▁on ▁their ▁own ▁ro cket - power ed ▁inter ceptor , ▁designated ▁as ▁the ▁Av ro ▁ 7 2 0 . ▁Of ▁the ▁six ▁companies ▁that ▁tender ed ▁propos als , ▁two ▁were ▁selected ▁for ▁development ▁contract s : ▁A . V . ▁Ro e ▁with ▁their ▁Av ro ▁ 7 2 0 ▁and ▁Sau nd ers - R oe ▁with ▁the ▁SR . 5 3 . ▁ ▁Iss ues ▁and ▁propos als ▁Sau nd ers - R oe , ▁recogn ising ▁that ▁it ▁would ▁need ▁to ▁out do ▁the ▁compet ing ▁Av ro ▁ 7 2 0 ▁if ▁the ▁SR . 5 3 ▁was ▁to ▁be ▁likely ▁to ▁surv ive , ▁upon ▁having ▁been ▁issued ▁with ▁the ▁contract ▁to ▁build ▁the ▁three ▁pro tot ypes , ▁set ▁a ▁schedule ▁that ▁called ▁for ▁a ▁first ▁flight ▁to ▁be ▁conducted ▁in ▁July ▁ 1 9 5 4 , ▁along ▁with ▁a ▁project ed ▁service ▁introduction ▁date ▁of ▁ 1 9 5 7 . ▁However , ▁Wood ▁obser ves ▁that ▁this ▁was ▁far ▁too ▁am bit ious ▁as ▁it ▁did ▁not ▁leave ▁time ▁to ▁address ▁the ▁complexity ▁of ▁the ▁aircraft , ▁nor ▁did ▁it ▁accommod ate ▁room ▁for ▁del ays ▁in ▁the ▁supply ▁of ▁the ▁separately - produ ced ▁Spect re ▁engine . ▁Un resol ved ▁issues ▁with ▁elements ▁of ▁the ▁design ▁caused ▁a ▁series ▁of ▁set back s , ▁including ▁one ▁notable ▁incident ▁in ▁the ▁form ▁of ▁an ▁explos ion ▁occurr ing ▁during ▁ground ▁tests ▁of ▁the ▁Spect re ▁ro cket ▁engine . ▁Const