for take-off, he elected to use runway 34L. The operator's crosswind limit for runway 34L was 33 kts.
The aircraft was fitted with an L3 Communications digital flight data recorder (DFDR). The ATSB analysed the recorded DFDR data to assist in establishing the sequence of events during the occurrence. During the take-off roll, control wheel (right) and rudder (left) inputs were made consistent with a right crosswind. The analysis showed that during the take-off roll the PIC used quick and precise roll control inputs in the gusty crosswind conditions. Fluctuations in the aircraft's calibrated airspeed (CAS) showed that variable wind conditions were experienced during the take-off roll, consistent with the ATIS values. The aircraft was rotated at the calculated Vr of 151 kts IAS. At lift-off, the aircraft's pitch attitude was +10.9 degrees3. By comparison, the average pitch attitude for the 23 previous takeoffs was +5.5 degrees. The average pitch rate of rotation was 3.7 degrees per second, compared with an average pitch rate of rotation of 2.2 degrees per second for the 23 previous flights. The data revealed that immediately prior to rotation, the aircraft was tracking on the runway centreline and the wings were level.
The operator's 737 Flight Crew Training Manual section 3.9 stated that, 'a 2 to 3 degree per second rotation rate is required to achieve a tail clearance of 51 cm'. Section 3.14 states that under gusty wind and strong crosswind conditions, 'do not rotate early or use a higher than normal rotation rate in an attempt to clear the ground and reduce the gust effect because this reduces the tail clearance margins'.
Actual brakes release weight at the start of the take-off run.
Indicated airspeed is the reading of the airspeed indicator instrument.
The pitch attitude mentioned is consistent, allowing for resolution limits, with the Boeing Flight Crew Training Manual (FCTM) tail strike pitch attitude (11.0 degrees).
Summary
On 1 February 2005, a Boeing Company 737-838 (737) was being operated on a scheduled passenger service from Sydney, NSW, to Darwin, NT with two pilots, five cabin crew and 151 passengers. The pilot in command (PIC) was the pilot flying for the take-off. At 1931 Eastern Daylight-saving Time, during lift-off from runway 34 Left (34L), in gusty crosswind conditions, the PIC and copilot felt the aircraft’s tail strike the runway. They queried the rear cabin crew, who confirmed that there was an unusual noise during the aircraft’s rotation. The pilots performed the 737 Quick Reference Handbook (QRH) Non-Normal Checklist for tail strike on take-off. Following completion of the checklist, the PIC elected to return to Sydney for an overweight landing. An engineering inspection confirmed that the aircraft had sustained a tail strike during the take-off. A crushable cartridge, fitted to minimise damage to the aircraft during a tail strike, was damaged and required replacement.
The investigation found that while the PIC needed to react quickly and precisely to manage roll in the gusty crosswind conditions, a more measured input of pitch control was required during the aircraft’s rotation to maintain the allowable tail clearance margin. This occurrence highlights that during a take-off manoeuvre, tail clearance margins can reduce to the point where a tail strike will probably occur if the recommended rotation rate is exceeded.
On the 25 January 2006, the operator advised the Australian Transport Safety Bureau they had developed a New Technologies training segment effective 18 January 2006. That training includes the use of the Heading Guidance System (HGS) on the Boeing 737 which will enhance situational awareness during takeoff and landing.
As a result of this occurrence, the operator advised the Australian Transport Safety Bureau that it had replaced both nosewheel steering cables with stainless steel cables. Stainless steel has a higher resistance to corrosion than carbon steel.
Factual Information
On 25 January 2005, a Boeing 727-51C aircraft, registered in Sierra Leone as 9L-LEK, was being operated on a non-scheduled positioning flight from Cairns to Brisbane, Queensland. The crew, which comprised the pilot in command, copilot and flight engineer, were supported by an aircraft maintenance engineer (a passenger) for away from base maintenance. The copilot was the handling pilot for the flight.
