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Minimum control speeds

Minimum control speeds refer to the calibrated airspeeds at which multi-engine aircraft maintain directional and lateral control following the failure of the critical engine, ensuring safe operation during takeoff, climb, or landing phases.^[1] These speeds are critical performance parameters defined in aviation regulations to prevent loss of control due to asymmetric thrust from an inoperative engine.^[2] In the air, the minimum control speed, denoted as V_MC or V_MCA, is the lowest calibrated airspeed at which full rudder deflection can counteract the yawing moment caused by the critical engine's sudden failure, with the aircraft in a standard configuration including takeoff power on the operating engines, landing gear retracted and flaps in the takeoff position, and maximum takeoff weight.^[3] This speed varies based on factors such as aircraft weight, center of gravity position, bank angle (typically limited to 5 degrees), and power settings, and for transport-category aircraft under 14 CFR Part 25, V_MC is determined with the aircraft trimmed at 1.13 VSR1 or the all-engines-operating best rate-of-climb speed if higher, and VMCA must not exceed 1.13 VSR1.^[2] V_MC testing simulates engine failure at the most adverse condition, often with the aircraft climbing at a 5-degree bank toward the operating engine.^[2] On the ground, the minimum control speed, V_MCG, applies during the takeoff roll and is the calibrated airspeed at which directional control can be maintained using aerodynamic rudder forces and nose-wheel steering after the critical engine fails, without deviating more than 30 feet from the centerline.^[4] Unlike airborne V_MC, V_MCG does not rely on lift and is influenced by factors like runway surface, tire friction, and nose-wheel steering limits; it is typically lower than V_MC and must be at or below the takeoff decision speed (V₁) for safe abort options.^[1] These speeds are established through rigorous flight testing during aircraft certification by authorities like the Federal Aviation Administration (FAA) or European Union Aviation Safety Agency (EASA), ensuring pilots can maintain heading within specified limits using available controls.^[2] Pilots must adhere to V_MC during engine-out procedures to avoid stalls or uncontrolled yaw, and operational margins are often conservatively set above certified values in flight manuals.^[5] Non-compliance can lead to accidents, as asymmetric thrust increases with decreasing speed, emphasizing the need for precise airspeed management in multi-engine operations.^[3]

Fundamentals

Definition and Physical Principles

Minimum control speed, denoted as V_{mc}, is defined as the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain directional control of the multi-engine aircraft using full rudder deflection toward the operating engine and a bank angle not exceeding 5 degrees toward the operating engine, with the remaining engine(s) at takeoff power.^[6] This speed ensures that the aircraft remains controllable in straight flight following an engine failure, preventing an uncontrollable yaw or roll into the failed engine.^[7] The underlying physical principle stems from the asymmetric thrust generated when one engine fails, producing a yawing moment that tends to rotate the aircraft toward the inoperative engine. This yawing moment can be expressed as N = T \times d, where N is the yawing moment, T is the thrust from the operating engine, and d is the perpendicular distance (moment arm) from the engine's thrust line to the aircraft's center of gravity.^[8] The magnitude of this moment is relatively independent of airspeed but increases with higher thrust settings and greater separation between engines and the center of gravity. To counteract this, the rudder generates an opposing aerodynamic force, but its effectiveness diminishes at lower speeds because rudder authority is proportional to dynamic pressure, q = \frac{1}{2} \rho V^2, where \rho is air density and V is airspeed; thus, below V_{mc}, even maximum rudder deflection cannot balance the yawing moment.^[7] Sideslip effects further influence control, as a slight sideslip angle can generate additional yawing moments from the vertical tail and fuselage, aiding or hindering stability depending on the direction.^[8] In propeller-driven multi-engine aircraft, additional asymmetric yaw arises from propeller effects, including P-factor (asymmetric blade loading due to the propeller's angle of attack), torque reaction from the operating engine, and the spiraling slipstream that unevenly affects the vertical tail.^[7] A windmilling propeller on the failed engine exacerbates the yaw by increasing drag and altering airflow over the wing and tail.^[8] These forces compound the thrust asymmetry, making the critical engine—the one whose failure produces the most severe yaw—the outboard engine on the side with clockwise-rotating propellers (typically the left engine in conventional twins). The concept of minimum control speeds was developed in the post-World War II era during the expansion of multi-engine aircraft design and certification standards to mitigate the risk of loss of control at low speeds after engine failure.^[9]

