Hubbry Logo
Stick shakerStick shakerMain
Open search
Stick shaker
Community hub
Stick shaker
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Stick shaker
Stick shaker
Stick shaker
View on Wikipedia
from Wikipedia

The BAC-111 cockpit includes a stick shaker/pusher following its 1963 crash

A stick shaker is a mechanical device designed to rapidly and noisily vibrate the control yoke (the "stick") of an aircraft, warning the flight crew that an imminent aerodynamic stall has been detected. It is typically present on the majority of large civil jet aircraft, as well as most large military planes.

The stick shaker comprises a key component of an aircraft's stall protection system. Accidents, such as the 1963 BAC One-Eleven test crash, were attributable to aerodynamic stalls and motivated aviation regulatory bodies to establish requirements for certain aircraft to be outfitted with stall protection measures, such as the stick shaker and stick pusher, to reduce such occurrences. While the stick shaker has become relatively prevalent amongst airliners and large transport aircraft, such devices are not infallible and require flight crews to be appropriately trained on their functionality and how to respond to their activation. Several instances of aircraft entering stalls have occurred even with properly functioning stick shakers, largely due to pilots reacting improperly.

History

[edit]

When many small aircraft approach the critical angle of attack that will result in an aerodynamic stall, the smooth flow of air over the wings is interrupted, causing turbulent airflow at the trailing edge of the wings. Depending on the aircraft size or design, that turbulent air, known as buffet, typically impacts the elevator at the rear end of the aircraft, and that in turn causes vibrations that are transmitted through control cables and can be felt by the pilot on the yoke as violent shaking. This natural shaking of the control yoke serves as an early warning to pilots that a stall is developing.

For very large aircraft, fly-by-wire aircraft and some aircraft with complex tail designs, there is no buffet effect on the control yoke, because the turbulent air does not reach the elevator, or because any movement in the elevator from buffet is not transmitted back to the control yoke. This deprives pilots of these aircraft of one of the important early warnings that they are about to enter a stall.[citation needed]

Boeing aircraft designers were the first to solve this problem by creating a mechanical device, which they named a stick shaker, that shakes the control yoke in a similar way to how a yoke is shaken naturally in smaller aircraft as the aircraft approaches its critical angle of attack.[citation needed]

Stick shakers were being developed as early as 1949.[1]

During 1963, a BAC One-Eleven airliner was lost after having crashed during a stall test. The pilots pushed the T-tailed plane past the limits of stall recovery and entered a deep stall state, in which the disturbed air from the stalled wing had rendered the elevator ineffective, directly leading to a loss of control and crash.[2] As a consequence of the crash, a combined stick shaker/pusher system was installed in all production BAC One-Eleven airliners. A wider consequence of the incident was the instatement of a new requirement related to the pilot's ability to identify and overcome stall conditions; a design of transport category aircraft that fails to comply with the specifics of this requirement may be acceptable if the aircraft is equipped with a stick pusher.[3][4]

Following the crash of American Airlines Flight 191 on 25 May 1979, the Federal Aviation Administration (FAA) issued an airworthiness directive, which mandated the installation and operation of stick shakers on both sets of flight controls on most models of the McDonnell Douglas DC-10, a trijet airliner. (Previously, only the captain's controls were equipped with a stick shaker on the DC-10; in the case of Flight 191, this single stick shaker had been disabled by a partial electrical power failure early in the accident sequence.)[5] In addition to regulatory pressure, various aircraft manufacturers have endeavoured to devise their own improved stall protection systems, many of which have included the stick shaker.[6] The American aerospace company Boeing had designed and integrated stall warning systems into numerous aircraft that it has produced.[7][8]

A wide range of aircraft have incorporated stick shakers into their cockpits.[8] Textron Aviation's Citation Longitude business jet is one such example,[8] as is the Pilatus PC-24 light business jet,[9] and Bombardier Aviation's Challenger 600 family of business jets.[10] Commercial airliners such as the newer models of the Boeing 737, the Boeing 767, and the Embraer E-Jet E2 family have also included stick shakers in the aircraft's stall protection systems.[11][12][13]

Function in stall protection systems

[edit]

The stick shaker is a major element of an aircraft's stall protection system. The system is composed of fuselage or wing-mounted angle of attack (AOA) sensors that are connected to an avionics computer, which receives inputs from the AOA sensors along with a variety of other flight systems. When this data indicates an imminent stall condition, the computer actuates both the stick shaker and an auditory alert.[8] The shaker itself is composed of an electric motor connected to a deliberately unbalanced flywheel. When actuated, the shaker induces a forceful, noisy, and entirely unmistakable shaking of the control yoke. This shaking of the control yoke matches the frequency and amplitude of the stick shaking that occurs due to airflow separation in low-speed aircraft as they approach the stall. The stick shaking is intended to act as a backup to the auditory stall alert, in cases where the flight crew may be distracted.[8]

