For the last month and a half, Boeing has been investigating a serious buffet in the inboard flaps of the 747-8F, Flightglobal affiliate FlightBlogger reports.

Turbulent air coming off of the outboard landing gear doors, identified as the cause of flap buffet, may have to be redesigned, say programme sources.

Boeing has devoted RC522, the company's 3rd 747-8F test aircraft, to further investigate the buffet.

747-8F RC522
 © Joe Walker

RC522 flew on 22 March without the outboard landing gear doors installed, and again 23 March with half of the outboard gear door structure installed, as flight test crews sought to narrow their investigation.

The impact of buffet, which occurs at maximum flap extension, on the programme schedule, if any, isn't yet known, though without a final external configuration of the aircraft, community noise testing cannot be completed.

The FlightBlogger report also includes an up-close look at the 747-8F's landing gear doors and flaps, as well as the history behind structural buffet on previous Boeing programmes.