Suppose a Muslim was on a long airplane flight, for example, New York to Hong Kong (16 hours). Would it be impossible for the this Muslim to pray at the correct times (i.e., just before sunrise, sunset, etc.) & to kneel in the right direction to Mecca?

It is not just airline passengers who would have difficulty obeying Allah's commands to face Mecca while praying.  Muslims may well have to avoid any space travel in order to comply with Allah's demand, as it would be virtually impossible to kneel toward Mecca while being weightless and traveling at 
28,000 kilometers per hour.

In the Quran, Allah does not tell Muslims how precisely to kneel facing Mecca in this situation.

At 28,000 km per hour orbiting the earth, weightless astronauts will not be able to face Mecca.