Disarm Safety Switch - Potential safety issue.

Discussion in 'ALTA' started by Rick Gerard, Apr 10, 2018.

  1. Rick Gerard

    Rick Gerard Member

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    I was out for some sunset shots this evening and when I was running through the preflight I always check the radio to make sure that all switches are in the right position and functioning properly. This time I had my Daughter with me.

    When running through the preflight I always check the radio section of the app and make sure that all of the controls and switches are doing what they need to be doing and are in the right position. I had just explained the Disarm Safety switch (I have it set to a spring loaded switch so you have to hold it up to turn off Disarm Safety) I moved the Throttle down and to the left and then to the right and the motors started. I had not noticed the LED's changing to solid and I was very surprised to see the motors start. So surprised that I started this thread and upon doing some research am now editing it. I thought there was some kind of software failure that allowed me to accidentally arm and start the motors.

    After a little research, I found that you do not have to move the Disarm Safety switch to arm and start the motors, you just have to hold it up (turn it off) to stop the motors. I had always been holding it up to Arm the Alta, so when the motors started it was a complete surprise.

    I think this is a safety issue. Moments before the accidental motor start my daughter was standing right next to the Alta and she could have been seriously injured. The only safety you have now is flashing LED's giving a visual warning that the Alta is not armed and ready to start. I think it would be a much better idea to require turning off the Disarm Safety switch to arm the Alta and prepare for the motor start. A couple of bumps of the stick can easily start the motors.

    Any thoughts from the group.
     
    #1 Rick Gerard, Apr 10, 2018
    Last edited: Apr 10, 2018
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Rick:
    What you have observed is, at least how I understand it, the correct behavior: the Disarm Switch (as the name implies) is only relevant for Disarming the motors -- the better to ensure you do not turn the motors off while the ALTA is airborne.

    What you are describing (where there is an ARM switch) is sometimes called "Throttle Cut" in the world of fixed wing aircraft. When the switch is in the safe position, then the motors cannot be started.

    My understanding (and, as an FF volunteer I do not and cannot speak for FF) is that for the motors to start requires specific and unusual stick movements for (a) arming and then (b) starting. Specifically throttle minimum and full left yaw for arming, and throttle minimum and full right yaw for starting.

    So I think your thoughtful comment comes down to the issue of whether you can both accidentally arm, and then accidentally start the motors? Correct me if I'm misunderstanding you.

    In my own (granted limited) experience, that doesn't seem to happen -- I certainly have knocked the throttle from its minimum position, but I've never managed to achieve pulling the left stick fully left and then fully right while it is at its minimum position. Your point is, of course, it can be done, not whether I have ever done it!

    I'll be interested to hear what other forum members have to say on this. (As I frequently say, "I'm often wrong, but I'm rarely uncertain! :) ).

    Cheers
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  3. Rick Gerard

    Rick Gerard Member

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    If you check the full range of the controls following a circular path which is a common pre-engine start procedure on a lot of aircraft checklists and something that I do by referring to the Alta App -> Radio section, and you do it in the wrong direction, you will start the motors. That is exactly what happened to me. Checking full range of the radio and motors started. I am surprised that it had not happened before. I'll verify again this morning. The wind came way up yesterday to 10 gusting to 25 and I did not fly.
     

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