Policy
Statement
Subject: Low-Speed Alerting and/or
Protection
Date: Proposed
Policy No:
PS-ANM-25-16
Initiated By:
ANM-111
Summary
This policy statement clarifies and supplements the advisory material related to the means of
compliance with Title 14, Code of Federal Regulations (14 CFR) 25.1329(h). It is intended to
clarify the existing advisory material and to ensure that applicants understand all appropriate
design considerations that are related to low-speed alerting and protection. The low-speed
alerting and protection must comply with related regulations that ensure that the flightcrew is
aware of the low airspeed condition and can determine the appropriate actions, or that flight
guidance systems (FGSs) prevent significant unwanted airspeed excursions outside the range of
the normal flight envelope. Compliance with § 25.1329(h) and related regulations
(e.g., §§ 25.1322, Flightcrew alerting, and 25.1309, Equipment, systems, and installations)
should preclude a majority of situations that have contributed to low-speed incidents and
accidents.
This policy statement is necessary to address a safety vulnerability, as evidenced in the following
four recent incidents and accidents that involved the failure to maintain proper airspeed:
1) Thomsonfly Ltd, Boeing Model 737-300, near Bournemouth, United Kingdom on
September 23, 2007—This incident involved deceleration after the flightcrew did not
notice the autothrottle failure or the autothrottle disengagement. The flightcrew allowed
the airspeed to decrease 20 knots below Vref before they initiated recovery. After multiple
stick shaker activations and an aerodynamic stall, the flightcrew eventually regained
control, and the airplane landed safely.
2) Empire Airlines, Model ATR-42-300, in Lubbock, Texas on January 27, 2009—This
accident involved a deceleration to stick shaker and autopilot disconnect following a flap
anomaly. The probable cause was the flightcrew’s failure to monitor and maintain a
minimum safe airspeed while executing an instrument approach in icing conditions,
which resulted in an aerodynamic stall at low altitude.
3) Colgan Air, de Havilland Model DHC-8-400, in Clarence Center, New York on
February 12, 2009—This accident involved decelerating to a low speed, which activated
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the stall warning while on approach. The probable cause of this accident was the
captain’s inappropriate response to the activation of the stick shaker, which led to an
aerodynamic stall from which the airplane did not recover. The flightcrew’s failure to
monitor airspeed also contributed to this accident.
4) Turkish Air, Boeing Model 737-800, in Amsterdam, Netherlands on February 25, 2009—
This accident involved a radio altimeter anomaly that led to an inappropriate autothrottle
thrust reduction. The flightcrew failed to recognize the airspeed decay and the pitch
increase until the moment the stick shaker was activated. Subsequently, the
approach-to-stall recovery procedure was not executed properly, causing the airplane to
stall and crash.
Some of the airplanes in the cited incidents and accidents may have conformed to the guidance
for low-speed awareness cues in paragraph 2.3 of Appendix 1 of Advisory Circular (AC)
25-11A, Electronic Flight Deck Displays, dated June 21, 2007. However, these accidents and
incidents indicate that the current means for flightcrew speed awareness have been ineffective,
especially when accompanied with multiple flightcrew distractions. In each of the cases, the
flightcrew did not respond to the low-speed cues until stall warning. The flight guidance system
did not provide adequate protection in any of these cases. Analysis of the factors leading up to
the incidents have demonstrated the need for more robust protections or low-speed alerting
beyond those that have been historically provided. The addition of §§ 25.1329(h) and 25.1322 to
the regulations in recent years in conjunction with applying the guidance in this policy should
improve the effectiveness of low-speed alerting.
Definition of Key Terms
In the text below, the terms “must,” “should,” and “recommend” have a specific meaning that is
explained in the Attachment to this policy.
Current Regulatory and Advisory Material
The regulations applicable to low-speed protection and alerting are §§ 25.1329(h), 25.1322, and
25.1309(b)(2). These sections lay out the regulatory basis for the installation and approval of
low-speed protection and/or alerting systems within the FGS.
Section 25.1309(b)(2) states: “The airplane systems and associated components, considered
separately and in relation to other systems, must be designed so that the occurrence of any other
failure conditions which would reduce the capability of the airplane or the ability of the crew to
cope with adverse operating conditions is improbable.”
