Remember that CPR will not restart a stopped heart. CPR's only use is to maintain some blood/air flow until you can get to a defibrillator or life-support machinery, in hopes of preventing damage to the brain or other vital bits.
And unless it's started pretty much immediately, it won't even accomplish that, which makes it futile.
It won't, but there are several shockable rhythms that present as "pulseless" that can indeed be converted. AEDs will shock VF and VT, and manual defib can help with others.
This type of situation is exactly the reason AEDs are now found all over in public places. Sure, CPR for several hours does not yield positive outcomes. But if this guy is slumped because of a shockable rhythm, that AED in the field is not at all useless - it will likely save his life, and minimize the deficits he experiences afterward. Especially on a plane, where the person was likely noticed down minutes after his problem started.
And unless it's started pretty much immediately, it won't even accomplish that, which makes it futile.