Stick pusher

[edit]

Other stall protection systems include the stick pusher, a device that automatically pushes forward on the control yoke, commanding a reduction in the aircraft's angle of attack and thus preventing the aircraft from entering a full stall. In the majority of circumstances, the stick pusher will not activate until shortly after the stick shaker has given its warning of near-stall conditions being detected, and will not activate if the flight crew have performed appropriate actions to reduce the likelihood of stalling by lowering the angle of attack.[4][8] Under most regulatory regimes, an aircraft's stall protection systems must be tested and armed prior to takeoff, as well as remain armed throughout the flight; for this reason, startup checklists normally include performing such tests as a matter of routine.[8]

Audio

[edit]

The vibration of the stick shaker is loud enough that it can be commonly heard on cockpit voice recorder (CVR) recordings of aircraft that have encountered stall conditions. This level of vigorous movement is intentional, the stick shaker having been designed to be impossible to ignore.[8] To unfamiliar flight crews, the stall warning system can be viewed as aggressive and impatient, hence why it has become commonplace for the system to be introduced to trainee pilots via a flight simulator rather than a live aircraft. To fly without them would increase the likelihood of the aircraft encountering, and improperly responding to, a stall event.[8]

Flight crew factor

[edit]

During the 2000s, there was a series of accidents that were attributed, at least in part, to their flight crews having made improper responses to the activation of the stall warning systems.[4][14] During the early 2010s, in response to this wave of accidents, the FAA issued guidance urging operators to ensure that flight crews are properly training on the correct use of these aids.[15][16]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Stick shaker

View on Grokipedia
from Grokipedia
A stick shaker is a mechanical device installed in many modern that rapidly vibrates the control column or to provide a tactile and audible warning to pilots of an impending aerodynamic , typically activating when the angle of attack approaches a critical value. This vibration simulates the natural buffeting experienced near conditions, ensuring pilots receive an unmistakable cue to reduce the angle of attack and avoid a loss of lift. The stick shaker operates as part of an aircraft's stall warning system, relying on sensors such as angle-of-attack (AOA) vanes mounted on the to detect changes in . When the AOA exceeds a predetermined threshold below the stall angle, an equipped with an offset flyweight or eccentric cam engages, producing high-amplitude, low-frequency oscillations on the control yoke. This activation occurs before the actual , providing pilots with time to apply corrective inputs like lowering the nose or increasing power, and it often accompanies other warnings such as aural horns or lights. Developed decades ago by engineers to address the limitations of relying solely on natural aerodynamic cues in high-speed jets, the stick shaker has become a standard feature in commercial and military aircraft, including models from , , and business jets like the Textron Citation series. It works in tandem with related systems, such as the , which automatically forces the control column forward if the warning is ignored, further preventing stalls in scenarios like high-altitude upsets or icing conditions. While highly reliable, the device can sometimes activate due to faulty AOA sensor data, as seen in certain flight incidents, underscoring the importance of pilot training to interpret and respond appropriately.

Definition and Purpose

Overview

A stick shaker is a mechanical device installed in aircraft that rapidly vibrates the control yoke or to provide pilots with a tactile and auditory warning of an impending aerodynamic . This vibration simulates the natural pre-stall buffeting experienced in older or simpler designs, ensuring pilots receive clear cues even when aerodynamic feedback is diminished. The primary purpose of the stick shaker is to alert the flight crew to a critically high (AOA), prompting an immediate reduction in AOA to prevent a full . In modern aircraft, natural stall warnings like buffeting may be absent or delayed due to advanced aerodynamic features, such as swept wings that alter progression or systems that filter control inputs and maintain stability. Unlike inherent aerodynamic cues, the stick shaker delivers a distinct, synthetic signal that integrates with broader protection systems for enhanced safety. While common in many commercial and , stick shakers are primarily equipped on commercial jet airliners like the , regional jets such as the ERJ series, transports, and select aircraft with advanced , where reliable stall detection is essential for operations at high altitudes or in varied configurations. Some designs, such as certain models, use alternative aural warnings instead.