Approaching Brisbane, the aircraft was cleared for an instrument landing system approach to runway 01 at Brisbane Airport. There was a 15 kts gusting crosswind from the east. The crew reported that they had visual contact with the runway at about 1,000 ft altitude and flew a stabilised approach to a normal touchdown at about 1606 eastern standard time. The wing spoilers and thrust reversers deployed normally.
The copilot said that as the speed reduced through 100 kts, the aircraft was tending to veer right and that, approaching 80 kts, he had maximum left rudder applied to maintain the aircraft tracking on the runway centreline. Nosewheel steering is controlled by the rudder pedals and by a steering wheel on the pilot in command's side panel. When the copilot is flying the aircraft, it is normal procedure as the aircraft slows during the landing roll for the pilot in command to take control of the aircraft to manoeuvre it using the nosewheel steering wheel. In accordance with normal procedures, the pilot in command took control of the aircraft at about 80 kts. As the copilot relinquished control, he informed the pilot in command that he had maximum left rudder applied.
The pilot in command said that when he placed his hand on the nose wheel steering wheel, it felt very loose as he turned the wheel left to maintain the aircraft on the runway centreline. However, there was no response to the steering wheel inputs and, despite the use of differential main wheel braking, he was unable to prevent the aircraft veering right and running off the runway at a speed of between 60 and 70 kts. The aircraft came to rest about 40 m from the runway edge, and was undamaged.
An examination of the nosewheel steering system revealed that one of the carbon steel nosewheel steering cables, linking the steering wheel to the nose gear steering valve, had failed approximately 2.35 m from the ball end. That location was within the forward fuselage section above the nose wheel where the cables were hidden from view and not readily accessible.
A subsequent specialist examination of the failed cable indicated that approximately 70 percent of the cable strands at the failure location exhibited characteristics of severe aqueous corrosion1. The remaining strands showed decreased diameter due to corrosion and had failed under applied tensile loads.
The aircraft had a total time in service of 54,200 hours and 48,000 flight cycles2. The operator advised that the most recent maintenance check on the aircraft was an 'A' check completed in December 2004 and the last 'C' check on the aircraft in December 2003. The operator also advised that, in its maintenance system for the aircraft, the nose wheel steering cable was an 'on condition' item and that, during a 'C' check, there was a requirement to conduct a visual inspection of the cable.
1 Aqueous corrosion is an electrochemical process by which metals or alloys are oxidised in the presence of solutions containing water. Corrosion rates are significantly affected by environmental conditions such as temperature, humidity, and oxygen availability. 2 A flight cycle is a completed take-off and landing sequence.
Summary
On 25 January 2005, a Boeing 727-51C aircraft, registered in Sierra Leone as 9L-LEK, was being operated on a non-scheduled positioning flight from Cairns to Brisbane, Queensland.
The Australian Transport Safety Bureau suggests that the Department of Defence distributes this report widely among controllers so that supervisors are aware that intervention in separation and sequencing at the tactical level has the potential to adversely affect the situational awareness of the controllers under their supervision. Further, they must be prepared to take control of a situation if necessary, until the controller is able to safely resume responsibility for separation.
Safety Advisory Notice 20060015
The Australian Transport Safety Bureau suggests that the Department of Defence ensures that controllers are aware of the importance of the separation assurance provisions of MATS 4.1.1.4.
Conclusions
CONCLUSIONS
Significant factors
The approach controller did not assign an altitude to the second formation that provided a vertical separation standard between the second formation and the Dash 8.
The tower supervisor advised the tower controller to cancel the instruction to the Dash 8 pilots to orbit on the downwind leg of the circuit at 2,500 ft, and to continue on the downwind leg of the circuit.
The tower controller was not aware that the second formation was inbound to the circuit.
The tower controller did not notify the approach controller that the Dash 8 was extending towards the lateral boundary of the ATZ.
The pilots of the Westwind did not join the circuit via the upwind leg as instructed by the tower controller.
Contributing factors
The code/flight plan association on the ADATS data block of the second formation terminated.
The approach controller removed the second formation's flight progress strip from the flight progress board.
The approach controller did not provide the tower controller with voice coordination on the second formation once the code/flight plan association terminated.
