Performance Class A (Jets) - Complete ATPL Subject Guide

Performance Class A, officially designated as ATPL Subject 034, represents the pinnacle of performance knowledge required for professional pilots. While Subject 032 introduced fundamental performance concepts primarily applicable to lighter propeller aircraft, Subject 034 delves into the complex world of certificated performance for large turbine-powered transport aircraft operating under the most stringent regulatory framework.

The distinction between Class A performance and other performance classes is profound. Class A operations require that the aircraft can suffer an engine failure at any point during takeoff, and still either safely reject the takeoff or continue the takeoff and climb away, clearing all obstacles with regulatory margins. This requirement fundamentally shapes how we plan and execute every departure, and understanding these requirements is essential for any pilot aspiring to command large transport aircraft.

The Philosophy of Certificated Performance

Commercial aviation operates on a foundation of proven, certificated performance rather than theoretical calculations or "best effort" attempts. When Boeing or Airbus publishes performance data for their aircraft, those numbers represent actual demonstrated performance during rigorous flight testing, reduced by regulatory safety factors to ensure that line pilots, operating production aircraft in normal service conditions, will consistently achieve or exceed the published performance. This philosophy means that certificated performance data is inherently conservative - the aircraft will almost always perform better than the charts indicate, providing a safety buffer that accounts for normal variations in pilot technique, minor aircraft wear, and environmental factors not explicitly captured in the chart parameters.

Understanding this concept is crucial because it explains why we never attempt to "add back" the safety factors or operate closer to theoretical limits. The safety factors aren't arbitrary bureaucratic requirements but carefully calculated margins based on decades of operational experience. They account for the difference between a test pilot flying a brand-new aircraft with meticulous preparation versus a tired line pilot on the fourth leg of a long day, flying an aircraft that's been in service for years, possibly with some systems operating on MEL relief, in weather that may not match forecasts perfectly.

Regulatory authorities divide aircraft performance into categories based on size, complexity, and intended operations. Class A represents large transport aircraft certificated under the most demanding standards - currently CS-25 (EASA) or Part 25 (FAA). These standards require multi-engine aircraft to demonstrate that safe operations can continue following an engine failure at any point, including the most critical phases of flight during takeoff and landing. The performance data published in the Aircraft Flight Manual represents legal requirements that must be met for every operation, not guidelines or recommendations.

Takeoff Performance and V-Speeds

The takeoff phase presents the most complex performance scenario in normal operations because it combines high weight, low speed, proximity to terrain, and the risk that an engine failure could occur at the worst possible moment. Understanding the web of V-speeds that govern takeoff operations, and the relationships between them, represents the foundation of Class A performance knowledge.

Every takeoff begins with fundamental stall speeds that establish minimum safe airspeeds. VS represents the stall speed in a given configuration - VS1 refers to stall speed in takeoff configuration with flaps in the takeoff position, while V_S0 indicates stall speed in landing configuration with full flaps. These speeds vary with weight, altitude, and temperature, and they form the basis for calculating all other takeoff speeds. Regulations require that all other takeoff speeds maintain specific margins above stall speed to ensure adequate maneuvering capability even in the most demanding situations.

Minimum control speeds present another constraint that becomes critical particularly at high power settings. VMC represents the minimum speed at which, following an engine failure, the pilot can maintain directional control using rudder alone with the remaining engine at takeoff power. Below VMC, the asymmetric thrust from the operating engine overwhelms the available rudder authority, and the aircraft will yaw uncontrollably toward the failed engine regardless of pilot inputs. VMCA specifies this minimum control speed in the air, while VMCG defines it on the ground. Both speeds depend on factors including aircraft weight, center of gravity position, bank angle permitted, and environmental conditions.

The minimum unstick speed, VMU, represents the slowest speed at which the aircraft can physically become airborne. Rotate earlier than VMU and the aircraft simply won't leave the ground because the wing cannot generate sufficient lift at that speed and angle of attack. This speed emerges from flight testing and depends on weight, configuration, and center of gravity position. Aircraft with forward CG positions require higher V_MU because the tail-down moment from the forward CG requires more elevator authority to rotate, and that elevator deflection creates drag that increases the speed required for liftoff.

V1, perhaps the most critical speed in transport operations, represents the decision speed or critical engine failure speed. It's the maximum speed at which a pilot can recognize an engine failure, decide to reject the takeoff, and bring the aircraft to a stop within the available runway length, or above which the pilot must continue the takeoff on the remaining engine and be able to safely become airborne and clear obstacles. This speed is not fixed but varies with runway length, aircraft weight, environmental conditions, and obstacle locations. For a given set of conditions, there exists a specific V1 value that balances these competing requirements, typically found where the accelerate-stop distance equals the accelerate-go distance - the balanced field length condition.

