What about making them use it similar to a 'need to fire' option - That is, the Stuka pilot assumes it needs to 'airbrake' once it starts a strafing run - or a decided attack on a target. Currently all it does is to pitch from its cruise altitude and if allowed to, fires bullets - Perhaps, if a combined logic regarding this attack strategy causes it to 'airbrake' it could turn of the siren
For fighters, they used to use airbrakes, thinking, I suppose that, like their Vanilla BF2 counterparts they were using boosters - For planes like the Hurricane, this made them almost drop from the sky and made them easy targets for artillery
I believe this was changed, so I'm not sure its hardcoded to to use 'airbrakes' or boost after an attack run - Perhaps it can be changed to use it before...