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Is it allowed to let the engine of an aircraft idle without a pilot in the plane. (For both helicopters and aircr).

Would there be a difference between a C172 and a 737?

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    $\begingroup$ There appear to be no specific regulations against it. $\endgroup$ – quiet flyer Oct 9 at 22:04
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    $\begingroup$ Go search up the video of a pilotless airplane that circled over (Perth?) for a couple hours one day, many years ago... Pilot was hand starting, brakes and/or chocks weren't set right, throttle was up a little because hard to start -- and away it went, took off by itself and flew until out of fuel. $\endgroup$ – Zeiss Ikon Oct 10 at 17:08
  • $\begingroup$ I mean technically ramp personnel can taxi the plane, so I guess.. yes 😉 $\endgroup$ – Pheric Oct 10 at 19:18
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    $\begingroup$ In the state of Washington, it is not permitted under RCW 46.61.600. (An airplane is a motor vehicle under the definition found at RCW 46.04.320; most of RCW 46.61 only applies to vehicles operating on public highways, but this one is applicable everywhere.) I'm not aware of any instances of enforcement, but if your plane gets stolen while you're letting it warm up, it's something to watch out for. $\endgroup$ – Mark Oct 11 at 2:01
  • $\begingroup$ It depends on the fed. One may think it's fine, the other may think it's careless and reckless. $\endgroup$ – acpilot Oct 11 at 18:31
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You won't see it done in the fixed wing world unless the aircraft is tied down or otherwise securely restrained (like when you tie off the tail to something when hand starting your no-starter taildragger; some pilots just use chocks or parking brakes to hand bomb their airplane, but it's a terrible idea).

However, it's common in the helicopter world especially in bush operations. With the collective and cyclic friction locks tightened down and the engine in ground idle, it can't really go anywhere and a pilot who lands in a remote area without assistance to hook up a sling load or lug something on board will often do it without shutting down.

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    $\begingroup$ Technically yes, but there will be a mechanic who is specifically qualified for ground runs and taxiing in the pilot's seat. $\endgroup$ – John K Oct 10 at 15:15
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    $\begingroup$ @JohnK. The bush helicopter example is good, but probably not doesn't speak one way or another about regulations. $\endgroup$ – Mad Physicist Oct 10 at 15:45
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    $\begingroup$ Well, there is no regulation as such, except for the one for careless operation, which is generally something that will only get applied after an incident in a case like this. $\endgroup$ – John K Oct 10 at 15:48
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    $\begingroup$ Even if you have the plane tied down while hand-propping it, there will still be a few seconds (or longer, depending on your agility) where you have to leave it idling while you get out to untie it. $\endgroup$ – jamesqf Oct 10 at 17:13
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    $\begingroup$ This is a problem, although once it's running at idle the risks aren't that great. My solution when flying hand started airplanes was to tie one end of a 50ft rope to something by the cockpit door or in the cockpit, loop it around a fence post or something in the ground, tie a slip knot at the tailwheel, with the end of the rope back in the cockpit. Just pull the end to release the slip knot, then reel the entire thing in. My current plane has a starter but I still carry a 50 ft lightweight rope in the baggage cmpt for this purpose in case of a dead battery or failed starter. $\endgroup$ – John K Oct 10 at 17:22
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I'd say no, you're likely to be busted under 91.13...

14 CFR § 91.13 - Careless or reckless operation

(a)Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.

Having had a parking brake slip on a small GA aircraft once or twice myself, I can say its generally a bad idea regardless of regulations.

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It would be very difficult for a lone pilot to hand prop start an aircraft without this occurring for some span of time, which would lead me to conclude that it is not forbidden.

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  • $\begingroup$ Logic cannot be denied... $\endgroup$ – Harper Oct 10 at 21:11
  • $\begingroup$ Glider pilots found a way to disconnect their glider from a tow rope without leaving the cockpit, so the same approach could be used here. $\endgroup$ – FooTheBar Oct 11 at 7:51
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    $\begingroup$ @Harper ... but logic can be incomplete. See JohnK's comment on his post re a 50 foot rope. He is not in the cockpit at some stage when the engine is running (logic passes) but the aircraft is never restrained when he is not in it (logic still passes by dinna tell all the tale). $\endgroup$ – Russell McMahon Oct 11 at 8:27
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Generally speaking, no. Legal or not, it is a very bad idea.

To add some detail, in the Navy we would "hot switch" pilots occasionally in the EA-6B - shutting down the left engine on the pilot side, but leaving the right one running. In these cases the plane was chocked, (chained when shipboard) and there was always an NFO in the right seat to monitor the engine and shut down if needed during the minute or so it would take the next pilot to climb in.

Otherwise the only other time you would not have a pilot in the plane is when a turn qualified engine mechanic was there instead, supporting maintenance. I would imagine similar policies are in effect at the airlines.

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