Step climb
Encyclopedia
A step climb in aviation is a series of altitude gains that improve fuel economy by moving into thinner air as an aircraft becomes lighter and becomes capable of faster, more economical flight.

Description

Since the early days of jet
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

 aircraft and commercial travel, the technique of gradually climbing in cruise altitude as fuel burns off and the aircraft becomes lighter has been widely used by pilots. The altitude that provides the most fuel-efficient cruise at the start of a long flight, when the aircraft is fully loaded with fuel, is not the same as the altitude that provides the best efficiency at the end of the flight, when most of the fuel aboard has been burned. This latter altitude is usually significantly higher than the former. By climbing gradually throughout the cruise phase of a flight, pilots can make the most economical use of their fuel.

Originally, a simple cruise climb was used by pilots. This amounted to a simple, continuous, very gradual climb from an initial cruise altitude to a final cruise altitude, and made the most efficient use of fuel. However, with increasing air traffic and the assignment of distinct flight level
Flight level
A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

s to specific flights, airway
Airway (aviation)
In aviation, an airway is a designated route in the air. Airways are laid out between navigational aids such as VORs, NDBs and Intersections ....

s, and directions of flight, it is no longer safe to climb continuously in this way, and so most flights compromise by climbing in distinct steps—a step climb—with ATC
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

 approval, in order to ensure that the aircraft is always at an appropriate altitude for traffic control. While not quite as efficient as a continuous cruise climb, step climbs are still more efficient than maintaining a single altitude throughout a flight. The step climb intervals may be 1000, 2000, or 4000 feet, depending on the flight level
Flight level
A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

 rules which apply on the particular airway being flown.

Where traffic is not an issue, cruise climbs may still be used. The Concorde
Concorde
Aérospatiale-BAC Concorde was a turbojet-powered supersonic passenger airliner, a supersonic transport . It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation...

, for example, used a continuous cruise climb throughout its flights, since there was never any other traffic at the same altitude (nearly 60,000 feet) in the same direction.

In most modern commercial airliners, computers such as flight management system
Flight management system
A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...

s (FMS
FMS
-Government agencies:* Federal Magistrates Service, the former name of the Federal Magistrates' Court of Australia* Federated Malay States , historical British protectorate in then British Malaya...

) calculate and/or execute the proper steps in a step climb, in order to maximize the efficiency realized by the technique.

Step and cruise climbs are not normally applicable to lower-flying aircraft propelled by conventional piston engines with propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

s or turboprop
Turboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

s, since their performance characteristics may be very different from those of Turbofan
Turbofan
The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...

 or Jet engined aircraft. In fact, the most efficient altitude for a small general-aviation aircraft may be only a few thousand feet above the ground, and increasing altitude may diminish efficiency rather than improve it.

Informal step climbs

Some pilots use "rules of thumb" for determining when to perform a step climb. These "rules" do not consider the effects of different winds at different levels; computerised flight planning
Flight planning
Flight planning is the process of producing a flight plan to describe a proposed aircraft flight. It involves two safety-critical aspects: fuel calculation, to ensure that the aircraft can safely reach the destination, and compliance with air traffic control requirements, to minimise the risk of...

 systems may be better at height optimisation, and may even include 'step descents' in certain weather conditions. Two of the information rules used by some pilots are:
  • Keep climbing whenever you are light enough to climb to the next highest available flight level
    Flight level
    A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

    , until it is time for descent.
  • If it is possible to stay at the next higher cruise flight level
    Flight level
    A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

     for 20 minutes or more before "top of descent
    Descent (aircraft)
    A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or climb. Descents are an essential component of an approach to landing...

    " (TOD
    Top of descent
    In aviation, the top of descent, also referred to as the TOD or T/D, is the computed transition from the cruise phase of a flight to the descent phase, the point at which the planned descent to final approach altitude is initiated...

    ) then it is cost-effective to make the climb
    Climb
    thumb|right|An [[Embraer ERJ 145]] climbingIn aviation, the term climb refers both to the actual operation of increasing the altitude of an aircraft and to the logical phase of a typical flight following take-off and preceding the cruise, during which an increase in altitude to a predetermined...

    .

See also

  • Air traffic control
    Air traffic control
    Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

  • Flight level
    Flight level
    A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

  • Flight management system
    Flight management system
    A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...

  • Flight planning
    Flight planning
    Flight planning is the process of producing a flight plan to describe a proposed aircraft flight. It involves two safety-critical aspects: fuel calculation, to ensure that the aircraft can safely reach the destination, and compliance with air traffic control requirements, to minimise the risk of...

  • North Atlantic Tracks
    North Atlantic Tracks
    North Atlantic Tracks are trans-Atlantic routes that stretch from the northeast of North America to western Europe across the Atlantic Ocean. They ensure aircraft are separated over the ocean, where there is little radar coverage...

  • RVSM
  • Fuel starvation
    Fuel Starvation
    Fuel starvation and fuel exhaustion are problems that can affect internal combustion engines fuelled by either diesel, kerosene, petroleum or any other combustible liquid or gas. If no fuel is available for an engine to burn, it cannot function...

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