The pilots of the Westwind incorrectly notified the tower controller that their aircraft was 'minimum fuel' when the aircraft was on left base.
The tower controller and the tower supervisor were relatively inexperienced, and each had responsibility for a controller-under-training.
Analysis
ANALYSIS
Introduction
The tower controller and the approach controller were unable to continue to apply a separation standard between the second formation of Hornets and the Dash 8. This analysis examines the development of the occurrence and highlights the safety issues that became evident as a result of the investigation.
Air traffic control separation standards and procedures
The approach controller's assignment of 3,000 ft to the pilots of second formation of Hornets when they had about 32 NM to fly to land, did not provide either a vertical separation standard or separation assurance between the second formation and the Dash 8. That action precipitated the sequence of events that followed. While a radar separation standard existed initially between the Dash 8 and the second formation, it relied on continuous monitoring by the approach controller. The allocation, by the approach controller, of an altitude to the second formation that would have provided the 1,000 ft vertical separation standard with the Dash 8 would have assured that a separation standard continued to exist. It would also have given the tower controller the option to assign further descent to the pilots of the second formation once a visual separation standard between the second formation and other aircraft joining the circuit could be applied.
The approach controller was required to establish a separation standard between the second formation and the Dash 8, and to have that standard in place before transferring the responsibility for separation to the tower controller. In not providing separation assurance between the second formation and the Dash 8, the approach controller did not demonstrate 'the proactive application of separation standards to avoid rather than resolve conflicts' as stated in the Manual of Air Traffic Services (MATS).
It was likely that the limited data block format displayed on the second formation adversely affected the situational awareness of both the tower controller and the tower supervisor at the time the tower controller advised the pilots of the Dash 8 that they could turn base 'when ready'. The tower controller did not provide traffic information about the location of the second formation to the pilots of the Dash 8 until after the pilots of the Dash 8 advised that they were on a traffic alert and collision avoidance system descent. At the time the tower controller instructed the pilots of the Dash 8 to turn base the second time, the relative locations of the second formation and the Dash 8 placed the aircraft in potential conflict. That would have been apparent to both the tower controller and the tower supervisor had either of them been aware of the location and intentions of the second formation at that time.
The traffic situation in the circuit area became quite complex in a very short period of time. The relative inexperience of the tower controllers may have limited their ability to realise the potential for a relatively simple inbound sequence to develop into an infringement of separation standards.
Communication between the tower controller and the tower supervisor may have been difficult due to the complexity of communication between trainees and their training officers, and between controllers in the various control positions in the tower. Had the Dash 8 remained at 2,500 ft conducting orbits in the downwind position as initially instructed until the tower controller could fit that aircraft into the landing sequence, there may have been more time for the tower controller to:
liaise with the tower supervisor
regulate the flow of traffic
identify the second formation on the situation data display (SDD)
assess options that may have ensured that separation continued to exist
evaluate the impact of the late declaration of 'minimum fuel' by the pilots of the Westwind
provide traffic information where appropriate
issue alternative instructions.
Once the tower controller notified the approach controller that the Dash 8 had been assigned a visual approach, the approach controller removed the flight progress strip from the flight progress board. After that, there was nothing to prompt the approach controller to critically re-evaluate the information on which the original evaluation, that the aircraft would not come into close proximity, was made, even though there remained a possible confliction between the inbound second formation and the Dash 8.
Although the decision by the tower supervisor to instruct the pilots of the Dash 8 to continue on the downwind leg of the circuit and not conduct the left orbit in the downwind position may have been appropriate, it unnecessarily increased the complexity of the traffic scenario, especially given the training workload in the tower at that time. It also reduced the options available to the tower controller once the Westwind joined the circuit on the left base leg rather than via the initial point, or the upwind leg of the circuit as instructed. The instruction issued to the pilots of the Westwind by the tower controller to enter the circuit via the upwind leg would have provided the Westwind with adequate priority and would not have compromised the safety of the flight. That may also have created an opportunity for the tower controller to locate the second formation on the SDD and therefore reduce the likelihood of an infringement of separation standards.
