FIGHTING FOR 9/11 JUSTICE WITH TED WALTER, page-256

https://www.veteranstoday.com/2021/...ty-of-flying-heavy-aircraft-without-training/

"Let it suffice to say that it is physically impossible to fly a 200,000-lb airliner 20 feet above the ground at 400 MPH.

At any rate, why is such ultra-low-level flight aerodynamically impossible?
Because the reactive force of the hugely powerful downwash sheet, coupled with the compressibility effects of the tip vortices, simply will not allow the aircraft to get any lower to the ground than approximately one half the distance of its wingspan—until speed is drastically reduced, which, of course, is what happens during normal landings.

In other words, if this were a Boeing 757 as reported, the plane could not have been flown below about 60 feet above ground at 400 MPH. (Such a manoeuvre is entirely within the performance envelope of aircraft with high wing-loadings, such as ground-attack fighters, the B1-B bomber, and Cruise missiles—and the Global Hawk.)"

The author, a pilot and aeronautical engineer, challenges any pilot in the world to do so in any large high-speed aircraft that has a relatively low wing-loading (such as a commercial jet). I.e., to fly the craft at 400 MPH, 20 feet above ground in a flat trajectory over a distance of one mile.