TRB Special Report 301: Traffic Controller Staffing in the En Route Domain A Review of the Federal Aviation Administration's Task Load Model (2010) / Chapter Skim
Currently Skimming:
4 Converting Task Loadinto Positions to Traffic
4 Converting Task Loadinto Positions to Traffic
Pages 46-57
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 46... ...
period -- presumes that at this point the combination of modeled R-side tasks and unmodeled D-side tasks fully occupies the controlling time available to the lead controller. The specific 600-second threshold was identified by model developers on the basis of consultations with facility managers, who found that the resulting PTT values were closer to their expectations of staffing levels associated with the modeled traffic than those generated by other cutoff points (550, 580, etc.)
|
From page 47... ...
FIGURE 4-1 Example use of 600-second (R-side) task load threshold to estimate PTT over 8-hour period.
|
From page 48... ...
Fuzzy Logic Modeling Even after rules for international and nonradar tasks were applied, CAASD worried that other variability in sector traffic patterns was creating even more variability in total task load than could be accounted for by the
|
From page 49... ...
CAASD concluded that the inference rules used in fuzzy logic modeling might be well suited to inferring total task load from these qualitative judgments. In an explanatory document submitted to the committee,1 CAASD described the fuzzy modeling process and its purpose as follows: Fuzzy logic involves setting multiple thresholds for each input variable, and then creating rules of interaction.
|
From page 50... ...
controller. Essentially, the translation produced by the PTT fuzzy model reflects how operational experts characterize position needs: low degree of workload is equivalent to one controller, medium degree of workload is equivalent to
|
From page 51... ...
Inference Rules Required Controllers Workload Tasks Entry Basic Tasks Exit Entry Basic Weight Exit Monitor Monitor Min/B Sum Task Weights Complex Tasks Separation Controllers CoM CoM Controllers CoM Basic Weight Separation Delay Complex Weight Complex Weight Controllers MoM Controllers MoM MoM Delay Other Weight Min/B Sum Transition Min/B Sum Transition Other Tasks Nonradar Other Weight Nonradar International International Min/B Sum FIGURE 4-3 Framework for fuzzy logic modeling process to infer PTT.
|
From page 52... ...
The committee sought, but was not was presented with, the total task loads that are implied by the different combinations of R-side tasks that generate specific PTT values. Making explicit these implied D-side task loads so that they can be assessed is essential to judging the validity of the PTT estimates produced through fuzzy logic modeling.
|
From page 53... ...
On the other hand, if the PTT model indicates a need for one controller when staffing records show that two were in position, it is much more difficult to ascertain whether the model underestimated the need for a second controller or whether actual staffing levels were too high for the experienced traffic activity. Review of PTT Estimates by Facility Personnel To assess its PTT estimates, CAASD presented the results to managers and controllers at 13 centers spread across the country.2 At each evaluation session, participants were given a general overview of the modeling process.
|
From page 54... ...
In this case, CAASD compared the number of controllers recorded on position with the number that would have been estimated using the earlier traffic-volume method and using the task load model's output converted to PTT using the 600-second and fuzzy logic methods. Traffic operation counts were evaluated for each of the nation's 20 en route centers to identify the 90th-percentile traffic days, that is, those days in which traffic volumes were higher than those experienced in 90 percent of the other days during the year.
|
From page 55... ...
. resultant impacts on total controller task load, CAASD believes that this is why the latter conversion method yields PTT values that are closer to the Cru-ART numbers.
|
From page 56... ...
COMMITTEE ASSESSMENT The CAASD task load model examines only one set of controller tasks: the R-side tasks performed by the lead controller. Because of this limitation, use of the model results to estimate PTT requires either supplemental measures of D-side task load or a creative means of converting the model output into measures of total task load.
|
From page 57... ...
All of the PTT conversion methods applied, including the current method of fuzzy logic modeling, exhibit the same fundamental flaw -- they imply an estimation of total task load without ever identifying the unmodeled tasks, much less measuring the time it takes to perform them. The conversions rely almost exclusively on experts to determine thresholds and to assign complexity weightings to the unidentified and unmodeled tasks.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.