Karl Kössler and Günter Ott, in their book "Die großen Dessauer: Junkers Ju 89, 90, 290, 390. Die Geschichte einer Flugzeugfamilie" (The Big Dessauers... History of an Aircraft Family), also examined the claimed flight and debunked the flight north of New York. Assuming there was only one aircraft in existence, Kössler and Ott note it was nowhere near France at the time when the flight was supposed to have taken place. According to Pancherz' logbook, the Ju 390 V1 was brought to Prague on 26 November 1943. While there, it took part in test flights which continued until late March 1944. They also assert that the Ju 390 V1 prototype was unlikely to have been capable of taking off with the fuel load necessary for a flight of such duration due to strength concerns over its modified structure; it would have required a takeoff weight of , while the maximum takeoff weight during its trials had been . Another explanation for this is that prototypes are never flown at maximum gross weight for their maiden flight until testing can determine the aircraft's handling. According to Kössler and Ott, the Ju 390 V2 could not have made the US flight either, since they indicate that it was not completed before September/October 1944.