Rotation speed, VR, is the speed at which the pilot initiates rotation by applying aft control column. This speed must be high enough that the aircraft can reach VLOF (liftoff speed) by the end of the runway, must not be less than V1, must not be less than 1.05 times VMC to ensure adequate control following engine failure at rotation, and must be high enough to reach V2 (takeoff safety speed) at the screen height of 35 feet with one engine inoperative. In practice, VR is typically about 5-10 knots above V1, though the exact relationship depends on aircraft type and conditions.

V2 defines the takeoff safety speed that must be achieved at the screen height of 35 feet with one engine inoperative. This speed represents the regulatory-mandated minimum safe speed for maneuvering after takeoff with an engine failed, and it must be at least 1.2 times VS (stall speed in takeoff configuration) for two-engine aircraft, or 1.15 times VS for aircraft with three or more engines. The lower multiplication factor for multi-engine aircraft reflects their better controllability and performance with one engine failed, as the asymmetric thrust is less severe with multiple engines.

The relationship between these speeds follows a hierarchy: VMCG and VS1 form the foundation, above which V1 must be selected, then VR must meet or exceed V1 and other constraints, leading to VLOF at the appropriate point, and finally achieving V2 by screen height. This progression isn't arbitrary but ensures that at every point during the takeoff, the aircraft maintains adequate control and performance margins even if an engine fails.

Rejected Takeoff and Accelerate-Stop Distance

The rejected takeoff scenario represents one of the most demanding decisions a pilot faces. The regulations require that if an engine fails at or before V1, the pilot must be able to reject the takeoff and stop within the available runway distance, including any stopway. Understanding the components of this accelerate-stop distance and the factors affecting it is essential for proper takeoff planning.

Accelerate-stop distance comprises several distinct phases. The acceleration phase covers the ground roll from brake release to V1, during which the aircraft accelerates with all engines operating. At V1, we assume an engine fails and the pilot requires a recognition time - typically one or two seconds depending on the certification basis - during which the aircraft continues to accelerate slightly or maintain speed. Once the pilot recognizes the failure and decides to reject, there's a transition time of about one second while the pilot closes throttles and applies brakes. Only then does deceleration actually begin.

The deceleration phase involves maximum braking using the aircraft's normal wheel brakes with anti-skid functioning normally, along with aerodynamic drag and, if installed, thrust reversers. However, for certification purposes, regulations do not credit thrust reversers in the accelerate-stop distance calculation because they're not considered sufficiently reliable - they might malfunction when needed most. Operators may use reversers during actual rejected takeoffs, and they certainly help, but they cannot be assumed available when demonstrating that the aircraft meets certification requirements.

Runway condition dramatically affects stopping performance, particularly on wet or contaminated surfaces where the coefficient of friction between tires and runway drops significantly. A perfectly dry runway might provide a friction coefficient around 0.8, while wet pavement reduces this to perhaps 0.4-0.6 depending on tire tread depth, runway texture, and presence of standing water. Slush, snow, or ice reduce friction further still, and can create additional drag that affects both acceleration and deceleration. Many performance manuals provide limited or no data for contaminated runways, effectively prohibiting operations when contamination exceeds specified limits unless special procedures and performance calculations are used.

Balanced field length represents an important concept in takeoff planning. This is the runway length at which, for a specific aircraft weight and environmental conditions, the accelerate-stop distance exactly equals the accelerate-go distance (takeoff distance with one engine inoperative). At balanced field length, V1 is optimized such that rejecting or continuing after engine failure requires exactly the same runway length. On longer runways, V1 can be increased, providing more speed and energy if the takeoff is continued, while still allowing a rejected takeoff within runway limits. On shorter runways, V1 may need to be reduced to ensure adequate stopping distance, though it can never be reduced below regulatory minima like V_MCG.

Operators consider several factors when selecting V1 on runways longer than the minimum required. Higher V1 values improve engine-out climb performance after liftoff because the aircraft has more airspeed and energy, making obstacle clearance easier. However, higher V1 also means higher energy that must be dissipated during a rejected takeoff, potentially causing brake overheating or exceeding tire speed limits. Some operators use a "maximum brake energy speed" concept, limiting V1 to prevent brake or tire temperature issues during rejected takeoffs. Others consider obstacle clearance requirements and select V1 to optimize the overall safety margin considering both rejected and continued takeoff scenarios.