Tower supervisors have the authority to become involved with tactical air traffic control decisions and may assume control responsibility for sequencing or separation, without formally taking over from the tower controller. Tower supervisors must consider how an instruction to the tower controller might affect the situational awareness of that controller. A supervisor must be prepared to take control of the situation, in which they have intervened at a tactical level, until the tower controller can resume responsibility for separation. Otherwise tower controllers may inherit a scenario from the tower supervisor that they may not entirely understand, with little time to react.
Although the extended downwind of the Dash 8 resulted from the Westwind not complying with a control instruction, the tower controller was required to notify the approach controller that the aircraft was extending and may track beyond the lateral boundary of the Aerodrome Traffic Zone (ATZ). The tower controller did not notify the approach controller that the Dash 8 was extending downwind. Therefore, the approach controller was unaware that the Dash 8 was tracking towards the right initial point, in potential conflict with the second formation.
Minimum Fuel
Military air traffic controllers are familiar with pilots declaring 'minimum fuel' and with their responses in such circumstances. However, the disposition of the Westwind relative to base and final, the relatively complex nature of the traffic pattern at the time of the broadcast, and the training environment that existed in the control tower at the time of the occurrence, all reduced the time available for the controller to consider the impact of the 'minimum fuel' broadcast on the traffic pattern.
By the time the tower controller had an opportunity to assess the impact that that transmission may have on the landing sequence, and to determine what priority could have been provided to the pilots of the Westwind, the Westwind was already on the final approach leg. The pilots of the Westwind did not comply with the instruction by the tower controller to join the circuit on the upwind leg, even though that would have been acceptable in such circumstances. The declaration of 'minimum fuel' in such close proximity to the landing threshold may have distracted the controllers in the tower and reduced the effectiveness of their scans of the tower environment, including the SDD, and added to the complexity of the situation.
Australian Defence Air Traffic System (ADATS)
The approach controller did not provide the tower controller with information on the second formation after the code/flight plan association for that formation terminated. Although the approach controller reported that the termination occurred close to the boundary of tower airspace, the tower controller appeared to be unaware of the proximity of the second formation. Had the approach controller provided the tower controller with coordination on the second formation, in accordance with local procedures, the tower controller's attention would have been drawn to the location of that formation on the SDD. That may have given the tower controller an opportunity to ensure that the Dash 8 remained clear of the inbound path of the second formation.
On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8) aircraft that was inbound to Williamtown Airport, NSW, on a scheduled passenger service from Brisbane, Queensland, passed within 1 NM laterally and 300 ft vertically of the second of two formations of two McDonnell Douglas Corporation F/A-18 (Hornet) aircraft that were inbound to Williamtown Airport after a training exercise. As the Dash 8 turned onto the base leg, the second formation was about 6 NM north-west of Williamtown Airport, at 2,900 ft above mean sea level. The pilots of the Dash 8 descended in response to a traffic alert and collision avoidance system (TCAS) resolution advisory (RA) they received on that formation. The approach controller did not provide the required separation standard of 1,000 ft vertically or 3 NM laterally between the Dash 8 and the second formation. The tower controller2 had not established a visual separation standard between the aircraft at the time the Dash 8 pilots received the RA. There was an infringement of separation standards. At about 1539:353,4 Eastern Daylight-saving Time, the pilots of an Israel Aircraft Industries Limited 1124A Westwind (Westwind) aircraft, that had been participating in a military training exercise, contacted the tower controller and advised that they were 7 NM to the north of Williamtown Airport, tracking to join the circuit on a left base leg for runway 12. At that time, the first formation of Hornet aircraft had passed the initial point5 (Figure 1) for runway 12, and the Dash 8 was in an early right downwind position. At 1540:10, the tower controller advised the pilots of the Dash 8 to conduct orbits to the south-west of the airfield at 2,500 ft. However, the tower supervisor assessed that the Dash 8 could continue on the downwind leg and advised the tower controller to cancel the orbit instruction. At 1540:20, the tower controller complied and instructed the pilots of the Dash 8 to continue on the downwind leg. The tower supervisor had intended to position the Dash 8 behind the first formation in the landing sequence.
