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Old 26th Aug 2010, 23:18
  #1997 (permalink)  
JD-EE
 
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bearfoil to me: "What is your thought re: the transmission of the last reported position? ACARS generated? Pilot/crew input?"

The transmission interruption is either from no messages, loss of power later restored (with no message mentioning this), or a roll probably more than 70 degrees. If I recall the plane was not quite "under" the satellite. So maybe a 60 degree roll would do it. A flat panel can have usable response out to perhaps 70 degrees off the normal to its surface. Since it's electronically steerable with a beamwidth of around 60 degrees if the plane REALLY suddenly (seconds?) rolled as little as 25 degrees from its normal flight position the antenna might lose lock. The antenna probably aims in 10 degree steps so that figure accounts for the antenna already being slightly off boresight to the satellite.

I believe the antenna gets some input from the IMU system for both position and plane attitude. If that's the case the roll would have to be really fast. If it's freely tracking then the roll could be slower. I'd hope it was designed to accommodate normal aircraft dynamics. Ship board units definitely are designed to track the satellites despite ship dynamics. I worked at qual testing such an antenna during my time at Magnavox in Torrance.

The ACARS generated basically tell me one thing within my expertise - something apparently caused the aircraft to be in an attitude or experiencing dynamics such that the antennas could not lock to the satellite so that data could pass back and forth.

Regarding the pilot and crew I cannot say anything meaningful beyond noting it's a wee tad hard to hold a joystick steady in the presence of externally generated high dynamic buffeting. (Fighter G forces don't hit with a rate of acceleration nearly as high as what wind buffeting could do. In the fighter the pilot is the driver of the car, if you will. He KNOWS when the plane is going to move one way or another. In the wind buffeting case the pilots would experience the G forces first and then have to react, much like the person in the passenger's seat of a car swerving in traffic. The driver sits steady knowing what's going to happen. The passenger sways with the sudden movement. I remember guys doing this on dates when I was younger to get me leaning on them. I learned to anticipate this when bucket seats became popular.

{^_-}
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