Role in Stall Warning

The stick shaker serves as a primary haptic cue within the stall warning hierarchy of modern aircraft, activating to vibrate the control column and alert pilots to an impending aerodynamic . This typically engages at a speed 5 to 10 knots above the speed, providing a critical margin for recovery by prompting immediate corrective action before the wing's critical angle of attack is exceeded. In the sequence of stall protection, it functions alongside aural alerts and visual indicators, offering a tactile warning that is particularly effective when pilots are focused on other tasks, ensuring the signal cannot be overlooked. By delivering an unambiguous and intense vibration, the stick shaker significantly enhances aviation safety, especially during high-workload phases such as final approach or in adverse conditions like airframe icing, where subtle aerodynamic cues might otherwise go unnoticed. It reduces the risk of inadvertent stalls by simulating the natural pre-stall buffeting familiar to pilots of smaller aircraft, thereby fostering instinctive responses that prevent escalation to full stall or loss of control. This preventive role is vital in scenarios where pilot attention is divided, contributing to fewer stall-related incidents overall. In aircraft designs where natural stall buffeting is diminished—such as those with T-tails or high-bypass engines—the stick shaker compensates by artificially replicating the sensory feedback of separation, ensuring pilots receive a clear warning regardless of configuration. This adaptation addresses the limitations of aerodynamic cues in advanced jet transports, where propwash or engine placement might otherwise mask impending stalls. The widespread adoption of stick shakers, mandated by FAA regulations such as 14 CFR 25.207 since the 1960s for certified transport-category aircraft, has played a key role in lowering incident rates by standardizing reliable warning systems across the fleet. These requirements demand clear warnings at least 5 knots above speed and have contributed to improved safety outcomes.

Technical Operation

Mechanism and Components

The stick shaker is primarily composed of an equipped with an offset flyweight or eccentric mass, which is mounted at the base of the control column or . This motor drives the eccentric mass to generate through rapid , creating an unbalanced that shakes the control . Some designs incorporate electromagnetic solenoids to facilitate quick oscillations, enhancing the shaking mechanism in certain configurations like knocker-style shakers. The device produces vibrations at a frequency of approximately 25-27 Hz, simulating the natural buffet of an approaching and alerting the pilot through tactile feedback on the . This shaking persists until the angle of attack decreases below the activation threshold, as determined by inputs from angle-of-attack sensors. In multi-crew aircraft such as the Boeing 737, dual stick shaker units are installed—one for the captain's yoke and one for the first officer's—to ensure independent warnings for each pilot. For general aviation aircraft, designs emphasize lightweight construction, often utilizing compact vibration motors that clamp directly onto the control stick or yoke to minimize added weight and simplify integration. Stick shakers are typically powered by the aircraft's 28 V DC electrical system, drawing from dedicated s to ensure reliable operation. To enhance reliability and prevent persistent false activations from malfunctions, systems include provisions allowing pilot-initiated disengagement, such as through pull or dedicated switches, thereby avoiding distraction during non-stall conditions.

Activation and Sensors

The stick shaker system relies on angle of attack (AOA) sensors, typically vane-type probes or heated sensors mounted on the or wings, to detect the incidence of airflow relative to the aircraft's wing chord line. These sensors provide real-time AOA data, often with redundancy through multiple units (e.g., two independent sensors per side on the ) to enable voting logic that ensures reliability and prevents erroneous activation from a single sensor failure. The sensor outputs are integrated with air data computers, which process AOA alongside parameters such as , altitude, and configuration to compute margins accurately. Activation occurs when the computed AOA exceeds a predetermined threshold, typically 5 to 10 degrees below the critical AOA for the current flight condition, providing a margin before actual . This threshold equates to activation at least 5 knots or 5% above the reference speed (V_SR), whichever is greater, during deceleration at rates up to 1 knot per second. In aircraft, software algorithms dynamically adjust these margins based on real-time inputs, incorporating to avoid oscillatory and deactivation near the threshold. Redundant voting requires agreement from multiple sources before triggering, mitigating single-point failures. The system accounts for environmental and operational factors by modulating thresholds according to configuration, such as flaps and positions, which alter characteristics. Adjustments also consider weight and loading effects on speed, as well as potential icing contamination on sensors or airfoils, which can reduce the effective margin and necessitate heated probes or separate icing-mode logic to maintain warning reliability. Deactivation happens automatically when AOA drops below the threshold, restoring normal control column feel without pilot intervention unless overridden.