Figure 1: Generic depiction of a military stream landing circuit showing the location of the initial point (left circuit depicted)
(adapted from the Manual of Air Traffic Services Pt 3 s3, effective 10 June 2004)
At 1541:10, the tower controller instructed the pilots of the Dash 8 to make a visual approach and to track for right base. At 1541:20, the tower controller instructed the pilots of the Westwind to join the circuit via the upwind leg. In response to that instruction, the pilots of the Westwind advised the tower controller that the aircraft was 'minimum fuel'6. The tower controller did not respond immediately to that broadcast and the Westwind continued the approach via left base. At about 1541:30, the radar data showed that the Dash 8 had already commenced the turn onto the right base leg of the circuit. At that time, the Westwind was established on left base. The Westwind pilots had positioned their aircraft behind the first formation in the landing sequence. In order to separate the Dash 8 and the Westwind, the tower controller instructed the pilots of the Dash 8 to continue on the downwind leg and that they were now to follow the Westwind.
At 1542, the tower controller advised the pilots of the Dash 8 that they could turn onto the base leg, when ready. At that time the aircraft was close to the airspace boundary separating tower and approach areas of responsibility, about 6.9 NM north-west of the airport.
At 1542:20, the approach controller provided traffic information, on the Dash 8, to the pilots of the second formation. A review of the recorded radar data showed that, at that time, the second formation was about 3 NM behind the Dash 8. Although the investigation was unable to accurately determine the vertical distance between the aircraft, from that radar data, it appeared that there was about 100 ft between the second formation and the Dash 8 when the approach controller provided traffic information to the pilots of the second formation. The pilot of the lead aircraft in the second formation advised the approach controller that he could see the Dash 8.
The recorded radar data also showed that the altitude of the Dash 8 increased from 2,500 ft on late downwind, to 2,900 ft as the aircraft commenced the base turn, before descending in response to the TCAS RA. The Dash 8 subsequently continued to descend for a landing. At 1542:50, the second formation passed abeam the Dash 8, when the Dash 8 was about to commence the turn onto the final approach leg. At that time, there was 0.6 NM laterally between the aircraft, and the Dash 8 was 300 ft vertically below the second formation. The pilots of the Dash 8 advised the tower controller that they had received an RA and that they were on a 'TCAS descent'.
At 1543, the pilots of the second formation called the tower controller and advised that they were at the right initial7 position. The tower controller then realised that the second formation was inbound and provided the pilots of the Dash 8 with traffic information on that formation.
Minimum fuel
In accordance with the Royal Australian Air Force (RAAF) Williamtown Standing Instructions, the Westwind was considered to be a military aircraft while participating in military exercises.
The copilot of the Westwind notified the tower controller that the aircraft was 'minimum fuel' when the aircraft was on a left base position for runway 12. The pilot in command of the Westwind later reported that the aircraft was not 'minimum fuel', and that the copilot had mistakenly made the 'minimum fuel' radio broadcast. The operator of the Westwind advised that the declaration of minimum fuel in that aircraft meant there was '…900 [pounds] or less total fuel remaining at the Base Turn Point when in the circuit, at an airport where a landing is assured'.
Air traffic control separation standards and procedures
Control of aircraft in the Williamtown Airport terminal area was provided by a tower controller using visual procedures and vertical separation, and by an approach controller using radar and procedural separation standards, in accordance with the Manual of Air Traffic Services8 (MATS) and local procedures. Coordination of control responsibilities was required between the approach controller and the tower controller in accordance with local procedures.
The required minimum vertical separation standard between the Dash 8 and other aircraft operating in the Williamtown airspace was 1,000 ft.
In relation to the provision of aircraft separation, the MATS 4.1.1.4 stated that:
Tactical Separation Assurance places greater emphasis on traffic planning and conflict avoidance rather than conflict resolution. This is achieved through:
the proactive application of separation standards to avoid rather than resolve conflicts;
planning traffic to guarantee rather than achieve separation;
executing the plan so as to guarantee separation; and
monitoring the situation to ensure that plan and execution are effective.
