Screening Commercial Aviation Passengers in the Aftermath of September 11, 2001. Slides from a presentation at the the University of Wisconsin-Madison on September 11, 2015.

1. A special colloquium on
homeland security and ISyE
“Developing Usable Metrics for Venue Security”
Dr. Paul Kantor
Honorary Associate, Industrial and Systems Engineering, University of Wisconsin-Madison
Distinguished Professor Emeritus, Rutgers University School of Communication and Information
Research Director at the Command, Control, and Interoperability Center for Advanced Data
Analysis (CCICADA) at Rutgers
“Screening Commercial Aviation Passengers in the Aftermath of September 11, 2001”
Dr. Laura Albert McLay
Associate Professor, Industrial and Systems Engineering, University of Wisconsin-Madison

2. Screening Commercial Aviation Passengers in
the Aftermath of September 11, 2001
Laura Albert McLay, PhD
Associate Professor
University of Wisconsin-Madison
Industrial and Systems Engineering
laura@engr.wisc.edu
@lauramclay
http://punkrockOR.wordpress.com/
Collaborators: Sheldon Jacobson, Alex Nikolaev, Adrian Lee, John Kobza
Jacobson’s research on aviation security has been supported
in part by the US National Science Foundation (CMMI-0900226)

3. Executive summary
Better security is achieved by targeting scarce screening resources at
the “riskiest” passengers and doing less screening on most passengers.
Underscreening / Overscreening occur given the uncertainty
associated with risk assessment and limited security resources
available.
Right Screening is ideal, but challenging to attain for all passengers.
TSA Precheck implicitly focuses on underscreening, which is why it
makes the air system safer, in low risk, cost-constrained environments.

4. Passenger screening:
Past, present, and future

5. One hijacking
encourages
copycats:
Hijackings are
contagious
Metal detectors and
X-ray machines go in
place

6. A brief history of passenger screening
• Dawn of time until 1970
• Not much!
• 1970
• Surveillance equipment, air marshals
• Feb 1972
• Armed guards to make people feel safe
• FAA adopted emergency rules to screen passengers
by at least one method including behavioral profile,
metal detector, and ID check
• Dec. 1972
• Metal detector / magnometer
• 1996
• Checked baggage for high-risk passengers screened
for explosives (run by airlines) – CAPPS
• Positive passenger baggage matching rejected
• Sept. 2001
• Times are a changin’

7. Security is a moving target
Changes in passenger and baggage screening
• November 2001 – Aviation
Transportation and Security Act
• Created the TSA
• Required all checked baggage to be
screened for explosives, Dec. 2002
deadline
• Driven by availably technology
• December 2001
• Remove shoes
• 2002 +
• CAPPS II, Secure Flight, etc. for risk-
based screening

8. Security is a moving target
Changes in passenger and baggage screening
• August 2006
• No more liquids after liquid
explosives used in a bomb attempt
• February 2010
• Random use of explosive trace
detection for carry on baggage in
response to Christmas bombing
attempt
• September 2012
• Less screening for seniors (75+) and
children (<12)
• December 2013
• TSA Precheck for reduced security

9. Why are homeland security problems good
ISyE problems?
• Limited resources
• Passenger risk assessments
• Tradeoffs among criteria (efficiency, security, cost)
• Note: TSA has a goal of <10 minutes waiting for screening
• System and goals are always changing
We will always have security challenges, and ISyE tools will
always help us address some of these challenges.
Security often improved through deterrent effect, not
detection.

10. Framework
• Passengers/bags screened by series of devices grouped in
classes
• System response a function of device responses
• Passengers check-in sequentially
• Passengers assigned to one of M classes upon check-in

11. Screening Assessments
Passenger risk assessments have been used since 1996.
What is known: As risk increases, likelihood of a security threat
outcome increases.
Most passengers are low-risk.
Risk-based security: Captured in the Dynamic Aviation Risk
Management System (DARMS) paradigm.
11

12. Retrospective Security & Resource Allocation
Know everyone’s risk before they enter security screening; allocate
security resources to match risk.
Assumptions:
Security resources are limited.
Screening procedures make errors
* False alarms, False clears.
Security resources allocated to a passenger match the retrospective
security resource allocation.
Multilevel Passenger Screening Problem (MPSP)* uses integer programming to
maximize the security of the system, subject to
1) security resource constraints / limitations,
2) performance limitations of these resources,
3) security devices / procedures may be assigned to multiple security classes.
* McLay, L.A., Jacobson, S.H., Kobza, J.E., 2006

