[ltp] Re: Linux-Thinkpad digest, Vol 1 #632 - 27 msgs

[morpheus]

Interesting...in both of these "incidents" you should notice that it is
ONLY THE FLIGHT CREW that "concludes" that it was electronic devices
that caused the problems.  With all due respect to flight crews (I am a
flight crew member, after all), we are certainly not experts in
electronics or RF, so we are not qualified to determine the cause of an
accident or incident.  That's why we have the NTSB to investigate
incidents scientifically.

By the way, I searched the NTSB incident database to try to find details
of both of these incidents.  The AA 727 report is here:
http://www.ntsb.gov/publictn/2001/AAB0101.htm
It's an interesting read.  The NTSB determined CONCLUSIVELY that the
cause of the crash was primarily two factors:
1. Autopilots must "desensitize" their receivers as they approach the
runway because the ILS signal emanates from a transmitter embedded under
the runway threshold.  As the signal gets stronger, the receiver lowers
its sensitivity.  The runway in question had no DME (Distance Measuring
Equipment), so the autopilot was set to reduce its sensitivity based on
elapsed time after descending through 1,500 feet.  However, the
autopilot had been programmed to an outdated time setting.  In the
1980s, 727s used to land with 40 degrees flaps, which meant a slower
approach.  In the 90"s that was changed to 30 degrees for a faster
approach.  American Airlines never had the autopilot updated (despite
receiving service bulletins from the manufacturer).  As a result, the
autopilot was expecting the plane to take 150 seconds to reach the
middle marker from 1,500 ft, but it only took 100 seconds at the faster
speed.  The autopilot sensitivity was much too high, resulting in
serious deviations.

2. The pilot failed to notice this situation quickly enough and take
corrective action.

Interference from laptops or other devices is not mentioned in the
report.  (BTW, this accident occurred on approach, when it is illegal to
use electronic devices anyway...)

I searched the NTSB for the second incident mentioned in the article,
reading through all incidents for 1996 but could not find it.  It was
likely not reported.

Incidentally, the article you sent me uses the Aviation Safety Reporting
System, a database maintained by NASA which consists entirely of
unverified, anonymous reports filed by flight crews.  While this type of
anonymous "whistleblower" database is useful in discovering safety
problems, as I have already mentioned, it is impossible for flight crews
to determine that radio interference from a PDA, cell phone or laptop is
the cause of a problem.  All they can do is make guesses based on
hunches.

All of the truly scientific, controlled studies that have been done on
this issue have concluded that electronic devices pose no danger to
aircraft.  Also, let's remember the last thing an airline or aircraft
manufacturer wants to see is a plane crash.  The engineers at aircraft
and avionics manufacturers know all about RF and have designed their
products to work in today's environment...one that includes passenger
use of electronic devices. 

-jr

On Sat, 2004-10-02 at 00:02, Szakacsits Szabolcs wrote:
> On Fri, 1 Oct 2004, morpheus wrote:
> 
> > As a pilot, I can tell you that most pilots have lots of stories to tell
> > you, and most get exaggerated over the years.  
> 
> So probably you're aware of these too:
> http://web.archive.org/web/20040211094605/http://search.nap.edu/issues/19.2/strauss.htm
> 
> 	Szaka