History and Development

Early Innovations

The stick shaker was conceptualized in the late as a tactile warning designed to replicate the natural aerodynamic buffeting that occurs during an approaching , providing pilots with an intuitive alert in where visual or aural cues alone might prove inadequate. This approach addressed the limitations of earlier indicators by delivering a physical through the control column, enhancing pilot situational awareness during critical low-speed maneuvers. In 1951, inventor Leonard M. Greene secured U.S. No. 2,566,409 for a vibratory alarm , which employed an driving an eccentric weight to induce controlled shaking of the control stick upon activation by a pre- sensor. The , filed in 1949, described a compact mechanism mounted directly on the control stick shaft, emphasizing reliability and minimal interference with normal flight controls. Early testing of stick shaker prototypes began in the late , coinciding with the , and extended into the early with evaluations on fighter jets to assess vibration efficacy and pilot response under dynamic conditions. These experiments, including those conducted by the U.S. Navy, focused on integrating the device into high-performance aircraft to mitigate risks during aggressive maneuvers. By the mid-, the technology advanced to incorporation in prototype transport aircraft, facilitating broader validation of its role in safety. A pivotal milestone came in when a prototype crashed during recovery tests near Chicklade, , entering an unrecoverable deep that killed all seven aboard and exposed vulnerabilities in existing . The , attributed to blanking and insufficient warning, accelerated refinements to stick shaker designs, including optimizations to vibration intensity for more assertive alerting and enhancements to sensor reliability for consistent activation across flap configurations. These improvements directly informed subsequent iterations, prioritizing operation in transport-category jets. Among the pioneering aircraft to feature stick shakers were post-modification models, which received the system alongside stick pushers following the 1963 incident to prevent deep stalls, and early 707 variants, where it served as a core element of the stall warning suite from the late onward. These installations marked the device's shift from experimental tool to standard safety feature in jet airliners, influencing future regulatory requirements for stall protection.

Regulatory Adoption

The adoption of stick shakers as a primary means of stall warning in was driven by evolving regulatory frameworks aimed at enhancing safety, particularly following the introduction of (FAR) Part 25 in 1965, which established standards for transport-category airplanes. The key provision, FAR 25.207, mandates clear and distinctive warnings with sufficient margin to prevent inadvertent stalling, typically requiring activation at least 5 knots or 5% above speed, and has been interpreted to include artificial systems like stick shakers for lacking natural aerodynamic cues. Similarly, the Joint Aviation Requirements (JAR-25), harmonized with FAR Part 25 since the 1970s and predecessor to the () (CS-25, initial issue 2003), impose equivalent requirements under CS 25.207, specifying measures such as stick shakers or aural alerts to ensure reliable detection across various configurations, including icing conditions. These mandates solidified by the mid-1970s, compelling manufacturers to integrate stick shakers into designs for compliance in certified . Industry-wide adoption accelerated in the as stick shakers became a standard feature in new jetliners to meet these regulations, exemplified by the , which entered service in 1970 with an integrated stick shaker system as part of its protection suite. For experimental and amateur-built aircraft, accessibility improved with the 2014 introduction of the SWZL-1A by MakerPlane and Vx Aviation, a low-cost, haptic stick shaker designed for easy integration with angle-of-attack sensors, marking the first such pre- warning device tailored for non-certified platforms. Recent developments reflect ongoing refinement and market expansion, with the global stick shaker and pusher systems market valued at $1.14 billion in 2024, driven by demand for advanced in both commercial and sectors. In 2025, the FAA issued an Airworthiness Directive for certain Model BD-100-1A10 airplanes to address potential erroneous angle-of-attack data that could trigger unintended stick shaker activations, requiring software updates to mitigate flightcrew distraction and enhance reliability. Regulatory requirements vary by aircraft category: stick shakers are effectively mandatory for transport-category airplanes under FAR/CS-25 to provide the prescribed stall margins, whereas they remain optional under FAR Part 23 for but are increasingly common in advanced designs, such as the 2024 Cirrus SR Series G7, which incorporates a first-in-class yoke-vibrating stick shaker for improved low-speed awareness in certified single-engine piston aircraft.

