Definition
A movable marker on the airspeed tape or airspeed indicator that the pilot sets to a chosen reference speed, such as a target approach speed, climb speed, or maneuvering speed. The bug provides a quick visual reference so the pilot can see at a glance whether current airspeed is above, below, or matching the selected target.
Plain English
A small marker the pilot slides to the speed they want to fly, so they can quickly see if they are on speed without reading numbers.
Context Anchor
Seen on a glass-cockpit airspeed tape, and on some round airspeed indicators, when setting or watching a target speed.
Derivation
The word 'bug' has been used since the early 1900s for a small movable pointer or marker on an instrument dial. It comes from the idea of a tiny insect-shaped indicator that 'sits' on the gauge at the chosen value. The same naming is used elsewhere in the cockpit, like the heading bug on the directional gyro.
Why Pilots Care
Provides an immediate visual cue for critical speeds during high-workload phases, reducing the need to read exact numbers and lowering the chance of missing target speeds.
Analogy
It is like putting a small sticky note on a gauge to show the number you want to match.
Intuition Check
Do not read “bug” as an insect or a fault here. In this context, a bug is a movable reminder marker set to a chosen airspeed.
Example Sentence 1
On downwind, she set the airspeed bug to 75 knots so she could fly a stabilized approach without constantly checking the exact number.
Example Sentence 2
During the climb checklist the student moved the airspeed bug to Vy to maintain best rate of climb.