Importance in Multi-Engine Aircraft

Minimum control speeds play a pivotal role in preventing loss-of-control accidents in multi-engine aircraft, particularly following an engine failure during critical phases like takeoff and climb. An NTSB special study (AAS-79-02) of light twin-engine aircraft accidents from 1972-1976 examined 2,229 total accidents, of which 610 were fatal; engine failures were involved in 477 of these accidents and contributed to 123 fatal incidents (about 20% of all fatal light twin accidents in the dataset), with approximately 72% of those fatal cases attributed to loss-of-control scenarios directly linked to inadequate speed management post-failure.^[10] The study also concluded that engine failure in light twins carried a fatality risk four times higher than in single-engine aircraft.^[11] More recent analysis of NTSB data from 2002-2011 confirms the elevated risks, finding that non-commercial twin-engine piston aircraft accidents had a 57% fatality rate compared to 18% for single-engine aircraft, with loss of control after engine failure remaining a primary factor.^[12] Training requirements emphasize Vmc awareness to mitigate these risks, mandating that pilots demonstrate proficiency in multi-engine operations during certification and type rating examinations. The FAA's Airman Certification Standards for commercial and ATP pilots include tasks such as simulated engine failure procedures, where applicants must maintain directional control at or above Vmc while applying full power to the operating engine.^[13] Additionally, training programs stress adherence to the "blue line" speed (Vyse), the best single-engine rate-of-climb speed marked on airspeed indicators, which provides a practical safety margin above Vmc—typically 5-10 knots—to ensure climb capability without encroaching on the minimum control threshold.^[7] This focus on Vmc demonstration and Vyse utilization is integral to multi-engine ratings, helping pilots develop instinctive responses to engine-out emergencies.^[14] In aircraft design, manufacturers incorporate Vmc margins to guarantee sufficient controllability, with certification standards requiring demonstration of Vmc to ensure adequate margin relative to stall speed, allowing a maximum 5-degree bank during determination to simulate realistic recovery without excessive rudder input, ensuring the aircraft remains flyable with one engine inoperative. By setting Vmc with this built-in buffer, designers prioritize operational safety, reducing the likelihood of control loss in engine-failure scenarios.^[7]

Primary Minimum Control Speeds

Minimum Control Speed Airborne (V MCA)

The Minimum Control Speed Airborne (V_MCA) is the calibrated airspeed at which directional control can be maintained in flight following the sudden failure of the critical engine, with the operating engine(s) set to takeoff power, full rudder deflection applied, and the aircraft configured for straight flight with zero yaw. This speed ensures that the yawing moment from asymmetric thrust can be counteracted solely by aerodynamic controls, preventing uncontrollable yaw or sideslip.^[15]^[3] The determination of V_MCA assumes the most adverse conditions: the critical engine (the one farthest from the CG or producing the greatest yaw moment) is inoperative, the propeller is windmilling in its most adverse position, the aircraft is at maximum takeoff weight or the weight yielding the highest speed (whichever is lower), the center of gravity is at its most aft limit, and the configuration includes landing gear retracted and flaps in the takeoff position. To aid controllability, a bank angle of 5 degrees toward the operating engine is permitted, which reduces the effective asymmetric rolling moment while maintaining near-zero sideslip. The test is conducted with maximum continuous takeoff power on the live engine(s) and no use of ailerons beyond that needed for the bank, emphasizing rudder authority alone for directional stability. Regulatory limits require V_MCA to be demonstrated such that it does not exceed values providing adequate stall margin, typically V_MCA ≤ 0.92 V_SR for transport aircraft.^[15]^[7]^[3] V_MCA arises from the balance of yawing moments in the aircraft's lateral-directional equations of motion, where the asymmetric yawing moment due to engine failure must be exactly offset by the combined effects of rudder deflection, sideslip-induced directional stability, and bank. In steady flight, the net yaw moment N = 0, leading to: N_{\text{thrust}} + N_{\beta} + N_{\delta_r} = 0 The thrust asymmetry produces a yaw moment N_{\text{thrust}} = T_{\text{crit}} \times d, where T_{\text{crit}} is the thrust of the failed engine and d is the engine's moment arm from the center of gravity. The directional stability term is N_{\beta} = \bar{q} S b C_{n_{\beta}} \beta, with \bar{q} = \frac{1}{2} \rho V^2 as dynamic pressure, S the wing reference area, b the wing span, C_{n_{\beta}} the yawing moment due to sideslip derivative, and \beta the sideslip angle. The rudder contribution is N_{\delta_r} = \bar{q} S b C_{n_{\delta_r}} \delta_r, where C_{n_{\delta_r}} the rudder yaw moment derivative (non-dimensionalized by wing S and b), and \delta_r the rudder deflection (maximum adverse). At V_MCA, the maximum rudder input and allowable sideslip just balance the thrust moment, with dynamic pressure scaling as V^2, yielding a square-root dependence on thrust and density. Full computations use iterative trim methods incorporating roll and side force equilibria.^[16]^[17]^[18] Variants of V_MCA exist based on configuration, such as with flaps extended (increasing the speed due to aft CG shift and reduced directional stability) or retracted (flaps up, often lower). Certification requires the highest value across configurations, but operational charts may provide flap-specific limits. For light twin-engine aircraft, typical V_MCA values range from 55 to 80 knots indicated airspeed, depending on model, weight, and conditions—for instance, 56 KIAS for the Piper Seminole in standard configuration.^[7]^[19]

