The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 9 Issue 28

Sunday 24 September 1989


o USAir 737-400 crash at LaGuardia
o Re: Hospital problems due to software bug
Steve VanDevender + Amos Shapir
o Computers, Planning, and Common Sense (John
J.G.) Mainwaring
o Synchronizing Clocks
Earl Boebert
o Re: Risks of Distributed Systems
Sung Kwon Chung
o Master clocks, etc.
Eddie Caplan
o ISO 9001 accreditation
Martyn Thomas
o Toxic Spill at the Department of Education [long]
Joe Pujals
o Info on RISKS (comp.risks)

USAir 737-400 crash at LaGuardia

"Peter G. Neumann" <>
Fri, 22 Sep 1989 16:21:29 PDT
At the very end of an article in the 22 Sep 89 San Francisco Chronicle from the
NY Times ("Cause of Accident a Mystery; Probers Can't Find Pilots in USAir
Crash") is this:

  ``Aviation experts said the controls of the 737-400, a modified and
  modernized version of a plane that has been one of the most reliable in
  commercial aviation for many years, are unusual in that they are integrated
  with computers.  Instead of pushing a throttle to accelerate, a pilot uses a
  computer-like keyboard to enter in a set of commands that set the power of
  the engines on takeoff.  It is possible, experts said, that an erroneous set
  of numbers was entered and that this accoutned for the insufficient power on

Earlier in the article was this:

  ``... the pilot had flown the planes for only two months, and the co-pilot
  was said to have been in a 737 cockpit for the first time. ... initial
  reports indicated that the co-pilot was at the controls during the take-off
  ...  the co-pilot told the Port Authority police shortly after the crash that
  the pilot had been "mumbling" and "acting irrationally" just before

    [Saturday's and Sunday's papers stated that officials had indicated that a
    wrong button had been pushed, although Sunday's paper suggested that there
    might have been mechanical failure as well...  The pilot and copilot have
    been suspended for disappearing afterwards.]

Re: Hospital problems due to software bug (RISKS-9.26)

Fri, 22 Sep 89 12:43:09 PDT
In RISKS-DIGEST 9.27, Will Martin asks:
>Does anyone know if this was one of the built-in magic-number
>date breakdowns that have previously been mentioned on RISKS? ...

I'm sure that many people will respond to Will Martin's question.  My lucky
guess was that September 19, 1989 was 32767 days past a certain magic date, and
I was off by one: September 19, 1989 is 32768 days past January 1, 1900.  I'm
shocked that the programmers for this system didn't think it would be used all
the way into 1989, or even worse didn't consider how long it would be used at

The only other date limit that I know of is the UNIX time() limit of Januray
19, 2038 at 3:14:08 AM, when the value returned by time() will become negative
if you treat it as a long.  If we start treating the value returned by time()
as an unsigned long, we push the magic moment back to February 7, 2106 at
6:28:16 AM.

All calculations were performed on my trusty HP-41CV with its time module,
which stores alarm times as the number of seconds past midnight, January 1,
1900.  Therefore, it can only represent times up to November 20, 2216, 5:46:39
PM.  However, the programmers put in a software limitation of December 31, 2199
on times.  This means that my HP-41CV clock will work longer than UNIX clocks
without modification; not bad for a handheld computer that's showing its age
even now.
                                 Steve VanDevender

    [Also noted by Amos Shapir (, who added:
    The risk of using 16-bit integers raises its ugly head again!  (I wonder
    how many of these are still left lurking in old code...)  Amos]

Computers, Planning, and Common Sense

John (J.G.) Mainwaring <CRM312A@BNR.CA>
Fri, 22 Sep 89 10:57:00 EDT
I've recently seen reports of the proposed new Canadian goods and services tax
which raise some disturbing questions.  It appears that a major part of the
proposal is to levy the tax on essentially all occasions when goods or services
are sold, and hence to make tax collectors of small businesses such as piano
teachers and people who do house cleaning.  Of course, such people are already
expected to pay income tax. The new proposal seems to be that they should also
collect 9% off the top and send that to the friendly feds without waiting for

