if you fleet up with someone from a different corp, and while doing whatever you’re doing one of you gets suicide ganked in high-sec, can the other step in to help the fleet member against the ganker without CONCORDE also blowing them up? or is the fleet member under attack on their own against the ganker until CONCORDE shows up to deal with the ganker?
Short answer yes. Longer answer - if someone is suicide ganked they get a flashing red criminal flag that allows anyone to engage them. This situation is different then say a war target who engages one fleet member who is part of a war but other fleet members are not. In that case fleet members who are not part of the war can’t help the member who is.
You are always free to engage anyone who is flashing red (default overview settings). Doesn’t matter if they have a criminal timer, below -5 sec status, or are a war target. Do note, however, that gankers tend to strike fast. Thus, I recommend fitting a reasonably large buffer tank, and, if you’re going to try to fight back, try to decrease your lock times (i.e. fitted scripted sensor booster) so that you can get dps on them as quickly as possible.
Same situation with yellow blinkies: As soon as one of your fleet mates is yellow blinking (e.g. did some unlawful looting), he can be attacked in highsec but no help allowed.
In mining fleets you have to be very careful, you may lose a lot of ships to CONCORD if you support a fellow can thief which is under attack.
Also a problem: Engagement timers do not extend to the whole fleet, either.
Solution: Set your safety to green or at least yellow to prevent being concordokkened.