On Airbus aircraft what is the 3 click tone that sounds once autopilot is disconnected? I have tried researching on the internet but could not find anything
There are two separate aural warnings that you might be referring to: one is indeed called 'Triple Click' and consists of three brief clicks, but is emitted when the landing capability becomes degraded or the autopilot otherwise changes mode.
The warning generated upon autopilot disconnection, instead, is the so-called 'Cavalry Charge' and consists of three longer beeping sounds; it's either played once or repeated continuously (cases 1 and 2 below).
From a table in the Airbus A320 FCOM, DSC-31-10 P 4/6:
Meaning: Landing capability downgrade or some cases of mode reversion.
Duration: 0.5 s (3 pulses)
- A/P disconnection by takeover push-button.
- A/P disconnection due to failure.
- 1.5 s
- Second push on takeover push-button.
- Press Master Warning light or takeover push-button.
More generally, the Flight Crew Techniques Manual describes the TRIPLE CLICK as:
...an attention-getter, designed to draw the flight crew's attention to the FMA.
The FMA will show a mode change or reversion by putting a white box around the new mode and pulsing the associated FD bar.