If you’re familiar with the usual flying profile of a commercial airliner, you’ll likely have heard the phrase “step climb.” If you have ever wondered what exactly that term means, then this article is for you. In the broadest of strokes, a step climb is a progressive altitude increase where the pilots go up and level off at different points before reaching the final cruise altitude.
The number of interim altitudes and the height at which they are set depend on a couple of basic variables: ultimate cruising altitude, weather, traffic, and, finally, fuel load. The whole point of the step climb is to conserve fuel because taking off and burning hard directly to the desired altitude of 30,000 to 40,000 feet wastes a lot of gas.
The medium to long-haul narrowbody and widebody jet flights typically employ some variation of a step climb because they take off heavy with a heavy fuel load on departure. Spending some time cruising lower down is more efficient until that weight burns off (literally) and then climbing is a better option for efficiency’s sake. The exception is on short legs when there isn’t much time or point in climbing to a higher altitude in between take off and landing.
A Crowded Sky
The natural question that pops up after learning about the step climb is: why don’t jets just fly a slow climb all the way up instead of leveling off? The answer is traffic. The need to monitor and track every aircraft’s altitude to deconflict planes means that it isn’t going to be safe to perform a “simple cruise climb” in many cases. The modern era of air travel has congested airspace around virtually every populated area, and even transoceanic and transcontinental air corridors are busy.
The ever-increasing focus on efficient fuel consumption and the push to keep planes in the air producing revenue means that every airline is trying to use the same optimal flight routes. Overlapping flight plans to and from busy hubs around the world makes it a hectic job for air traffic controllers to keep everyone moving as smoothly as possible, with safety being their top priority.
Bustling airways mean that the safest and simplest way for jets to execute an efficient climb profile is to confirm a number of different altitude changes with air traffic control on the way up to cruising height. Some exceptions exist if the route has no other traffic along the way. One interesting example is the Concorde, which always flew a simple cruise climb because it flew so high (18,000 meters or 60,000 feet), there was no need to deconflict, according to Heritage Concorde.
Fast Movers Only
The theory of how a step climb saves fuel is only really applicable to high-flying, fast jets that have turbofan engines. The propeller and turboprop performance profile and service ceiling limitation generally eliminate any useful results from a step climb profile. The reason is two-fold: range and efficiency.
Propeller-powered aircraft lose efficiency in thinner air as the prop is not ideal at such high altitudes. That means that a cruising altitude above 10,000 feet may be good for some high-performance models, but in general, it isn’t desirable for a lot of small planes in general aviation (GA) or even light commercial flying or cargo hauling. Turboprops can go higher, but also hit a limit of efficiency well before the range that jetliners often fly in.
GA, bush pilots, light commercial aircraft, and anything else flying by prop-power tend to have a shorter range than even a regional jet. Some rare models may be outliers, but since these aircraft don’t fly as far as a jetliner, the motivation to use a step climb profile is even further diminished. Since propeller aircraft don’t climb as high, even on longer distance flights, step climbs are generally reserved for jet aircraft.
Computer-Assisted Climbing
In 2025, the capability of flight management systems (FMS) is better than ever. The options for autopilot have reached a level where they can virtually fly the entire flight plan with minimal intervention from the pilots, as Honeywell outlines. The algorithms run by these incredibly powerful avionics can find the most ideal path to the top of climb (TOC) from departure that will conserve fuel as much as possible.
This technology has been continuously developed over the last several decades to reach the current level of maturity it has today. FMS can calculate a continuous climb or a step climb, depending on the desires of the flight crew. Simply by changing the setting on the flight computer, the pilots can program the perfect route to cruising altitude and the autopilot will follow that plan exactly.
Due to its extremely high reliability, the FMS saves money for the airline by flying routes as accurately as possible. That has motivated carriers to encourage pilots to monitor and correct FMS for the majority of the flight, instead of flying hands on unless necessary. The never-ending push to reduce operating costs means that autopilot is almost always the one at the stick when the plane is climbing to altitude.
The Case Against Step Climbs
The ultimate goal of climbing to altitude for any revenue service, passenger or cargo, is to achieve the most efficient flight profile that requires the least gas possible. Real-world considerations like traffic, weather, timelines, and others can interfere, but that is the basic principle. Technically, a continuous, simple cruise climb would be the best in absolute terms. The difference is generally negligible enough not to warrant a change in the way that air traffic is managed.
Research, however, has restated that a perfect flight profile would follow a continuous climb, rather than a step climb. That would yield small percentage improvements in fuel economy but also in emissions. One such case is a 2014 research study by Ramon Dalmau-Codina and Xavier Prats of the Technical University of Catalonia, where they used an Airbus A320 as the model.
The research’s conclusion showed that a continuous climb to TOC is more efficient by as much as 10% on longer distances. On short itineraries, the difference becomes less impressive. The introduction of longer-range narrowbodies than ever before, like the A321XLR and 737 MAX jets, means that even the smaller jetliners will be looking for every way to optimize operations.
Is Step Climb Inefficient?
The International Civil Aviation Organization (ICAO) recommends continuous climb operations (CCO) to achieve fuel savings, but real world operations do not always allow for that. Furthermore, studies have stated that reducing thrust levels near TOC has a noticeable improvement on fuel efficiency as well. A study by Ryota Mori of Kobe University, in conjunction with Eurocontrol found that changing the FMS power level to maximum cruise thrust (MCR) just before reaching TOC saved approximately 100 pounds of fuel.
Mori conducted multiple simulations with different variables, like headwinds or no wind, before observing the technique in a live flight. The pilots that conducted the test gave positive remarks, saying:
“MCR climb is unique and straightforward. If achieving sufficient fuel saving is feasible through MCR climb, I am willing to adopt this approach. The adjustment of cruise thrust settings is executed within the CDU, with no discernible increase in workload. With the maximum thrust reduced, the pilot monitors vertical speed more frequently, which presents a minor concern”
FMS set-ups often automatically calculate step climb profiles as default options, as do pilot navigation and planning software like Foreflight. The continued prevalence of the step climb by necessity means that it remains a common choice on many flight plans. However, a continuous climb is also popular when opportunity allows.
Relaxed Cruise Climbing
The idea of “relaxed cruise” operations is currently being explored as a middle ground between the conventional step climb and continuous, simple cruise climb. ATC clearance is always required for a step climb, and the precise location along the route is contingent upon several factors, including aircraft size, the weather, and the distance between two successive flight levels.
FMS assistance has made it possible to fly more precisely than any human can achieve, and safety sensors keep planes deconflicted automatically. In 1982, the International Civil Aviation Organization (ICAO) launched the Reduced Vertical Separation Minima (RVSM) program with the aim of effectively doubling airspace capacity. That was achieved by cutting VSM from 2,000 feet to 1,000 feet, making RVSM acceptable up to 41,000 feet.
In 2017, Ramon Dalmau-Codina and Xavier Prats published an analysis in Aerospace Science and Technology of how shallower climbs between separation altitudes would reduce fuel consumption and emissions. Their conclusion proposes that with SESAR and NextGen air traffic management (ATM) programs, the relaxed step climb could be introduced safely to improve both the efficiency and emissions of air travel worldwide.