Minimum Control Speed Ground (V MCG)

The minimum control speed on the ground, denoted as V_{MCG}, is the calibrated airspeed during the takeoff run at which, following the sudden failure of the critical engine, directional control of the multi-engine airplane can be maintained using nose wheel steering (with rudder for trim up to 150 pounds pedal force), with the airplane's path deviating no more than 30 feet laterally from the runway centerline.^[2] This speed ensures the pilot can counteract the yawing tendency from asymmetric thrust. Differential braking may assist operationally but is not credited in certification.^[4] The certification conditions for V_{MCG} include takeoff power setting on the operating engines, a dry runway surface, zero wind, the most adverse center of gravity position, and the airplane in takeoff configuration with landing gear extended.^[2] No aerodynamic lift is assumed, and the test focuses on ground-based control, allowing a brief reaction time (typically 1 second) before corrective action.^[4] Unlike the airborne minimum control speed (V_{MCA}), which depends on aerodynamic surfaces like the rudder for yaw control in flight, V_{MCG} relies primarily on mechanical inputs such as nosewheel steering to generate counter-yawing moments.^[5] This ground-oriented approach typically results in a lower V_{MCG} value compared to V_{MCA}, as steering provides effective directional stability even at reduced speeds where aerodynamic forces are minimal.^[20] In practice, V_{MCG} sets a lower limit for the takeoff decision speed V_1, which must exceed V_{MCG} to guarantee directional control if an engine fails during the initial rollout phase. Conceptual models for V_{MCG} often involve balancing yaw moments from thrust asymmetry against steering and friction-based forces, though certification uses dynamic simulations without crediting differential braking.^[21]^[22]

Certification and Regulatory Aspects

FAA and EASA Standards

The Federal Aviation Administration (FAA) defines minimum control speed (V_MC) under 14 CFR Part 25.149 for transport category airplanes as the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with the remaining engines at takeoff power, up to a bank angle of 5 degrees into the operating engine, while the airplane is airborne and in the takeoff configuration. Similarly, for normal, utility, and commuter category airplanes under Part 23.149 (prior to the 2017 rewrite), V_MC is the minimum calibrated airspeed at which, with any engine suddenly inoperative, control can be recovered with full rudder deflection, maximum available power on operating engines, and the landing gear and flaps retracted.^[1] These definitions emphasize directional and lateral control to counteract asymmetric thrust, with rudder force limited to 150 pounds in historical Part 23 requirements and zero thrust on the failed engine.^[23] The European Union Aviation Safety Agency (EASA) equivalents in Certification Specifications (CS) CS-25.149 for large aeroplanes mirror the FAA's Part 25 definition closely, defining V_MC as the calibrated airspeed where control is maintained after critical engine failure, with all engines at takeoff power except the failed one at idle, a maximum 5-degree bank toward the operating engine(s), and the airplane in the most unfavorable takeoff configuration. CS-23.149 for small aeroplanes aligns similarly, requiring determination of V_MC for critical takeoff and landing configurations to ensure controllability with engine failure. These standards are harmonized through joint efforts like the Aviation Rulemaking Committee (ARAC), minimizing differences in certification requirements for multi-engine aircraft while incorporating EASA-specific considerations such as gust loads during low-speed operations.^[24] For transport category airplanes under both FAA Part 25 and EASA CS-25, while there is no direct numerical limit on V_MC relative to the one-engine-inoperative, gear-up stall speed (V_S1G), safety margins above stall are ensured through related requirements, such as the second segment climb speed V₂ being not less than the greater of 1.13 V_S1G or 1.13 V_MCA. For smaller multi-engine airplanes under FAA Part 23 and EASA CS-23, the limit was historically 1.2 V_S1 in takeoff power conditions, with requirements applying only to multi-engine designs where engine failure could compromise control, unlike single-engine airplanes.^[1] In 2017, the FAA rewrote Part 23 (Amendment 23-64, effective 2018 with post-2020 implementation), shifting from prescriptive rules to performance-based standards that simplify V_MC certification for light twin-engine aircraft by reducing mandatory testing burdens and allowing equivalent safety demonstrations for configurations below 6,000 pounds maximum takeoff weight.^[25] This update facilitates innovation in small aircraft while maintaining equivalent safety levels for minimum control speeds.^[26]