Stick Pusher

The stick pusher is a safety device installed in certain fixed-wing aircraft to prevent aerodynamic stall by actively intervening in the flight controls. It functions as a hydraulic or electro-mechanical actuator that forcibly applies forward pressure on the control column or elevator system when the aircraft's angle of attack (AOA) approaches a critical value, thereby reducing the AOA and incidence to avert stall entry. This proactive mechanism contrasts with the stick shaker's reactive warning function, which provides tactile and aural alerts of an impending stall; the pusher activates shortly after the shaker if the pilot does not initiate recovery, ensuring prevention rather than mere notification. Key components of the stick pusher include linear actuators mechanically linked to the controls, which extend to push the column forward. These actuators are typically powered by the aircraft's hydraulic system for primary operation, with redundant electric modes using servo motors or pitch servos to maintain functionality in case of hydraulic failure. The system relies on inputs from sensors, air data computers, and sometimes flap or load factor monitors to determine activation thresholds, ensuring reliable response across flight configurations. Stick pushers are particularly standard in T-tail aircraft designs, such as the ATR series and Embraer regional jets (e.g., ERJ and E-Jet families), where the horizontal stabilizer's position increases susceptibility to deep stalls that can blank the elevators. In these applications, the pusher delivers a forward force of up to approximately 80-100 pounds on the control column, sufficient to lower the nose while allowing the pilot to override if necessary. This intervention is sequenced to follow stick shaker activation, providing a brief window for pilot correction before automatic action.

Other Stall Indicators

Aural warnings serve as essential auditory alerts in stall protection systems, typically manifesting as horns or synthetic voice announcements like "Stall, !" that activate at a predetermined , generally 5 to 10 degrees below the critical stall to provide advance notice. These systems reduce ambiguity in high-workload scenarios by prioritizing stall alerts over other cautions, ensuring pilots receive clear, unambiguous cues during approach to stall conditions. Visual indicators complement aural and tactile warnings by providing direct displays of proximity, including dedicated warning lights, messages on the Engine Indicating and Crew Alerting System (EICAS) such as "AIRSPEED LOW" in aircraft, and angle-of-attack (AOA) gauges featuring color-coded zones—often for caution and for imminent . AOA indicators, in particular, offer pilots a real-time graphical representation of relative to airflow, enhancing across various configurations like takeoff or landing. In contemporary aircraft, integrated envelope protection systems expand safeguards beyond isolated indicators; for instance, Airbus's Alpha Floor mode automatically commands maximum (TOGA) thrust upon detecting low-energy states or excessive AOA, thereby preventing entry while coordinating with auto-throttle and other warnings in normal law operation. This feature, introduced on the A320 family, maintains aircraft energy margins during maneuvers like encounters, ensuring seamless integration with primary cues. Before the development of mechanical stick shakers in the mid-20th century, vintage aircraft depended on inherent aerodynamic phenomena for stall detection, primarily pre-stall buffeting—a vibration from airflow separation over the wings that pilots could sense through the airframe or controls, often occurring just prior to full stall. These natural cues, while effective in lighter general aviation planes, were less reliable in larger or higher-speed transports, prompting the evolution toward engineered warning devices.

Human Factors

Pilot Training and Response

Pilot training for stick shaker activation emphasizes standardized protocols to ensure rapid recognition and execution of stall recovery procedures, as outlined in FAA (AC) 120-109A. Training requirements include simulator sessions using Level C or higher full flight simulators (FFS) for hands-on practice of full stall demonstrations, where pilots learn to ignore non-critical distractions and focus solely on the core recovery steps of reducing (AOA) through nose-down pitch, followed by power application. These sessions, mandated under 14 CFR § 121.423(c) for operators of transport-category airplanes, prioritize the "nose low, power up" principle to minimize altitude loss during recovery. The standard response procedure upon stick shaker activation involves immediately disconnecting the and , applying gentle nose-down pitch to reduce AOA until the shaker ceases, rolling wings level, and then applying thrust as needed to regain speed without excessive power that could induce secondary stalls. This sequence ensures wings-level flight and a smooth return to the desired flight path, with the shaker's persistent vibration providing clear auditory and tactile cues for prompt recognition. Skill development in shifts focus from traditional monitoring to AOA awareness, teaching pilots that onset depends primarily on AOA rather than , which can vary with configuration and conditions. Recurrent , required for initial, transition, upgrade, and ongoing proficiency under 14 CFR § 121.418, incorporates scenarios such as high-altitude s and operations in icing conditions to build proficiency in diverse environments. Such programs integrate briefly with calls to confirm recovery actions without shifting primary focus from individual pilot execution. Proper training has demonstrated effectiveness in enhancing pilot responses, with studies indicating improved recognition and execution that contribute to safer stall recoveries by prioritizing AOA reduction over other factors.

