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B738, Perth Australia, 2008

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Description

On 9 May 2008, the crew of a Boeing 737-800 (PK-GEF) being operated on a scheduled passenger flight from Denpasar, Indonesia to Perth made a low go around after observing vehicles on the closed section of the runway without apparently recognising where the expected temporarily displaced landing threshold was located. A second similar approach led the TWR controller to instruct the aircraft to go around but instead, the aircraft was observed to fly level at a low height before eventually touching down just beyond the correctly notified and marked displaced threshold.

Investigation

The occurrence was classified as an “Operational Non Compliance” by the Australian Transport Safety Bureau (ATSB) but a full Investigation was carried out into the circumstances. It was established that both flight crew were familiar with Perth but the occurrence arrival was their first since the runway works requiring a landing threshold temporarily displaced by 888 metres had commenced. The crew were aware of the Notice To Airmen advising of this work prior to making their approaches and it was noted that both the landing clearances they had received included reference to the displaced threshold. The prevailing weather conditions were good.

On the first approach, using a LOC-only procedure because the Instrument Landing System (ILS) GS was de-activated due to the displaced threshold, the crew had queried the presence of vehicles on the runway with ATC when about 15 seconds from landing and elected to conduct a go around. On the second approach, the TWR controller “recalled observing the aircraft on what appeared to be an approach to land on the closed section of the runway and instructed the flight crew to go around”. This instruction also “included information to assist the flight crew in identifying where the aircraft should be landed”. The flight crew of an aircraft waiting to depart reported that the 737 had flown level over the runway works area at between 30 feet and 50 feet agl before landing soon after the displaced threshold. The 737 flight crew subsequently stated that during the second approach, “they only heard a clearance to land and did not recall hearing the instruction to go around or any other information”. It was considered by the Investigation that the additional information on the location of the displaced threshold in the context of their “high workload” at that time “may have momentarily confused them” with the result that neither of them assimilated or acted on the instruction to go around.

The Runway activity which had required the (correctly marked) displaced threshold was found to involve lighting installation and to only involve partial runway closure between 0730 and1700 local time each day. This meant that there was no requirement to obscure the permanent threshold and touchdown markings and it was only necessary to identify the works/closed area using four 6 metre crosses on the runway surface. The flight crew involved subsequently stated that they had not seen these crosses on their first approach and had seen them “too late” on their second approach. They also stated that upon disconnecting the AP and checking the temporary Visual Approach Slope Indicator Systems positioned to guide aircraft to the correspondingly displaced touchdown zone, they had noted that “the aircraft was undershooting the approach path to the displaced threshold”.