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Compressor stall

Compressor stall is an aerodynamic instability in the compressor section of a gas turbine engine, particularly in axial-flow designs, where airflow separates from the rotor blades due to an incompatible pressure ratio relative to the engine's rotational speed, leading to disrupted smooth passage of air through compressor stages and potential reversal of mass flow.^[1] This condition manifests as a local or propagating disruption in the airflow, often indicated by a sudden rise in exhaust gas temperature, fluctuations in engine RPM, and audible banging or rumbling noises.^[1] If unchecked, compressor stall can escalate to more severe instabilities, potentially causing engine flameout or physical damage to compressor components.^[1] Compressor stall encompasses two primary forms: rotating stall and surge. Rotating stall involves localized regions of separated flow, or stall cells, that propagate circumferentially around the compressor annulus at a speed typically 30-70% of the rotor speed, creating a persistent but non-axisymmetric flow distortion without immediate full reversal of flow.^[2]^[3] In contrast, surge represents a more violent, system-wide oscillation where the entire compressor experiences a breakdown in pressure rise, resulting in pulsations, reverse mass flow, and high-frequency pressure waves that can propagate through the engine.^[4] These instabilities are mapped on compressor performance characteristics, with the surge line delineating the boundary of stable operation; operating beyond this line, often at low mass flow rates or high pressure ratios, triggers the onset of stall.^[4] Common causes of compressor stall include sudden disruptions to inlet airflow, such as from foreign object ingestion, ice buildup, or bird strikes, as well as internal factors like blade erosion, fouling, or mismatches in compressor matching due to engine transients.^[3] In multi-stage compressors, boundary layer separation on blades or stators exacerbates the issue, particularly during acceleration or deceleration phases where the incidence angle of incoming air deviates from design conditions.^[4] Prevention strategies focus on maintaining a sufficient surge margin through design features like variable inlet guide vanes, bleed valves to vent excess pressure, and multi-spool architectures that decouple compressor and turbine speeds for enhanced stability.^[4] Historically, compressor stall has been a critical challenge in aviation, prompting extensive research since the mid-20th century to improve engine reliability and safety.^[3]

Fundamentals

Definition and Overview

Compressor stall refers to a disruption in the smooth airflow through the compressor stages of a gas turbine engine, where local or global flow separation on the compressor blades occurs, leading to instability, reduced pressure rise, or even reversal of airflow direction.^[5] This aerodynamic phenomenon arises when the angle of attack on the rotor blades becomes excessive relative to the incoming airflow, causing boundary layer separation and a partial breakdown of the flow field.^[6] Unlike flutter, which involves aeroelastic structural vibrations of the blades, or choke, where excessive mass flow overwhelms the compressor's capacity without separation, stall specifically entails this flow detachment and its consequences.^[5] Key characteristics of compressor stall include a sudden loss of compressor pressure rise, often accompanied by audible symptoms such as banging, rumbling, or popping noises as stalled regions propagate through the engine stages.^[7] These disturbances can manifest as increased engine vibrations, elevated exhaust gas temperatures, and in severe cases, visible flames expelled from the intake or exhaust due to airflow reversal affecting combustion.^[5] The phenomenon primarily impacts axial-flow compressors, which are prevalent in turbojets, turbofans, and turboprops for their high efficiency in generating thrust, though it can also occur in centrifugal compressors used in some smaller or auxiliary engines. Compressor stall was first prominently observed during World War II testing of early jet engines, where it was initially mistaken for catastrophic engine failure due to the unfamiliar symptoms and lack of understanding of high-speed axial flows.^[5] These early designs, often single-spool configurations optimized for specific operating speeds, were particularly susceptible during off-design conditions like low-RPM taxiing, highlighting the challenges in achieving stable airflow across varying engine demands.^[6]

Aerodynamic Principles

Axial compressors operate through a series of stages that progressively increase air pressure by imparting energy to the airflow. Each stage consists of rotating blades, known as rotors, which accelerate the air by adding tangential velocity, and stationary vanes, called stators, which redirect and slow the flow. This process relies on the diffusion principle, where the kinetic energy gained in the rotor is converted into static pressure in the stator as air velocity decreases while moving through converging-diverging passages designed to manage adverse pressure gradients.^[9] Compressor stall arises when the incidence angle—the angle between the incoming relative airflow and the blade chord—exceeds the aerodynamic design limits of the blades. This mismatch causes the boundary layer on the suction surface of the blade to separate due to the adverse pressure gradient, leading to a breakdown in smooth airflow attachment. The separation results in a significant reduction in aerodynamic lift generated by the blade and a sharp increase in drag, which collectively blocks the flow passage and disrupts the pressure rise across the stage.^[10] A key metric for assessing stall risk is the diffusion factor (DF), which quantifies the loading on compressor blades and the potential for boundary layer separation. It is defined as

DF = \frac{U_1 - U_2}{U_1} + \frac{\Delta C_\theta}{2 \sigma U_1}

where U_1 and U_2 are the relative velocities at the blade inlet and outlet, respectively; \Delta C_\theta is the change in absolute tangential velocity across the blade row; and \sigma is the blade solidity (chord length divided by spacing). Values of DF exceeding 0.6 typically indicate high risk of stall inception, as they correspond to excessive deceleration of the relative flow, promoting separation on the blade suction surface.^[11] The overall behavior of an axial compressor is characterized on a performance map, which plots total pressure ratio (\pi = P_{out}/P_{in}) against flow coefficient (\phi = V_{ax}/U, where V_{ax} is axial velocity and U is blade tip speed). The operating line traces the steady-state trajectory of compressor performance under varying conditions, while the surge line marks the stability limit, representing the locus of peak pressure ratios at minimum stable flow rates beyond which aerodynamic instability, including stall, occurs.^[12]