13. Screening Procedure Reality
Screening decisions must be made in real-time.
* Control Theory models1
* Markov Decision Processes2
Based on the Sequential Stochastic Assignment Problem (SSAP).
1 Lee, A.J., McLay, L.A., Jacobson, S.H., 2009
2 McLay, L.A., Jacobson, S.H., Nikolaev, A.G., 2009
Each passenger has a risk profile
* Used to determine the security resources allocated to their
screening.
Three possible scenarios:
Right Screening
Under Screening
Over Screening

14. Real-time simulation of optimal
policy
Time
Passenger
risk

15. Conditional distribution of passenger risk assessment
values
Passenger risk

16. Over / Under Screening
Security resources allocated to a passenger do not match the
retrospective security resource allocation
Under  too few resources are allocated to that passenger
Over  too many resources are allocated to that passenger
Consequences: security resources not utilized correctly.
Will the system be more vulnerable?
Over/under-estimating risk
Overestimating risk*: True risk level () < estimated risk level (’).
Understimating risk: True risk level () > estimated risk level (’).
* The tendency is to overestimate risk 16

17. Discussion
17
When risk is overestimated, high value security resources get
used on low risk passengers, which may leave fewer high value
security resources available for high risk passengers.
When risk is underestimated, high value security resources get
used on high risk passengers, which targets more closely the
high value security resources for high risk passengers

18. Resource matching
Sensitivity analysis with respect to perceived risk in the system
Overestimate risk
True risk level <
estimated risk level.
Underestimate risk
True risk level >
estimated risk level.
Estimated risk level 𝜇′

19. Key Observations
In low risk environments, overestimating risk leads to a greater
mismatch between security resources and passenger risk.
In low risk environments, underestimating risk leads to lower levels
of underscreening and (for M small) lower levels of overscreening,
compared to overestimating risk.
* Better resource matching
* TSA PreCheck
* Giving TSA Officers the (limited) flexibility to assign
passengers to PreCheck lanes is an indirect way to mimic
underestimating risk
19

20. Gaming Strategies
Blocking
Overtaxing / decoys
Timing
Trial and Testing
All can disrupt the system in limited resource environments
20

21. Bad intentions
We are trying to prevent attacks
Is the goal to identify non-threat passengers with banned
items or threat passengers with bad intentions (and no
banned items)?
Risk based security focuses on the latter
21

22. Security systems
http://www.tsa.gov/about-tsa/layers-security

23. Thank you!
Laura Albert McLay, PhD
Associate Professor
University of Wisconsin-Madison
Industrial and Systems Engineering
laura@engr.wisc.edu
@lauramclay
http://punkrockOR.wordpress.com/
Blog posts:
• Aviation security, there and back
again
• Aviation security: is more really
more?
23

24. 24
References
Jacobson, S.H., McLay, L.A., Kobza, J.E., Bowman, J.M., 2005, “Modeling and Analyzing Multiple
Station Baggage Screening Security System Performance," Naval Research Logistics, 52(1), 30-
45.
Jacobson, S.H., McLay, L.A., Virta, J.L., Kobza, J.E., 2005, “Integer Program Models for the
Deployment of Airport Baggage Screening Security Devices," Optimization and Engineering,
6(3), 339-359.
McLay, L.A., Jacobson, S.H., Kobza, J.E., 2006, “A Multilevel Passenger Screening Problem for
Aviation Security,” Naval Research Logistics, 53(3), 183-197.
McLay, L.A., Jacobson, S.H., Kobza, J.E., 2007, “Integer Programming Models and Analysis for a
Multilevel Passenger Screening Problem, “IIE Transactions, 39(1), 73-81.
Nikolaev, A.G., Jacobson, S.H., McLay, L.A., 2007, “A Sequential Stochastic Security System
Design Problem for Aviation Security,” Transportation Science, 41(2), 182-194.
McLay, L.A., Jacobson, S.H., Kobza, J.E., 2008, “The Tradeoff between Technology and
Prescreening Intelligence in Checked Baggage Screening for Aviation Security,” Journal of
Transportation Security, 1(2), 107-126.
McLay, L.A., Jacobson, S.H., Nikolaev, A.G., 2009, “A Sequential Stochastic Passenger Screening
Problem for Aviation Security,” IIE Transactions, 41(6), 575-591 (2009 Outstanding IIE
Publication Award).
Lee, A.J., McLay, L.A., Jacobson, S.H., 2009, “Designing Aviation Security Passenger Screening
Systems using Nonlinear Control,” SIAM Journal on Control and Optimization, 48(4), 2085-
2105.
McLay, L.A., Lee, A.J., Jacobson, S.H., 2010, “Risk-Based Policies for Aviation Security Checkpoint
Screening,” Transportation Science, 44(3), 333-349.