Shīlián de kèjī fāshèjī yìngdáqì tíngzhǐ le gōngzuò.
The transponder of the missing airliner stopped functioning.
Tips
memory
Read it piece by piece: 发射机 (transmitter) + 应答器 (response device) = a transmitter that answers back. In aviation news the shorter 应答机 (yìngdájī) is much more common.