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I've recently been watching videos of the Solar Impulse 2 (HB-SIB) flights, and I noticed that on several occasions, instead of giving clearance for takeoff, the tower told the pilot that "departure is at your own risk".

In particular, this happened at Kalaeloa (PHJR) in Hawaii, at Dayton (KDAY) and at Lehigh Valley (KABE).

But, at Moffett Field (KNUQ), Tulsa (KTUL), and out of KJFK, the flight was "cleared for takeoff".

I couldn't spot anything obvious in the tower conversations to suggest why departure was at the pilot's own risk. Out of KDAY, the tower said that the runway the plane was using was closed (of course it's closed, there's an experimental solar airplane and ground crew on it), and at KABE the tower mentioned a jet that landed on the other runway a few minutes prior.

What happened here? Why was departure at the pilot's own risk?

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    $\begingroup$ Perhaps the presence of a ground crew caused the runway to revert to something other than a "legal" runway. Maybe the controllers, unwilling to fromally clear a plane for takeoff from something other that a legal runway, opted instead to tell the pilot to "go on and give it a whirl if you think it's safe." I wish I knew the answer...good question. $\endgroup$
    – acpilot
    Jul 28, 2016 at 5:27
  • $\begingroup$ @acpilot Maybe. But the crew was present at all of these departures. At JFK (and several others) you can clearly see bicycles on the runway as he gets clearance for takeoff! $\endgroup$
    – Michael Hampton
    Jul 28, 2016 at 5:29
  • $\begingroup$ Could be as simple as a controller succumbing to force of habit. Plane on runway usually equals "cleared for takeoff." Being caught up in the moment and dealing with a goofy situation could trip people up. I'm looking forward to learning the right answer! $\endgroup$
    – acpilot
    Jul 28, 2016 at 5:31
  • $\begingroup$ "Roger tower -- I'm going to cross the ocean in this thing. I think that is risky." $\endgroup$
    – orique
    Jul 28, 2016 at 18:42
  • $\begingroup$ Holy f… that thing is slow! And how short was that takeoff roll? Why do they even close a runway for that thing, you could get it airborne by just sneezing at it! $\endgroup$
    – Jörg W Mittag
    Jul 28, 2016 at 22:22

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Interesting question. The ATC orders mention only two reasons that controllers have to say "at your own risk":

  • The pilot "insists" on using a closed or unsafe runway (3-3-2)
  • A helicopter takeoff or landing uses a non-movement area (3-11-2, 3-11-6)

Obviously Solar Impulse 2 isn't a helicopter, so that leaves the closed or unsafe runway reason. I don't know for sure why the tower used the "own risk" phraseology - it would be great to hear from an actual controller - but some possibilities are:

  • The runway was marked as closed (for Solar Impulse 2) on the tower controller's displays, and he said "at own risk" more or less out of habit
  • There were vehicles on the runway, therefore it was "unsafe"
  • Solar Impulse 2 is such an unusual aircraft that the controller felt he couldn't contribute anything to the safety of the takeoff, so he was simply saying "go for it, I can't do much to help you"

Of course, the problem with all those suggestions is that they should apply at all the airports, not just half of them. But I did find this quote from a controller on the AOPA forums (members only):

Although it's normal for helicopters, I issued this "departure will be at your own risk" to an aircraft once. The runway was open, he wasn't departing from a taxiway or anything like that. The problem was fog, where I couldn't see the runway from the tower, and therefore I couldn't determine whether the runway was actually "clear" for his takeoff.

I don't know if this is the right response in this situation or not, but I was a pretty new controller at the time, hadn't faced this situation before, and figured the "at your own risk" was appropriate.

That could have applied to the Solar Impulse situation: with other vehicles and personnel on the runway, the controller can't say it's "clear". And just like the controller on the forum, perhaps some of the controllers handling Solar Impulse 2 felt that the non-standard wording was appropriate for a very unusual situation. The other controllers who did issue a takeoff clearance presumably felt differently.

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