Flight Testing Procedures

Flight testing procedures for determining minimum control speeds are critical during aircraft certification to ensure compliance with regulatory standards for multi-engine airplanes. These tests simulate engine failure scenarios under controlled conditions to establish the lowest speeds at which directional and lateral control can be maintained using available aerodynamic surfaces, rudder, and brakes. Procedures are outlined in FAA Advisory Circulars AC 25-7D for transport-category airplanes and AC 23-8C for normal-category airplanes, emphasizing safe, repeatable methods that minimize risk while capturing precise data.^[27]^[28] For the minimum control speed airborne (V_MCA), tests are conducted at high altitudes to achieve low dynamic pressure, simulating conditions that maximize the challenge to directional control. The aircraft is configured for takeoff with flaps extended, landing gear retracted, maximum continuous power on the operating engine(s), and the most unfavorable center of gravity position, typically forward. At a stabilized speed above the estimated V_MCA, the critical engine is suddenly failed—often via fuel cutoff to represent the most adverse asymmetric thrust—while the pilot applies maximum available rudder deflection and aileron to counteract yaw and maintain wings-level flight or a bank not exceeding 5° toward the operating engine. Speed is then gradually reduced in increments until the control limit is reached, defined as the point where yaw exceeds 20° or bank exceeds 5° despite full rudder input, or where rudder pedal force reaches 150-180 pounds without maintaining straight flight. Tests are repeated for both engines to identify the critical one yielding the higher V_MCA, with multiple runs at decreasing speeds starting from approximately 1.2 times the estimated V_MCA to build pilot familiarity.^[27]^[28] The minimum control speed ground (V_MCG) is determined through ground runs on a smooth, dry, hard-surfaced runway under zero crosswind conditions. The aircraft is set in takeoff configuration with flaps as for takeoff, maximum takeoff power on all engines initially, and the most critical weight and center of gravity. During the takeoff roll, at a speed corresponding to V_EF (engine failure speed), the critical engine is suddenly failed using a fuel cutoff, and the pilot applies maximum rudder and differential braking or nosewheel steering to maintain alignment with the runway centerline, measuring lateral deviation. Control is considered maintained if deviation does not exceed 30 feet from the intended track, with no use of excessive skill. Tests are conducted bilaterally for left and right engines, starting at speeds above the estimated V_MCG and decrementing until the limit, where directional control cannot be held despite full inputs. Brakes are fully serviceable but worn to simulate operational use, and runs are aborted if deviation risks runway excursion.^[27]^[28] Safety protocols are integral to all tests, with abort criteria established for excessive bank, yaw, altitude loss, or structural loads, allowing immediate power restoration or configuration changes. Chase aircraft accompany airborne tests for visual monitoring and emergency support, while flight data recorders (FDR) or equivalent instrumentation capture time histories of parameters like airspeed, control inputs, and attitudes. Ground tests use wide runways to provide margin for error, with emergency vehicles on standby. Pilots must demonstrate average skill levels, avoiding exceptional maneuvers, and tests progress from conservative setups (e.g., throttle reduction before cutoff) to full simulations.^[27]^[28] Instrumentation ensures accurate measurement and calibration. Calibrated airspeed systems, often using pitot-static booms or trailing cones, provide primary speed data, with GPS or ground-based methods for true airspeed verification against wind influences via anemometers or vane systems. Yaw meters and bank angle sensors, integrated into the aircraft's attitude heading reference system, record deviations to 0.1° precision, while rudder force transducers monitor pedal inputs. Torque meters and propeller RPM gauges support data analysis for propeller effects, and onboard video or data acquisition units log all variables for post-test review and extrapolation to sea-level conditions if needed.^[28] Recent advancements in certification leverage validated flight simulators for initial V_MC demonstrations, particularly for high-risk scenarios, to reduce live flight test exposures while correlating simulation data with flight results for credibility. This approach, guided by FAA and EASA frameworks, has gained traction since 2020 for low-speed controllability assessments, including engine-out conditions, enabling safer iteration before confirmatory flights.^[27]^[29]

