ALTA 6 Radio LOS

Discussion in 'ALTA' started by alex ryan, Aug 4, 2017.

  1. alex ryan

    alex ryan Member

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    Hi everyone,

    I was flying in the middle of Sydney city today.

    We were surrounded by tall buildings and flying above some buildings around 30m high.

    GPS signal was very sketchy (one second was connected to 9 sats then the next was connected to 4) so didn't use position mode.

    Shortly into the first flight just as I got above the tallest building on the block we were filming, the orientation lights started flashing. I immediately tried to descend and land, but the ALTA was unresponsive. Then it lurched in our direction uncommanded for about a second. Then I regained control and landed.

    In the next few flights I was super tentative and nervous, but we didn't encounter any problems.

    I just reviewed the flight logs and it appears there was a radio LOS incident occurring on both receivers precisely at the same time.

    I have two questions.

    1. Does anyone have any idea what could have caused this? This has never happened before in my experience flying the ALTA. I thought it may have been something on the roof of the building that interfered with the signal?

    2. The ALTA looked as if it initiated a return to home and then when the signal was regained I took control and returned it myself. My question is in this instance, when GPS signal was highly unreliable, would the ALTA have found its way home OK if I hadn't been able to regain control?

    Bit of a scary one. especially considering all the buildings around. Thankfully we had control of the street below, so if something worse had happened it would have most likely just been damaged property, not damaged people, but still it got the blood flowing pretty fast, and didn't make the following flights particularly pleasurable.
     
  2. Gary Haynes

    Gary Haynes Administrator
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    Alex in a crowded city, tall buildings, close together the chance of EMI from RF sources is pretty high. Just a guess but you may have flown thru a point to point high focus microwave system. Something like what a TV station would use to beam their signal from the center city studio to their transmitter site. There is just a lot of electrical noise center city. Take a look at Google earth of the spot where you were flying and check out the roof tops. A couple of years back someone lost control of their Cinestar. Looking at the flight area, unknown to the operator on the ground was huge number of celestial microwave dishes pointed out to satellites. TV station beaming their signal up.
     
  3. alex ryan

    alex ryan Member

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    I thought that might have been what happened, but I did have a look at google maps and couldn't see anything of interest on the roofs we were flying above.

    And on the second question, in this circumstance where gps was unreliable. How accurately do you think the Alta will find its own way home?
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Without GPS it can't. If it never got a firm lock on the home position all bets are off. If you have a home position that is good then it may still get home with a low number of satellites, may struggle and may not be able to do all of the altitude maneuvers. But it might make it back, or at least close enough to reestablish a control signal. Hope and prayer would be called for, but in the heat of the moment not likely to be the first thing that pops into your frontal lobe :)
     

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