400 feet sounds kinda far, but can someone convert this to normal measurement please?
Well considering this event took place in FAA controlled airspace using the official and standard units of altitude for flight characteristics, I'm not sure how to help you.
I guess 400feet = 8.1498E-10au if that helps?
All US federal contracts are required by federal law to use metric. This is an issue of the media using stupid units for their audience
https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap4_section_5.html
Methinks you don't know what you are talking about. The FAA operates in feet. All domestic flights in the US are separated by flight levels specified in feet. If you get your pilots license in America, everything about it from runway length, controlled flight altitudes, wing spans, etc, will be in feet.
For another example, just let me know how many metric units are used here: https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap3_section_10.html