Factors Influencing Minimum Control Speeds

Aerodynamic and Design Factors

The size and authority of the rudder play a critical role in determining minimum control speeds, particularly V_MCA, by providing the necessary counteracting yaw force against asymmetric thrust from an engine failure. Larger rudders generate greater side force at low speeds, thereby lowering V_MCA as they allow the aircraft to maintain directional control at reduced airspeeds. The effectiveness depends on the rudder's area relative to the vertical stabilizer, often expressed as the critical area ratio, which ensures sufficient authority without exceeding structural limits during certification.^[3]^[20] Engine placement significantly influences minimum control speeds through the yawing moment produced by asymmetric thrust, with outboard engines typically being the critical ones due to their greater distance (moment arm) from the aircraft's center of gravity. In twin-engine aircraft, failure of the engine with the longer effective arm—often the left engine owing to P-factor effects—creates a larger yaw moment toward the inoperative side, increasing V_MCA. For example, in quad-engine configurations, outboard engine failure amplifies this moment compared to inboard ones, necessitating enhanced rudder authority or higher control speeds. In contrast to twins, multi-engine designs with widely spaced engines demand careful balancing of thrust lines to mitigate these effects.^[7]^[30] Propeller configuration affects minimum control speeds by altering thrust asymmetry and drag characteristics during engine failure. Counter-rotating propellers, where engines turn in opposite directions, eliminate the critical engine concept by symmetrizing P-factor and torque effects, thereby reducing V_MCA compared to conventional same-direction rotation setups. High-bypass turbofan engines exhibit less asymmetry than propeller-driven systems, as they lack significant P-factor influences and produce more uniform thrust distribution, contributing to lower minimum control speeds in jet multi-engine aircraft.^[7]^[31] Wing design elements, such as sweep and dihedral, impact minimum control speeds via their influence on roll-yaw coupling and lateral-directional stability. Swept wings provide an effective dihedral that enhances roll stability in response to yaw, helping to counteract the rolling moment from asymmetric thrust and potentially lowering the required control speed. Dihedral angles further couple yaw disturbances to restorative rolling moments, improving overall directional control margins during engine-out scenarios. However, extended flaps typically increase V_MCA due to heightened drag and lift asymmetry, which exacerbates the rolling tendency toward the inoperative engine.^[7]^[3] V_MCA exhibits high sensitivity to bank angle, as banking toward the operating engine introduces a horizontal lift component that assists the rudder in countering yaw, allowing control at lower speeds. The change in V_MCA can be approximated by the relation \Delta V_{MCA} = V_{MCA} \times (1 - \cos \phi), where \phi is the bank angle in radians; this derives from the reduction in effective asymmetric yaw moment as the vertical lift vector tilts, providing a sideslip-reducing force proportional to \sin \phi for small angles, while the load factor scales with $1 / \cos \phi. Full derivation involves balancing lateral-directional equations of motion, incorporating thrust yaw moment N_T, weight mg, and rudder deflection \delta_{r \max}, under the small-angle assumption \sin \phi \approx \phi. Certification limits bank to 5° to standardize testing and prevent overly optimistic values.^[17]^[7]

Operational and Environmental Factors

Operational and environmental factors significantly influence minimum control speeds (V_MC) in multi-engine aircraft, as these variables can alter the balance between asymmetrical thrust, drag, and available control authority during engine-out scenarios. Aircraft weight and center of gravity (CG) position play key roles in determining V_MC. According to FAA guidance, V_MC increases as aircraft weight decreases, with the lightest allowable weight representing the most unfavorable condition because the horizontal component of lift from the bank angle, which assists the rudder, is proportional to weight and thus smaller at lower weights, necessitating a higher airspeed for control.^[7] An aft CG further elevates V_MC by shortening the moment arm between the CG and the rudder, thereby reducing rudder effectiveness against asymmetrical forces; forward CG positions are more favorable, lowering V_MC by enhancing this arm length.^[7] Power settings on the operating engine directly impact V_MC, with higher thrust—such as full takeoff power—producing greater yaw-inducing asymmetry, thus raising V_MC to maintain directional control.^[7] Conversely, reducing power on the operating engine (e.g., to idle on the failed engine while maintaining moderate power on the live one) decreases V_MC by lessening the yaw moment. Icing conditions exacerbate this by accumulating on the rudder, reducing its control effectiveness by approximately 8%, thereby increasing V_MC due to diminished aerodynamic authority in countering asymmetry.^[32] Wind effects, particularly crosswinds, raise the effective V_MC by adding lateral forces that demand additional rudder input, compounding the challenge of directional stability during takeoff or low-speed flight.^[33] Density altitude influences V_MC through reduced air density, which lowers engine thrust (especially in normally aspirated engines) and propeller efficiency, decreasing the indicated airspeed (IAS) value of V_MC; however, the corresponding true airspeed (TAS) for V_MC increases as TAS = IAS / √σ, where σ is the density ratio (less than 1 at altitude), meaning pilots must account for higher ground-relative speeds at high density altitudes to ensure safe margins.^[7] Configuration changes like flap and landing gear positions also affect V_MC. Extended flaps increase drag asymmetry, particularly if positioned behind the operating engine, which can raise V_MC by 5-10 knots in landing configurations due to heightened yaw tendencies from uneven airflow disruption.^[7] Similarly, retracted landing gear increases V_MC by removing the stabilizing keel effect, whereas extended gear lowers V_MC by enhancing directional stability through increased surface area interaction with airflow.^[7] Pilot technique, especially bank angle management, critically influences V_MC in practice. Maintaining a 5° bank toward the operating engine reduces V_MC by offsetting yaw with a lateral lift component, lowering it by about 3 knots per degree up to that limit; improper technique, such as flying wings-level, can increase V_MC by more than 15 knots overall, risking loss of control well above published values.^[7]

