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cockpit the thrust levers do not even move!
We have described the results of the content analysis
elsewhere (Holder and Hutchins, 2000; Hutchins and
Holder, 2001). We noted there that the number of
conceptual difficulties reported concerning the
descent phase of flight far outnumbers the number of
difficulties reported for all other phases of flight
combined. Managed descents are based on
engineering principles (e.g., an energy dissipation
schedule) that lie outside the realm of pilot concepts.
Pilots do not normally use engineering concepts to
understand autoflight. This is not surprising given
that these concepts are not well represented in
training materials and cannot be inferred from the
behavior of the system without significant
background preparation. What pilots do seem to learn
on the line is when they can expect the automation to
help them and how they can shape their operations to
minimize automation surprises. In this paper I
explore the utility of some quantitative analyses of
the interview corpus as indices of change in pilots’
conceptual understandings as they acquire experience
in the Airbus A320.
Quantitative Measures of Conceptual Change
To explore what simple statistical methods could
reveal about changes in the pilots’ conceptual
structure concerning autoflight across the interviews,
two types of quantitative analysis were performed: a
term frequency analysis and a term co-occurrence
analysis. A subset of 22 autoflight-related terms was
chosen for examination. In choosing the terms, we
sought a range of terms that included the most
important technical terms (e.g., idle, managed),
operational terms (e.g., climb, restriction) and
informal pilot jargon (e.g., box).
Term frequency analysis
Terms that occur frequently in interviews are likely
to be more salient conceptually than terms that occur
rarely, and changes in the relative frequencies of
various terms is an indication of changing conceptual
structure. We therefore computed the relative
frequency of each automation term in each interview
set. To ensure that we were not measuring the
behavior of the interviewers, we performed the
frequency analysis separately for interviewer and
pilot portions of the transcripts.
Term frequency analysis results: The frequency
analysis suggests some interesting changes in
conceptual structure. For example, consider the use
of the word ‘computer’. This word accounts for
more than a third of all autoflight related word
instances in the initial interview set. The fact that the
Airbus airplanes are highly computerized is THE
salient fact for the pilots as they arrive at the training
center. When we spoke to the pilots after they had
completed training and had been flying the airplane,
the use of this term dropped to about one instance in
twenty of autoflight related words. Once they are on
the airplane, the specifics of what the computers do
become salient, and the presence of the computer is
assumed rather than remarked.
The term speed follows a pattern of use that is almost
exactly the inverse of the pattern for computer.
Speed accounts for less than 5% of the instances of
autoflight related words in the initial interview set. In
1L, speed accounts for 22% and in 2L for 26% of the
autoflight related word instances. Once they are
flying the airplane, the pilots’ discourse concerning
autoflight is dominated by the term speed. The
frequency analysis does not reveal what it is about
speed that makes it so important to the pilots. That
requires a different method. The content analysis of
the interviews (Hutchins and Holder, 2001) showed
that pilots entering training for the airbus airplane are
not yet aware of the conceptual challenges associated
with the management of speed in this airplane. Pilots
do not have a clear idea of what the autoflight system
does in the first days of training. Once they begin
flying the airplane, however, a model begins to form.
It appears that in the first year on the airplane, the
concepts associated with the simpler vertical modes
are more salient than the concepts associated with the
most highly automated vertical modes.
The following words have higher relative frequencies
in the first or second line interview than they have in
the last line interview: speed, descent, climb, open,
vertical, selected, select, restriction. All of these
terms decrease in salience in the period between one
year and eighteen months on the line. The terms
open, selected, and select are unambiguously
　
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