This question shows a couple of air hostesses dancing during mid-flight and the co-pilot came out of the cabin to record it.
This made me wonder: Can flight crew or passengers moving around in flight cause the airplane to stall?
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6 Answers
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I used to teach sport parachuting, and we occasionally pranked the pilots by shifting the weight around.
A Cessna 206 set up for parachuting will have all but the pilot's seat removed, the jumpers sit on the floor. Everyone moves forward for takeoff and then sits back for the ride up. The instructor (me) sits on the floor where the co-pilot would normally be, facing aft, everyone else faces forward. I would wait until the plane was trimmed for climb (and well above 1000 feet) and then motion the passengers to come forward a bit (the pilot cannot see this happen). He adjusts trim as usual, thinking nothing of it. Passengers come forward some more. Trim adjusted again. Eventually we have 5 people wearing 20kg packs all jammed up into the first 2 "rows" and the trim almost fully nose up.
One signal, and 1/3 of the airplane's gross weight quickly moves almost 2 meters aft (in a 4 meter cabin), followed by a sharp pitch up in both the nose and the pilot's blood pressure. The stall alarm usually goes off too.
Mid-size tailgate aircraft used for jumping are regularly stalled by too many people on the tailgate for too long. The rule there is stay forward until it's your turn, then go aft and get out (if the buzzer goes, you get out NOW).
So it's possible to stall a small aircraft by moving the passengers around.
Scaling this up to airline sizes, we find that the passengers are a rather smaller percentage of the airplane's gross weight, and the presence of things like seats, bulkheads and galleys at the rear prevent 300 people from gathering rapidly at the back. The rather large hydraulically powered elevator also has substantial authority over the aircraft's attitude.
So no, a small group of passengers won't be stalling an airliner out of the sky no matter where they stand. Noticed by the pilots: possibly.
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6$\begingroup$ A stall warning at 1000ft with a fully loaded plane does not sound entertaining at all all right :O $\endgroup$ Apr 5, 2014 at 17:50
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16$\begingroup$ @yankeekilo - probably depends on if you are planning to jump out of it anyway! $\endgroup$ Apr 6, 2014 at 4:04
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2$\begingroup$ Notice I said "well above 1000 feet". And any pilot who can't recover from a soft stall in a jump-modified airplane shouldn't be flying. ( biggest engine and prop available, leading edge cuffs, flap-gap fillers, winglets - every high-lift mod on the market) $\endgroup$– PaulApr 7, 2014 at 3:55
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2$\begingroup$ @Paul Just because they should doesn't make this a good 'prank'. Do you prank your friends by pulling up on the handbrake as they drive along the road too? $\endgroup$– CloudJul 16, 2018 at 13:07
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$\begingroup$ @Cloud I know some friends doing this in winter on snow. Good prank is a mix of good theme, perfect timing and good target. You can do it to someone you really knows good enough. $\endgroup$– CrowleyAug 8, 2018 at 7:50
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Theoretically? Yes.
Practically? No.
Passengers moving around in an aircraft will have some effect on the balance (center of gravity) of that aircraft, but the proportion of weight for a few flight attendants or passengers moving around on a modern airliner is likely so small as to be negligible. It's not enough of a change to exceed the control authority of the aircraft and cause it to pitch up enough to stall (unless as mah notes you have a substantial number of extremely heavy folks on board and they all stand right up against the aft bulkhead - and even then it's not likely).
I can't find the link to it, but I recall either reading about or hearing about a mostly-empty flight (I want to say on some kind of smaller multi-engine piston aircraft)in in which the half-dozen or so passengers (having had a few "adult beverages") decided to play a friendly prank on the pilots by slowly moving to the furthest aft seats, waiting there for a while, and then slowly moving back to the furthest forward seats.
As I recall the story the aircraft in question had no autopilot, so the pilots had to manually re-trim the aircraft after each round of seat changes. The end result ultimately being that the pilots announced that everyone had to pick a seat and stay in it, or the beer cooler would be locked for the remainder of the flight.
(As you can probably imagine there was no further need to re-trim due to unexpected CG changes following that announcement.)
answered Mar 20, 2014 at 20:35
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3$\begingroup$ In large aircraft, practically no. In a commuter, see Filair L410 at Bandundu on Aug 25th 2010, impacted building. $\endgroup$ Mar 21, 2014 at 7:49
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5$\begingroup$ I remember a post on CompuServe of a veteran pilot who ferried live pigs in Vietnam. One of the pigs broke its cage and started running up and down the cargo hold. This excited other pigs, an soon he had a number of them running around, all together. In the end, he had to lower the rear cargo ramp and let them go in mid flight. $\endgroup$ Oct 8, 2014 at 6:25
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9$\begingroup$ @PeterKämpf . . . I think the important question is "Does this count as pigs flying?" $\endgroup$– voretaq7Oct 8, 2014 at 7:45
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1$\begingroup$ :-) yes, flying along a ballistic curve ... $\endgroup$ Oct 8, 2014 at 8:06
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$\begingroup$ I know almost nothing about aviation. Can someone please explain to me what "trim" and "re-trim" mean? $\endgroup$– GMAFeb 3, 2015 at 11:32
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There was a crash in the Congo that is presumed to be caused when a loose crocodile in the cabin sparked panic, and catastrophically shifted the balance of the aircraft. Not something you hear every day.
