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with independently determined 3D present
position of the aircraft, defined routes,
destination(s), and navigation solution (course,
distance) to destination.
8 Loss of Air traffic control determination of 3D
location, velocity vector, and identity of each
aircraft operating in a domain.
9 Loss of Air traffic control determination of
location, identity, and velocity vector of each
participating vehicle operating in the airport
movement area domain.
FAA System Safety Handbook, Appendix B: Comparative Risk Assessment (CRA) Form
December 30, 2000
B-4
10 Loss of approach guidance to runway. Precision
– horizontal and vertical guidance; Nonprecision
– horizontal guidance, vertical
procedures.
11 Loss of ground vehicle or aircraft operator
independent determination of present position,
destination(s), and navigation solution on the
airport movement area.
12 Hazardous runway surface precludes safe
takeoff or touchdown and rollout.
FAA System Safety Handbook, Appendix B: Comparative Risk Assessment (CRA) Form
December 30, 2000
B-5
SAFETY ASSESSMENT SUMMARY
(Conclusions/Recommendations)
Summarize your conclusions. Which option is best (and 2nd, 3rd, etc) and why. Include enough detail to
appropriately communicate with the audience.
Recommendations: Provide additional controls to further mitigate or eliminate the risks. Follow the safety order
of precedence, i.e., (1) eliminate/mitigate by design, (2) incorporate safety features, (3) provide warnings, and
(4) procedures/training. See Chapter 4 for further elaboration of the Safety Order of Precedence). Define SSE
requirements for reducing the risk of the design/option(s).
FAA System Safety Handbook, Appendix B: Comparative Risk Assessment (CRA) Form
December 30, 2000
B-6
HAZARD CLASSIFICATION RATIONALE Do one of these sheets for each hazard
1 Hazard: Loss of communication between air traffic controllers and aircraft
Summarization
Summarize the risk assessments for hazard No. 1 for each alternative that was examined.
Baseline Option A
Severity: 1-Catastrophic Probability: E-Improbable Assessment: Medium Risk
Option B
Severity: NA Probability: NA Assessment: NA
Severity
Rationale for Severity:
In this section explain how you came up with the hazard severity. This is where you will convince the
skeptics that you were logical and objective.
The hazard is a component of the hazardous conditions required for NMAC, CFIT, WXHZ, NLA, and
RIA’s. For the baseline NAS system the severity of the “loss of communication” hazard is highly dependent
upon the environmental conditions surrounding the event and is therefore categorized as a flight essential
function of the NAS. In a “day, VFR, low density” environment the severity is very low resulting in minor
effects. During a night/IFR high-density environment the occurrence of this hazard has a good chance of
becoming catastrophic. The reason for this is that the purpose of this communication system is to provide
aircraft in a region of airspace with direction, clearance, and other services provided by Air Traffic Control
(ATC). In an environment of low outside visibility and many aircraft this function becomes critically
important to air vehicle separation. The following points highlight the severity:
Air Traffic Controllers (ATCs) are able to observe wide volumes of space using airspace surveillance
systems. These systems enable the ATCs to observe the location, velocity, and sometimes the identity of the
aircraft detected by their systems. The ATCs are trained to direct the flow of traffic safely to prevent midair
collisions, flight following, approach clearances, and emergency assistance.
Loss of the entire communication system would result in the rapid onset of chaos as approaching aircraft
attempt to land and enroute aircraft converge on navigation waypoints and facilities. The risk of mid air is
high in these conditions.
In the event that a loss of communication occurs, then complex emergency procedures are established for
IFR and VFR aircraft. The procedures are necessarily complex and if followed should result in a safe
landing, but once initiated can be difficult to follow especially for a single pilot in IFR.
The AIM states “Radio communications are a critical link in the ATC system. The link can be a strong bond
between pilot and controller or it can be broken with surprising speed and disastrous results”.i
FAA System Safety Handbook, Appendix B: Comparative Risk Assessment (CRA) Form
December 30, 2000
B-7
Probability
Rationale for Probability:
Use this section to explain how you derived the probability. This may be quantitative or qualitative. In
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