Duba wurin da ke ƙasa sannan ka amsa tambayar daga baya a cikin harshe ɗaya kamar yadda wurin yake:  Fitowa: A lokacin gwaji na gaba na jirgin, gwajin faduwa ya nuna cewa fuka-fuki suna yin motsi a ƙarƙashin wasu yanayi. An warware wannan matsala ta hanyar rage karfin wasu bangarorin fuka-fuki. Duk da haka, musamman tsanani high-gudun flutter matsala da aka warware kawai ta hanyar saka depleted uranium counterweights matsayin ballast a cikin outboard engine nacelles na farkon 747s. Wannan matakin ya haifar da damuwa lokacin da waɗannan jirage suka yi hadari, misali El Al Flight 1862 a Amsterdam a 1992 tare da kilo 282 (622 lb) na uranium a cikin jirgin sama (mai daidaitawa na kwance). An hana shirin gwajin jirgin ta hanyar matsaloli tare da injunan JT9D na 747. Matsaloli sun hada da injin injin da aka haifar da saurin motsi na motsa jiki da kuma karkatar da kayan turbin bayan ɗan gajeren lokaci na sabis. Matsalolin sun jinkirta isar da 747 na watanni da yawa; har zuwa jiragen sama 20 a masana'antar Everett sun makale yayin jiran shigarwar injin. Shirin ya kara jinkiri lokacin da daya daga cikin jirage biyar na gwaji ya sami mummunar lalacewa yayin yunƙurin sauka a Filin jirgin saman Renton, wurin masana'antar kamfanin Renton. A ranar 13 ga Disamba, 1969 ana ɗaukar jirgin gwajin don cire kayan gwajin da kuma shigar da ɗaki lokacin da matukin jirgi Ralph C. Cokely ya sauka a kan gajeren filin jirgin saman. Jirgin 747 na dama, an cire kayan saukowa na waje kuma an lalata na'urorin injin guda biyu. Koyaya, waɗannan matsalolin ba su hana Boeing ɗaukar jirgin gwajin zuwa 28th Paris Air Show a tsakiyar 1969, inda aka nuna shi ga jama'a a karon farko. Jirgin 747 ya sami takardar shaidar jirgin saman FAA a watan Disamba na 1969, yana share shi don shigar da shi cikin sabis.  Tambaya: Wace matsala ce ta haifar da ƙarin jinkiri a gwajin 747?
Jirgin gwajin guda biyar ya sami mummunar lalacewa yayin yunƙurin sauka