Was Dallas hideously incompetent as a captain?
1. He landed his ship to investigate a purported distress signal without properly identifying if it is indeed a distress call
2. He didn’t scan the planet’s surface from orbit (A capability that they shown as having available to them as they were able to detect the location of the vessel “in distress”) -
3. He didn’t cut short the “rescue mission” when it was clear that there was no one to “rescue”
4. He didn’t fix the ship
5. Not quarantining Kane, even after the facehugger fell off
In short, Dallas violated the basic operating procedures that his company demanded that he follow, brought an unknown organism onboard thus exposing his crew to multiple dangers, and then when faced with the alien danger, he didn’t shutoff areas where it might have been hidden to isolate it from the rest of the vessel.
https://www.quora.com/Was-Dallas-a-bad-captain-in-Alien/answer/Jon-Mixon-1