Hello Don,

Your description is very vague. I don't know if this 400 has flown well in the past? or you just built or bought it and this is your maiden? How much piloting and RC experience you have. Those would be helpful for us at this end in helping you.

Lets assume your heli flew before this problem cropped up. A loose wire, or what is called and "cold soldering joint" will produce your condition because the higher the RPM vibration as the motor revs up will wiggle any loose connections on the ESC to the motor. They will come apart momentarily causing the motor to shut down. It could be the connection from the ESC to your receiver too, or the receiver itself. If that wire lead from receiver to the ESC is not firmly plugged in the signal from your radio to the ESC would be lost again resulting in a shut down condition.

Do this next time, when the heli comes down after the motor shuts off see if all of the other servos are still active. If so and they work then the BEC of the ESC is good. Then you might look at the ESC itself as it might be the culprit and it might be dying. There have been many problems with the 400 35 amp ESC's as they were maxed out during hard flying. A lot of the guys moved up to 40 amp ESC's for that reason. Follow some of these tips and see where you go. Just check every connection on the heli. Feel free to PM me if you need more help.

Good Luck JPEE