Airline pilots rarely use full-rated takeoff thrust—and for good reason. Modern turbofan engines are designed with significant performance margins, meaning they can produce more than enough thrust without the need to apply maximum power on every departure. Under the right conditions, most operators intentionally reduce takeoff thrust because lower exhaust gas temperatures (EGT) decrease engine wear and improve long-term reliability, ultimately lowering maintenance costs and minimizing the risk of engine malfunction.

From safety considerations to engine preservation and operational efficiency, reduced-thrust procedures such as the Assumed Temperature Method (ATM) and certified fixed derates have become standard practice in global airline operations. These methods fully comply with regulatory takeoff performance requirements and often provide operational benefits that go beyond cost savings. For these reasons, full power takeoffs are usually unnecessary.

Why Pilots Avoid Full Thrust On Light Aircraft

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When aircraft are light, full rated thrust creates extremely high acceleration and climb rates. While this is within certified limits, it can lead to unusually steep pitch attitudes after liftoff, giving the sensation of a “rocket-like” takeoff. This procedure is still safe, but it can lead to handling characteristics and pitch attitudes that are less desirable, particularly for passenger comfort. While comfort alone is not the primary reason for selecting reduced takeoff thrust, it can be a contributing factor when full thrust is unnecessary with light payload.

The rocket-like performance of a light aircraft is especially noticeable during demonstration flights, where airplanes often depart with minimal payload. With significantly reduced weight, engines are capable of producing thrust levels that result in exceptionally high climb rates and steep pitch attitudes—at times appearing almost like a near-vertical departure. Unless you are an aviation geek, the steep pitch attitude and rapid acceleration during a light-weight takeoff are generally not preferred by most passengers.

For pilots, using reduced takeoff thrust rather than full thrust can feel noticeably different in terms of controllability and handling, especially during rotation and the initial climb. On the Boeing 737, a takeoff with reduced thrust requires increased back pressure during rotation. Pilots may also choose between full rated climb thrust and a reduced climb thrust setting. On some routes, such as departures from Incheon International Airport to Yantai, aircraft are initially cleared to FL240, with this clearance later revised to 7,200 meters (FL236) once they cross into Chinese airspace. When the aircraft is light and full climb thrust is used, the climb rate can be high enough to reach FL240 well before entering Chinese airspace. As a result, pilots who regularly operate this route may manage thrust or adjust the climb rate to avoid overshooting the level that will shortly be assigned.

Engines Are Built to Deliver More Than Needed

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Turbofan engines are engineered to produce maximum certified thrust even at temperatures up to their flat-rating limits, such as 30°C for the CFM56-7B series. This means that, unlike piston engines, turbofan engines are flat-rated. In other words, they can produce a constant amount of thrust up to a specified ambient temperature. Below these temperatures, the engine produces more capability than needed for a safe takeoff, even when thrust is reduced. This extra capability is why pilots trick their engines into thinking the temperature is hotter than usual or why they use fixed derates.

Modern twin-engine jet airliners are designed to safely continue a takeoff even if one engine fails after V1. Aviation enthusiasts often hear the “V1” callout in cockpit videos; once the aircraft passes V1, takeoff must continue even with an engine failure. This is possible because the remaining engine provides enough thrust for the aircraft to climb, maintain control, and configure for a safe return or diversion. Certification standards require that the aircraft demonstrate adequate one-engine-inoperative performance, ensuring it can safely meet mandatory climb gradient requirements.

To guarantee safety, the one-engine-inoperative takeoff flight path is divided into four regulated segments, each with specific climb criteria. These segments cover the transition from lift-off through gear retraction, maintaining takeoff thrust, accelerating in level flight, retracting flaps and slats, and climbing at maximum continuous thrust. Aircraft performance data ensures obstacles can be cleared by at least 35 feet, and takeoff weight must be reduced if required to meet these margins. What’s more, when pilots use a reduced-thrust takeoff, it still complies with all regulatory performance requirements.

Why Pilots Lie To Their Airplane

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Remember how turbofan engines produce the same thrust up to a certain temperature? Once the outside air temperature exceeds that limit, the engine begins to produce less thrust. Simply put, hotter air is less dense, and air density matters because air is a key ingredient in any internal combustion engine. The thinner the air, the less mass the engine can ingest, and the less thrust it can generate.

