A robotic submarine deployed to search for the missing Malaysia Airlines plane in the southern Indian Ocean has had its first mission cut short.The Bluefin-21 was sent to search the sea floor for wreckage after signals believed to be consistent with "black box" flight recorders were detected.But the drone exceeded its operating limit of 4,500m (15,000ft) and was brought back to the surface.It was due to return later on Tuesday if weather conditions permitted."To account for inconsistencies with the sea floor, the search profile is being adjusted to extend the sonar search for as long as possible," an update from the US Navy – which operates the Bluefin-21 – said. (Source–BBC News)
I am unsure whether the highlighted phrase means "it was because of". My perception is that The robot returned but it was in order to ( it was due to) make a comeback later on Tuesday if weather conditions permitted. ( second conditional )
Best Answer
Due to can mean because of or caused by as you said, but in this context, it means expected or arranged to happen at a particular time (See Sense 2 of due on the OALD).
Therefore, "It was due to return later on Tuesday if weather conditions permitted" basically means the same as "It was expected to return ..."
Note that if has a lot of different uses, and the uses don't need to be one of the 3 (or 4, or 5, or more) types of conditionals you have learnt. If is usually used to give a condition, and here the condition is the weather.
As you know, we use the second and the third conditionals to talk about an 'unreal' (hypothetical, untrue, imaginary etc) situation. The second for the present, the third for the past.
Here, since nobody could really tell whether the weather would be good enough for the robot to return at the time the author wrote the news, the author simply used if to give a condition and used the same tense as other sentences, which is the past tense, in this news.
He or she wasn't talking about an imagined scene, so there was no need to change to tense to be more past as in the second or the third conditional.