Types

Rotating Stall

Rotating stall manifests as localized regions of stalled flow within the compressor annulus, forming one or more discrete cells that propagate circumferentially in the direction of rotor rotation at a speed typically between 20% and 70% of the rotor speed.^[13]^[14] These cells, typically numbering from 1 to 10 or more, create persistent blockages that modulate the circumferential pressure distribution, leading to alternating stalled and unstalled passages as viewed from the rotor frame.^[15] The phenomenon is distinct from uniform stall, as the disturbances remain confined azimuthally without immediate axisymmetric reversal. Initiation of rotating stall typically begins in a single blade row, most commonly in the rear stages of multistage axial compressors, where axial flow reduction increases incidence angles and promotes local flow separation due to mismatch between incoming flow and blade geometry.^[15] This initial disturbance then propagates upstream and downstream through the compressor via acoustic or convective waves, establishing the rotating cells as the instability sustains itself.^[15] The effects of rotating stall include a gradual degradation in overall compressor performance, characterized by reduced pressure rise and efficiency as the stalled cells disrupt the mean flow field.^[13] This leads to increased structural vibrations at the frequency of cell rotation relative to the casing, though the engine can often continue operating in a subnormal mode without immediate shutdown.^[13] Detection relies on frequency analysis from circumferential arrays of pressure transducers, which reveal peaks corresponding to the cell passage frequency.^[16] Modeling of rotating stall draws from Emmons' seminal theory, which describes the propagation of stall cells as a result of cyclic stalling and unstalling of blade passages in the relative frame.^[17] The theory predicts the angular speed of the stall cell \omega_c (with respect to the stationary frame) as a fraction k < 1 of the rotor angular speed \omega_r:

\omega_c = k \omega_r

where k represents the fractional propagation speed, typically derived from assumptions of irrotational inlet flow and balanced lags between stalled and unstalled regions.^[17]^[15] This kinematic model has been foundational for understanding cell dynamics in axial compressors.

Surge

Surge represents the most severe form of aerodynamic instability in axial compressors, characterized by a complete, axisymmetric breakdown of the compressor flow that propagates through the entire engine, resulting in large-amplitude oscillations of pressure and mass flow with axial flow reversal.^[18] This instability manifests as violent pulsations where the compressor momentarily loses its pressure-raising capability, often accompanied by a loud audible noise such as a bang or whistle.^[7] The typical cycle frequency of surge ranges from 1 to 20 Hz, driven by the system's Helmholtz resonance, which is significantly lower than the frequencies associated with other instabilities.^[19] The dynamics of a surge cycle begin with stall initiation at the compressor's peak pressure rise point on its characteristic curve, where the operating condition crosses into the unstable region, causing the flow to abruptly jump to a reversed state.^[18] During reversal, the mass flow reaches near zero or negative values, leading to a rapid drop in pressure across the compressor as momentum in the downstream plenum dissipates.^[19] Recovery follows as the reversed flow exhausts the plenum's stored momentum, allowing positive flow to re-establish along a different path on the compressor map; however, the system then re-enters the stalled condition, perpetuating the limit cycle oscillation.^[18] This cyclic behavior can escalate from a precursor like prolonged rotating stall, producing intense vibrations and potentially causing combustor flameout due to disrupted airflow.^[7] A key feature of surge is the hysteresis observed on the compressor map, where the line defining surge onset differs from the recovery line, forming a loop that requires a greater adjustment in operating conditions—such as increased flow—to exit the instability than to initially enter it.^[18] This hysteresis arises from the nonlinear compressor characteristic and system compliance, complicating control efforts as the operating point follows an S-shaped trajectory during transients.^[19] Unlike milder, localized instabilities, surge involves global, axisymmetric flow disruptions that affect the entire compression system, often evolving from rotating stall but distinguished by its high-amplitude axial pulsations and potential for reverse flow throughout the engine.^[7] Engineers quantify the buffer against surge using the surge margin (SM), defined as

SM = \frac{(P_{s, surge} - P_{s, op})}{P_{s, op}} \times 100\%

where P_{s, surge} is the pressure ratio at the surge line and P_{s, op} is the operating pressure ratio; this metric represents the percentage distance from the current operating point to the surge boundary, serving as a design parameter to ensure stable operation under varying conditions.^[18]

Causes

Aerodynamic Factors

Compressor stall can be triggered by flow incidence mismatches, where high inlet distortion alters the incoming airflow nonuniformity, elevating the local angle of attack on compressor blades beyond their stall margin. Such distortions often arise from inlet geometry constraints or aircraft maneuvers, leading to regions of elevated incidence that promote boundary layer separation on blade surfaces. For instance, circumferential or radial total pressure distortions reduce the overall stable mass flow range by inducing localized stall precursors, as demonstrated in experimental studies on axial compressors.^[20] Boundary layer effects further contribute to stall susceptibility by accumulating low-energy fluid along blade surfaces, which thickens the boundary layer and diminishes aerodynamic loading capacity, thereby eroding the stall margin. In particular, tip clearance flows exacerbate this issue, as the leakage vortex from the rotor tip interacts with the endwall boundary layer, promoting early flow separation and reducing efficiency near the casing. These phenomena are pronounced in high-pressure-ratio stages, where even modest increases in tip gap can shift the onset of separation upstream, limiting stable operation.^[21] Stage interactions play a critical role in stall inception through the impingement of upstream wakes on downstream blades, generating unsteady aerodynamic loading that amplifies flow instabilities. These wakes, originating from prior rotor or stator rows, introduce periodic perturbations in incidence and momentum, which can trigger modal or spike-type disturbances propagating as rotating stall cells. The Moore-Greitzer model captures this dynamic interplay, describing stall inception via coupled equations for pressure and flow coefficients; a key relation for pressure dynamics is given by

