Definition
In instrument flying, a supporting bank instrument is a flight instrument that confirms or backs up the bank information shown on the primary bank reference. During straight-and-level flight, the heading indicator and the turn coordinator serve as supporting bank instruments — they verify that the wings are level and that no turn is developing, supporting what the attitude indicator (the primary bank reference) is showing.
Plain English
It's an instrument you cross-check to confirm what your main bank instrument is telling you. If the attitude indicator says the wings are level, the supporting bank instruments should agree by showing a steady heading and no turn.
Context Anchor
Seen in instrument scan discussions, especially when the FAA handbook explains which instruments are primary and which ones support them during straight-and-level flight.
Derivation
"Supporting" comes from the Latin supportare, meaning to carry or hold up. In this context, the instrument 'holds up' or backs up what another instrument is showing — it provides confirming evidence rather than the primary indication.
Why Pilots Care
Using supporting bank instruments prevents over-controlling and helps maintain precise heading and coordination when the primary instrument is temporarily unreliable.
Intuition Check
Do not read bank as money or the side of a river. In this context, bank means the airplane’s side-to-side tilt. Supporting means it helps confirm the main indication; it does not replace the main instrument for that task.
Example Sentence 1
While holding straight-and-level on instruments, the pilot scanned the heading indicator and turn coordinator as supporting bank instruments to confirm the attitude indicator was showing wings level.
Example Sentence 2
The turn coordinator functioned as the supporting bank instrument when the pilot verified that the turn rate matched the heading change shown on the primary instrument.