The phrase "has been kept flying" is correct and can be used in written English.
You can use the phrase when you are talking about something that is continuing to progress or stay active despite potential obstacles. For example, you could say, "The success of the company has been kept flying despite the difficult economic conditions."
The flags of the four wartime Allies have been kept flying in front of the building through all these years, even though Germany has not been governed from it since March 20 , 1948 when Marshal Vasily Sokolovski walked out of the place in anger.
A flag that, in recent decades, had been kept flying mostly over old parish churches in preened and polished villages, has become an unlikely partner in the creation of an In-ger-land where Pakistanis and Afghans, Ghanaians, Ukrainians and the descendants of the Iceni can live cheek by painted jowl.
National Geographic: Oscar-night fact check: regarding "Life of Pi" (which won four statuettes), could the starving occupants of the lifeboat (spoiler alert) have been kept alive by flying fish?
We found that within 72 hours after either 20 or 30 day-old HS-lacZ PEV reporter flies (BL2) are switched from a low to a high calorie food, or from a high to low calorie food, the percent of cells showing lacZ expression in tissues of these "switched" flies changes toward the level of gene silencing for flies that have been kept on the "switched-to" diet throughout their lives.
Excellent examples are the incorporation of Lindsley and Zimm (1992) into FlyBase, the impressive compendium by M. Ashburner (Ashburner et al. 2005), Fly Pushing (Greenspan 2004), or the fact that valuable genetic fly strains have been kept alive for many decades in public stock collections.
He has been flying for a long time but he keeps on flying.
People would have kept flying round otherwise.
The design methodology yields a stable control system which has to be kept operative under flying conditions.
It is a tribute to Iranian ingenuity that Iran has been able to keep the planes flying, given US sanctions in place since 1979.
