RJ85 Landed Alongside Runway Obscured by Dust
The Australian Transport Safety Bureau (ATSB) have reported on an incident involving a BAE Systems Avro RJ85 landing alongside an unsealed runway at Darlot, WA on 20 January 2017. Cobham‘s VH-NJW was conducted a FIFO (Fly In Fly Out) charter flight from Perth to the airport located next to the Darlot-Centenary Gold Mine. It landed on the graded runway strip* to the left of the runway itself, due to raised dust obscuring the markers on the right side of the runway and runway strip.
The Airport
Darlot has no electronic approach path guidance. The ATSB explain that the airport:
…used identical white frangible cones as markers for both the runway and the runway strip. The runway was 30 m wide and 1,969 m long. The runway strip was 90 m wide. Therefore the lateral spacing of the cones for the runway and the runway strip either side of the runway were equidistant.
[A]aiming point markers are not required…on unsealed runways [but] the airport operator can elect to ‘implement an aiming point marking by providing an appropriate marking.’ Darlot Airport used three frangible white cones, either side of the runway on the edge of the runway strip, as aiming point markers.
* A runway strip, for a runway without an instrument approach, includes a graded area around the runway and stopway, intended to: (1) to reduce the risk of damage to aircraft running off a runway; and (2) to protect aircraft flying over it during take-off or landing operations.
The Incident Flight
When the aircraft joined the final approach leg, the captain noticed dust in the vicinity of the runway.
Although this was initially suspected to be due to a vehicle…
…at about 2.5 NM (4.6 km) from the runway the captain concluded that the dust was from the strong easterly wind…
The aircraft landed without incident. However, as the aircraft slowed to taxi speed, the PF [Pilot Flying] observed cones and runway lights on the right side of the aircraft, but only cones on the left side of the aircraft. The PF then noticed that the raised dust on the right side of the runway strip [had] covered both the runway markers and runway strip.
Darlot Airport runway 14 and left side of runway strip as viewed from the right seat of the aircraft with white frangible cones used as markers. Raised dust extends from the centre of the runway across the southern side of the runway strip. (Credit: ATSB/Pilot)
They had landed the aircraft on the graded area of the runway strip to the left of the runway. The PF manoeuvred the aircraft back onto the runway, taxied to the apron and shutdown… The aircraft was not damaged.
The aircraft operator provided services to three other airports with unsealed runways. Following this incident, the operator reviewed the other airports and found that at two airports the aiming point markers were located inside the runway strip (one used gable markers and the other cones), either side of the runway…
Gable aiming point markers within the runway strip at a different unsealed runway used by the operator (Credit: Cobham via ATSB)
… and at the third airport the aiming point markers had been removed. Therefore, the aiming point markings were inconsistent between all four airports.
ATSB Analysis
The PF advised that the final approach to land at Darlot, was a period of high workload because the aircraft was flown manually with cross-checks of distance and altitude used to manage the descent profile.
On the incident flight, the PF’s attention was initially captured by raised dust… About halfway down the final approach, the PF discounted the presence of a vehicle, but then incorrectly identified the left runway strip markers as the left runway markers because the right runway and runway strip markers were obscured by the raised dust.
This was confirmed in their mind by the presence of the aiming point markers on the left side of the runway strip. The PF was seated in the left seat and therefore used the aiming point markers on the left side as their visual guidance cue for the aircraft landing.
The siting of aiming point markers at airports with unsealed runways used by the aircraft operator was not standardised…
The pilot had experience, from operating into other unsealed runways, of aiming point markers positioned in the runway strip next to the runway. Therefore, the position of the aiming point markers on the left side of the runway strip markers was not recognised by the PF as an indicator that the aircraft was landing to the left of the runway.
Visual Illusions
The Flight Safety Foundation (FSF) say visual illusions occur when:
…conditions modify the pilot’s perception of the environment relative to his or her expectations, possibly resulting in spatial disorientation or landing errors.
Factors which can result in visual illusions are the airport environment, runway environment and weather conditions.
Further information is available in the FSF approach-and-landing accident reduction tool kit: Briefing Note 5.3 – visual illusions
ATSB Comments
On approach to land, the PF must scan between the near end and far end of the runway for their visual judgement of flare height and alignment of the aircraft with the runway centreline.
A greater amount of visual processing is dedicated to the central region of the retina (fovea) than to the peripheral regions of the retina. Consequently, central portions of a visual image are seen to a higher resolution than peripheral portions.
For a pilot focused on the runway centreline, the aiming point markers will move from central vision to peripheral vision at three times the distance for markers laterally displaced 45 m in lieu of 15 m from the runway centreline.
The ATSB notes that the aiming point markers are a visual guidance cue for the PF. Increasing the lateral displacement of the markers from the runway may divert the PF’s scan further from the runway centreline at a critical stage of flight.
Safety Actions
The operator has conducted their own internal investigation of the incident, which included a review of the unsealed runways they operate the AVRO 146 into.The operator submitted a discussion paper to the Civil Aviation Safety Authority on the provision of aiming point markers for unsealed runways. The paper proposes the standardisation of aiming point markers in accordance with the system previously tested by the United States Federal Aviation Administration. The results of [that] testing can be found in ‘Marking and Lighting of Unpaved Runways – Inservice Testing’: DOT/FAA/CT-84/11.
Darlot Airport agreed to move the markers to outside the runway strip after consulting the air operator.
Aerossurance is pleased to sponsor the 9th European Society of Air Safety Investigators (ESASI) Regional Seminar in Riga, Latvia 23 and 24 May 2018.
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