Crew Considerations

In multi-crew operations, effective integration of Crew Resource Management (CRM) principles is essential during stick shaker activation to foster shared situational awareness and coordinated response. Standard callouts, such as the pilot not flying (PNF) announcing "Stall" or "Stall warning" upon shaker onset, prompt the pilot flying (PF) to confirm with "Check, recovering" while initiating recovery actions. The PNF's role as pilot monitoring includes verifying angle of attack (AOA) data through cross-checking instruments like pitch-limit indicators or raw flight parameters, ensuring discrepancies from sensor faults do not mislead the crew. Workload challenges can exacerbate delays in recognizing stick shaker cues, particularly in autopilot-engaged flight or turbulent conditions where is divided among multiple tasks. Distractions from communications or configuration changes may lead to overlooked reductions, while false activations due to erroneous AOA sensor inputs—such as icing or electrical faults—can create confusion and increase . In such scenarios, the PNF's proactive monitoring of speed and attitude helps mitigate task saturation by verbalizing deviations, like "Speed, speed," to refocus the PF. Fatigue further compounds error risks in multi-crew environments, with studies indicating higher misresponse rates to critical warnings like stick shaker in fatigued teams due to degraded vigilance and slower decision-making. Extended duty periods or circadian disruptions impair the crew's ability to integrate shaker feedback with other cues, potentially leading to persistent high AOA despite activation. To counter these factors, pre-flight briefings should emphasize stick shaker persistence as a reliable indicator, even amid anomalies, and outline override procedures for verified false activations, such as disengaging the system only after AOA confirmation. Task-sharing protocols, including PNF-led execution and mutual fatigue checks, promote workload distribution, while leveraging automation like flight directors during non-critical phases preserves mental reserves for shaker events.

Notable Incidents

Historical Accidents

One of the earliest significant incidents highlighting deficiencies in stall warning systems occurred on , 1963, when a 200AB (registration G-ASHG) crashed during a stall recovery test near Chicklade, , . The aircraft, on its 53rd test flight with only 81 hours of operation, was conducting stability and handling evaluations at 16,000 feet with 8 degrees of flaps extended when it entered a stable deep condition from which recovery proved impossible, resulting in a high vertical descent speed, near-horizontal attitude, and minimal forward speed. All seven occupants, including test pilot Mike Lithgow, were killed, and the aircraft was destroyed. The lack of an effective tactile stall warning contributed to the inability to avert the deep , as the prototype relied on inadequate cues during the test; this tragedy motivated aviation authorities to mandate enhanced stall warning devices, including stick shakers, to simulate buffeting and provide pilots with clearer pre- indications. In the pre-stick shaker era of the 1950s, early accidents frequently demonstrated the limitations of relying solely on visual, aural, or natural buffeting cues for avoidance, as high-speed operations often masked impending s until recovery margins were minimal. These incidents underscored the value of buffeting technologies like the emerging stick shaker, which by mid-decade was being tested to provide consistent pre- vibrations approximately 20 knots above speed, regardless of attitude or configuration, thereby reducing surprise s in swept-wing jets. A more modern pre-2000 example of stick shaker limitations under adverse conditions took place on October 31, 1994, involving , an ATR 72-210 (N401AM), which crashed near , after encountering severe in-flight icing during a holding pattern at 10,000 feet. The aircraft, en route from to , flew into supercooled large droplet (SLD) conditions with droplets up to 2,000 microns—far exceeding the certification limits of 5-50 microns under 14 CFR Part 25, Appendix C—leading to ice accretion aft of the de-icing boots on the wings. This formed ridges up to 1 inch high, causing airflow separation, uncommanded aileron hinge moment reversal, and a rapid roll excursion beyond pilot recovery capability, even as the stick shaker activated at angles of attack around 5.2 degrees (vane AOA) or 11-12.5 degrees depending on flap settings. Despite the crew's activation of anti-icing systems and attempts to maintain control, the upset occurred at airspeeds well above stall (e.g., 175-184 KIAS), resulting in a loss of control, structural breakup at low altitude, and the deaths of all 68 people on board. These historical accidents revealed critical vulnerabilities in stall warning reliability, particularly emphasizing the necessity for heated or anti-iced angle-of-attack (AOA) probes to prevent icing from false or delayed stick shaker activations in SLD environments, as unprotected probes in the ATR were overwhelmed by supercooled droplets. They also highlighted the need for in shaker systems and enhanced standards for icing beyond Appendix C, prompting recommendations for improved AOA sensitivity, pilot training on SLD encounters, and operational limits in aircraft flight manuals to mitigate unrecoverable s.

