Nov 2013 - CHG 1
The term alert is used in several different ways throughout the regulatory and guidance documents. In some cases, it is used as a general term to refer to a wide range of “normal”* pilot indications, such as annunciator switches indicating mode or operating status, as well as “non-normal” or more serious indications such as warnings, cautions, and advisories (see Table 4.1). In other regulatory and guidance documents, the term “alert” is used only to refer to indications of more serious or non-normal indications which require some type of immediate pilot action or awareness (see Table 4.2). The guidance in this chapter uses the term “alerts” in the most generic sense to cover all types of alerts, including warnings, cautions, and advisories, as well as messages and annunciations. All of these items are intended to attract the pilots attention, may take many forms (e.g., switches, lights, flags, prompts, or messages), and vary in their criticality. The terms warning, caution, and advisory are generally used consistently in regulatory and guidance material to refer to the following [Definitions excerpted from 14 CFR 25.1322]:
· Warning: For conditions that require immediate flightcrew awareness and immediate flightcrew response
· Caution: For conditions that require immediate flightcrew awareness and subsequent flightcrew response
· Advisory: For conditions that require flightcrew awareness and may require subsequent flightcrew response
Table 4.1. FAA regulatory and guidance material that appear to use the term alert in a general sense to refer to indications of both normal or non-normal conditions.
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FAA Regulatory and Guidance Material |
“Alert” Definition |
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AC 20-131A, Airworthiness and Operational Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders |
Indicator (aural or visual) which provides information to the flight crew in a timely manner about a converging aircraft or a potential collision. [4.d] |
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Advisory Circular AC 20-151A, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) Version 7.0 & 7.1 and Associated Mode S Transponders |
Indication (aural or visual) that informs the flight crew in a timely manner about converging aircraft or potential collision. [Appendix E, 1.d] |
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AC 20-138C, Airworthiness Approval of Positioning and Navigation Systems |
AC 20-138C does not specifically design the term “alert”, but the term appears to be used generically as in the example below: “Aircraft with ILS capability that is interfaced to GPWS or Class A TAWS (Mode 5 GPWS) alert for ILS deviations below the ILS glideslope must also include a glideslope alerting function during a GPS/SBAS LPV approach. It is desirable to provide an alerting function on any GPS/SBAS approach with vertical guidance.” [14-6.8.a] |
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Advisory Circular AC 23-18, Installation of Terrain Awareness |
Alert: A visual, aural, or tactile stimulus presented to either attract attention or convey information regarding system status or condition, or both. Aural Alert: A discrete sound, tone, or verbal statement used to annunciate a condition, situation, or event. [3.a-b] |
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Advisory Circular AC 25-23, Airworthiness Criteria for the Installation Approval of a Terrain Awareness and Warning System (TAWS) for Part 25 Airplanes |
Alert: A visual, aural, or tactile stimulus presented either to attract attention or to convey information regarding system status or condition, or both Aural Alert: A discrete sound, tone, or verbal statement used to enunciate a condition, situation, or event. [3.a-b] |
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TSO-C151c, Terrain Awareness and Warning System (TAWS) |
Alert: A visual, aural, or tactile stimulus presented to attract attention and convey information regarding system status or condition. Aural Alert: A discrete sound, tone, or verbal statement used to annunciate a condition, situation, or event. [2.2] |
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AC 27-1B, Certification of Normal Category Rotorcraft |
A visual or aural stimulus presented either to attract attention or to convey information regarding system status or condition, or both. [AC 27 MG 18.d(1); AC 29 MG 18.d(1)] |
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AC 29-2C Certification of Transport Category Rotorcraft |
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TSO-C146c /RTCA DO-229D |
For the definitions of missed alert, false alert, and time-to-alert, an alert is defined to be an indication that is provided by the GPS/SBAS equipment when the positioning performance achieved by the equipment does not meet the integrity requirements. This alert is one of the conditions that would cause a navigation alert. [1.7.3] |
Table 4.2. FAA regulatory and guidance material that use the term alert to refer only to indications of more serious or non-normal conditions.
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FAA Regulatory and Guidance Material |
“Alert” Definition |
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AC 25-11A, Electronic Flight Deck Displays |
A generic term used to describe a flight deck indication meant to attract the attention of and identify to the flightcrew a non-normal operational or airplane system condition. Warnings, Cautions, and Advisories are considered to be alerts. [Appendix 3] |
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AMC 25.1302, Installed Systems and Equipment for Use by the Flight Crew** |
A generic term used to describe a flight deck indication meant to attract the attention of the flight crew, and identify to them a non-normal operational or aeroplane system condition. Warnings, Cautions, and Advisories are considered to be alerts. (Reference definition in AMC 25.1322) |
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AC 25.1322-1, Flightcrew Alerting |
A generic term used to describe a flight deck indication meant to attract the attention of and identify to the flightcrew a non-normal operational or airplane system condition. Alerts are classified at levels or categories corresponding to Warnings, Cautions, and Advisories. Alert indications also include nonnormal range markings (for example, exceedences on instruments and gauges.) [Appendix 5] |
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AC 25.1329-1B, Approval of Flight Guidance Systems |
A generic term used to describe a flight deck indication meant to attract the attention of the flightcrew to a nonnormal operational or airplane system condition without implying the degree or level of urgency for recognition and corrective action by the crew. Warnings, cautions, and advisories are considered alerts. [Appendix 2] |
* AC 25.1322-1 defines “normal” conditions as “any fault-free condition typically experienced in normal flight operations. Operations are typically well within the airplane flight envelope and with routine atmospheric and environmental conditions” (AC 25.1322-1, Appendix 5).
** Note that AC 25.1302-1 does not define the term “alert”.