\frac{\partial \psi}{\partial t} + \frac{U}{R} \frac{\partial \psi}{\partial \theta} = -\frac{1}{B} \frac{U}{R} \frac{\partial \bar{\phi}}{\partial t},

where \psi is the pressure rise coefficient, \phi the flow coefficient, U/R the rotor speed parameter, \theta the azimuthal angle, and B the Greitzer stability parameter, illustrating how spatial and temporal variations lead to cell growth without detailed derivation.^[22]^[23] Off-design operating conditions, such as reduced Mach numbers below design intent, erode the compressor map's stable operating envelope by narrowing the surge margin through diminished diffusion efficiency and increased flow separation risks. At part-speed operations, the mismatch between blade speed and airflow velocity alters incidence angles across stages, compressing the usable mass flow range and heightening vulnerability to stall. This effect is evident in multistage compressors, where predictive models show that deviations from peak efficiency points can reduce stall margin by up to 20-30% depending on the loading.^[24]

Operational and Design Factors

Operational and design factors play a significant role in precipitating compressor stall by altering the compressor's operating conditions relative to its stability limits. Throttle transients, such as rapid acceleration or deceleration, can shift the engine's operating point across the surge line, reducing the available surge margin and potentially inducing stall. For instance, during acceleration from idle to full power, the compressor's flow demand increases suddenly, while the rotational speed lags, temporarily decreasing the stall margin by up to 20-30% in some engine configurations.^[25] High-altitude starts or operations on hot days exacerbate this by further compressing the margin due to lower air density.^[26] Inlet conditions also contribute to stall through flow distortions that unevenly load compressor stages. Bird strikes or foreign object damage (FOD) can deform inlet geometry or blades, introducing circumferential distortions that propagate through the compressor and reduce stall margin by disrupting uniform airflow.^[27] Battle damage to the airframe or nacelle similarly distorts inlet flow, increasing incidence angles on the first rotor stages and promoting local stall inception.^[28] Ice ingestion, though less common with anti-icing systems, can cause sudden blockages leading to similar effects.^[29] Internal factors such as blade erosion from prolonged exposure to abrasive particles or fouling from atmospheric contaminants (e.g., dust, salt) can gradually degrade blade aerodynamics, thickening boundary layers and reducing stall margin over time.^[3] Design choices in early engines often incorporated insufficient surge margins, making them particularly susceptible to stall under off-design conditions. Modern mitigations include variable stator vanes to adjust incidence and bleed valves to vent excess flow, but calibration errors can still lead to failures if not tuned to specific operating envelopes.^[30] Environmental factors like high ambient temperature or humidity erode compressor stability by affecting air density and corrected parameters. Elevated temperatures increase the temperature ratio θ (inlet temperature to standard), reducing the corrected speed N_corr = N / √θ, which shifts the operating line closer to the stall boundary on the compressor map.^[31] Humidity contributes by lowering air density through water vapor, further decreasing mass flow and compressing the surge margin, particularly in hot, moist conditions common to tropical operations.

Effects

Performance Impacts

Compressor stall significantly degrades engine performance by disrupting the normal airflow through the compressor stages, leading to an immediate and substantial reduction in thrust output. During a stall event, particularly surge, the compressor pressure ratio can drop sharply, with documented cases showing reductions of up to 35% in overall engine thrust at high altitudes due to the operating point shifting away from the stable region on the compressor map.^[32] This collapse in pressure ratio, often exacerbated by flow distortions, directly diminishes the air mass flow and compression work, resulting in a temporary thrust loss typically ranging from 20% to 30% depending on the severity and engine configuration. For instance, in axial-flow compressors under distorted inlet conditions, thrust losses of 23% at mid-altitudes and 35% at 50,000 feet have been observed, primarily from the stalled sections failing to contribute to overall compression.^[32] The efficiency of the engine is also severely impacted, as stalled compressor stages behave like drag-inducing elements rather than efficient compressors, lowering the polytropic efficiency by as much as 20% compared to nominal operation.^[33] This reduction in compressor efficiency propagates through the engine cycle, increasing specific fuel consumption (SFC) by 6% to 9% to maintain equivalent thrust levels, as the engine compensates for the lost compression by burning more fuel.^[33]^[34] Prolonged stall conditions further compound this by causing elevated temperatures in the turbine inlet, acting as localized hotspots that reduce overall cycle efficiency and necessitate adjustments in fuel scheduling to avoid exceeding thermal limits.^[33]^[34] Post-stall operation imposes operational limits on the engine, including derating of maximum thrust to prevent recurrence and mandatory cooldown periods to stabilize temperatures before resuming full power. Recovery from a surge typically takes 5 to 10 seconds, during which the engine experiences sustained reduced output until the operating point stabilizes, with fuel flow adjustments aiding restoration.^[35] These impacts are more pronounced in commercial engines during cruise, where sustained efficiency losses can degrade long-haul performance, whereas military engines may tolerate brief derates better due to variable geometry features that enhance surge margin recovery. Overall, these performance degradations shift the engine's operating point on the compressor map toward lower efficiency regions, limiting achievable pressure ratios and requiring careful management to restore nominal cruise capabilities.^[32]

