Theoretical discussion - Clearance void if not airborne...

[digits_]

Hi all,

the whole IFR system is set up in such a way that -at least in controlled airspace- IFR aircraft will never hit each other, even if there is one failure present (comm failure, altimeter inaccuracies etc). The procedures also always allow you a way out: missed approaches, alternates etc. There are contingencies for wind changes (min reserve fuel), airport closures, emergencies etc. So theoretically, if you follow the rules, you should never find yourself in a corner where there is no safe and legal way out. Right?

Ok. Let's assume you receive a clearance with a clearance void time: "clearance cancelled if not airborne by 1234Z". So, hypothetically and theoretically speaking, what happens if you reach this clearance void time between V1 and Vr? You can either abort and stick to the clearance, which will create an unsafe situations and will break SOP and POH/AFMs, or you can continue without a clearance.

Very theoretically, and nobody really cares, but what would be the correct by the book action in this case?

Are there any other such loopholes in the IFR system?

Regards,
digits

[jschnurr]

The decision to fly has been made at V1, so stopping would not be a viable option. In this extremely hypothetical case, continuing is not a viable option either without clearance. So there is technically no correct answer, but I would side on the side of safety and which decision would result in the least loss.

[montado]

These hypothetical situations haunt me. Sometimes I think I would rather just pack it in than have the embarrassment of a cadors, being yelled at by atc, or having to lie about off time. I think I just let go of all control and give up. /s

[Zaibatsu]

Like everything else IFR, most likely padding built in, and it can be modified.

If you’re getting close to clearance cancelled time, just ask for an extension or a new clearance. Lots of time they put those in there so there isn’t a plane holding up approach clearances indefinitely, not because the minute after there’s going to be a plane cleared for the approach.

On the other hand.. “do not depart until Bozo 123 lands or cancels IFR”.. doesn’t mean you can just blast off right away as soon as one of those conditions is met without considering airmanship first.

[BE20 Driver]

Flow times are given a 3 minute window either side of the wheels up time for this very reason. Wheels up time are often to accommodate other aircraft nearby. If you're that close, just ask for a new time. Odds are ATC gave the other traffic a good enough buffer that they can still let you sneak out.

[bradley]

We once had a crew get violated because the time expired during their takeoff roll.

The answer to your question is you could very well be violated, and you shouldn’t be taking off in the first place. It’s based on wheels up time, not V1, so if you only have seconds left, don’t take off, and get an extension. Starting a takeoff roll planning to reject if the time elapses prior to V1 would be about the worst airmanship I could imagine.