Thanks, my initial post seems to have drifted down a bit. I deleted it, as yours has a better title.
The Navy reported that an MH-60S Knighthawk operating from the Abraham Lincoln (CV-72) went into the ocean about 60 miles off shore. Six souls on board, one recovered so far. Early report from a local newspaper here.
Some
follow up information that doesn't really answer many questions (Navy has confirmed that the other 5 personnel on board have lost their lives
).
I have gone through the Naval Safety Center web page and can't find the summary the news sources are referring to.
The helicopter reportedly touched down on the flight deck and "experienced side-to-side vibrations." It caused the main rotor to strike the deck and fall over the side of the aircraft carrier.
Another source described it a little differently
The MH-60S Knighthawk began undergoing ``side-to-side vibrations'' while landing on the aircraft carrier USS Abraham Lincoln during a routine flight operations roughly 60 nautical miles from shore about 4:30 p.m. last Tuesday, according to a brief preliminary accident summary released by the Naval Safety Center. As the aircraft lurched back and forth, its main rotor struck the deck of the ship, and the impact caused the helicopter to tumble into the sea, the agency reported.
My estimate is something like dynamic rollover (presuming a heading roughly in the direction ship was heading near spot 3 or 4 on the port side of the flight deck, which is where helicopters usually arrive and depart on a CVN)
but
since I have no idea what "experienced side to side vibrations" refers to it's not a very well informed estimate.
Note: I flew and instructed in Seahawks but it's been a while. Based on the information available, which is sparse, that's all I can come up with for why (a) the main rotor blades struck the deck and (b) it then went over the side.
There may be another explanation, though, which may render this estimate moot as more information becomes available.
The "lurched side to side" observation may point toward a hydraulic, or flight control, system anomaly of some kind.
FWIW, an old version of the NATOPS manual for the CH-60S identifies 15 degrees as a critical angle (regarding sloped landings/takeoffs) but points out that there's a lot more to it than that ...
Dynamic rollover is a condition that can occur during takeoff or landing with one wheel on the ground. It is not definable by a single number, nor is it simply a function of slope angle or lateral control authority. These factors will aggravate it, but the main contributor to dynamic rollover is a buildup of angular velocity at the helicopter’s center of gravity about the wheel touching the ground. When the resulting angular momentum of the helicopter about that wheel is greater than can be countered with full opposite lateral cyclic, the helicopter will roll over. (Chapter 11, CH-60S NATOPS from over a decade ago)
Since the helicopter went over the side, which I'll assume is the port side, my suspicion is that it had an amount of left drift, a mainmount contacted the flight deck, and there was sufficient inertia that the dynamic rollover critical angle was reached or exceeded.