She is eating ice cream and is enjoying the snow.
Can we drop the second is?
is compounding main verbs (eating, enjoying) +objects (ice cream, the snow) Subject+auxilary verb
is the same for both parts of the sentence, so you can omit is
Aviation officials have
to determine the cause of the crash
demands by the pilots union that the investigation be expedited
As you can see, "have" applies to both participial phrases and does not need to be repeated.