Re: in-flight engine shutdown / antiquated ATC equip

From:         johnk@opel.secondsource.com (John Kennedy)
Organization: Second Source, Inc.  Annapolis, MD
Date:         05 May 95 03:27:15 
References:   1
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In article <airliners.1995.518@ohare.Chicago.COM> lchiluku@ucsd.edu (R. & L. Chilukuri) writes:
>Our local newspaper had an article today on an in-flight shutdown of
>a B767 engine:
>
>ATC lost radio contact with a UA jetliner over the North Altlantic as
>
> [deletia]
>
>A private subcontractor, Aeronautical Radio Inc., was used to relay radio
>messages between the airliner and the ATC. The company transcribes
>reports and then transmits them by teletype to the Controllers at he
>FAA's New York Center. The controllers keep track of locations in their
>heads, or use grease pencils on Plexiglas!!!!
>
>The controller on duty received the information on teletype,
>telephoned Aeronautical Radio, and asked to be patched through to the
>plane. -- that took 5 minutes and was considered to be pretty quick!

I'm very glad to see this group established.  This group contains the
highest signal to noise ratio of any I've seen.

Maybe this is a good time to introduce myself to this group.  I am a
software developer and a consultant to ARINC.  I have worked since 1989
on the systems used at NYC, SFO, and HNL to transcribe ATC communications
between aircraft and FAA centers.  It's not quite as bad as this posting
and _Newsweek_ would say it is.

First of all, this system is in place because of a dearth of radar over
the oceanic airspace.  After a flight is so many miles offshore, it is
out of range of both ladn-based radar and VHF communications.  Communications
are maintained via HF radio:  ancient technology, but it works for non
line-of-sight paths.  Pilots give position reports, weather updates,
and other information to the ARINC communications center.  The position
reports are forwarded to the parent airlines, relevant FAA centers, and a
system called ODAPS (Oceanic Display and Processing System).  These are
communications over a network between modern Unix workstations, not
teletypes.  The ARINC operators do not keep track of locations via grease
pencils or other means.  That is the job of the controllers at the FAA
centers.

The ODAPS system is an interesting simulation of a typical center's radar
scope, only its data comes from these position reports, not from radar.
Thus, trans-oceanic flights are being monitored on the same kind of
displays and at the same centers as are terrestrial flights.  The flights
have tags containing flight ids and altitude, and are advanced periodically
by the ODAPS computer, based on the position report histories.

In the other, uplink, direction, any ATC clearance information has a
potential lifetime of three minutes;  if not delivered to the aircraft
in that time, it is considered obsolete.  This does not mean the
deliveries typically take that long.  A controller determines an ATC
directive, and instead of contacting the aircraft, phones the comm center.
The radio operator transcribes the clearance, then passes the clearance to
another operator, who contacts the aircraft via HF.  This relayed uplink
clearance typically takes less than a minute.   Because a clearance directive
could stay active for up to three minutes, the in trail separation is much
greater for transoceanic flights.

This system will be eventually replaced due to the increasing number
of SATCOM equipped aircraft, which can generate automatic GPS-derived
position reports and other communications.  Due to the very high cost
of so equipping aircraft, this has been a very slow transition.
United probably has the most SATCOM-equipped flights at this time;
the FAA still has not blessed this as a primary medium for delivering
clearances without the HF radio backup.
>
>Newsweek had an article just last week on the antiquated ATC equipment!
>

Newsweek also didn't mention that a typical HF relay can take as little as
6 seconds and SATCOM messages have taken up to 4 minutes.  The emerging
technology is still, well, emerging.

John

Disclaimer:  I don't speak for ARINC, and I've been wrong before.

--
John Kennedy                     johnk@secondsource.com
Second Source, Inc.
Annapolis, MD