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9$\begingroup$ What's up with this referring to accident news from mainstream media that rarely verify their facts or update the stories? The crash you mention, Filair L410 at Bandundu on Aug 25th 2010, impacted building, is indeed suspected to have been caused by too many passengers moving, but the survivor later changed their testimony regarding the reason. $\endgroup$ Mar 21, 2014 at 7:46
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2$\begingroup$ @JanHudec On the other hand, the account in the article you link also doesn't make sense. If you look at Bandundu airport on Google maps, there is clearly no "reserve strip" at the side of the runway, just a bunch of scrubby land about 150m wide on each side. But even if a temporary grass strip had been prepared, how would the passengers be able to tell, more than 2km from the runway that the crew were off-line by only 50-100m? $\endgroup$ Apr 6, 2014 at 16:49
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$\begingroup$ @DavidRicherby: Indeed, that story does not make sense. And after more than three years, there does not seem to be any outcome from official investigation either. $\endgroup$ Apr 6, 2014 at 19:04
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An aircraft stalls when it exceeds its critical angle of attack.
Unless the dancing flight attendants all gather aft, and are much heavier than any normal human could be (and even then), I think it's not possible for them (dancing, or being wall flowers) to modify the aircraft's angle of attack.
In short: no.
Further information on aircraft stalls: http://en.wikipedia.org/wiki/Stall_(flight)
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In short possibly...
But only if the aircraft is already heavily laden and there is a large mass shifting all at the same time. In the case of parachutists on a bare floor with no restraints, yes of course.
This 747 took off from Bagram airfield in Afghanistan with five armoured vehicles and they are thought to have broken free and shifted aft during take off:
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I think it's a very interesting question (related one here). Let's look at an extreme example:
For an airliner, if all pax and cabin crew move rapidly in a coordinated manner to the extreme aft or front, could they take the airplane out of CG limits? Make it uncontrollable? (So, not referring to small/medium aircraft, or a few pax moving randomly or to the lavatory, which obviously doesn't endanger the aircraft.)
I'd love to see a more thorough answer, idealiter with reference to a POH or Weight & Balance manual, but here's a shot for, say, an A320:
Total mass is about 80 tons, the pax are about 15 tons (200 x 80kg). Length of the aircraft is some 38m. If everyone moves from their seat to the aft, they move (on average) around 16m (32m cabin length, say, and half of that because some move more, some less).
Thus, the CG moves by $15 \text{ t} \cdot 16 \text{ m} / 80 \text{ t} = 3 \text{ m}.$ The mean aerodynamic cord of an A320 is about 4.2 m (see discussion here, #7 or EASA here), so this represents a 70% MAC CG shift, or (if I understand it correctly) around 240 IU move. (Note that when all pax run to front and then to back, we'd have a 140% MAC shift).
As far as I can tell, the A320 has CG limitation of (at most) 15% to 45% MAC (see e.g. here, p. 81), thus accommodating at most a 30% MAC shift. So, it seems to me that the answer is yes, coordinated pax movement could take an airliner out of its certified CG load. Whether it remains controllable, I don't know.
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1$\begingroup$ Just because the plane is out of CG, it doesn't mean the plane will stall. With aft CG, the danger is thatIF the plane stalls, there is not enough forward elevator authority to break the stall. $\endgroup$– rbpMay 2, 2017 at 22:20
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$\begingroup$ @rbp What happens if CG is moved past CL (centre of lift)? Now tail horizontal stabiliser lift is upward, aren't we now statically unstable? $\endgroup$– FabMay 2, 2017 at 23:54
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$\begingroup$ A stall is defined as exceeding the critical angle of attack of the wing. $\endgroup$– rbpMay 3, 2017 at 0:09
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$\begingroup$ Airflow defines how the tail plane flies, not stability $\endgroup$– rbpMay 3, 2017 at 0:11
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$\begingroup$ @rbp I think you're being slightly pedantic but you are correct. Being unstable doesn't mean you have stalled but it makes it a LOT more likely. $\endgroup$– Notts90May 3, 2017 at 6:28