Structural and Safety Consequences

Compressor stall, particularly in its rotating form, induces high-frequency vibrations that can lead to fatigue in compressor blades, with the most vulnerable areas being 25-35% of the blade span from the base where over 40% of failures occur.^[36] These vibrations arise from unsteady aerodynamic loads during stall, reducing blade fatigue life significantly; for instance, a small 0.010-inch nick at the leading or trailing edge can decrease endurance from 10^8 cycles to as low as 2.3 \times 10^5 cycles under vibratory stresses of \pm 70,000 psi.^[36] In severe surge conditions, pressure pulses generate rapid rotor thrust reversals, overloading thrust bearings and causing wear on rub-strips or even blade liberation through internal damage to labyrinths, diaphragms, and rotors.^[37] Thermal effects exacerbate structural vulnerabilities during surge events, as flow reversal recirculates hot combustor gases upstream into the compressor, potentially overheating blades and increasing inlet temperatures by up to 60.6% of pre-surge levels.^[38] This hot gas recycling elevates discharge temperatures, leading to seal and bearing failures, while prolonged exposure risks thermal distortion or creep in affected components.^[37] Such overheating can propagate damage to downstream turbine blades if not contained, compounding fatigue from vibrational stresses.^[36] Safety risks from compressor stall include engine flameout and resultant power loss, which can produce turbulence, pressure fluctuations, and visible flames at the intake or exhaust, heightening the chance of in-flight shutdowns.^[39] In multi-engine aircraft, a stall-induced shutdown on one engine may cause asymmetric thrust, inducing yaw and potential autopilot disengagements, particularly during critical phases like takeoff or climb.^[40] Compressor surge contributes to a notable portion of reported turbofan engine malfunctions; a 2009 analysis of 79 events indicated 54 involved surge, often resulting in uncommanded power reductions that demand immediate crew response to avoid loss of control.^[40] Recent incidents underscore these risks. On February 10, 2025, a Hop-A-Jet Learjet 24 crashed on Interstate 75 near Naples, Florida, due to a non-recoverable dual rotating compressor stall caused by corrosion in the variable stator vane systems, resulting in four fatalities and highlighting structural degradation leading to catastrophic failure.^[41] Additionally, a Qantas Airbus A330-200 experienced a right engine compressor stall during descent into Los Angeles on November 27, 2024, and another during climb from Brisbane to Los Angeles on an unspecified date in 2024, both recovered safely but prompting investigations into performance impacts.^[42] In response to ongoing issues, the FAA issued Airworthiness Directive 2025-13-06 in June 2025 for CFM International LEAP-1A engines, requiring inspections following reports of high-pressure compressor stalls causing aborted takeoffs.^[43] Long-term consequences necessitate rigorous post-event inspections, as sustained stalls or surges often reveal cracks in blades or rotors, prompting hardware examinations to assess fatigue damage.^[44] FAA and EASA guidelines mandate such evaluations after surge occurrences; for example, Airworthiness Directive 2023-24-04 requires inspections and potential electronic control unit replacements on affected Honeywell engines to prevent recurrent surges and associated structural degradation.^[45] These protocols, including borescope checks and component overhauls, ensure engines remain serviceable, with non-compliance risking progressive fatigue leading to blade failure.^[44]

Detection and Mitigation

Detection Techniques

Compressor stall detection relies on a variety of real-time monitoring techniques that capture aerodynamic instabilities through acoustic, pressure, vibration, and operational signals. These methods enable early identification of precursors to rotating stall or surge, allowing for timely intervention to maintain engine stability.^[46] Acoustic signatures provide a non-intrusive means of detecting stall events, with engine-mounted microphones capturing characteristic sounds such as the continuous rumbling associated with rotating stall or the loud bangs indicative of surge. Frequency spectrum analysis of these signals reveals oscillations tied to flow disruptions, often in the low-frequency range (e.g., 0.3-0.7 times rotor speed for rotating stall precursors), enabling differentiation between stable operation and impending instability.^[47]^[39]^[48] Pressure and vibration sensors offer direct measurement of flow perturbations within the compressor. Dynamic pressure transducers installed at various compressor stages detect rapid oscillations in static or total pressure, signaling the onset of stall through increased amplitude in the pressure signal correlation. Accelerometers mounted on the casing monitor blade vibration and structural stress, identifying high-frequency components linked to rotating disturbances or surge cycles, which can precede full instability by several seconds.^[46]^[49]^[50] Engine control systems, such as Full Authority Digital Engine Control (FADEC), integrate these sensor inputs into algorithms that track key parameters like compressor pressure ratio, rotor speed deviations, and surge margin thresholds. By continuously monitoring for anomalies—such as a sudden drop in pressure ratio below a predefined limit—FADEC can flag stall risks and adjust fuel flow or variable geometry to avert progression, ensuring stable operation across flight regimes.^[51]^[52]^[48] In operational settings, pilots receive visual and auditory cues including master caution lights triggered by FADEC alerts, along with exhaust gas temperature (EGT) spikes from reversed hot flow during surge events. During ground testing in engine cells, high-speed cinematography and schlieren imaging visualize flow separation and stall cell propagation, providing qualitative confirmation of detected anomalies for validation and design refinement.^[39]^[53]^[54]