Section 25.1329(h) states: “When the flight guidance system is in use, a means must be provided
to avoid excursions beyond an acceptable margin from the speed range of the normal flight
envelope. If the airplane experiences an excursion outside this range, a means must be provided
to prevent the flight guidance system from providing guidance or control to an unsafe speed.”
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Section 25.1322 requires that flightcrew alerting provide information about non-normal
operation and appropriate reactions. It further provides requirements for the various types
(e.g., warnings, cautions, and advisories) and characteristics of alerts.
Section 25.1329(h) was introduced with Amendment 25-119. It pertains to the FGS, which
includes the functions of autopilots, flight directors (FDs), and automatic thrust control.
Section 25.1329 also addresses both fully automatic and combined automatic-manual flight using
any portion of the FGS (i.e., autopilot, FD, or automatic thrust control). The remaining manual
flight scenarios (those not covered by § 25.1329) are generally covered by the use of stick force
gradients that deter further speed decreases, or by the use of flight envelope protection features
of the primary flight control system.
Section 25.1322 provides the criteria that alerts must meet. It was revised with
Amendment 25-131. This amendment is a substantial update of previous alerting requirements to
include requirements for alerts that are readily and easily detectable and intelligible by the
flightcrew under all foreseeable operating conditions and timely attention-getting cues through at
least two different senses.
AC 25.1329-1B, Change 1, Approval of Flight Guidance Systems, dated October 16, 2012;
AC 25.1322-1, Flightcrew Alerting, dated December 13, 2010; and AC 25-11A; provide
guidance on this subject.
Relevant Past Practice
Before Amendment 25-119 (effective May 11, 2006) was added to the regulations, low-speed
protection and/or alerting other than stall warning was not specifically required during automatic
flight, and stall warnings were considered to provide adequate protection. However, with the
adoption of Amendment 25-119, protection against low airspeed excursions is now required
whenever the FGS (which includes the autopilot, FD, and autothrust functions) is in use.
When the FGS is in use, a means must be provided to avoid excursions beyond an acceptable
margin from the speed range of the normal flight envelope. If the airplane experiences an
excursion outside this range, the FGS must not provide guidance or control to an unsafe speed.
The phrase “to an unsafe speed” is intended to mean that the FGS should not control or provide
guidance that would eventually lead to an aerodynamic stall (or even to a stall warning) or a
speed that is in excess of the maximum operating speed, regardless of the maneuver being
conducted at the time.
Section 25.1329(h) is intended to eliminate unwanted airspeed excursions, through automatic
FGS control or through alerting the flightcrew. The preferred implementation is for the FGS to
automatically provide control and/or guidance to avoid these excursions. However, an acceptable
means of compliance with § 25.1329(h) may also be to implement an alert to increase the
flightcrew’s awareness, recognition, and ability to intervene when a potential airspeed excursion
occurs. AC 25.1329-1B provides guidance for several methods of implementing such an alert.
Previous accidents have shown that visual alerts alone with no accompanying aural alert have
been ineffective in ensuring flightcrew awareness of low airspeed excursions. Therefore, an aural
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alert is considered an essential aspect of any alerting intended to show compliance with
§ 25.1329(h).
In addition to § 25.1329(h), other changes to part 25 also relate to the issue of low-speed
alerting:

Amendment 25-121 (effective October 9, 2007) revised the majority of subpart B to
mandate more stringent requirements for performance and handling qualities in icing
conditions. Stall warning, as part of the Amendment 25-121 package, must meet the
new regulatory margins specified in § 25.207, Stall warning, for flight in icing
conditions. Although these stall warning requirements are not “low-speed alerting,”
they are functionally similar since they increase the warning margin for flight in icing
conditions.

Amendment 25-131 (effective January 3, 2011) introduced new and updated
regulatory requirements for flightcrew alerting (§ 25.1322), as well as new flightcrew
alerting guidance material and definitions (AC 25.1322-1).
The combination of these new regulatory requirements affects the low-speed protection and/or
alerting requirement of § 25.1329(h) because they provide additional, more specific
requirements. This policy statement clarifies and supplements existing guidance on the subject.
In addition to the policy considerations described above, the reliability requirements of
§ 25.1309(b)(2) apply to low-speed alerting and protection systems. According to that regulation,
failure conditions that would reduce the ability of the crew to cope with adverse operating
conditions must be improbable. A low-speed excursion is an example of this type of adverse
operating condition. This may not be clearly understood from previous guidance.