I somehow doubt if the visionary stupidity necessary to develop such a proposal
to the point of law could have existed unaided by computers.  I have no inside
contacts in the Canadian finance department, but I envisage beaurocrats working
over spreadsheets projecting total annual cash flows, no doubt consolidating
all the char ladies in the country into one cell, and eagerly taking the
results to weekly 5 minute sessions with the minister, refining all the guesses
until the spreadsheet projects exactly what the minister wants to hear.

The beauty of a spreadsheet is that it doesn't require any common sense to
operate.  I'm sure that if it occurred to anyone to question the validity of
lumping all the char ladies into one cell, he kept it to himself if he valued
his career.  After all, it should be easy enough for the char ladies to change
the accounting packages on their PCs to deal with the new tax, and surely they
would have no trouble delivering their collections by electronic funds transfer
at essentially no cost to anyone - in fact, surely, time spent thinking about
the char ladies at all was time wasted?

I'm not sure what one can hope to do about this sort of thing.  I suppose
ethics and social responsibility courses at university might help, but it may
be too much to hope that government officials would concern themselves with
such issues, even if we could get them into computer science curricula.
Perhaps all we can hope is that our universities will find ways of increasing
the small minority of all their graduates in whom they have developed the habit
of occasionally thinking about what they think.

It should be obvious that these views do not represent those of my employer, or
probably even myself on a sunnier day.

Synchronizing Clocks

Fri, 22 Sep 89 12:35 EDT
I cannot resist adding a note of industrial archeology to this discussion.
People interested in how grandpa solved these problems should look into the
design of the Synchronome clock, invented in the 1920's by one F.  Hope-Jones.
This consisted of a master pendulum unit (accurate to a second a year or so)
electrically driving any number of slave dials.  One ran as a siderial clock at
Greenwich from 1926 to 1935 without failure, a total of 284 million swings of
the pendulum.  Plans and instructions for making one of these magnificent
beasts can be found in the old Scientific American "Amateur Telescope Making"
series, Book Two, pp 427-446.

Gears and casting sets used to be available to amateurs from the (presumably)
long-gone supplier.  [The Synchronome Co., Alperton, Wembley, Middlesex,
England is given as the 1935 address, in case any of our British Correspondents
wish to go hunting for the site.] Today you would have to gain access to gear
cutting machinery; the castings (mainly brackets) could be built up from bar
stock using modern adhesives.

Re: Risks of Distributed Systems (RISKS-9.26)

Sung Kwon Chung <>
Thu, 21 Sep 89 20:35:00 -0700
>..... This message is an example of asynchronous inter process
>communication. I can guarantee you that i'm doing other things until you
>respond or acknowledge (or this message gets dropped in a bit bucket somewhere)
>and neither RPC nor the rendezvous allows that. ....

This is a rather common misunderstanding (at least) of RPC.  With the RPC
model, the idea is to separate concurrency from communication mechanism.  If
there are concurrent activities (e.g., sending-message-receiving-reply and
doing-other-work), each of them can be encapsulated in a concurrency unit
(process or thread) while communication is done synchronously by RPCs.  In
fact, it's the very synchronous nature which makes a lot of things simple in
such a situation.  So please don't tout RPC is bad because of its

Master clocks, etc.

Fri, 22 Sep 89 15:49:39 EDT
In RISKS 9.27, the Peters Jones and Neumann suggested ways of faking a
distributed performance of Beethoven's 9th so that it would appear to be

Film-music recording has a virtually identical problem.  Here, it is critical
that the music is precisely synchronized with the action onscreen.  Rather than
depending on the conductor for cues, each musician has her own headphone and
listens to a click track: one electronic click for each musical "beat".  The
film-music conductor's job is then reduced to course-grain musical issues, such
as volume balancing.