Recovery and Prevention Strategies

Recovery from compressor stall in flight typically involves pilots throttling back the engine to reduce fuel flow, thereby moving the operating point away from the surge line on the compressor map and restoring stable airflow. This maneuver decreases the pressure ratio across the compressor, allowing the stall to clear without further disruption. In cases involving variable geometry features, such as closing bleed valves after the initial stall event, additional airflow management can aid recovery by relieving excess backpressure.^[55] Design strategies to prevent compressor stall emphasize incorporating sufficient surge margins and adaptive components in modern engines. Surge margins of 15-20% are targeted in contemporary axial-flow compressors to provide a buffer against instabilities during off-design conditions, ensuring safe operation across the flight envelope. Variable inlet guide vanes (VIGV) adjust the incidence angle of incoming airflow to the low-pressure compressor, optimizing blade loading and delaying stall inception, particularly at part-load or transient operations. Active clearance control systems minimize tip clearances in the compressor stages by modulating casing temperatures, reducing leakage flows that contribute to stall precursors and enhancing overall stability.^[56]^[57]^[58] Testing and simulation play critical roles in validating prevention measures before engine certification. Wind tunnel tests with distortion screens simulate inlet flow irregularities, allowing engineers to assess stall margins under adverse conditions like crosswinds or bird ingestion. Computational fluid dynamics (CFD) simulations predict stall onset by modeling unsteady flows and boundary layer behaviors, enabling iterative design refinements to extend stable operating ranges. Ground-based engine run-ins using artificial inlets replicate flight-like distortions, providing data on transient responses and informing control schedules.^[59]^[60]^[61] Post-1980s advancements in bleed systems have significantly improved stall resilience, particularly during transients. Variable bleed valves extract air from intermediate compressor stages to reduce backpressure and maintain operability margins when acceleration demands push toward the surge line. These systems, refined through programs like NASA's High Stability Engine Control (HISTEC), dynamically adjust bleed flows based on real-time distortion estimates, minimizing fuel penalties while preventing stall in high-performance aircraft.^[62]^[63] Since 2020, further progress has integrated machine learning (ML) and advanced active flow control for enhanced detection and prevention. ML techniques, such as long short-term memory (LSTM) networks and convolutional neural networks (CNN), enable early stall warnings 50 milliseconds to several seconds in advance by analyzing sensor data patterns, achieving accuracies up to 97.7%. Active flow control methods, including unsteady tip air injection and self-recirculating casings, have extended surge margins by 13-44% with minimal mass flow penalties (e.g., 1-3.6%), improving engine efficiency and reliability in axial compressors for gas turbines.^[64]^[65]

Historical Incidents

Engine Development Events

During World War II, the Junkers Jumo 004 turbojet engine, which powered the Messerschmitt Me 262, highlighted the vulnerabilities of early axial-flow designs to aerodynamic instabilities under varying inlet conditions, particularly in its eight-stage axial compressor.^[66] Post-war, the U.S. National Advisory Committee for Aeronautics (NACA, predecessor to NASA) conducted extensive testing on captured Jumo 004 engines starting in 1946 at facilities like the Aircraft Engine Research Laboratory in Cleveland, Ohio, to study performance and improve compressor stability.^[67] This research laid foundational knowledge for subsequent jet engine designs by quantifying instability precursors and emphasizing the need for wider operating margins in axial compressors. In the 1950s, the Rolls-Royce Avon turbojet encountered compressor surges during rapid acceleration, prompting a redesign that included revised blade profiles to reduce incidence angles and the incorporation of bleed valves at intermediate stages to vent excess air and stabilize flow.^[68] These modifications, implemented in the RA.14 variant type-tested in 1953, enabled the Avon to achieve reliable operation at higher pressure ratios, powering aircraft like the English Electric Canberra and de Havilland Comet.^[69] The Rolls-Royce/Snecma Olympus 593 engine, developed for the Concorde supersonic airliner in the 1960s and 1970s, faced repeated compressor stalls during transonic wind tunnel tests at facilities like the National Gas Turbine Establishment in Farnborough, England.^[70] These stalls arose from inlet-engine mismatches, where distorted airflow from the variable-geometry intake—simulating Mach 1.7 to 2.4 conditions—exceeded the compressor's surge margin, leading to spatial and temporal pressure distortions.^[71] Resolution involved refining variable intake ramps for better flow matching and enhancing engine mapping through integrated testing, which prevented stalls in subsequent prototypes and ensured stable operation across the flight envelope.^[72] These development challenges drove broader advancements in compressor design during the 1950s and 1960s, shifting toward multi-stage axial configurations with interstage bleed systems to enhance stall margins and accommodate higher pressure ratios.^[27] Bleed valves, in particular, became standard for transient flow control, significantly reducing stall incidence in prototypes from frequent occurrences in early axial designs to more reliable performance in production engines.^[68]

