Vertical Speed Indicator


  • The Vertical Speed Indicator (VSI) is an instrument that displays rate of climb and descent to the pilot
    • This information helps the pilot determine the aircraft's trend
    • Reacts before changes in the altimeter is sensed allowing the pilot to be alerted quicker
    • May be referred to as a Rate-of-Climb indicator, a Vertical Speed Indicator, or a Vertical Velocity Indicator (VVI)
  • Calibrated differently depending on the country and its use as:
    • Feet Per Minute (FPM)
    • Meters Per Second (MPS)
    • Nautical Miles Per Hour (Knots)
  • The VSI can go by many different names to include:
    • Variometer
    • Rate of Climb Indicator
    • Vertical Velocity Indicator
    • Vertical Speed Indicator (VSI) is however, most common
  • Instantaneous VSIs (IVSIs) use two accelerometer actuated pumps to give you a lag free indication
Vertical Speed Indicator
Figure 1: Instrument Flying Handbook, Rate of Climb or Descent in Thousands of Feet Per Minute


  • There are no regulations that require a vertical speed indicator by federal aviation regulations
  • Always check the Pilot Operating Handbook for different requirements

How The Vertical Speed Indicator Works:

  • Measures rate-of-pressure change
  • The air enters the aircraft through the static port
  • This air enters a diaphragm (aneroid) where it expands/retracts to indicate a climb/descent by measuring the ambient changes in pressure within the static system
    • Through a calibrated leak/orifice, the air leaves the instrument case slower than the aneroid and allows for a stabilized indication of pressure change on the face of the instrument
  • As pressure drops, the aneroid compresses, indicating a climb
  • As the pressure increases, the aneroid expands, indicating a descent
  • As the aircraft levels off, pressure no longer changes and the pointer returns to its zero position

Instrument Errors:

  • The vertical speed indicator inherently lags, but is more sensitive than an altimeter
  • This can result in a 6-9 second lag to stabilize which will inhibit accurate readings during turbulence or abrupt control movements
  • Alternate sources of static, when selected, will typically show a momentary climb
    • This is due to pressure differences in the cockpit than outside
  • A blocked static port will give a zero indication

Preflight Check:

  • The VSI should read 0
  • If it indicates anything other than a zero feet per minute climb or descent on the ground, then the instrument can still be used, but that indication is the new "zero"
    • This, of course, is highly discouraged if the error is such that a mistake could create a serious hazard to flight, especially in weather

Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS)

  • IRUs are self-contained systems comprised of gyros and accelerometers that provide aircraft attitude (pitch, roll, and heading), position, and velocity information in response to signals resulting from inertial effects on system components
    • Once aligned with a known position, IRUs continuously calculate position and velocity. IRU position accuracy decays with time. This degradation is known as "drift"
  • INSs combine the components of an IRU with an internal navigation computer
    • By programming a series of waypoints, these systems will navigate along a predetermined track
  • AHRSs are electronic devices that provide attitude information to aircraft systems such as weather radar and autopilot, but do not directly compute position information
  • Aircraft equipped with slaved compass systems may be susceptible to heading errors caused by exposure to magnetic field disturbances (flux fields) found in materials that are commonly located on the surface or buried under taxiways and ramps
    • These materials generate a magnetic flux field that can be sensed by the aircraft’s compass system flux detector or "gate", which can cause the aircraft’s system to align with the material's magnetic field rather than the earth's natural magnetic field
    • The system’s erroneous heading may not self-correct
    • Prior to take off pilots should be aware that a heading misalignment may have occurred during taxi
    • Pilots are encouraged to follow the manufacturer’s or other appropriate procedures to correct possible heading misalignment before take off is commenced