Here's the text for page 19.
There was the "mayday", then nothing.
よし わかった。 だが諸君 私が来たからにはもう大丈夫だ事故など絶対起こさせはしない
Ok, got it. Ladies and gentlemen, since I am here now, nothing bad's going to happen.
You thought this was the intercom, didn't you.
Now that I think about it, I haven't seen the girl from that seat in a while.
"desu" is just "is", or confirmation of the previous statement. By itself, it has no meaning. So, we have to take the leap with "that's right".
"mazui" is "not good". Rather than coming right out and saying it, we can imply it with "uh oh".
Eh--!? This is a designated empty seat!
No-, not according to the "flight plan".
Ok, now THIS is one of the hardest jokes for me to figure out so far. First, Io's statement looks like "from the beginning, this has been an empty seat", or "this seat's always been empty". But, the woman (who seems to be a regular in Runerune Company, but hasn't been given a name here) starts out with "sonna", which is an expression of disbelief. "sonna" can mean "that", but in this context it's closer to "I can't believe that". Then, it's followed by "flight plan is not" ("mai" here means "probably isn't"). In conjunction with "flight plan" then, we're left to believe that rather than the seat having always been empty, according to the flight plan it's supposed to be reserved, and then been left empty, or later designated by the flight crew as an empty seat. And the woman is saying, no, that's not the case.
Maybe it's that thing that's sometimes seen in airplanes. Plane fairies!
"zashiki-warashi" are spirits that look like children and haunt big, old houses. Generally not found on airplanes. The principle is calling Kurin a "hikouki-warashi". Interestingly, there's a famous inn in Japan, called Ryokufuso, that was a popular tourist destination for it's one room said to be inhabited by a zashi-warashi, but it was damaged in a fire just a couple of days ago.
トーキョータワー こちらアキータ航空4649 どうぞ
Tokyo Tower, this is Aki-ta Air flight 4649. Over.
This is Tokyo Tower, is everything ok!?