Aviation Accidents

One notable aviation accident involving compressor stall occurred on April 4, 1977, when Southern Airways Flight 242, a McDonnell Douglas DC-9-31, encountered severe hail and heavy rain while flying through a thunderstorm near Rome, Georgia. The ingestion of massive quantities of water and hail, combined with thrust lever adjustments, induced severe stalling in the high-pressure compressors of both Pratt & Whitney JT8D engines, leading to a complete loss of thrust. The crew attempted an emergency landing on a highway, but the aircraft struck vehicles and a roadside structure, resulting in 72 fatalities among the 85 people on board and on the ground. This incident prompted the Federal Aviation Administration to revise thunderstorm penetration guidelines and enhance hail avoidance procedures for commercial aircraft.^[73] In the 1980s, the U.S. Navy's Grumman F-14A Tomcat experienced multiple fatal accidents attributed to compressor stalls in its Pratt & Whitney TF30 engines, particularly during carrier launches where inlet distortion from high angles of attack disrupted airflow. One such incident involved an F-14A suffering engine failure shortly after catapult launch from a carrier deck, caused by uneven inlet air distribution leading to stall and subsequent loss of control; the pilot ejected safely, but the aircraft was destroyed. These recurring issues, which contributed to the loss of up to 40 F-14As overall, highlighted the TF30's vulnerability to stalls under asymmetric conditions and led to fleet-wide modifications, including improved engine controls and eventual replacement with the General Electric F110 in later variants.^[74] On December 6, 1997, a Russian Air Force Antonov An-124-100 crashed shortly after takeoff from Irkutsk Northwest Airport due to compressor surges in multiple Progress D-18T engines. The surges were triggered by fuel contaminated with water, which froze and formed ice particles that clogged filters and disrupted compressor operation during the initial climb, combined with a structural defect in the high-pressure compressors. The aircraft stalled and impacted a residential area, killing all 23 occupants and 45 people on the ground, with the total loss of the plane underscoring vulnerabilities in fuel system redundancies for large transport aircraft. The investigation emphasized the need for stricter fuel quality controls and engine surge protection in cold-weather operations.^[75] An earlier commercial incident took place on November 6, 1967, involving Trans World Airlines Flight 159, a Boeing 707-131, during takeoff from Cincinnati/Northern Kentucky International Airport. As the aircraft accelerated past a stationary Delta Air Lines DC-9, jet blast from the DC-9's idling engines disturbed airflow into the No. 4 Pratt & Whitney JT3C-6 engine, causing a compressor stall and a loud bang that prompted the crew to abort takeoff. The 707 overran the runway and collided with a fence and an embankment, resulting in one passenger fatality four days later from injuries and minor harm to others among the 36 on board, with no structural damage severe enough to prevent evacuation. This event was instrumental in developing early engine surge detection systems and runway spacing protocols to mitigate wake turbulence effects.^[76] Compressor stall also played a role in the December 27, 1991, accident of Scandinavian Airlines System Flight 751, a McDonnell Douglas MD-81 departing Stockholm Arlanda Airport. Clear ice accumulated on the wings during de-icing detachment broke off during rotation and was ingested into both Pratt & Whitney JT8D engines, damaging fan stages and inducing surges that reduced thrust to idle. The crew executed an emergency landing in a snowy field near Gottröra, Sweden, with all 129 occupants surviving despite the aircraft breaking apart on impact. The Swedish Accident Investigation Board recommended global improvements in wing anti-icing procedures and de-icing fluid residue management to prevent similar ice shedding. These incidents illustrate common triggers for compressor stall in operational aviation, such as environmental ingestion and airflow distortions, which often resulted in loss of thrust and forced landings or ejections. Post-2000, advancements in engine design, including more robust compressor stages and surge margin enhancements, have significantly reduced such accidents in commercial and military fleets as of 2025. However, rare events persist, particularly from bird strikes that can induce stalls, as seen in isolated cases like the 2020 Canadian Forces Snowbirds CT-114 crash.^[77]