Pilots use this exact principle to their advantage during takeoff. If the engine produces less thrust on a hot day, then reducing thrust on a cooler day can be achieved simply by pretending the temperature is higher than it really is. By entering a higher “assumed temperature” into the aircraft’s flight management computer, the system behaves as though it is operating in hotter, less dense air. The electronic engine control (EEC) automatically reduces thrust accordingly, providing a lower—but still fully certified and performance-compliant—takeoff thrust setting.

On Boeing aircraft, this process is called the Assumed Temperature Method (ATM). For our counterparts who fly with the privilege of a built-in tray table, the same thing is known as a FLEX takeoff. ATM is inherently conservative because higher temperatures raise the true airspeed and reduce thrust. In reality, actual true airspeed is lower than the value calculated using the assumed temperature, so the aircraft uses less runway than the performance limit predicts. And since the actual density altitude is lower than the ATM value, safety margins exist.

Fixed Derate: A Certified Lower Thrust Rating

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A fixed derate is a certified thrust level lower than full rated thrust. Selecting it changes minimum control speeds, stabilizer trim settings, and establishes the derate as a takeoff operating limit. Because of these changes, pilots should not advance thrust beyond the derated level during takeoff unless absolutely necessary, such as during windshear or insufficient climb performance after V1.

Fixed derates can actually improve performance in certain situations. For example, on a contaminated runway, using a lower thrust setting reduces VMCG—the minimum speed at which the aircraft can be controlled on the ground with one engine failed. A lower VMCG means the aircraft needs less runway to maintain directional control, which can allow for a higher takeoff weight when the limiting factor is control capability rather than runway length itself.

Engine studies have shown fixed derates dramatically improve turbine blade life, even by an order of magnitude under maximum derate usage cycles. Lower internal temperatures and slower rotational speeds directly correlate with reduced fatigue stress, longer on-wing time, and delayed maintenance intervals. Reduced EGT deterioration also helps preserve fuel flow performance, resulting in long-term economic benefits.

Combining ATM and Derates

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Operators frequently combine a fixed derate with an assumed temperature to reduce thrust even further, provided all limitations for both methods are observed. This two-stage approach begins with selecting a derate (TO-1 or TO-2) and then entering an assumed temperature to further reduce thrust by up to 25% below full rated levels. Although combining a fixed derate with an assumed-temperature reduction isn’t prohibited by manufacturers, airline policies vary. Some operators allow the two methods to be used together, while others restrict it. Ultimately, it comes down to each carrier’s Standard Operating Procedures (SOP) and how they manage performance margins.

Because fixed derate is the operating limit, thrust levers cannot be advanced beyond the derated limit if an engine fails unless terrain clearance cannot be ensured. This protects the directional control margins tied to the derated thrust level. Nevertheless, the FMC continues to protect minimum control speed margins and adjusts V1 accordingly, ensuring the takeoff maintains certified performance.

Operational Impact:

Combined thrust reduction is particularly beneficial for short-haul airlines that perform many cycles per day. Since takeoff is the most engine-intensive phase, reducing thrust on every cycle yields significant long-term engine preservation and cost reductions. It also reduces cockpit workload by providing more predictable rotation characteristics compared to the aggressive pitch profiles that occur when taking off light with full thrust.

Safety and the Operational Tradeoffs

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The single most important safety benefit of reduced thrust is lowering the probability of engine failure during the most critical phase of flight. By keeping EGT and internal loads low, reduced-thrust takeoffs extend engine life and prevent hot-section deterioration, which is a major driver of in-service failures. This makes reduced thrust not just economical, but operationally safer in the long term.

Reduced thrust is not appropriate in all conditions. Full power is recommended whenever windshear is suspected, when runway contamination prohibits ATM use, or when anti-skid or EEC limitations prevent reduced-thrust operation. In such cases, maximum thrust is essential for performance and safety, demonstrating that pilots choose thrust settings based on conditions—not habit.

Reduced-thrust takeoffs are a carefully engineered and thoroughly studied part of modern airline operations. Far from compromising safety, they enhance it by reducing engine wear, minimizing the chance of failures, and providing performance margins that exceed certification requirements. While full thrust remains essential in specific conditions, it is rarely needed in day-to-day operations.