Foot (unit)
customary unit of length
When en route from China to France, must pilots know their altitude in the imperial foot?
Most international airports and aviators use the foot to measure altitude  China and North Korea require pilots to use meters for altitude Pilots must communicate their altitude with local air traffic control 
Which unit of altitude does France require pilots to use? Which unit of altitude does China require pilots to use? Is #1 or #2 the imperial foot?