Engine-Out Climb Performance

Following an engine failure after V1, the aircraft must continue the takeoff, and this requires adequate climb performance to clear obstacles and climb to a safe altitude. Regulations specify minimum climb gradients that must be achievable at specific speeds and configurations with one engine inoperative, and these requirements shape aircraft design and operational limits.

The first segment climb begins at liftoff and continues until gear retraction is complete, typically reaching a height of about 400 feet above the runway. During this segment, the landing gear remains extended in most cases, creating significant drag that severely impairs climb performance. With one engine failed, the remaining engine must overcome total drag, compensate for the failed engine's drag, and provide excess thrust for climbing, all while maintaining V2 speed. The regulatory requirement mandates a minimum gross climb gradient - the actual climb gradient achieved - that varies with number of engines: two-engine aircraft must achieve zero percent or better (simply avoid descending), three-engine aircraft must achieve 0.3 percent, and four-engine aircraft must achieve 0.5 percent.

This graduated requirement based on engine count reflects the reality that losing one engine on a two-engine aircraft removes half the available thrust, while losing one engine on a four-engine aircraft only removes one quarter. The asymmetric thrust issue is also less severe on multi-engine aircraft because the operating engines are distributed more evenly about the centerline. Importantly, these are gross gradients - the actual geometric climb path over the ground. Net climb gradients, used for obstacle clearance calculations, are the gross gradients reduced by 0.8 percent for two-engine aircraft, 0.9 percent for three-engine aircraft, and 1.0 percent for four-engine aircraft, providing a safety buffer to account for variations in pilot technique and aircraft condition.

Second segment climb begins when gear retraction is complete and continues until the aircraft reaches acceleration altitude, typically 1,000 feet above runway elevation or specified by departure procedures. During second segment, the aircraft maintains V2 or a higher speed if obstacle clearance requires it, with landing gear retracted but takeoff flaps still extended. The drag reduces significantly compared to first segment once the gear is retracted, and climb performance improves accordingly. Regulatory requirements specify minimum gross climb gradients of 2.4 percent for two-engine aircraft, 2.7 percent for three-engine aircraft, and 3.0 percent for four-engine aircraft. These more demanding gradients reflect the improved configuration and the need to climb above the most significant obstacle clearance altitudes near airports.

Third segment climb, also called the acceleration segment, begins at acceleration altitude where the pilot allows the aircraft to accelerate while either maintaining altitude or climbing at a reduced gradient. This segment exists because takeoff flaps, while necessary to reduce stall speed and enable takeoff at reasonable airspeeds, create substantial drag that limits cruise climb performance. The aircraft must transition from takeoff configuration to a clean or low-drag configuration suitable for cruise climb, and this requires accelerating from V2 to the flap retraction speed and then to the final climb speed. During acceleration, climb gradient naturally reduces or may even become zero as thrust is used to increase kinetic energy rather than potential energy.

Fourth segment climb begins when the aircraft reaches final climb speed in the clean or reduced flap configuration appropriate for cruise climb. This segment represents the final part of the departure where the aircraft climbs to cruise altitude. Regulatory requirements mandate minimum gross climb gradients of 1.2 percent for two-engine aircraft, 1.5 percent for three-engine aircraft, and 1.7 percent for four-engine aircraft. These relatively modest gradients reflect the efficient clean configuration but must still be achievable at the reduced power setting typical of cruise climb power rather than maximum continuous thrust.

Obstacle clearance during engine-out departure follows specific rules that ensure adequate terrain and obstacle clearance throughout the departure path. The departure path is constructed using net climb gradients, which are gross gradients reduced by the safety factors mentioned earlier. This departure path must clear all obstacles within a defined area - typically 300 feet laterally on each side of the intended track, with this area sometimes widening with distance from the airport. The aircraft must clear these obstacles by at least 35 feet vertically, with some procedures requiring greater clearances.

Temperature, altitude, and weight profoundly affect climb performance, and on hot days at high-elevation airports, these factors may severely limit the allowable takeoff weight. Engine thrust decreases with increasing temperature and altitude due to reduced air density. Higher weight increases drag and requires higher speed (V2 increases with weight), further reducing climb gradient. An aircraft might be able to depart at maximum structural weight from a sea-level airport on a cold day, while the same aircraft might be restricted to 70 percent of maximum weight when departing from Denver on a hot afternoon, purely due to the requirement to meet minimum climb gradients with one engine inoperative.

