What is FLC mode and how do I use it in a flight simulator?

FLC (Flight Level Change), also shown as FLCH or LVL CHG, is an autopilot vertical mode that pitches the aircraft to hold a selected airspeed while climbing or descending to a preselected altitude. In most general-aviation aircraft, you manage power manually; the autopilot controls pitch and captures the target altitude.

How does FLC mode work?

FLC is a pitch mode, not a throttle mode or a fixed climb-rate mode. You select an altitude and an indicated airspeed, or Mach where supported, and the autopilot changes pitch to maintain that speed while moving towards the altitude.

During a climb, FLC lowers the nose if the aircraft becomes too slow and raises it if the aircraft becomes too fast. The resulting vertical speed changes with power, weight, altitude and atmospheric conditions. During a descent, the same pitch-for-speed logic applies, but you normally need to reduce power before the aircraft can descend.

The selected speed is therefore the command; vertical speed is the result. Our explanation of pitch, flight-director and autopilot logic covers how these components work together.

How do I use FLC in a flight simulator?

The basic FLC procedure is the same across most flight simulators, although button labels and speed controls vary by aircraft.

1. Select the target altitude. Set an altitude above the aircraft for a climb or below it for a descent. An incorrect selected altitude is the most common reason FLC moves the aircraft in the wrong direction.
2. Set up the flight director and autopilot. With only the flight director active, you must hand-fly the command bars. Engage the autopilot if you want it to move the controls.
3. Select FLC, FLCH or LVL CHG. Confirm the mode on the flight-mode annunciator at the top of the primary flight display. The annunciator, not the button light, tells you which mode is actually controlling pitch.
4. Set a safe target speed. Many systems initially capture approximately the speed at which FLC was selected. Adjust the reference with the aircraft's speed or pitch-reference control, using small changes rather than commanding a large pitch change at once.
5. Manage power. Apply suitable climb power when ascending. For a descent, reduce power enough for the aircraft to maintain the selected speed while losing altitude.
6. Monitor altitude capture. As the aircraft approaches the selected altitude, the active vertical mode should change from FLC to altitude capture and then altitude hold. Be ready to intervene if the mode does not change.

G1000-equipped aircraft commonly provide FLC through the autopilot controller; our practical guide to G1000 autopilot controls explains the associated buttons and annunciations. Microsoft Flight Simulator users can also follow our simulator-wide autopilot setup and mode checks.

Does FLC control the throttle?

FLC normally does not control the throttle in general-aviation aircraft. If the aircraft lacks autothrottle, power remains entirely under your control even though the autopilot is holding airspeed through pitch.

Airliners can behave differently. Their FLCH or LVL CHG mode may work with autothrottle to command climb thrust or idle thrust, depending on the aircraft and its active automation modes. Check both the pitch and thrust annunciations; never assume that selecting FLC has moved the throttles.

FLC also cannot create performance the aircraft does not have. With insufficient climb power, it may reduce the climb rate to maintain speed, level temporarily, or fail to climb. With excessive power during a descent, it may produce a very shallow descent or remain close to level.

Can I use FLC for descents?

Yes, FLC can command a speed-controlled descent when a lower altitude is selected and power is reduced sufficiently. It is useful when controlling airspeed matters more than maintaining a particular descent rate.

FLC does not guarantee a three-degree path, a specific vertical speed or compliance with waypoint altitude restrictions. Use VNAV for a programmed vertical path when the aircraft supports it, or VS when you need a predictable rate and can monitor airspeed closely.

FLC versus VS: which mode should I use?

Choose FLC when airspeed protection is the priority and VS when the required vertical rate is the priority.

FLC is not stall protection: an unsafe reference speed is still unsafe, and the autopilot has pitch and performance limits. For selecting sensible rates when using VS, see our climb and descent rate guidance.

Why is FLC not climbing or descending?

FLC usually fails to produce the expected vertical movement because of an incorrect altitude, unsuitable power or a mode that never became active.

• Wrong selected altitude: verify that the target is above you for a climb or below you for a descent.
• FLC is only armed or has been cancelled: read the flight-mode annunciator. ALT, VS or another vertical mode may still be active.
• Autopilot is not engaged: with the flight director alone, the command bars move but the aircraft does not follow them automatically.
• Power is unsuitable: add climb power or reduce descent power. FLC uses pitch to hold speed and cannot override inadequate or excessive thrust.
• The speed reference is wrong: an unusually low or high target can cause an extreme pitch attitude, a weak climb or an unexpectedly steep descent.
• A controller is cancelling the mode: a duplicated button assignment or a hardware switch sending ALT or VS commands can replace FLC immediately after selection.
• The aircraft models different logic: FLC, FLCH and LVL CHG are not implemented identically in every default aircraft or add-on. Use the cockpit annunciations and the aircraft's included documentation rather than relying on one universal key sequence.