CHAPTER 5. STUDY 1 RESULTS
5.3.2. Coding framework 1.2: Areas of changes requested by the NTSB to address
A subsequent analysis was conducted to identify which changes were asked by the NTSB to the FAA in order to address the “controller lack-of-response” concern. This analysis classified the NTSB safety recommendations that were issued in order to solve this concern depending on the nature of change they requested. The analysis identified three areas of change: (i) human machine interface design, (ii) procedure, and (iii) nuisance reduction.
1. Human Machine Interface (HMI) design. This area of change includes 5 requested changes (RC), corresponding to 10 safety recommendations, which demanded changes to be made to the alarm design to improve its visual and audio presentation to air traffic controllers. In particular, the NTSB issued the following requested changes:
One requested change, RC1, aimed at improving the informativeness of the MSAW aural alert. This change was motivated by the fact that the MSAW aural alert was identical to that of another alarm, the conflict alert or CA—an alarm system intended to warn controllers of the risk of mid-air collisions6 (MACs). Thus, the same aural tone could signify the risk of a CFIT or that of a MAC. For this reason the NTSB wanted to differentiate the aural alerts of the two alarms; One requested change, RC2, aimed at making the MSAW flashing rate more
visually appealing compared to that of the data block—the block appearing on the radar display containing flight’s alphanumerical information—during transfer between different sectors;
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Two requested changes, RC3 and RC4, aimed at decreasing the exposure to alerts generated by other working positions in the same control room. In particular, RC3 aimed to direct the alarm only to the controller with direct control of the aircraft that activated the MSAW; RC4 included the request to incorporate an alarm inhibition function, so to silence MSAW alerts activated by other working positons;
One final requested change, RC5, requesting the total redesign of the HMI to make the alert more attention capturing. In the fifth and final safety recommendation letter reporting on the lack-of-response concern, the NTSB questioned the ability of the entire MSAW alerting method to reliably capture the attention of air traffic controllers.
2. Procedure. This area of change includes two corrective changes—RC6 and RC7, corresponding to two safety recommendations—that demanded the FAA changes to existing procedures to improve the controller’s response to the MSAW. RC6 asked the FAA to include the shift supervisor in the alerting loop, so as to ensure that whenever the MSAW was activated s/he could intervene to ensure that that the relevant controller responded appropriately. RC7 demanded regulatory changes to make it mandatory for air traffic controllers to transmit the MSAW alerts to the relevant pilot whenever the aural alert was heard.
3. Nuisance alert reduction. This area of change consists of one requested change, RC8— corresponding to one safety recommendation that asked the FAA to reduce the rate of unwarranted nuisance alerts in control centres, because the NTSB had noted that controllers were exposed to such alerts on a routine basis.
The matrix reported in Table 10 provides a chronological overview of (i) the areas of change and (ii) the changes requested by the NTSB to address the lack-of-response problem. The matrix distributes the NTSB requested changes, grouped by area of change, across the five safety recommendation letters in which they were issued. The cells in the matrix show the identifier of the safety recommendation that carried a given change. Identifiers in bold signal safety recommendations that have triggered a non- implementation rationale on the part of the FAA.
The matrix shows that the first area of change, “HMI design”, is both (i) the older and (ii) the denser area of change. Safety recommendations belonging to this area were issued first in 1981 (n=2), then in 1984 (n=1), in 1990 (n=3), in 1997 (3), and lastly in 2006 (n=1).
Chapter 5. Study 1 results
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This makes a total of 10 safety recommendations (=77% of the total) issued by the NTSB in relation to this area of change. The “HMI design” area is followed by the second improvement area, “Procedure”, which includes two corrective actions issued in 1984 and 1997 by means of two safety recommendations (=15%). The third area, “nuisance alert reduction”, is instead the sparser and younger area, including only one requested change issued by means of one safety recommendation in 2006. As an intermediate conclusion, it can be said that, over the period 1981–2006, the NTSB viewed the “controller lack-of- response” concern mostly as an issue of improving the HMI Design and the procedural response to the MSAW. It is in 2006, that the NTSB considered the importance of tackling the problem of nuisance alerts as a stand-alone problem.
Table 10. Matrix of the changes requested by the NTSB to the FAA. NTSB Safety
Recommendation Letters 1rst, Oct 6,
1981 2nd, Aug 13, 1984 3rd, Sept 28, 1990 4th, Apr 16, 1997 5th, July 12, 2006 Areas of
Change Requested Change (RC)
1. HMI
Design 1. Disambiguate between MSAW and
CA aural alerts
A-81-134* A-84-83 A-90-161 - -
2. Make MSAW
flashing at a higher rate than the data block during transfer
A-81-135 - A-90-163 A-97-25 -
3. Direct MSAW aural
alarm to the relevant controller only Included under A-81-134 Included under
A-84-83 A-90-162 A-97-26 -
4. Include possibility to
inhibit the alarm - - - A-97-26 -
5. Completely
redesign MSAW
alerting method - - - - A-06-44
2. Procedure
6. Include supervisor in
the alerting loop - - - A-97-27 -
7. Amend regulations
to make mandatory the transmission of MSAW alert to pilots - A-84-84 - - - 3. Nuisance Alert reduction 8. Reduce exposure to
nuisance alerts - - - - A-06-45
LEGEND
Identifiers in the cells correspond to safety recommendations; *= Safety recommendations in bold have been dismissed by the FAA.
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Also, the matrix suggests that the first and second areas of change, i.e., “HMI design” and “Procedure”, include some changes that were resisted by the FAA. In particular, the FAA expressed a non-implementation rationale for RC1, “Disambiguate between the MSAW and the CA aural alert”, and RC7, “Amend regulations to mandate the transmission of MSAW alert to the pilot”. The different positions of the NTSB and the FAA regarding these changes are qualitatively analysed in the next section. They contain important insights for the understanding of the history of the nuisance alert problem.