| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 20 April 2021, a Fairchild SA227 aircraft taxied at Townsville Airport, for a freight charter flight to Brisbane, Queensland. At about 1854 Eastern Standard Time,[1] air traffic control (ATC) cleared the aircraft to line up on runway 01 from taxiway Alpha 1.
It was dark, as last light [2] had occurred approximately 56 minutes earlier. Rain showers had also passed through the area intermittently during the preceding 30 minutes. The automatic terminal information service[3] reported runway conditions at the time as wet, with visibility reducing to 4 km in rain and scattered cloud at 700 ft above ground level.
As the aircraft was entering the runway, and 20 seconds after issuing the line-up clearance, ATC advised the pilot that the aerodrome QNH[4] had changed. This change required the pilot to adjust the altimeter datum that had been set prior to line-up. Twelve seconds later, ATC cleared the aircraft for take-off. As the pilot read back this clearance, completed the before take-off drills, and taxied the aircraft into position on the runway, they reported becoming aware that the aircraft ‘had deviated from the lead-in line’ and ‘started correcting the turn immediately to…regain a track to the centreline’. Having made this correction, and assessing that the runway centreline would be regained shortly after beginning the take-off roll, the pilot commenced a rolling take-off and reported no unusual indications throughout departure.
During routine aerodrome inspections carried out 48 minutes after the aircraft departed, it was discovered that an above ground runway light on the left side of runway 01 had been struck and damaged by an aircraft (Figure 1).
Figure 1: Aircraft tyre tracks and runway light damage
Source: Townsville Airport, annotated by the ATSB
Pre-flight inspections carried out on the aircraft the next day found damage to a propeller blade on the left engine that was consistent with the propeller impacting a foreign object (Figure 2).
Figure 2: Damage sustained to aircraft’s propeller
Source: Operator, annotated by the ATSB
Subsequent engineering inspections by the operator discovered ‘slight witness marks’ of yellow paint on the left main landing gear that was the same colour as the above ground runway lighting fixtures on Townsville’s runway 01.
The operator found that the clearance between an empty SA227 propellor’s tip and the ground was 260 mm. The height of the aerodrome light that was struck was 250 mm. However, it was concluded that a combination of the 789 kg of freight that was on board the aircraft at the time of the occurrence, and the normal range of oleo compression that would be expected during take-off, would reduce the clearance between the propellor blade and the runway light sufficiently to allow a propellor blade to strike the light.
As the landing gear on the SA227 is mounted in the engine nacelle directly behind the propeller, the operator concluded that a propellor blade had struck the runway light during the aircraft’s take-off run, partially destroying the light. The left main wheels then passed over the mounting location of the runway light, impacting the remains of the runway light fixture and leaving the paint witness marks visible on the landing gear assembly. This also resulted in the tyre tracks that remained visible on the runway surface the next day (Figure 1).
The operator concluded that the pilot had become spatially disorientated during the runway line-up sequence, and commenced the take-off from a position further left of the runway centreline than they had perceived (Figure 3), resulting in a propeller blade on the left engine contacting the runway light. An internal investigation by the operator found that a number of factors contributed to the aircraft striking the runway light on take-off. These included:
- the runway lead-in lighting not extending to the runway centreline when entering the runway from the Alpha 1 holding point
- distraction and high workload of the single pilot while completing the line-up sequence
- difficulty in sighting the painted runway lead-in lines due to low lighting conditions and standing water on the ungrooved section of the runway’s surface.
It was further reported by the pilot that the design of the runway, and the wider paved section at the runway’s end to accommodate military aircraft movements, contributed to their not identifying the runway misalignment.
Figure 3: Approximation of planned, perceived, and actual aircraft path during line-up
Source: Google earth, annotated by the ATSB
Historical context
Townsville Airport is a joint user facility with both military and civilian aircraft movements. Runway 01/19 is equipped with an Operational Readiness Platform (ORP) (Figure 4) which is a large, paved apron section at either end of the runway, where military aircraft can be parked. The ORP section is only intended for use by military aircraft, and as such, recessed lighting and markings indicate the normal runway dimensions within this area, as well as the outer edges of the ORP area. At the end of the ORP area, the pavement width reduces to normal runway dimensions and lighting.