Modern Events

In the 2009 crash of , a Bombardier Q400 encountered supercooled large droplets during approach to Buffalo-Niagara International Airport in icing conditions, leading to ice accumulation on the and erroneous activation of the stick shaker warning. The captain responded inappropriately by pitching up, exacerbating an aerodynamic that resulted in the aircraft crashing into a residence in , killing all 49 people on board and one on the ground. This incident, investigated by the (NTSB), highlighted vulnerabilities in pilot response to stick shaker cues amid fatigue and icing, ultimately prompting the FAA to implement stricter pilot fatigue regulations through the Airline Safety and Federal Aviation Administration Extension Act of 2010. A 2017 incident involving Flight 29, a operating from to , saw the stick shaker activate repeatedly during a holding pattern on approach due to aerodynamic warnings triggered by high angle-of-attack conditions. The activations, accompanied by multiple stick pusher engagements, occurred amid atmospheric , causing the to experience significant pitch oscillations and injuring 15 passengers, one of whom required hospitalization. The Australian Transport Safety Bureau (ATSB) investigation emphasized the need for enhanced disengagement protocols and recovery training, leading to revise its pilot procedures for such events. The 2023 crash of , an ATR 72-500 approaching , involved the pilot monitoring inadvertently feathering both propellers by pulling the wrong levers on the center pedestal, mistaking them for the flap extension controls. This sudden loss of caused a rapid increase in , activating the stick shaker at 311 feet above ground level as a stall warning, but the crew's delayed recognition and inaction prevented recovery, resulting in the aircraft stalling and crashing shortly after, with all 72 people on board fatalities. Nepal's Aircraft Accident Investigation Commission final report identified human error in lever selection as the primary cause, underscoring persistent challenges with interface design in regional turboprops. In contrast, a 2023 bird strike incident on Flight 984, a 737-900ER en route from to , demonstrated effective system resilience when the stick shaker activated during approach to Hartsfield-Jackson Atlanta International Airport following a bird strike that damaged the , causing erroneous indications. The crew maintained control, executed a , and landed safely without injuries or further anomalies, as confirmed by databases tracking the event. This case illustrated the stick shaker's role in providing timely warnings that pilots could address amid transient disruptions. On July 24, 2024, Saurya Airlines Flight (ferry flight), a CRJ-200ER (9N-AME), crashed shortly after takeoff from , , due to an aerodynamic stall caused by improper weight and balance, overweight conditions, and configuration errors. The stick shaker activated multiple times starting about 3 seconds after liftoff at 11 feet altitude, but the crew's inputs led to a loss of control, resulting in 18 fatalities out of 19 on board. 's investigation highlighted deficiencies in oversight, loading procedures, and pilot response to stall warnings. On August 9, 2024, Voepass Flight 2283, an ATR 72-500, crashed near Vinhedo, , after entering a flat spin due to severe in-flight icing during descent in , killing all 62 on board. Preliminary investigation found that ice accumulation on the wings and tail led to an aerodynamic stall, but the stick shaker and other stall warnings did not activate, possibly due to the rapid onset or sensor limitations in supercooled large droplet icing. This incident renewed focus on icing certification and warning system reliability in adverse weather. From 2000 to 2025, stick shaker incidents have shown a trend toward increased false activations stemming from angle-of-attack (AOA) discrepancies, particularly in variants including the MAX series, where mismatched inputs can trigger unwarranted warnings during cruise or climb phases. Such nuisances, often due to vane freezing or disagreements, have prompted FAA airworthiness directives, including those mandating AOA disagree alerts and inspections to mitigate erroneous activations. In the 737 MAX context, these issues contributed to regulatory scrutiny post-2018/2019 accidents, with ongoing directives through 2024 addressing stick shaker suppression logic to reduce pilot distraction without compromising safety.

