An ineffective tailplane makes the aircraft incapable of recovering

from the stall condition, which is due to

Stall warner's and stick pushers.

Stall warners are either an artificial audio warning and/or a stick shaker, which usually are activated at or just before the onset of the prestall buffet. Stick pushers are normally used only on aircraft with superstall qualities and usually activate after the stall warning but before the stall, giving an automatic nose-down command. Both systems normally receive a signal from an incidence-measuring probe.