At the southern end of the runway, runway lighting indicates the correct path for an aircraft to vacate the runway onto taxiway Alpha 1. However, this lighting is unidirectional, and does not indicate the correct path for an aircraft to take when lining up on the runway from the direction of taxiway Alpha 1 (Figure 4).
Figure 4: Runway lighting and layout of departure end of Townsville Airport Runway 01
ORP area illustrated, as well as the runway lead-in lighting that is not visible to an aircraft entering the runway from taxiway Alpha 1
Source: Townsville Airport, annotated by the ATSB
This is the second occurrence of this type on Townsville’s runway 01. An ATSB investigation examined a previous occurrence on 11 February 2009 that involved a Bombardier DHC-8 aircraft taking off at night (AO-2009-007). The DHC-8 had also lined up and commenced its take-off roll on the runway 01 edge lighting, after entering the runway from holding point A1. The DHC-8 crew had realised their misalignment during the take-off roll, and rejected the take-off after striking a runway side light with the landing gear.
As a result of this and similar occurrences at other airports, the ATSB undertook Aviation Research and Analysis Report Factors influencing misaligned take-off occurrences at night (AR-2009-033), which examined these types of incidents and their causes. This analysis identified eight factors that increased the risk of a misaligned take-off or landing. These factors were,
distraction or divided attention of the flight crew; confusing runway layout; displaced threshold or intersection departure; poor visibility or weather; air traffic control clearance/s issued during runway entry; no runway centreline lighting; flight crew fatigue; and recessed runway edge lighting.
A number of these factors were present during the take-off of the SA227:
- The pilot reported being distracted and ‘head down’ during the initial line-up sequence to configure the aircraft for take-off.
- Townsville’s runway 01 includes a wider ORP section at its end, which contributed to the pilot’s false perception that they had not travelled across the runway as far as they actually had during the line-up phase.
- The weather at the time, which was similar to that of the 2009 DHC-8 occurrence, was wet with rain intermittently reducing visibility.
- A change in local QNH had required ATC to contact the pilot during the line-up sequence, adding to the pilot’s workload during this phase.
- Townsville’s runway 01 does not have centreline lighting, which reduces the visual cues available to a pilot to confirm the correct runway orientation.
- Recessed runway lighting is used to denote the outline of the normal runway dimensions within the ORP area. This has the potential to contribute to spatial disorientation during the line-up phase, as this type of runway lighting is normally used to indicate the centreline on a runway equipped with centreline lighting.
With the exception of crew fatigue, seven of the eight major factors identified by the ATSB as increasing the risk of a misaligned take-off or landing were present in this occurrence.
Safety action
As a result of this occurrence, the aircraft operator has advised the ATSB that a Safety Advisory will be sent to all flight crew identifying the hazards associated with runway alignment on runways equipped with an ORP area. Flight crew have also been reminded of the importance of identifying and managing distractions, and of the option to delay take-off where there is any doubt about the aircrafts position during the line-up sequence.
Townsville Airport has advised the ATSB that it is currently reviewing the existing runway lighting arrangement on runway 01/19, with a view to ensuring that the runway lighting is sufficient to ensure correct alignment with the runway during line up.
Safety message
This incident highlights the potential hazards in runway misalignment, as well as the primary factors previously identified by the ATSB as contributing to these occurrence types. In addition, runways that are equipped with Operational Readiness Platforms pose additional challenges in correct runway identification and alignment.
It is also a reminder to crew of the importance in managing distraction and interruption during critical phases of flight. These threats will always be present in the operational aviation environment, but through effective identification and management, the potential impact on flight safety may be mitigated.
In this occurrence, the pilot correctly identified that they had lost situational awareness during line-up, but had elected to continue the take-off before re-establishing sufficient situational awareness of the aircraft’s position. By halting the line-up to fully re-establish situational awareness, the pilot may have been able to identify the runway misalignment prior to commencing the take-off roll.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
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- Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
- Last light: when the centre of the sun is at an angle of 6 degrees below the horizon after sunset.
- ATIS: the automated broadcast of information relating to operations at an airfield during tower hours.
- QNH: the altimeter barometric pressure subscale setting used to indicate the height above mean sea level.