Landing Performance Requirements

Landing performance for Class A aircraft involves considerations as complex as takeoff, though the approach differs because engine failures during landing are less critical than during takeoff. The aircraft approaches landing at a relatively low power setting, and adding power from a windmilling or even completely failed engine isn't necessary to ensure a safe landing - the aircraft will land regardless, and the challenge is ensuring it stops within available runway length.

The regulatory requirement for landing distance calculation assumes the aircraft crosses the runway threshold at a screen height of 50 feet, at an airspeed of VREF, which equals 1.3 times V_S (stall speed in landing configuration). This speed provides adequate stall margin while not being so fast that stopping becomes problematic. From the 50-foot point, the calculation assumes the aircraft continues descending at a normal rate, touches down at a reasonable distance beyond the threshold, and then decelerates using wheel brakes with anti-skid functioning, aerodynamic drag, and properly deployed spoilers/speedbrakes if normally used.

Like takeoff calculations, regulatory landing distances do not credit thrust reversers even though they're normally used and significantly reduce actual stopping distance. This conservative approach ensures that if reversers fail to deploy or are unavailable for any reason, the aircraft can still stop safely. Similarly, the calculations assume specific brake system operation, typically normal brakes, not emergency or alternate brake systems that might be less effective.

The landing distance actually demonstrated during certification flight testing is then multiplied by 1.67 (or divided by 0.6, which is equivalent) to determine the required landing distance for operational planning. This substantial safety factor accounts for normal variations in pilot technique, possible runway contamination not accounted for in the demonstrated data, non-standard approach profiles, and the statistical reality that not every landing will be as precisely executed as those performed by test pilots during certification. The effect is that only 60 percent of the available landing distance is considered usable for performance planning purposes.

For wet runways, additional factors may apply depending on the aircraft type and the specific performance data available. Some aircraft have demonstrated wet runway performance showing smaller increases in landing distance on wet surfaces, while others require significant additional distance or prohibit operations on wet runways exceeding certain contamination depths. Aquaplaning, where a layer of water builds up between the tire and runway surface, dramatically reduces braking effectiveness and can occur at speeds above a certain threshold that depends on tire pressure.

Landing climb requirements ensure that if a go-around becomes necessary during the approach, the aircraft can safely climb away even if an engine has failed. The regulations require a minimum climb gradient of 2.1 percent for two-engine aircraft with landing flaps set, landing gear extended, one engine inoperative, and the operating engine at maximum available go-around thrust. While this seems like a modest gradient, consider that landing flaps typically create more drag than takeoff flaps, and the gear is extended, creating significant drag. This requirement can limit landing weight on hot days at high-elevation airports, and some airports with challenging go-around procedures may publish maximum landing weights specifically related to go-around performance requirements.

Operational Performance Management

In airline operations, performance calculations occur for every flight, and the operational flight plan includes detailed performance data for takeoff at the departure airport and landing at both destination and all planned alternate airports. These calculations consider actual runway in use, forecast or actual temperature, pressure altitude (based on altimeter setting), runway condition if not dry, any relevant obstacles in the departure or approach path, and aircraft weight at each phase.

Modern flight planning systems automatically generate this data based on aircraft type, weight, and environmental conditions, producing tables of V-speeds for takeoff and maximum takeoff and landing weights for all applicable runways. The flight crew reviews this data before departure, verifying that it makes sense and that the aircraft weight is within all applicable limits. If conditions change - temperature different than forecast, runway changed, contamination reported - new performance calculations must be conducted before departure or arrival.

The before-takeoff briefing includes performance data, with the pilot flying announcing the planned V-speeds: "V1 is 140 knots, V_R 145 knots, V2 150 knots." Both pilots set speed bugs on their airspeed indicators at these speeds. This brief serves multiple purposes: it ensures both pilots know the planned speeds, confirms that performance calculations were completed, and establishes clear expectations for the takeoff. The speeds may seem like simple numbers, but they represent the culmination of complex calculations ensuring that the takeoff can be safely rejected or continued regardless of when an engine might fail.

During the takeoff roll, the pilot monitoring calls out specific speed milestones. The first calls typically occur approaching V1, with calls like "80 knots" (crosscheck that both airspeed indicators agree), then "V1" at decision speed. After V1, the pilot flying is committed to continuing even if an engine fails, and the pilot monitoring calls "Rotate" at V_R. If an engine fails before V1, the pilot flying should reject the takeoff. If it fails at or after V1, the takeoff must continue. This discipline ensures that the regulations' carefully balanced performance requirements are actually utilized as designed.

