Videos contain a Bell 429 crash in China, everyone does survive
Just recently a Bell 429 globalranger, a twin engine helicopter, crashed in China. Thankfully everyone survived, the inital reports state that the Bell 429 experience LTE. Or what is known as “Lost of Tail Rotor Effectiveness”
So I know what you are asking,
"Mark, what’s LTE?!
So glad you are asking this question!
Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.
So let’s break this down even more, when does LTE take place?
- Low Altitudes
- Low Airspeeds
- High Power applied
- With winds coming between 120 degrees to 330 degrees
- Wind speeds from 8 - 10 knots or greater.
- High density
- Gross Weight
Let’s discuss the certain type of wind’s that will get us into LTE
Weathercock Stability occurs from 120 degrees to 240 degrees. If you’re thinking to yourself “This seems like a tail wind” you are absolutely correct this is a tail wind. We, as helicopter pilots, like to avoid landing into the wind. If you get into this situation the helicopter will attempt to weather vane into the retaliative wind. The ship will turn left or right depending on where the wind is coming from. To avoid this push your collective forward and gain airspeed. Airspeed is a friend.
Tail Rotor Vortex Ring State
Tail Rotor Vortex Ring State occurs from 210 degrees to 330 degrees. The Tail rotor creates a vortex, just like any other aircraft, while this is small it can create a huge problem. The Tail rotor VRS will push the Vortex through the main rotor, this creates another situation known as,
Main Rotor Disk Vortex Interference
As the Tail Rotor VRS increases the Tail Rotor AOA increase also. The tail of the helicopter will turn forcing the tail rotor AOA to continue increasing, As this happens the helicopter begins to spin.
Well Mark, this sounds scary how does one avoid this?
That’s another great question! The way we avoid even began to have LTE is to make sure the Tail Rotor is properly secured and works as it should be.
While operating at 30 knots or below avoid tail winds, head winds are our friends. We avoid Out of Ground Effect (OGE) Hovering that requires high power requirements, Low speed turns.
The way we recover is apply pedal (depending on your ship either left or right), slowly give the helicopter forward cyclic and reduce power if able.
Here’s some great clips of LTE