Firstly, let’s talk about Kim-Jong-Un’s “Air Force Un” (private jet) is a Soviet made aircraft. This jet, the Ilyushin IL-62, has a magnificent appearance after being polished but, it has a deadly defect, besides the wearing out of the inner components.
The old Ford engines are put on the tail of the plane. Modern planes usually have the engines put on the wings. This makes the center point of the body move to the back.
When the aircraft encounters turbulence, it might make the plane stall.
Even the upgraded version of the IL-62 has a high accident rate and some pilots don’t dare to even fly it. Also, it has already ceased production in the late 90s.
Currently, most of the president’s private jets in the work are either made by Boeing or Airbus but, there are some exceptions, for example, Putin’s private aircraft is a IL-96. However the engines of his jet, are on the wings and it is a high degree custom made IL-96-300. The production cost is 1 billion US dollars, and Kim Jong-Un’s plane cannot be compared with it in terms of safety.
Another exception is the Ex-President of Poland’s Tu-154. On April 2010, the plane had 96 people on board, including the president, died when the plane crashed while it was on final approach. It is a rare case that a president’s plane would crash.
Kim Jong-Un took a Air China Boeing 747-400 to Singapore. It is probably because of all the things I listed. 