Mast bumping?

Not the same incident. That video ending up in the fog was in 2019.

So mast bumping, would that be a hazard to the whole mast and transmission attachment? Or, just the top of the mast?

I too wondered and then went off and found this:
Educational for non-helo people.

Horrific images.
But I thought the rotor head separated from the mast in mast bumping accidents?
The video appears to show an intact mast and part of the transmission separated from the aircraft and falling into the water.
Can any pilots or engineers comment on what in general might cause such a failure?

Those poor people. Just horrific.

Mast bumping does usually separate the rotor head from the shaft. This one has the transmission attached - can't imagine how that could happen. Even if the blades and head and shaft got so out of balance that they were flogging I would have thought the blades or head or mast would have come off not the transmission from the deck?

If the main rotor blade struck the tail then this would cause the blades to try to rotate about the new contact point, putting a side load on the main rotor shaft where the blades mount. Since this is high up on the helicopter structure it produces a bending load going down into the mast and transmission mount. That makes it possible for the separation happen at the place where the bending load on the mast structure exceeds the ability to resist it.

It may be that mast bump was one of the steps along the way to contacting the tail with the main rotor blade but given that the tail was chopped off and a good amount of the main rotor system also departed,

As a more mundane example - hitting a rock with a lawnmower blade and bending the lawnmower shaft.

From what I understand (fixed wing pilot) abrupt and significant aft cyclic can cause a main rotor tail boom strike - is that right?
What other control inputs or modes of flight that can cause a main rotor blade to hit the boom?

This video shows the sad outcome. It looks like the tailboom is off a clean break around one of the circular framed ribs.

It was a Bell 206L-4 LongRanger, a full seven seater including the pilot.

As mentioned already a mast bump usually (emphasise usually) results in damage to the mast and not the removal of the transmission from the fuselage, as appears the case here. The usual caveats about waiting for the Accident Investigation but removing the tail boom when the MRBs go independent of the flight controls is also not unusual.

https://cimg0.ibsrv.net/gimg/pprune....f021dbc9e4.png
The tailboom break point indicates in the above video link that it separated just forward of the horizontal stabiliser frame maybe

Mast bumping is caused by a stress riser on the main rotor shaft which causes the top portion of the shaft, the head and the rotor blades to separate. They usually go through the cockpit; however, they could hit the tail boom. If this was mast bumping, the transmission will be found with the airframe.

Fatigue / service life.

The tail will snap off when the fuselage twists due to the forces, we’ve seen that plenty of times before in videos.

I found the “ex-spert” media commentators to be especially clueless today.

“The Bell 206 has a fully articulated rotor system”
”When the engine quits the pilot must feather the blades”
One good quote: “Helicopters are complicated!”

Of course they brought in some people who advocated such things as “No unnecessary flights over New York!”
That would reduce accidents nationwide if not worldwide since airline flights to vacation destinations or travel to visit family aren’t really necessary are they? I guess you would have to prove your travel is necessary….I wonder what the criteria would be?

Sorry Clutter. What is a stress riser? Are you referring to bending forces being applied to the mast by the rotor head and blades.

Isn’t it the blades and head flapping excessively, especially in a low or -G situation causing. the bump stops on the head to impact the mast causing it to deform, lose strength and break.
Hence occurrences of mast bumping in nap or the earth flying when the aircraft comes over a ridge line and the pilot abruptly moves the cyclic forward and perhaps even decreases collective pitch to follow the terrain. Low or even negative G, low power, rotor system flapping…the holes in the swiss cheese line up quickly.
I vaguely remember being told the G limits were -0.5 G to +2G and to especially avoid low or -G to avoid bumping.

An amazing amount of non-helicopter folks think the mast is a solid steel rod not a cylinder.

Isn't a mast bumping event a very low G, too much rotor disc forward, rather than back situation? I was taught that very low G, or excess forward cyclic could result in mast bumping, can too much aft cyclic also result in mast bumping? In any case, would this be a possible mast bumping event, believing that the whole transmission can be seen departing the fuselage?

I recall that the 206B has a pin down from the transmission case, to restrict that transmission tilting motion in a mast bumping situation. If I recall correctly the 206L had a "Noda-Matic" transmission mounting, which was a little different to the 206B.

As for the whole rotor assembly seeming to be doing its own very slow autorotation in the video, my understanding has been that the rotor could sever the tailboom, and itself remain intact (so tailboom being cut does not mean that the rotor blade(s) were necessarily broken). If an event of in flight tailboom strike/loss caused the remaining fuselage to then "flail", might that motion be enough to cause the transmission to separate from the deck?

New video - horizontal flight, spins, tail separates, fuselage spins once or twice, rotor separates and fuselage begins the plunge.

https://www.reddit.com/r/Damnthatsin...to_the_hudson/

Edit: It has been removed. Probably because damnthatsinteresting usually doesn't include crashes and probably avoids showing incidents where people died.


Edit 2: reposted at https://www.reddit.com/r/Catastrophi...ash_in_hudson/

Sounds crazy but between the cabin and the rotor, does one make out a single engine plane in a 45 degree left bank, trailing a parachute,,......

Post 16 picture

Most likely something departing the 206, maybe out of the baggage compartment.