The FAA’s analysis shows that adherence to the contents of the regulatory and guidance material
outlined in this policy statement likely could have prevented the situations that led to the
incidents and accidents previously described. In 2011, the Aviation Rulemaking Advisory
Committee working group was tasked to provide information to use to develop standards and
guidance material for low speed alerting. The FAA initiated rulemaking activity. However, after
further review, the FAA determined that the combination of current existing regulations and
guidance could provide adequate protection.
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Policy
To improve the effectiveness of low-speed alerting, this policy is intended to clarify design
considerations related to the low-speed alerts and protection requirements. In addition to
applying the guidance provided in AC 25.1329-1B, AC 25.1322-1, and AC 25-11A, an airplane
that has Amendments 25-119, 25-121, and 25-131 in its certification basis must satisfactorily
address the following regulations for low-speed alerts and/or protection:
1.
Alerts for Excursions Outside Acceptable Margins.
If a low-speed alert is used as the means of compliance with § 25.1329(h), the alert should
ensure that the flightcrew is immediately aware of any excursions beyond an acceptable
margin from the speed range of the normal flight envelope. In accordance with
§ 25.1322(b), this alert must be a caution or a warning. Since automatic flight control
presupposes that the flightcrew will not have their hands on the controls, aural and visual
indications are presumably the essential attention-getting senses required by
§ 25.1322(c)(2). In addition, the alert should be time-critical for warnings and for cautions,
and be consistent with the elements of the related time-critical warning in accordance with
AC 25.1322-1.
2.
Reliability of Protection/Alerts.
The reliability of the low-speed protection or alert required by § 25.1329(h) must meet the
requirement of § 25.1309(b)(2). Failure of the low-speed protection or alert required by
§ 25.1329(h), which would reduce the capability of the airplane or the ability of the crew to
cope with adverse operational conditions, must be improbable.
3.
Icing Conditions.
If certification is for flight in icing conditions, the low-speed protection or alert should also
meet § 25.1329(h) in 14 CFR appendix C icing conditions. In addition, the low-speed
protection or alert should meet the criteria stated in items 1 and 2 in this policy for
appendix C icing conditions.
Effect of Policy
The general policy stated in this document does not constitute a new regulation. Agency
employees and their designees and delegations must not depart from this policy statement
without appropriate justification and concurrence from the FAA management that issued this
policy statement. The authority to deviate from this policy statement is delegated to the
Transport Standards Staff Manager.
Whenever a proposed method of compliance is outside this established policy, the project aircraft
certification office has to coordinate it with the policy issuing office using an issue paper.
Similarly, if the project aircraft certification office becomes aware of reasons that an applicant’s
project should not be approved even if its proposal meets this policy, the office must coordinate
its response with the office that issued this policy. Applicants should expect that certificating
officials would consider this information when making findings of compliance relevant to new
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certificate actions. In addition, as with all guidance material, this policy statement identifies one
means, but not the only means, of compliance.
Implementation
This policy discusses compliance methods that should be applied to new type certificate,
amended type certificate, supplemental type certificate, and amended supplemental type
certification programs. This policy applies to new designs and to significant changes to existing
designs, unless an exception can be shown in accordance with § 21.101(b)(2) or § 21.101(b)(3).
The compliance methods apply to those programs with an application date that is on or after the
effective date of the final policy. If the date of application precedes the effective date of the final
policy, and the methods of compliance have already been coordinated with and approved by the
FAA or its designee, the applicant may choose to either follow the previously acceptable
methods of compliance or follow the guidance contained in this policy.
Conclusion
The FAA has concluded that it is necessary to clarify the policy on low-speed alerting and/or
protection items. This policy statement provides new guidance on the recommended steps to
address low-speed alerting and/or protection. If other data were to be presented that
demonstrated otherwise, the FAA might reconsider the intent and content of this policy.
END
Attachment
Attachment
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Terms
Table A-1 defines the use of key terms in this policy statement. The table describes the
intended functional impact.
Table A-1 Definition of Key Terms
Regulatory
Requirements
Acceptable Methods of
Compliance (MOC)
Recommendations
Recommend
Language
Must
Should
Meaning
Refers to a regulatory
requirement that is
mandatory for design
approval
Refers to instructions for Refers to a
a particular MOC
recommended
practice that is
optional
Functional
Impact
No Design Approval
if not met
Alternative MOC has to
be approved by issue
paper
None because it is
optional