If windshear is encountered during F/D takeoff or go–around,
In this case surely toga toga are the active modes!
the F/D pitch command bar provides commands to maintain the target speed until vertical speed decreases to approximately +600 fpm. At this point, the F/D pitch bar commands a 15 degree nose–up pitch attitude. If vertical speed continues to decrease, the F/D continues to command a 15 degree pitch attitude until a speed of approximately stick shaker is reached. It then commands pitch attitudes which result in intermittent activation of the stick shaker.
If fpm is the controlling input then capturing an altitude would reduce the v/s to zero. This would be below 600fpm so 15 degrees nose up would be commanded (if ws was still detected)
As the airplane transits the windshear condition
Ie the airplane is no longer in wind shear, all bets are now off and fd mode reverts to normal. If you were above commanded mcp altitude you would continue in toga toga until you made another selection. Below mcp alt then yes it would capture (if ws condition is left)
In any other mode below the reactive wind shear threshold, you need to activate toga by pushing the toga button. Otherwise the airplane tries to maintain the commands and uses thrust to the appropriate limit to recapture airspeed. If those modes were arm lvl change speed then..... Well that's a bad day below the reactive wind shear threshold.
Autopilot on a single approach disconnects because you have two ils receivers and one fmc I believe. Therefore the fd system is going from one system monitoring the master ils signal to one system monitoring one system, there is a break in the signal. On a dual channel approach below the self test, you have two systems monitoring two signals, there doesn't have to be a break to go to one system monitoring one fmc signal as something else takes the strain while it thinks.
It's all there it's just not written good
Cheers