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Below is a merged response that consolidates all the information from the provided summaries into a comprehensive overview of **Pressure Ratio, Flow Coefficient, Operating Line, and Surge Line** in the context of axial compressors, as derived from NASA SP-36 (1965) and related NACA reports. To retain maximum detail, I’ve organized the information into a dense, tabular format where appropriate, supplemented by narrative explanations. The response includes all specifics mentioned across the segments, such as numerical values, equations, figures, and contextual explanations, while avoiding redundancy where possible.
[13]
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Rotating stall is an instability with cells of stalled flow rotating at a fraction of rotor speed, reducing performance and causing vibrations.
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Jul 1, 2022 · Compressor surge is shown by the application of several types of instrumentation (notably a hot-wire anemometer) to consist of two distinct types of phenomena.
[18]
[PDF] Rotating Stall and Surge in an Axial Compressor - IIT Kanpur
The total to total pressure rise and efficiency of the compression system is effected by aerodynamic instabilities. We have to restart the gas turbine engine ...
[19]
[PDF] Modeling and Control of Surge and Rotating Stall in Compressors
This thesis contains new results in the eld of modeling and control of rotating stall and surge in compressors. A close coupled valve is included in the Moore- ...
[20]
Effects of rotating inlet distortion on the stall mechanism of an axial ...
Nov 14, 2023 · In practical operation, inlet distortion is one of the key factors that induce flow instability of compressor. Since the compressor is a ...
[21]
The Influence of Tip Clearance, Stage Loading, and Wall ...
The results showed that tip clearances and stage loading levels exerted a very strong influence on casing boundary layer growth.<|separator|>
[22]
A Theory of Post-Stall Transients in Axial Compression Systems
Moore, F. K., and Greitzer, E. M. (January 1, 1986). "A Theory of Post-Stall Transients in Axial Compression Systems: Part I—Development of Equations." ASME ...
[23]
Experimental study on unsteady wake impacting effect in axial-flow ...
In the present study, the specific wake impacting effect (WIE) in compressors was used to control unsteady separated flows inside axial-flow compressors.
[24]
[PDF] Off-Design Computer Code for Calculating the Aerodynamic ...
A good design for a multistage axial compressor requires an adequate part-speed per- formance with s&cient part-speed stall margin and determination of required.
[25]
[PDF] A Risk Management Architecture for Emergency Integrated Aircraft ...
A throttle transient produces a temporary drop in compressor stall margin, and the amount of this drop increases (i.e., the stall margin is further reduced) if ...
[26]
[PDF] Transient Optimization of a Gas Turbine Engine
Engine transients tend to cause a reduction in compressor operability margin, which must be addressed by the engine control system and accounted for in the ...
[27]
Instabilities Everywhere! Hard Problems in Aero-Engines
Oct 14, 2022 · “Engine-related” events exclude mishaps caused by foreign object damage (FOD), bird strike, or failure of support systems external to the engine ...
[28]
None
### Definition, Characteristics, and Effects of Compressor Stall
[29]
The Big Bang – Bird Strike Certification Testing
In recognition of these dynamics, engines are designed with a surge recovery bleed between the booster and core compressor to compensate for this flow mismatch.Missing: FOD | Show results with:FOD
[30]
Stall Analysis in a Transonic Compressor Stage and Rotor
The reduction in operating surge margin ... engines upon launch which may induce compressor stall. ... First, turboprop engines were developed and modified ...
[31]
[PDF] Transient Optimization of an Electrified Gas Turbine Engine Using ...
The High-Pressure Compressor (HPC) is designed such that the operating line is far enough from the stall line to ensure that it will never stall under normal ...
[32]
Performance Corrections for Compressor Maps - Concepts NREC
Mar 29, 2019 · The plot below shows this corrected result. Corrected map consolidating the performance with noramlized mass flow and ratational speed.
[33]
A Compressor Fouling Review Based on an Historical Survey of ...
Jan 10, 2017 · Fouling mechanisms involve three specific aspects: (i) the environmental conditions (airborne contaminant, salt, etc.) in which the gas turbine ...
[34]
[PDF] RESEARCH MEMORANDUM
The more severe thrust loss at high alti- tude resulted from the blocked portion of the compressor encountering the stall region} which made it necessary to ...Missing: impacts | Show results with:impacts
[35]
[PDF] RESEARCH MEMORANDUM
During tip stall, compressor efficiency is as much as 20 percent lower than rated-speed efficiency. The overlap in engine speed for each type of operation shown ...<|control11|><|separator|>
[36]
[PDF] NACA RESEARCH MEMORANDUM
Several factors are Involved in this thrust decrease, namely: (1) loss in compressor performance, (2) decrease In average exhaust-gas temperature and, (3) ...Missing: impacts | Show results with:impacts
[37]
[PDF] NATIONAL ADVISORY COMMITIE FOR AERONAUTICS
Fatigue strength was the criterion used to determine the extent of dam- age to blades, because fatigue is the principal cause of compressor fail- ure in jet ...
[38]
https://www.sciencedirect.com/science/article/pii/S1270963822006836
[39]
https://skybrary.aero/articles/compressor-stall
[40]
Compressor Stall | SKYbrary Aviation Safety
A compressor stall is abnormal airflow due to compressor blades stalling, caused by an imbalance between airflow supply and demand, resulting in loss of thrust.
[41]
[PDF] Turbofan Engine Malfunction Recognition and Response Final Report
Jul 17, 2009 · This report develops training for recognizing and responding to turbofan engine malfunctions, addressing a shortfall in pilot training and a ...
[42]
None
### Summary of Guidelines on Engine Surge, Inspections, and Safety Implications from AC 33.65-1
[43]
[PDF] FAA AD 2023-24-04 - Engine Compressor Surge
Dec 6, 2023 · This AD is effective January 10, 2024. ADDRESSES: AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA–2023–1050;.
[44]
A Study on the Stall Detection of an Axial Compressor through ...
Meanwhile, compressor stall and surge are the main influencing factors that cause inherent aerodynamic instabilities in the compressor operational envelope [1,2] ...
[45]
[PDF] OBSERVATIONS OF PROPAGATING STALL IN AXIAL-FLOW ... - DTIC