Additional Concepts and Speeds

Minimum Control Speeds for Aircraft with More Than Two Engines

In aircraft with more than two engines, such as trijets and quadjets, the definition of the critical engine adapts to the configuration's asymmetry. The critical engine is the one whose failure produces the most adverse yawing moment.^[34] This contrasts with symmetric twin-engine designs, where engine criticality may depend on propeller rotation or crosswind conditions, but the principle remains focused on maximizing yaw and roll tendencies during failure. Adjustments to minimum control speeds (V_MCA and V_MCG) for these aircraft account for the reduced relative thrust asymmetry from engine failure. With three or more engines, the loss of one represents a smaller percentage of total thrust, resulting in a lower yaw moment, as the remaining engines provide more balanced propulsion. Regulations under FAR 25.149 require certification with the critical engine inoperative at maximum takeoff thrust on the others, ensuring directional control within a 5-degree bank, but the distributed thrust in multi-engine designs inherently lowers the calibrated airspeed threshold for controllability.^[7] Asymmetric thrust limits are governed by the same regulatory framework, mandating that aircraft maintain control against the maximum imbalance from any single engine failure without exceeding rudder authority. In practice, this allows multi-engine aircraft to operate at V_MC values where the net yaw is counteracted more effectively due to the partial thrust continuity from additional engines. Modern widebodies like the Airbus A350 benefit from fly-by-wire systems that automatically allocate control surfaces to counteract asymmetry, effectively reducing the pilot workload through optimized rudder and aileron inputs.^[35] Emerging electric and hybrid multi-propeller designs further adapt these speeds through distributed propulsion. Systems like those developed by magniX for hybrid-electric applications, such as retrofitting the four-engine De Havilland Dash 7, distribute thrust across multiple smaller electric motors, minimizing asymmetry upon single-unit failure and potentially reducing V_MC compared to concentrated propulsion layouts, as the incremental thrust loss is negligible relative to total output.^[36] This approach enhances low-speed controllability in certification testing under evolving standards like those explored in NASA's Electrified Powertrain Flight Demonstration program.^[37]

Safe Single-Engine Speeds and Approach Considerations

In multi-engine aircraft, the safe single-engine enroute speed, denoted as V_SSE, represents the minimum calibrated airspeed at which level flight can be maintained with one engine inoperative and the other at maximum continuous power. This speed, originally termed the safe single-engine speed, also serves as the lower limit for intentionally simulating engine failures during flight training to prevent inadvertent loss of directional control. Manufacturers determine V_SSE based on aircraft-specific performance data, ensuring it provides a practical safety buffer above the minimum control speed (V_MC) while allowing for enroute operations or demonstrations.^[7]^[38] The best single-engine climb speed, V_YSE, is the airspeed that yields the optimal rate of climb with one engine inoperative, typically achieved by applying maximum available power to the operating engine, feathering the propeller on the failed engine, and retracting flaps and landing gear to minimize drag. Marked by a blue radial line on the airspeed indicator, V_YSE is flown during engine-out climbouts to maximize altitude gain and is positioned above V_MC to maintain directional stability, often incorporating a design margin of approximately 1.3 times V_MC in certification testing for many light twin-engine airplanes. Pilots must monitor airspeed closely to avoid decelerating toward V_MC, as V_YSE balances climb performance with control requirements.^[7]^[38] During approach and landing phases with one engine inoperative, the minimum control speed increases to V_MCL (minimum control speed for landing) due to the adverse effects of extended landing gear and flaps, which amplify yaw from asymmetric thrust and drag. Federal Aviation Administration (FAA) certification under 14 CFR § 25.149 requires V_MCL to be established in the most critical landing configuration, with the aircraft trimmed for a 3-degree approach path, go-around thrust on operating engines, and a bank angle not exceeding 5 degrees toward the operating engine. This speed ensures controllability post-failure but is higher than the clean-configuration V_MCA, necessitating careful speed management to avoid excursions.^[6] For single-engine landings, the reference landing speed (V_REF) must incorporate a margin above V_MCL to account for gusts, configuration drag, and potential power adjustments, with common operational guidance recommending at least 5 to 15 knots above the published V_MC depending on aircraft type and conditions. The inoperative engine's windmilling propeller or unfeathered state increases drag, further elevating the effective minimum control speed, which heightens the risk of directional instability if airspeed decays. Pre-landing pilot briefings stress maintaining V_REF or higher throughout the approach, using partial flaps initially to preserve controllability, and avoiding abrupt power reductions that could exacerbate yaw. Single-engine go-arounds demand prompt reconfiguration to climb speeds like V_YSE, with regulations requiring the approach climb capability at not less than 1.23 times the reference stall speed in landing configuration to ensure a positive gradient.^[38]