The tower controller cleared the pilot of the Dash 8 for further descent on a visual approach when the aircraft was in a late downwind position. A visual approach authorised the pilots to continue descent visually for a landing. A review of the recorded radar data showed that the Dash 8 maintained 2,600 ft for about 1.5 minutes on the downwind leg of the circuit. It reached a minimum altitude of 2,500 ft, on descent, when the aircraft was on a late downwind position, and climbed to 2,900 ft as it turned onto the base leg.
The Aeronautical Information Publication (AIP) advised pilots that they must report to ATC 'when the aircraft has left a level at which level flight has been conducted in the course of climb, cruise or descent'. The pilot in command of the Dash 8 did not recall climbing the aircraft from 2,500 ft on the downwind leg to 2,900 ft on the base leg of the circuit.
Approach control
At Williamtown Airport, the approach controller was responsible for providing an air traffic control service between instrument flight rules (IFR) category aircraft in accordance with the MATS and local procedures. That included ensuring that a separation standard existed between arriving IFR aircraft, and providing an orderly flow of arriving aircraft.
There was an approach controller and a supervisor rostered in the Williamtown approach control unit at the time of the occurrence. Both positions were staffed by an appropriately rated military air traffic controller (ATC). The approach controller had about 6 years experience as an ATC, and had been rated in the approach radar position at Williamtown Airport for 6 months. The approach supervisor was responsible for the supervision of the approach control unit at Williamtown Airport. He had considerable experience as an ATC, and had held a rating in approach control at Williamtown Airport for about 18 months.
A review of the recorded radar data showed that, at the time the approach controller cleared the pilots of the second formation to descend to 3,000 ft, the second formation was approximately 27 NM from the airport, with about 32 NM to fly to land. Had the pilots of the Dash 8 not been instructed to extend the downwind leg, the Dash 8 would have had about 6 to 8 NM to fly to touch down. The assignment of 3,000 ft to the pilots of the second formation did not provide either a vertical separation standard, or separation assurance, between the second formation and the Dash 8 in the circuit. The approach controller was not concerned about the separation between the Dash 8 on the downwind leg, and the second formation on descent to 3,000 ft, because of the distance the second formation was from the airfield at the time the approach controller issued the descent clearance.
The normal circuit direction at Williamtown Airport, on runway 12, was right. Military aircraft would track from the initial point along the dead side9 of the circuit and turn right, into the circuit, once the pilot saw the other traffic operating in the circuit (see Figure 1). The approach controller cleared the Westwind to enter the circuit via a non-standard left base leg and to descend on a visual approach.
The tower controller was required, by local procedures, to advise the approach controller when the Dash 8 pilots were cleared to descend on a visual approach.
On receipt of that advice, the approach controller removed the Dash 8's flight progress strip10 from the flight progress board11. Although the aircraft was still visible to the approach controller on the situation data display (SDD)12, the potential for an infringement of separation standards was no longer presented to the approach controller on the flight progress board. The approach controller later reported that the flight progress strip was removed from the board because there was an expectation that the second formation would remain clear of the Dash 8 in the circuit.
Tower control
The tower cabin was equipped with an SDD that provided the tower controller with the same display of air traffic that was provided to the approach controller. The MATS addressed the use of tower radar in an aerodrome control service. It stated that the tower radar display was available for the determination of the altitude, position or tracking of an aircraft to establish or monitor separation. However, the MATS also stated that:
…the use of the tower radar should not impinge upon an aerodrome controller's primary function of maintaining a visual observation of operations on and in the vicinity of the aerodrome.
There were three operational control positions established in the control tower; a supervisor position, a tower control position and a surface movement control position. Each position was staffed by an appropriately rated military ATC. The supervisor and the tower controller each had 18 months tower control experience. The control tower was also a training environment at the time of the occurrence. There was a controller-under-training in each of the three control positions. Each rated military controller, in each of the positions, was also a qualified training officer.