(This itself is an exaggeration of the traditional conductor/performer
relationship, wherein the performer takes care of the fine-grain details of her
particular instrument while the conductor concerns herself with the orchestral
sound as a whole.)

For the Beethoven example, you would need <n> copies of a common click track
which a local conductor would have the responsibility of following.  Now the
problem has been reduced to starting the performances "together".  I quote
"together" because to make the final performance sound synchronized, the click
tracks startup would have to be staggered to overcome the satellite delays.

Finally, I think that this sort of synchronization has a lot of precedent in
human endeavors.  Consider trapeze artists who get synchronized at the
beginning of a complicated stunt and must then rely on their own "internal
clock" to be at the right place at the right time.  Same for well-tuned sports

ISO 9001 accreditation

Martyn Thomas <mct@praxis.UUCP>
Fri, 22 Sep 89 10:36:17 BST
Jon Jacky asks for UK input on the ISO 9000 accreditation system.

ISO 9000 is the international standard for quality management systems. It
does not define a system, it defines what a system must contain. ISO 9000 is
actually a series of standards, and ISO 9001 covers all of design,
manufacture, test and maintenance.

ISO 9001 is not specific to software - it is generic, and needs to be
interpreted for each industry (or "economic sector"). It is based on British
Standard BS 5750. The EC (European Commission) has directed that each sector
should introduce a "sector certification scheme" to certify compliance with
ISO 9000/9001. In the UK the software sector certification scheme will be
called TickIT. [ just the tickit ... getting your tickit ... ...]

In the UK the BSI (British Standards Institute) has run a Registered Firms
Scheme since 1979. To get BSI accreditation you have to have in place a
quality management system which complies with BS5750 (now ISO 9001), and BSI
audit you to ensure that throughout your organisation, every project and
activity complies with your quality management standards in every respect.
It's fairly tough to get.

To retain your registered firm status, you have to agree that BSI auditors
can come in to the company without notice (we get 24 hours, usually) up to
four times a year (we have had three each year) and repeat the spot audit.
Typically they may ask what projects are active, and inspect the current
list; choose a project and look at the latest status report; select a recent
deliverable and look at the review reports; select an identified defect and
demand evidence that the defect was corrected before delivery.  Or they may
pick a standard and look at how it has been applied on several current
projects across the company.  If they find discrepancies they insist that
they are corrected, and they may withdraw accreditation.

It's good consultancy - ISO 9001 is a *process* standard, and the Praxis
quality management system is heavily based round formal reviewing, so it
seems right that the application of the quality standards should themselves
be subject to formal independent review.

Some clients take comfort from the accreditation and do not themselves audit
our standards; some make BS 5750 mandatory in requests for tender. The EC
will mandate iso 9001 compliance in all public procurement at some point in
the future.

And yes, before someone else points it out, it is Praxis that advertises as
"the first systems house to achieve BS 5750 (ISO 9001) certification for all
software development". We believe in formal QA as an essential component of
software engineering, so we built a company round it.

If anyone wants more details, email me for some article reprints.
Martyn Thomas, Praxis plc, 20 Manvers Street, Bath BA1 1PX UK.
Tel:    +44-225-444700.   Email:   ...!uunet!mcvax!ukc!praxis!mct

Toxic Spill at the Department of Education

Joe Pujals <>
Fri, 22 Sep 89 15:20:40 pdt
The following is a description of a toxic spill that came close to having
disastrous consequences for the California Department of Education.  The State
learned a lot form this experience and I thought others might find it

   Joe Pujals, State Information Security Manager, Office of Information
   Technology, 915 L Street, Sixth Floor, Sacramento, CA 95814, (916) 445-1777,


At 3:02 AM, Tuesday, February 21, an electrical switch located in a vault in
the garage of the California Department of Education arced.  The resulting
explosion spewed 10 gallons of coolant oil containing polychlorinated biphenyl
(PCB) through the electrical equipment vault.  The loss of the switch and
associated transformer was immediately noted in the control room of the
Sacramento Municipal Utility District (SMUD) and a repair crew was dispatched
to the trouble area.