References

[1]
[PDF] Code of Federal Regulations Sec. 23.149
Sec. 23.149. Minimum control speed. (a) VMC is the minimum calibrated airspeed at which, when any engine is suddenly made inoperative ...
[2]
14 CFR § 25.149 - Minimum control speed. - Law.Cornell.Edu
§ 25.149 Minimum control speed. (a) In establishing the minimum control speeds required by this section, the method used to simulate critical engine failure ...
[3]
Minimum Control Speed (air) (Vmca) | SKYbrary Aviation Safety
Vmca is defined as the minimum speed, whilst in the air, that directional control can be maintained with one engine inoperative.
[4]
[PDF] Code of Federal Regulations Sec. 23.149
VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made ...
[5]
Minimum Control Speed (ground) (Vmcg) | SKYbrary Aviation Safety
Vmcg is defined as the minimum calibrated airspeed, during the takeoff run at which, if the critical engine suddenly fails, it is possible to maintain ...<|control11|><|separator|>
[6]
V-Speeds Explained (Vx, Vy, Va, Vs, Vfe, Vmc, Vno, Vne, etc)
Jan 15, 2025 · VMC, or minimum control speed, represents the lowest speed at which a multi-engine aircraft can maintain controlled flight with one engine ...What Are V-Speeds? · V-Speeds List · VA: Maneuvering Speed
[7]
14 CFR 25.149 -- Minimum control speed. - eCFR
V MC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that ...
[8]
[PDF] Airplane Flying Handbook (FAA-H-8083-3C) - Chapter 13
... control are performed by flight test pilots while gradually reducing the speed with each attempt. VMC is the minimum speed at which directional control could.
[9]
[PDF] ASYMMETRIC FLIGHT
The yawing moment is also affected initially by the rate of thrust decay of the 'dead' engine and ultimately by its drag. In addition, the yaw is aggravated by ...Missing: physics | Show results with:physics
[10]
A Brief History of the FAA | Federal Aviation Administration
The modern age of powered flight began in 1903 when Orville Wright made the first sustained, powered flight on December 17 in a plane he and his brother ...Missing: Vmc | Show results with:Vmc
[11]
Twice Bitten - Aviation Safety Magazine
One NTSB study examined 2,229 accidents, of which 610 involved fatalities. Engine failures were involved in 123 of the fatal accidents. The pilots had lost ...
[12]
[PDF] NTSB/AAS-79-02 - Library Collections
Dec 13, 1979 · NTSB-AAS-79-02 studied 477 light-twin aircraft accidents from 1972-1976 involving engine failures, finding many lacked pilot proficiency and ...
[13]
[PDF] Commercial Pilot for Airplane Category Airman Certification Standards
The FAA created FAA-G-ACS-2, Airman Certification Standards Companion Guide for Pilots, to provide guidance considered relevant and useful to the community. The ...
[14]
Multiengine Training - AOPA
Although you must maintain VMC or faster to maintain control of the aircraft, remember that VMC decreases when you decrease power on the operating engine.Single-Engine Aerodynamics... · Emergency Procedures · Decision Making And...
[15]
McDonnell Douglas DC-10-10 | Federal Aviation Administration
Aug 19, 2025 · The resulting lift asymmetry caused an uncontrollable left roll and loss of control of the airplane. The airplane crashed inverted, killing all ...
[16]
https://labs.engineering.asu.edu/aircraft-design/wp-content/uploads/sites/115/2023/05/AIAA-2017-3764.pdf
[17]
[PDF] Minimum Control Speed Estimation for Conceptual Design
May 11, 2023 · This paper describes the formulation of methods used to provide high quality estimates of minimum control speeds (VMCG and VMCA) at the ...<|separator|>
[18]
None
### Formula for VMCA
[19]
[PDF] VMCAv1.m User's Manual - Virginia Tech
Aug 3, 2004 · A MATLAB m-file, VMCAv1.m, has been written to calculate the single engine minimum control speed (VMCA) of a jet powered aircraft.Missing: formula aviation
[20]
What is Minimum Control speed V MC or V MCA really? - AvioConsult
Minimum Control speed V MC or V MCA is the lowest airspeed which can be obtained with full directional and/or lateral control inputs.Video on YouTube · VMCA testing · VMCA definition · Display of VMCA
[21]
(PDF) A Method to Calculate the Aircraft Ground Minimum Control ...
Aug 6, 2025 · A method to calculate VMCG based on mathematical simulation is provided. All forces and moments act on the aircraft in the takeoff run are ...
[22]
Using Vmcg-Limited V1, Controllability Issues on Contaminated ...