MEL considerations affect performance planning because certain equipment may be inoperative while still permitting dispatch. An inoperative anti-skid system, for example, significantly degrades braking performance and requires using alternate performance data that assumes no anti-skid function. Inoperative engine bleed air systems affect takeoff performance because the aircraft cannot use engine anti-ice during takeoff if engine anti-ice is required by conditions. Each MEL item that affects performance requires careful evaluation to ensure the resulting performance remains acceptable for the planned operation.

Operational variations from standard procedures must be carefully considered. A non-standard flap setting selected for some operational reason - perhaps to reduce takeoff noise - requires using performance data specific to that flap setting. An intersection takeoff using less than full runway length requires performance calculations based on the reduced length actually available. Wind components must be conservatively estimated, with some operators applying wind limits (using only 50 percent of reported headwind but 150 percent of reported tailwind) to account for gusts and variations.

EASA Learning Objectives

The EASA syllabus for Subject 034 requires comprehensive understanding of Class A operations certification basis and operational requirements. Candidates must demonstrate detailed knowledge of all takeoff V-speeds including their definitions, regulatory minima, relationships to each other, and factors affecting their values. The calculation of takeoff distances in various scenarios - all-engines operating, one-engine-inoperative, on various runway surfaces, in different environmental conditions - must be thoroughly understood, as must the meaning and application of balanced field length.

Climb performance requirements for each segment of the departure profile require detailed knowledge including minimum climb gradients, speeds to be maintained, configurations applicable, and how to use this information for obstacle clearance analysis. The regulations' net and gross gradient concepts must be clear, along with the safety factors involved. Candidates must understand how environmental factors affect climb performance and how this translates into operational weight limitations on specific departures.

Landing performance calculation procedures and requirements form another major component, including the basis for demonstrated landing distance, the 1.67 safety factor, and how to account for wet or contaminated runways. Landing climb requirements for go-around scenarios and their implications for landing weight limits must be thoroughly understood. The integration of performance requirements with operational procedures - how performance data is actually used in flight operations - completes the learning objectives.

Exam Tips and Practical Considerations

Performance Class A questions test both theoretical knowledge and practical application ability. You must understand the regulatory basis for requirements while being able to apply performance data to operational scenarios. Common question types include determining whether a planned takeoff is acceptable given specific conditions, calculating or identifying V-speeds for particular situations, determining maximum allowable weights for given conditions, and analyzing obstacle clearance scenarios.

V-speed relationship questions frequently appear, testing whether you understand which speeds must be greater than others and by how much. Remember that V1 cannot be less than VMCG (ground minimum control speed) and cannot exceed VR (rotation speed). VR must be at least 1.05 times VMCA (air minimum control speed) when there is one engine inoperative at VR. V2 must be at least 1.2 times VS for two-engine aircraft or 1.15 times V_S for three or more engines. These relationships aren't arbitrary but reflect the balanced requirements for control and performance following engine failure.

Balanced field length concepts require understanding the trade-off between accelerate-stop and accelerate-go distances, and how V1 selection affects both. Higher V1 provides better performance for a continued takeoff but requires more distance to stop if rejected. Lower V1 allows shorter stopping distance but may compromise climb performance or even be prohibited by minimum control speed requirements. Questions often present scenarios and ask for the appropriate action - increase or decrease V1, reduce weight, or select a different runway.

Climb gradient questions may ask you to determine if obstacle clearance is adequate given specific performance capabilities and obstacle heights/locations. Remember to use net climb gradient (gross minus the regulatory reduction) for obstacle clearance, not gross gradient. Understanding that a 2.4 percent gross gradient for a two-engine aircraft translates to only 1.6 percent net gradient (2.4 minus 0.8) is essential for correctly evaluating whether obstacles can be cleared.

Landing distance questions often involve the 1.67 factor and may ask whether a given runway provides adequate length for landing. If the runway is 2,500 meters long, only 1,500 meters (2,500 / 1.67) can be credited for performance calculation purposes. Questions may also address what happens if the actual landing is longer than planned - perhaps landing beyond the touchdown zone or with excess speed - and whether the aircraft can still stop within the remaining runway.

Related Articles:

• General Performance - ATPL Subject 032
• Mass & Balance - ATPL Subject 031
• Flight Planning - ATPL Subject 033
• Aircraft General Knowledge - ATPL Subject 021
• Operational Procedures - ATPL Subject 070