Originally posted by Miracula
Originally posted by ColdGalaxy
"The pilots of Asiana Flight 214 that crashed at San Francisco airport have told investigators they were relying on automated cockpit equipment to
control their speed, turning a focus of the accident investigation toward whether a mistake was made setting the autothrottle or if it
Why would the plane's autopilot reduce speed unless the radar altimeter was malfunctioning to reduce altitude thinking it was higher than it was?
Do they cross check with barometric altimeters?
The autopilot uses data from radio altimeters, not from barometric altimeters.
The US FAA reported that the Asiana aircraft experienced several shifts of mode on the autothrottle on final descent and it does not seem logical to
me that the pilots would be manipulating these mode changes....
That causes me to suspect there was a system malfunction.
I do not mean that the system was unserviceable, rather that there may have been electronic interference disrupting the system.
I am not an expert on aircraft systems but I have had a few hours flying a 737NG. I stand to be corrected but i believe the autothrottle gets a cue to
retard throttles as altitude reaches minimums. Autothrottles have a display into which you input the desired speed and then after that whether you put
the nose up or down the system then reduces or increases power to maintain the same airspeed.
In another mode it can also be set to hold a certain preselected altitude but this was not the mode it should have used at the time of the crash.
Pilots preselect the mode and either the speed or the altitude as required then the system is left alone. On approach one would not be constantly
fiddling with the selector to make changes. One chooses the speed and mode before descent to land and usually would leave it alone after that.
When the autothrottle retards without pilots commanding it, that is called autothrottle rollback. That is a serious problem which ahs apparently
caused several crashes or incidents and may be the real explanation behind Egyptair Flight 990's crazy dive into the sea where the co-pilot was
It certainly was the cause for Turkish Airlines Flight 1959 in 2009 at Schipol, Amsterdam.
What is more relevant to ask about the altimeter is could lap top devices or cell phones inside the cabin have caused interference with the radio
In my view radio interference may have caused a rogue signal which rolled back the throttles prematurely.
A signal might have originated from outside the aircraft perhaps from a powerful radar, but that is less likely because the aircraft's cabin forms a
Faraday cage to prevent outside interference.
In June 1995 a Dash 8 from Ansett New Zealand collided with the ground after the radio altimeter hung up during an instrument approach. The Captain
reported the radio altimeter sudenly flipped a thousand feet as he watched it and at precisely the same moment the GPWS sounded a 4.5 second warning
prior to impact when in fact it should have given about 20 seconds warning.
It later emerged a passenger inside the aircraft used her cell phone to call the airline call centre and complain about the late arrival of the
aircraft. New Zealand Police refused to investigate this phone call and crash investigators ignored the issue entirely.
It is a tragedy that people like the Police and crash investigators in this New Zealand case deliberately ignored a possible cause which might years
later have taught lessons to prevent another accident however the crash investigation scene is full of egocentric prima donnas.