The supervisor was responsible for airspace management and operations on the airport. The supervisor had the authority to assess and amend the decisions of the tower controller and the surface movement controller if required. Unless the tower controller considered that such intervention compromised safety, the tower controller was obliged to comply with the decisions of the supervisor.
The first formation joined the circuit on a right crosswind leg on descent from 1,500 ft. Once the tower controller was able to apply a visual separation standard between the Dash 8 and that formation, the tower controller instructed the pilots of the Dash 8 to descend on a visual approach.
The tower controller was also required to notify the approach controller of any aircraft that were extending towards the aerodrome traffic zone (ATZ) lateral boundary which was the lateral boundary of tower airspace13. Neither the tower controller nor the supervisor advised the approach controller that the Dash 8 was extending downwind, and would be turning onto the base leg in the vicinity of the lateral boundary of the ATZ. The approach controller was not expecting to see the Dash 8 in that position. The approach controller observed, on the SDD, the Dash 8 turning onto the base leg of the circuit in the vicinity of the lateral boundary of the ATZ, and in the vicinity of the second formation.
The approach controller immediately provided traffic information to the pilots of the second formation about the Dash 8, but could not provide traffic information to the Dash 8 pilots as they were operating on the tower frequency.
The tower controller later reported that he originally intended to instruct the pilots of the Dash 8 to remain in the downwind position at 2,500 ft because it enabled him to better regulate the circuit traffic, especially given that he was instructing a controller-under-training at the time.
Instructing pilots to maintain 2,500 ft on the downwind leg was a common practice at Williamtown Airport. The AIP En Route Supplement Australia (ERSA) advised that all civil aircraft operating at Williamtown Airport were required to carry 30 minutes holding fuel. The tower controller later reported that that holding fuel enabled Williamtown air traffic control the flexibility to hold civil aircraft for up to 30 minutes, if necessary, for sequencing with arriving military aircraft.
Australian Defence Air Traffic System (ADATS)
Air traffic controllers at Williamtown Airport used the Australian Defence Air Traffic System (ADATS) to control aircraft operating within the Williamtown airspace. The ADATS associated a flight plan to an allocated transponder code14 and displayed that information to the controller as a data block, attached to the aircraft track symbol, on the SDD.
The data block could either be a full or limited data block. The full data block was white and included the call sign, altitude and radar derived ground speed, of airborne aircraft equipped with a serviceable transponder. It could also include other control information entered by a controller. A code and flight plan remained associated for a predetermined period of time depending on the nature of the flight. Once that time expired, the code/flight plan association terminated and the data block presented to the controller became a limited data block. The limited data block format did not display the call sign, and the colour of the data block changed from white to green. The limited data block format displayed an aircraft's allocated transponder code, altitude and radar derived ground speed.
The colours allocated to the track symbol and data block indicated the relevance of that aircraft to controllers. A green data block normally indicated that the aircraft was no longer of concern to the controller, as the flight plan was no longer active. The data block and track symbol colours assisted controllers with situational awareness.
The information displayed to the approach controller was also displayed to the tower controllers on the tower SDD. All information on relevant inbound, locally-based, military aircraft was displayed in the aircraft data block, including sequencing and tracking information. In accordance with local procedures, while a flight plan was associated with a specific transponder code, there was no requirement for the approach controller to provide voice coordination to the tower controller.
That applied to locally-based, military aircraft, as that information was available on the tower SDD. The tower controller was required to scan the SDD to determine the sequence and tracking details of arriving locally-based military aircraft. Tower controllers relied on the accuracy of the information presented in the data block, including the colour and sequencing instructions, to assist them in determining an estimated time of arrival, the arrival sequence and the inbound route of each aircraft.
Controllers reported that occasionally the code/flight plan association terminated while aircraft were still airborne. In those circumstances, in accordance with local procedures, the approach controller was required to use voice coordination to advise the tower controller about relevant inbound aircraft. The tower controller would not necessarily detect an inbound aircraft on the SDD if the code/flight plan association had terminated, unless voice coordination was received from the approach controller.
