Introducing User-Centered Systems Design - Foundations for Designing User-Centered Systems - page 8

Table 1.1 Summary of some of the causal factors in the Kegworth air accident and lessons to

note
• The Engine Instrument System (EIS) used digital displays. A survey of the airline's pilots after
the Kegworth accident showed that nearly two-thirds of them believed that the new EIS was
not effective in drawing their attention to rapid changes in the engine parameters. If it had, the
accident might have been avoided. Thus, the design of the interface for the EIS did not present
data in a format that could easily be perceived by the pilots
Lesson: You need to understand how people look at the user interface to extract information
which they then use to make decisions and take actions
• Neither pilot could recall having seen any indication of the abnormally high vibration levels on
the EIS. The Captain noted that he rarely scanned the vibration gauges because he had found
them to be unreliable in other aircraft in the past. Experts, such as pilots, have a highly
developed mental model of the world in which they normally operate, which helps them carry
out their tasks. The Captain appears to have excluded the vibration gauges from his mental
model because he believed the readings were unreliable
Lesson: You need to understand how people create and use mental models to help them use a
system
• The B737-400 was a glass cockpit aircraft, in which the information is presented on digital
displays, rather than on analogue instruments and electro-mechanical displays. The airline
(BMA) did not have a glass cockpit flight training simulator for the B737-400, so pilots could
only gain experience through actually flying it (i.e., on the job). The only training the pilots
were given for the B737-400 was a 1-day audio-visual conversion course
Lesson: You need to understand how people learn to use new and, particularly, complex
systems
• Three members of the cabin crew said they saw evidence of the fire in the #1 engine, but they
did not report this to the pilots. The flight crew believed that the problem was with the #2
engine. This seems to have been a failure in what is called Crew Resource Management, a
procedure designed to ensure that all the members of a flight crew (pilots and cabin crew)
communicate with one another and work together as a team
Lesson: You need to understand how social issues, including communication, can affect how
people use a system
• The B737-400 was fitted with a new type of engine. The engine was thoroughly tested on the
ground before being certified by the appropriate authorities. The engine was not tested either
in an altitude test cell (which simulates the conditions of flying at high altitudes) or in flight,
however. This scenario illustrates how decisions that are made at remote distances from the
user interface in a system can have an impact on the way that the users behave. Emergency
events, like engine failures, are normally covered by checklists in the QRH (Quick Reference
Handbook) that is used by all pilots to deal with known situations
Lesson: You need to understand that decisions taken at a place and time that are greatly
removed from where the system is used can affect the way the system will behave

memories of how we behaved are subject to the inherent frailties of human
memory. We are also not very good at estimating time accurately and have trouble
keeping track of successes and failures. Finally, there are some particular aspects
of our own behavior that are very hard to observe, such as basic perception, and
some that are hard to describe and reason about verbally, such as performing some
spatial reasoning tasks.