Staffing Standards for Aviation Safety Inspectors (2007) / Chapter Skim
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2 Modeling as Applied to Staffing
2 Modeling as Applied to Staffing
Pages 28-45
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From page 28... ...
. At the Federal Aviation Administration (FAA)
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From page 29... ...
We were asked to examine and evaluate both the FAA's model and possible alternative models for ASI staffing. The more faithfully a model represents reality, of course, the more likely it is that staffing processes based on it will satisfy staffing demands.
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In this project we have focused on predictive models because our charge is to articulate methods for determining the appropriate numbers and types of aviation safety inspectors as a function of the factors that drive the demand for their services. Unless a staffing model can predict with some level of precision how well the inspection system will perform given the need structure, it would be impossible to estimate appropriate staffing levels.
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From page 31... ...
However, if the variability is not likely to affect model predictions, or the variability is small and unimportant, a deterministic model -- one that ignores the stochastic properties of the system -- should suffice.1 For example, if one were developing models to estimate the time that airplanes spend waiting for safety inspections, the variability associated with the arrival rate of airplanes into the inspection process would need to be incorporated. However, if the goal instead were to estimate the total number of aviation safety inspection hours required, this variability would be far less important, and it would be sufficient simply to enter average arrival rates.
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From page 32... ...
We think the present effort should emphasize the decision support role, since the complexity of the need structure and the difficulty of quantifying ultimate criteria render summative evaluation problematic at this time. Finally, models, such as one for ASI staffing, may be either allocation models or sufficiency models, or both.
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From page 33... ...
For example, is it useful for predicting ASI staffing needs for regions as well as the entire nation? Can it provide guidance on staffing at the flight standards district office or other facility level?
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From page 34... ...
Rather, it assumes that the relationship between future staffing requirements and the factors driving those needs -- whatever the underlying processes may be -- is relatively stable. If one has historical data on which to build statistical relationships between staffing demand factors and staffing requirements, then these statistical relationships can be projected onto new situations without understanding what accounts for them.
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From page 35... ...
For the purposes of ASI staffing, a process model would probably not require a very detailed task analysis, although the level of detail required would have to be determined during the model requirements definition process. Outputs of process models can be as varied as the systems they represent.
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From page 37... ...
The mathematical formulas are estimated from the observed historical data on the system, such as records of work accomplished by known staffing resources over a given time under known environmental demands and other relevant conditions. Thus a statistical staffing model is dependent on accurate work recording systems to provide the data it uses to estimate critical relationships.
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From page 38... ...
An example of this would be to gather a group of ASI subject matter experts and ask them to estimate how long it takes to perform Activity x, given their experience with the activity. Of course, expert judgment is subjective, so a model with parameters estimated in this way may not be considered credible unless it is empirically validated by testing predictions generated by the model against observed outcomes.
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From page 39... ...
Before proceeding further, however, one fundamental question must be addressed: Is modeling a potentially useful approach for aviation safety inspector staffing? Although once again we must note that neither modeling per se nor any approach relying exclusively on manpower management tools can ensure optimal staffing, we think modeling does have potential in two areas that correspond, respectively, to the distinction between sufficiency and allocation models.
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From page 40... ...
That is, it should be able to estimate aggregate staffing demand, provide predictions regarding the consequences of alternative levels of staffing, and help guide the allocation of resources across functions, regions, and offices. A single model would help ensure consistency across both aggregate and local staffing decisions.
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From page 41... ...
in order for its output to yield a useful estimate of total workload. Actual staffing demand will thus vary over time with changes in the distribution and mix of workload drivers (e.g., for the FAA, numbers of certificates, public airports, and pilots requiring oversight; job specifications; technological innovations; regulations and other policy mandates)
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From page 42... ...
For the purposes of a staffing model, something as simple as a minimum time to complete a task may be appropriate. For example, if experience has shown that four hours are required to do a thorough job of Task x, then a record of having performed Task x in one hour would not be accepted as documentation of satisfactory performance, and the model should incorporate in its demand functions that Task x requires four staff hours each time it is performed.
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From page 43... ...
3The FAA has this year proposed a Composite Safety Indicator to quantify overall airline safety, for purposes of evaluating the effectiveness of FAA programs (Flight Plan 20062010, Federal Aviation Administration, 2006)
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From page 44... ...
The primary parameters to be estimated in a staffing model are the relationships among demand factors, workload, staffing inputs, and staffing productivity. Any of the estimation methods described earlier may be used, but for any given staffing model the decisions about parameter estimation should be made by expert modelers with input from people who understand the practical realities of the system to be modeled.
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From page 45... ...
In the committee's view, the ASI situation does call for a formal modeling approach, one that supports staffing decisions in both the allocation and sufficiency functions through valid predictions of systemperformance consequences. We wish to emphasize again that a staffing model is not, and should not be, the only tool used in the development of manpower or staffing plans (called staffing standards at the FAA)
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