The code/flight plan association for the second formation terminated as the formation tracked to the circuit area and the data label changed colour from white to green. The approach controller reported that, as the termination occurred close to the circuit area, the tower controller would already have been aware that the formation was inbound. As a result, no voice coordination was provided to the tower controller.
Meteorological information
The weather was reported as fine and clear and was not considered to have been a factor in the occurrence.
Only those investigation areas identified by the headings and subheadings were considered to be relevant to the circumstances of the occurrence.
A tower controller employed by the Department of Defence provides a similar air traffic control service as a civil aerodrome controller.
The 24-hour clock is used in this report to describe the local time of day, Eastern Daylight-saving Time, as particular events occurred. Eastern Daylight-saving Time was Coordinated Universal Time (UTC)+ 11 hours.
Due to the limitations with the audio recording, all times are accurate to within about +/- 5 seconds.
The initial point for runway 12 at Williamtown Airport was located about 4 NM from the threshold of runway 12 along the extended centreline of taxiway Alpha, at 1,500 feet above mean sea level.
This phrase is used to advise air traffic control that the pilot requires priority for landing based on the amount of fuel remaining, calculated at a particular stage of flight (Manual of Air Traffic Services, pt 10, effective 9 June 2004).
The left, right and straight initial positions are 30 seconds prior to the initial point with wings level.
The Manual of Air Traffic Service is a joint civil/military publication used by Department of Defence and Airservices Australia air traffic controllers.
The dead side of the circuit is the side of the airfield or active runway, opposite to that of the circuit pattern in use, and from which arriving aircraft joining the circuit.
A flight progress strip is a thin cardboard strip used to record flight data relating to control of an aircraft.
A flight progress board is a piece of equipment used to display flight progress strips. Controllers use the information on the flight progress board to assist in managing the traffic situation.
The situation data display was an electronic display of radar derived information that depicted the positions and movements of aircraft.
The ATZ is that airspace within 5 NM of the tactical air navigation equipment ground based navigation aid, over land, from ground level to 1,500 ft above mean sea level. At Williamtown Airport, the stream landing circuit pattern (see Figure 1) is contained entirely within the ATZ.
A transponder is a receiver/transmitter which will generate a reply signal upon proper interrogation, in this case, of a signal generated by a ground based transmitter/receiver.
Summary
On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8) aircraft that was inbound to Williamtown Airport, NSW, on a scheduled passenger service from Brisbane, Queensland, passed 0.6 NM laterally and 300 ft vertically by the second of two formations of two McDonnell Douglas Corporation F/A-18 (Hornet) aircraft that were inbound to Williamtown Airport after a training exercise. As the Dash 8 turned onto the base leg, the second formation was about 6 NM north-west of Williamtown Airport, at 2,900 ft above mean sea level. The pilots of the Dash 8 descended in response to a traffic alert and collision avoidance system resolution advisory (RA) they received on that formation. The approach controller did not provide the required separation standard of 1,000 ft vertically or 3 NM laterally between the Dash 8 and the second formation. The tower controller had not established a visual separation standard between the aircraft at the time the Dash 8 pilots received the RA. There was an infringement of separation standards.
The investigation found that the factors that contributed to the occurrence included:
The approach controller did not assign an altitude to the second formation that provided a vertical separation standard between the second formation and the Dash 8
The tower supervisor advised the tower controller to cancel an instruction to the Dash 8 pilots to orbit on the downwind leg of the circuit at 2,500 ft, and to continue on the downwind leg of the circuit
The tower controller did not notify the approach controller that the Dash 8 was extending towards the lateral boundary of tower airspace
The pilots of a Westwind incorrectly notified the tower that their aircraft was 'minimum fuel' and did not join the circuit via the upwind leg as instructed by the tower controller.
Occurrence summary
Investigation number
200500355
Occurrence date
31/01/2005
Location
Williamtown, Aero.
State
New South Wales
Report release date
26/06/2006
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Mode of transport
Aviation
Aviation occurrence category
Loss of separation
Occurrence class
Incident
Highest injury level
None
Aircraft details
Manufacturer
De Havilland Canada/De Havilland Aircraft of Canada