the compressor was in full stall, but only a continuous rumbling sound was ... "A Theory of 'Rotating Stall' in Axial-Flow Compressors", by W. R.. Sears ...
[46]
US6059522A - Compressor stall diagnostics and avoidance
A pressure sensor (12) is located in the compressor stage of a gas turbine engine (10) to provide a pressure signal (PR1) that shows the compressor flow ...
[47]
[PDF] INTERPRETATION OF STALL PRECURSOR SIGNATURES - HAL
By cross- correlating signals from circumferentially distributed wall pres- sure sensors, the propagation speed of aerodynamic disturbances will be determined ...
[48]
Incoming Stall Identification in Axial Compressors by Vibration ...
Aug 4, 2013 · Four vibration signals were simultane- ously measured by means of accelerometers, while the acoustic signals were measured by means of two ...Missing: detection | Show results with:detection
[49]
[PDF] Application and Evaluation of Control Modes for Risk- Based Engine ...
When considering improvements in transient thrust response, the primary risk is usually high-pressure compressor (HPC) stall. Thus, the design of the FR control ...
[50]
How does the FADEC prevent compressor stall during rapidly ...
Oct 10, 2017 · My question is how exactly does the FADEC do this? Which parameters (air temperature / pressure) are being monitored, and what are the signs ...Compressor variable geometry and Engine pressure ratioWhy is it that low fuel gauge is one indication of a compressor stall?More results from aviation.stackexchange.comMissing: algorithms | Show results with:algorithms
[51]
engine surge with EGT rising - PPRuNe Forums
Jul 11, 2008 · If the problem is a surge/stall, and the problem may be resolved by simply reducing thrust on that engine, it may well be worth an attempt to ...Missing: master caution spike
[52]
[PDF] Techniques of Flow Visualization - DTIC
The techniques of flow visualization and their appUcation in wind tunnels, water channels, and experiments related to propulsion research are reviewed.
[53]
https://www.pprune.org/tech-log/334719-engine-surge-egt-rising.html
[54]
[PDF] Engine Concept Study for an Advanced Single-Aisle Transport
For the low fan pressure ratio cases, a variable area nozzle was needed to achieve a desired 20% fan surge margin throughout the operating envelope. For the ...
[55]
Inlet Guide Vane Stagger Effects on Multistage Compressor ...
Mar 11, 2024 · Previous investigations have shown that variable inlet guide vane restaggering may change the stall inception mechanism of axial flow ...
[56]
[PDF] Turbine Engine Clearance Control Systems: Current Practices and ...
Improved blade tip sealing in the high pressure compressor. (HPC) and high pressure turbine. (HPT) can provide dramatic reductions in specific fuel consumption.
[57]
Wind Tunnel Compressor Optimization and Efficiency Roll-off ...
Nov 11, 2012 · Wind Tunnel Compressor Optimization and Efficiency Roll-off Prediction Using Fuzzy Logic. Roland Rosario,; Keith Boyer and; Kelly Cohen.
[58]
Centrifugal Compressor Stall Control by the Application of ... - MDPI
Apr 18, 2021 · The main objectives are: (a) perform a 3D steady CFD analysis to study the effects of stall for SRV2-O compressor and surface roughness effect ...
[59]
[PDF] Test-engine and inlet performance of an aircraft used for ...
The test runs performed at the Ames Outdoor Static Test. Stand utilized the same engine-nacelle-pylon hardware as was used in the tunnel. Also shown in figure ...Missing: artificial | Show results with:artificial
[60]
[PDF] Aircraft Turbine Engine Control Research at NASA Glenn Research ...
The VBV is to prevent the LPC from entering stall at any operating condition by providing pressure relief at the LPC exit. The. VSV are typically located at the ...
[61]
[PDF] Utilizing Electrical Power Extraction for Stability Bleed Reduction ...
For this study, HPT polytropic efficiency is adjusted then PT polytropic efficiency is adjusted equally and opposite relative to the LPT polytropic ...
[62]
Messerschmitt Me 262 A-1a Schwalbe (Swallow)
Nov 6, 2023 · The world's first operational jet fighter, the Me-262 Schwalbe, was powered by two Junkers Jumo 004 ... compressor stall. The museum's ...
[63]
18 July 1942 | This Day in Aviation
Jul 18, 2025 · The Jumo 004 was tested at the NACA Aircraft Engine research Laboratory, Cleveland, Ohio, in March 1946. (NASA). The Me 262 A-1 was powered ...
[64]
None
Below is a merged summary of the Rolls-Royce Avon engine development, compressor stall, surge, bleed valves, and redesign in the 1950s, combining all information from the provided segments. To maximize detail and clarity, I’ve organized the key information into a table in CSV format, followed by a concise narrative summary. This approach ensures all details are retained and easily accessible.
[65]
Rolls Royce Avon - Moorabbin Air Museum
Redesign of the inlet guide vanes and compressor bleed systems and other modifications resulted in pre production engines designated RA 2, completing a test ...Missing: surge valves
[66]
[PDF] Engine Surge Simulation in Wind-Tunnel Model Inlet Ducts
In the 1960's the need arose to simulate the surge pressures of the Rolls Royce Olympus 593 engine in a Concorde air intake wind-tunnel model, an investigation ...<|separator|>
[67]
[PDF] Aircraft and Engine Development Testing - DTIC
Transonic Wind Tunnel at NASA-Langley has often been used for such tests. Similar tests can be done in several of the larger supersonic wind tunnels. The ...
[68]
https://www.valentiniweb.com/piermo/meccanica/mat/Rolls%20Royce%20-%20The%20Jet%20Engine.pdf
[69]
[PDF] NTSB/AAR-78-03
Jan 26, 1978 · DC-9, operating as Southern Flight 242, crashed in New Hope, Georgia. After losing both engines in flight, Flight 242 attempted an emergency.
[70]
Grumman F-14 Tomcat: The Iconic Big Cat - PlaneHistoria
Oct 4, 2022 · ” It has been estimated that up to 40 F-14As were lost due to accidents caused by compressor stalls in the TF30 engines. Navy Secretary John F.
[71]
Accident Antonov An-124-100 08 Black, Saturday 6 December 1997
Dec 6, 2024 · An Antonov 124-100 transport plane was destroyed when it crashed immediately after takeoff from Irkutsk-2 Airport, Russia.
[72]
[PDF] aircraft accident report. trans world airlines, inc. b707, n742tw, ...
The first officer of Flight 159 was making the takeoff. In the takeoff roll, he heard a loud report from the right side of the aircraft, and experienced a ...
[73]
Bird strikes in aviation: A systematic review for informing future ...
Bird strikes with aircraft have been increasing, leading to higher safety risks for passengers and crew, and rising costs for airlines.Missing: post- | Show results with:post-