Asiana: one of several similar events
By David Learmount on 11 July, 2013 in Uncategorised
The Asiana Airlines Boeing 777 accident at San Francisco is one of several events that emphasise the need to review, in precise detail, what the effects of high levels of aircraft automation are, not only on the way pilots carry out their task, but also how they perceive their role in the control of the aircraft.
Evidence, although circumstantial at present, suggests this perception is changing and they are beginning to feel functionally peripheral.
Some work on specific areas has begun, but more is needed. Following the 2007 Thomsonfly 737-300 incident at Bournemouth, UK, in which the approach airspeed decayed 20kt below the reference figure before being noticed, the airline arranged for pilot eye movement tracking to be carried out. The carrier found that instrument scans were often un-methodical and incomplete.
Since pilots are still provided with the same basic flying training syllabus that has been used for many decades, it is important to understand whether this ineffective scanning habit is widespread, whether a disciplined instrument scan was never learned, or whether this represents a gradual degradation from a previously adequate level. Finally we must examine whether excessive trust in automated systems has anything to do with that degradation.
The Thomsonfly incident and the 2009 Turkish Airlines 737-800 crash on approach to Amsterdam Schiphol share with the Asiana accident a failure by the crew to recognise airspeed degradation until the situation was dangerous. In the Turkish case, recognition came so late the aircraft stalled fully.
According to National Transportation Safety Board investigation so far, the difference of these two from the Asiana case is that Thomsonfly entailed an autothrottle failure, Turkish involved a malfunctioning radio altimeter affecting a serviceable autothrottle, whereas – so far – no systems problem has been detected in the 777. Autopilot mode selection is therefore under examination, as well as further checks on serviceablility, to determine why the throttles remained at the idle position.
But back to scanning. On a visual approach like that of Asiana flight 214, aircraft attitude can be determined pretty accurately by reference to the real horizon, and the approach path ascertained from the runway perspective and precision approach path indicators. But the other factors critical to the performance of a safe approach can only be determined by looking at the instruments. Frequent reference to the airspeed indicator, altimeter and engine power indications is vital, because if the automatic systems deviate from their expected performance, divergence from the safe approach parameters is very rapid.
The airspeed indicator in particular needs to be scanned at least every 5s on long final, and every 2-3s on short final approach. So there is plenty for the eyes to do, both outside and in.
But the evidence shows this is not happening.
Why? We need to know.
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