Three minutes later, at 3:05 AM, heat and smoke sensors located in a computer
room on the third floor of the building activated.  The fire detection system
sounded an alarm at the office of the California State Police.  Following
procedure in responding to the alarm, State Police called the fire department.
In addition they called two Department of Education Supervisors, telling them
that the fire detection system in the computer room had alarmed and requesting
that they send personnel with appropriate keys to the building immediately.  A
passing taxi cab driver, hearing the explosion and seeing the smoke, also
reported the incident to his dispatcher who in turn called the fire department.

By the time Department of Education employees arrived, approximately 40 minutes
later, the smoke had cleared and locks to the garage and electrical vault had
been cut.  Fireman and SMUD crews had determined that there was no immediate
danger from fire or loose electrical wiring.

The switch and transformer involved in the incident also provided power to the
State Office Building one (Jesse Unruh Building) located one block away.  The
loss of power forced closure of that building until approximately 1:00 PM that
afternoon.  The California State Treasurer, Department of General Services and
several other agencies were affected by the power outage.

The fire department had cordoned off the building to keep all but emergency
personnel away.  Education personnel gave fire department personnel their keys
to the 3rd floor computer room and requested that they check for a fire in that
area since the fire detection system had sounded.  Firemen dressed in
protective clothing went to the computer room.  On entering, they did not see
any smoke and they noted that the room temperature was normal.

The computer at the department of education consists of a TANDEM EXT25
computer, printers and terminals.  The computer is used as a remote processor
and print driver.  Data files are maintained and computer processing is done at
one of the State's two major computing centers located a few miles away.  The
department has approximately 475 personal computers in the building that are
mainly used as productivity enhancement tools.  The department spokesman
indicated that some production jobs were done on microcomputers but were not
sure how many applications or what they were.  However, they did feel that the
impact to the department, if they should be lost, would be minor.

Within hours, SMUD called the American Environment Management Co. to begin the
cleanup and PCB decontamination process of the electrical vault and garage

Because this was an industrial accident CAL-OSHA was called.  CAL-OSHA
recognized that there could be additional problems associated with the PCB
spill.  PCB produces the carcinogens, dioxin (polychlorinated dibenzo dioxins)
and furan (polychlorinated dibenzo furan), when subjected to high heat.  At
this time, it was unknown if the heat generated by the arcing and subsequent
explosion was sufficient to generate dioxin.  One other nagging question raised
concerns: what had set off the fire detection system in the computer room?  Was
it toxic material or had the sensors been activated accidentally?  At the time
of the explosion, the air conditioning system in the computer room and in
another computer support area had been operating.  Had toxic material been
sucked into the return air intake and contaminated other parts of the building?

SMUD representatives at first believed that the toxic material had been
contained in the electrical vault but could not explain the coincidental
activation of the fire detection system.  Examination of the vault revealed
that there was space between holes cut in the vault for conduit and the conduit
which carried the electrical cables.  It was possible for toxic material to
have escaped through the gap.  The conduit lead into switching equipment in an
adjoining room.  After passing through the switching equipment power was
transferred to the electrical closets located on each of the five floors
directly above the switching equipment room.

Toxic experts from the Department of Health Services were called for advice.  A
consensus was reached that extensive tests would have to be conducted to insure
that the building was safe before employees could be allowed to return.  Tests
were started immediately.  Test material was taken from around the holes cut
into the electrical vault and from various areas throughout the building,
including the computer room.  The tests conducted were extensive and would not
be completed before Saturday, February 25th, five days following the toxic


Within a few hours of the incident, it was recognized that normal operations of
the Department of Education's staff housed in the affected building could not
resume that day.  The decision was made to inform employees to remain at home.
Critical management staff were told to report to another location of the
Department of Education, some blocks away, to begin the recovery planning

Space was cleared at the new location for the director and executive staff.
Training rooms and additional space in the same building were obtained from the
building owners and from a local University to house the essential displaced

A public information office established a media information center in order to
provide accurate and timely information to radio, television and newspaper
reporters.  One of the first and most important steps was to enlist the aid of
the radio and television stations to make announcements requesting people to
stay at home.  The announcements also contained a special telephone number for
emergency information.  The special number was for a voice mail system.

