I was list building and I came up with this timing interaction tidbit.
Corran takes his end phase attack and scores a direct hit on an x-wing with 1 damage to hull and an R5.
Can R5 flip the Direct hit over to save the X-wing or does immediately destroyed apply?
The only thing I have to support any argument is that R5 can overrule the general "immediately destroyed" rule as R5 is an upgrade card, but that seems a little week for an argument.
I think immediately destroyed is going to win this one, and I strongly suspect that will be the general consensus here. That said, this game does occasionally play a little loose with timing things (looking at you turrets) so it's probably worth submitting for official clarification.
The X-Wing is destroyed. Part of that is timing. Corran attacks at the Start of the End Phase while R5 works During the end phase. Just like in the Combat phase, a ship is removed (effectively) immediately upon receiving enough damage. it doesn't stick around long enough for other events to happen in case you might be able to save it.
...
I just had a curious thought about saving a ship. Scenario:
Airen Cracken
Luke Skywalker + R5D8
Enemy craft of PS8
The enemy attacks Luke at PS8, managing to get a third hit on Luke. Simultaneous fire rule kicks in an Luke is not immediately removed from the board. Cracken fires at something and passes an action to Luke, who uses R5D8 to remove the damage card. Then Luke attacks. At the end of his attack, he has fewer damage cards than hull. I need to reread the rules to see if this works.
The X-Wing is destroyed. Part of that is timing. Corran attacks at the Start of the End Phase while R5 works During the end phase. Just like in the Combat phase, a ship is removed (effectively) immediately upon receiving enough damage. it doesn't stick around long enough for other events to happen in case you might be able to save it.
...
I just had a curious thought about saving a ship. Scenario:
Airen Cracken
Luke Skywalker + R5D8
Enemy craft of PS8
The enemy attacks Luke at PS8, managing to get a third hit on Luke. Simultaneous fire rule kicks in an Luke is not immediately removed from the board. Cracken fires at something and passes an action to Luke, who uses R5D8 to remove the damage card. Then Luke attacks. At the end of his attack, he has fewer damage cards than hull. I need to reread the rules to see if this works.
I think once the Simultaneous Fire rule kicks in, the ship will be destroyed:
After this ship has had its opportunity to attack this round, it is immediately destroyed and removed from the play area.
Simultaneous Fire doesn't say to check for destruction or damage count or hull - it just says the ship is destroyed and removed after it attacks. So you could remove the damage card, but that doesn't actually do anything to stop the ship from being removed. Cool idea, though 
For the Corran/R5 issues, the ship would definitely be destroyed by R5. We generally accept that "start" things trigger and resolve before "during" has an opportunity to do anything, so the ship is gone before R5 hits his trigger window.
I sent both the R5/Corran and the Luke/Airen scenario into the rules gurus. Any response I'll post here.
The X-Wing is destroyed. Part of that is timing. Corran attacks at the Start of the End Phase while R5 works During the end phase. Just like in the Combat phase, a ship is removed (effectively) immediately upon receiving enough damage. it doesn't stick around long enough for other events to happen in case you might be able to save it.
...
I just had a curious thought about saving a ship. Scenario:
Airen Cracken
Luke Skywalker + R5D8
Enemy craft of PS8
The enemy attacks Luke at PS8, managing to get a third hit on Luke. Simultaneous fire rule kicks in an Luke is not immediately removed from the board. Cracken fires at something and passes an action to Luke, who uses R5D8 to remove the damage card. Then Luke attacks. At the end of his attack, he has fewer damage cards than hull. I need to reread the rules to see if this works.
This is a tough call, but my gut says Luke would be destroyed.
So first, from the "Destroying Ships" section on page 16 of the core rules:
Based on the actual wording of Simultaneous Fire, I think I agree with you guys. Just didn't have time to check it before leaving for the day when I posted earlier. Too bad. At least I found a way to get destroyed and still have hull left, which is an accomplishment of sorts.
I also asked the opposite for the R5 question.
What if the X-wing has a direct hit but gets a hit applied from Corran Horn's End phase attack?
Does the R5 flip the direct hit and the X-wing survive or does it get destroyed?
It could be like the R2-D2 regen shields vs obstacles/mines ruling... dependant on factors we don't know.
With the Luke/R5-D8 scenario, I'd also agree that he's toast. In the FAQ it says all abilities, upgrade cards and damage cards are still active until he performs an attack, at which point he's removed. Checking the rules on Destroying Ships, as soon as the damage equals or exceeds the hull value, the ship is considered inmmediately destroyed. So I don't think R5-D8 would be able to help, regardless of being handed a free action. The damage kicks in before the free action.
It's a handy droid until you get that last, fatal hit.
How many more headscratchers have you got like that, Sable? That was a good one. 
Rule Question:
Corran Horn takes his second attack during the beginning of the end phase.
He gets a direct hit on an X-wing that has no shields and 1 damage on its hull and it is carrying an R5.
Does the R5 get the opportunity to flip the direct hit over before the X-wing is destroyed?
If there was a direct hit on the X-wing before the end phase, and Corran put a hit on it, would the R5 be able to flip that direct hit or would the X-wing be destroyed?
During each phase there is a “start” and an “end” at both of those times there may be various abilities that can trigger. In between those timing windows are when “during” things can happen. This means that something that triggers at the “start" of a phase would fully resolve before something that happens “during” the phase.
Therefore in this example, the X-wing would be destroyed at the start of the end phase and wouldn’t have the opportunity to flip it facedown.
Thanks for playing,
Frank Brooks
Associate Creative Content Developer
Fantasy Flight Games
Only Chewbaca is immune to Critical hits because it says in the card (Without resolving the critical damage effects). You can fix something that has been damaged but once destroyed it is destroyed.
I wouldn't say that R-5 is useless in an E-Wing. It can still fix all the other ship critical damage. It is just that direct hit is the most common (7 cards) out of the deck.