Yup. Absolutely correct. Suicide. No doubt. Muzzie or Amish is the only question.
Just to make it more interesting, let’s say the plan was to hijack the plane, not crash it. (It does not make sense that it would be put on a slow descent if the intention was to take it down.) Then let’s assume the outside pilot is the bad guy, who already incapacitated the inside pilot and set the plane on a slow descent, left the cabin........could he get back in?