The voice mail system proved to be one of the most valuable tools in providing
staff with information.  The voice mail system, capable of handling 50 incoming
calls at a time, handled approximately 2500 during a seven hour period.  This
is considered to be a volume of calls handled in 53 hours of normal operation.

As is normal in an emergency, the situation is not always clear, information is
not always timely and new problems always seem to appear from nowhere.  The
possible release of carcinogenic toxic substances, such as PCB or much more
dangerous dioxin and furan, in a public building was considered by the various
emergency response offices to be a unique event.  As a result, there was not
much past experience to guide the authorities in their actions.  Because of the
many unknowns concerning the toxic spill, the decision was reached to be
cautious in the reestablishment of normal operations in the building.
Extensive testing would be required, and that would take time.  If the tests
proved to be positive, that is, if toxic elements were found in other parts of
the building, a relocation of personnel to a new site would be necessary.

The Space Management Office of the Department of General Services was alerted
to the problem and was asked to begin the process of finding space for
approximately 650 people.  Potentially usable space was found, but lease
negotiations were held off until the results of the tests were determined.

The immediate problem was what to do with 590 people until normal operations
could be reestablished. Of the 590 staff, 150 people were on business trips
throughout the State and would not represent a placement problem until they
returned.  The department examined travel plans and attempted to reschedule
planned business where it was reasonable.  Others were asked to take scheduled
vacations.  Where it was practical, staff were directed to do their normal
office work at alternate sites within the department or other agencies.  The
remaining employees were simply put on administrative leave.  Since the
decisions affected both professional staff as well as nonprofessional staff,
the department included the California State Employees Association when
bargaining unit staff were involved.

By the end of the second day, the department was reasonably sure that toxic
substances had been contained but could not be certain until more definitive
tests were concluded. If the toxic material had not been contained as it
appeared, but had indeed spread to the rest of the building then there would be
a number of new questions to be answered.  For example, could the tons of
documents, paper files, magnetic tapes and floppy diskettes be decontaminated
or would they simply be buried?  Could the hundreds of microcomputers,
terminals, typewriters and other pieces of office equipment be decontaminated
or would they have to be replaced.  How do you, or should you, replace
information contained in the paper files?  These and many more questions would
have to be answered in the next few days if any test came back positive.

On Saturday afternoon the results of the tests came in; they were negative.
Employees could reenter the building on Monday.

The cost of this disaster probably will not be known for a few weeks.  It will
take time to calculate the cost of lost time.

It is interesting to note that in the course of the week the process of cleanup
and recovery had involved the Sacramento Municipal Utility District, the
American Environment Management Co., the Sacramento Fire Department, the Toxic
Substances Control Division and Hazardous Materials Laboratories of the
Department of Health Services, CAL-OSHA, Sacramento County, the State
Architect, the divisions of Buildings and Grounds, and Space Management from
the Department of General Services, and the California State Employees
Association.  If toxic tests had been positive, there would have been many more
organizations involved and many more very difficult decisions to be made before
recovery could have been completed.


PCB, dioxin, and furan were found in the switch equipment room and in the
electrical closets on the floor above.  But no trace of the toxic material was
found outside of the electrical closets.  Since the conduit passed through all
six floors, SMUD has been asked to decontaminate the electrical closets on each

The reason that the fire detection system activated will probably never be
known. It is assumed that the system was activated as a result of fluctuations
in the electrical power.

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