Jan 29, 2019 · V m c g V mcg , or ground minimum control speed, is established by aircraft manufacturers during the aircraft certification process.
[23]
[PDF] Federal Aviation Administration, DOT § 23.149 - GovInfo
(e) At VMC, the rudder pedal force re- quired to maintain control must not exceed 150 pounds and it must not be necessary to reduce power of the opera- tive ...
[24]
[PDF] Flight Test Harmonization Working Group - Task 3 harmonize ...
Because the minimum required speed margin between VMU and VwF is partly there to reduce the probability for an airplane to reach a takeoff pitch attitude beyond ...
[25]
[PDF] Part 23 Amendment 23-64 Implementation Procedures Guide
Jun 15, 2022 · This worksheet provides a means to compare the baseline safety intent of amendment 23-64, which is the prescriptive language from amendment 23- ...
[26]
Understanding Part 23 Rewrite - AOPA
The FAA has rewritten the entire 14 CFR Part 23, changing the existing prescriptive certification standards to performance-based standards for a number of ...
[27]
[PDF] AC 25-7D, Flight Test Guide for Certification of Transport ... - FAA
Apr 5, 2018 · This advisory circular (AC) provides guidance for the flight test evaluation of transport category airplanes. This AC includes flight test ...
[28]
None
Below is a merged summary of the flight testing procedures for Minimum Control Speed (VMC) from AC 23-8C, consolidating all provided segments into a comprehensive response. To maximize detail and clarity, I’ve organized key information into tables where appropriate (in CSV format within the text) and provided a narrative overview. All relevant details from the summaries are retained, including test techniques, procedures, criteria, safety protocols, instrumentation, and useful URLs.
[29]
[PDF] CS 29/27 LOW-SPEED CONTROLLABILITY
The process developed by the RoCS team provides guidance on the use of flight simulation in certification and features four case studies that illustrate.
[30]
Multi-Engine Airplanes - My CFI Book
Oct 5, 2024 · Following an engine failure in flight, the airplane yaws toward the inoperative engine due to asymmetrical thrust. The rudder must be used to ...<|control11|><|separator|>
[31]
Counter-Rotating Propellers | SKYbrary Aviation Safety
The principle advantage of counter-rotation is to balance propeller torque effects thus eliminating any problems associated with a Critical Engine. Counter- ...
[32]
[PDF] Icing Effects on Aircraft Stability and Control Determined From Flight ...
The artificial ice reduced the elevator and rudder control effectiveness by 12% and 8% respectively for the 0° flap setting. The longitudinal static stability ...
[33]
[PDF] FAA Aviation Rulemaking Advisory Committee FTHWG Topic 22 ...
Jun 24, 2024 · control, and the effect of an adverse crosswind on VMCG increases significantly as runway friction decreases. As mitigation for these ...
[34]
[PDF] AC 91-70D - Advisory Circular
Mar 4, 2025 · This advisory circular (AC) contains both general information and detailed guidance for operators planning flights in oceanic and remote ...
[35]
Critical Engine | SKYbrary Aviation Safety
The critical engine is the one whose failure will result in the most adverse effects on the aircraft. The term is applicable to multi-engine fixed-wing ...
[36]
[PDF] NASA FAA-R CR .D-76 AIRWORTHINESS CRITERIA ...
the minimum control speed related to propulsion failure. This, then, would be tied to airspeed as opposed to angle of attack. .But, a single equivalent.
[37]
[PDF] special edition - Safety First | Airbus
F speed is the minimum speed at which flaps should be retracted from CONF 3 or 2 to CONF 1+F. It is represented by a green “F” on the PFD speed scale and ...
[38]
[PDF] A Review of Distributed Electric Propulsion Concepts for Air Vehicle ...
The emergence of distributed electric propulsion (DEP) concepts for aircraft systems has enabled new capabilities in the overall efficiency, capabilities, ...
[39]
magniX Launches Next Phase in NASA Program to Electrify Aviation
Aug 22, 2024 · magniX unveils De Havilland DHC-7 (Dash 7) demonstrator aircraft, launching next phase in NASA's Electrified Powertrain Flight Demonstration ...Missing: distributed Vmc
[40]
[PDF] Flying Light Twins Safely - FAA Safety
At least 5 degrees, and up to 10 degrees, angle of bank should be used to maintain directional control. The pitch attitude for Vyse should be assumed. • ...