<prompt> Bheka isigaba esingezansi bese uphendula umbuzo emva kwalokho ngolimi olufanayo nesigaba: I-Passage: Ekuqaleni kwawo-1990, i-Gulfstream Aerospace ne-Sukhoi Design Bureau baqala umzamo ohlanganyelwe wokuthuthukisa indiza yebhizinisi encane engaphansi kwezwi, igama lekhodi elithi S-21. Ngenxa yesidingo emakethe ezingabazisayo commercial indiza supersonic travel, ukuzibophezela iphrojekthi buthaka futhi ukubambezeleka mounted. Gulfstream ekugcineni ziqedwe ubambiswano, nakuba Sukhoi waqhubeka umsebenzi S-21. Umbuzo: Yayiyini indiza eyakhiwa yizinkampani zombili ndawonye?  <response>: I-S-21 