how high can an airplane fly into the atmosphere before its systems fail?

Question: how high can an airplane fly into the atmosphere before its systems fail?
- Keywords:
  airplane,
  altitude,
  flight,
  plane
Asked by stop_that to Alessandra, Dimitrios, Niamh, Becky, Stacey, Tony on 20 Jun 2017.
- Stacey Marple answered on 20 Jun 2017:
  
  In theory until it hits space. Air moving over the wings is what gives the aircraft lift. Air is also required by the engines. In space, there is no air, so none of these work. Most civil aircraft can fly up to 51,000ft, which is what their systems are certified to.
- Niamh Ryall answered on 21 Jun 2017:
  
  Stacey is the expert on this, but I’ll add that maybe it’s not just height we need to consider. Planes could not take off in Pheonix yesterday because the temperature is so high there that there isn’t enough air density for smaller planes, which is a similar problem to those high altitudes.

Question: how high can an airplane fly into the atmosphere before its systems fail?