Civil Engineering Reference
In-Depth Information
communication breakdown. These issues are illustrated below, using the example of
aircraft accidents.
POOR VISUAL DISCRIMINABILITY
The flight disaster with Singapore Airlines flight SQ 006 in Taipei is an example of poor
visual discriminability. The pilot had been cleared for taking off with a Boeing 747 to
Los Angeles (Lim, 2004). It was night time, and there were strong winds and heavy rain
as it was typhoon season. This made it difficult to see the runway, which was also very
poorly illuminated. Several light bulbs that delineated the taxiway leading to the runway
were out. The pilot could not see the taxiway. The only runway that the pilot could see
was an old runway that was being rebuilt into a taxiway. For reasons we don't
understand, it was lit up. The pilot selected the only visible option and took off on the
taxiway. Halfway down the taxiway he saw the construction vehicles that blocked the
runway. The pilot could not see them when he started taking off. The aircraft crashed into
the construction vehicles. Eighty-one of 179 passengers were killed. Neither the correct
runway nor the construction activities that led to the accident could be seen.
You wonder if the blame should not have placed on the airport authorities rather than
the pilot. International standards require that old runways under repair should be blocked
off with visible signs, and that all runways must be clearly illuminated. The pilot and the
copilot were declared guilty of causing the accident. A human factors systems approach
to the accident would take into consideration all contributing factors before blaming the
pilots alone.
MEMORY LAPSES
A system with mode control can be difficult to control, and sometimes a user selects the
wrong mode. The system operates so that one action is appropriate in one mode of
operation, and another action in another mode; in Mode A the operator must take action
X, in mode B he must do Y, and so forth. The problem with mode controls is that people
are easily distracted and forget what mode they are in. This has happened several times
with aircraft.
In the 1990 Bangalore air disaster, Air India Airlines flight with Airbus A320 crashed
on the final approach to Bangalore airport (Sarter and Woods, 1995). All 90 persons on
board were killed. This was a clear automation mode error. The pilots accidentally
selected a control mode called “Open Descent.” In this mode the aircraft cuts back engine
power and maintains its speed by progressively losing height. As a result, the rate of
descent was too great and the aircraft landed half a mile before the runway. The pilots
discovered their error only 10 seconds before impact—too late to correct it.
This and other aircraft accidents have highlighted pilot's vulnerability in using mode
controls. Airbus has since redesigned the aircraft. There are no mode controls, because
pilots may be distracted and forget what mode they are in.