References

  1. https://www.flyingmag.com/how-it-works-stick-shaker-pusher/
  2. https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/06_afh_ch5.pdf
  3. https://www.safeflight.com/commercial-aviation/products/stick-shaker/
  4. https://skybrary.aero/articles/stall-warning-systems
  5. https://skybrary.aero/articles/stick-pusher
  6. https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/20_afh_glossary.pdf
  7. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_120-109A.pdf
  8. https://avweb.com/features/stall-warning-systems/
  9. https://www.aopa.org/news-and-media/all-news/2021/february/pilot/mentor-matters-callouts-shakers-pushers
  10. https://www.linkedin.com/pulse/ever-felt-stick-shaker-heres-whats-really-going-michelle-marais-cgqjc
  11. https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25/subpart-B/subject-group-ECFR1cd58fc7d4bfee0/section-25.207
  12. http://www.b737.org.uk/stallwarningsys.htm
  13. https://ptacts.uspto.gov/ptacts/public-informations/petitions/1555828/download-documents?artifactId=CjhHhuQzlZl1kXgmeZ6albtiofOUQLU82dqXe5EwkuMQiy2JpWhGXpY
  14. https://data.ntsb.gov/Docket/Document/docBLOB?ID=40320920&FileExtension=.PDF&FileName=Cockpit%2520Voice%2520Recorder%252012%2520-%2520Stick%2520Shaker%2520Spectrum%2520Study-Master.PDF
  15. https://www.flaps2approach.com/journal/2014/4/4/oem-boeing-737-stick-shaker-interfacing-and-operation.html
  16. https://makerplane.org/new-stick-shaker-product/
  17. https://www.aviationhunt.com/boeing-737-circuit-breakers/
  18. https://avweb.com/flight-safety/stick-shaker-disagreement-threatens-max-consensus/
  19. https://www.atsb.gov.au/sites/default/files/media/5780853/ao-2021-027-final.pdf
  20. https://patents.google.com/patent/US2566409A/en
  21. https://taylorandfrancis.com/knowledge/Engineering_and_technology/Aerospace_engineering/Stick_shaker/
  22. https://rosap.ntl.bts.gov/view/dot/33668/dot_33668_DS1.pdf
  23. https://www.law.cornell.edu/cfr/text/14/25.207
  24. https://www.easa.europa.eu/en/document-library/easy-access-rules/online-publications/easy-access-rules-large-aeroplanes-cs-25
  25. https://growthmarketreports.com/report/stick-shaker-and-pusher-systems-market
  26. https://www.federalregister.gov/documents/2025/06/12/2025-10683/airworthiness-directives-bombardier-inc-airplanes
  27. https://cirrusaircraft.com/story/unmatched-safety-with-the-sr-series-g7/
  28. https://www.faa.gov/documentlibrary/media/advisory_circular/ac%20120-109.pdf
  29. https://ifr-magazine.com/avionics/tech-talk-stall-warning-systems/
  30. http://www.jettairx.com.br/backup/wp-content/uploads/2015/07/Dash8-200-300-Warning_Systems.pdf
  31. https://www.pprune.org/tech-log/270567-b747-400-no-stick-pusher.html
  32. https://www.studyaircrafts.com/aircaft-warning-systems
  33. https://aviation.stackexchange.com/questions/87761/what-s-the-difference-between-an-airspeed-low-warning-and-a-stall-warning
  34. https://www.boldmethod.com/learn-to-fly/systems/angle-of-attack-indicators/
  35. https://www.airbus.com/en/newsroom/stories/2023-02-safety-innovation-7-flight-envelope-protection
  36. https://pilot.sinej.com/airbus-a320-alpha-floor-protection-explained/
  37. https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/instruments-and-avionics/a-look-at-stall-warning-devices
  38. https://www.tc.canada.ca/sites/default/files/migrated/multicrewsops.pdf
  39. https://skybrary.aero/sites/default/files/bookshelf/2299.pdf
  40. https://www.psychologicalscience.org/news/releases/crew-schedules-sleep-deprivation-and-aviation-performance.html
  41. https://aviation-safety.net/wikibase/333011
  42. https://www.key.aero/article/how-did-bac-1-11-help-pave-safer-air-travel
  43. https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9601.pdf
  44. https://www.ntsb.gov/investigations/accidentreports/reports/aar1001.pdf
  45. https://aircrafticing.grc.nasa.gov/documents/2009_DHC8-400_Clarence_Center_NY_Accident_Final_Report.pdf
  46. https://asn.flightsafety.org/wikibase/194812
  47. https://australianaviation.com.au/2019/03/atsb-releases-final-report-on-qantas-747-stick-shaker-incident/
  48. https://asn.flightsafety.org/asndb/318707
  49. https://bea.aero/fileadmin/user_upload/9N-ANC_FINAL_Report.pdf
  50. https://asn.flightsafety.org/wikibase/347362
  51. https://avherald.com/h?article=51b861c3
  52. https://www.pprune.org/accidents-close-calls/660783-atr-72-crash-sao-paulo-brazil-flight-ptb2283-9th-august-2024-a-17.html
  53. https://www.federalregister.gov/documents/2021/12/28/2021-27957/airworthiness-directives-the-boeing-company-airplanes
  54. https://boeing.mediaroom.com/news-releases-statements?item=130431
Add your contribution
Related Hubs
User Avatar
No comments yet.