Newsgroup: comp.risks

RISKS-LIST: Risks-Forum Digest  Saturday 19 June 1999  Volume 20 : Issue 46

   FORUM ON RISKS TO THE PUBLIC IN COMPUTERS AND RELATED SYSTEMS (comp.risks)
   ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

***** See last item for further information, disclaimers, caveats, etc. *****
This issue is archived at <URL:http://catless.ncl.ac.uk/Risks/20.46.html>
and at ftp.sri.com/risks/ .

***** THE ANNUAL SEASONAL SLOWDOWN BEGINS NOW. *****
***** BIG BACKLOG of incremental stuff not included. ***

  Contents:
NASA discloses space station blunder (SigmaXi ScienceInTheNews)
Y2K test sends sewage flowing in Los Angeles (Henry Baker)
Resetting the A320 computer (Diomidis Spinellis)
Intuit/Quicken Force Users to Internet & MS Internet Explorer (Lauren Weinstein)
MS Word not as helpful as it thinks (Bill Shymanski)
YANTBOF: yet another NT buffer overrun flaw (Epstein Jeremy)
New ATM hazard (Aahz Maruch)
Yet another ATM scam (Mike Williams)
The cell phone that wouldn't stay OFF (Michael Heilman)
Another case of credit-card 'security' (David Alexander)
Maldesigned computer system slows background checks (Kragen Sitaker)
Factoid paranoia (Mike Giroux)
Risks of keywords in CSV files (Rex Black)
REVIEW: "Intrusion Detection", Edward G. Amoroso (Rob Slade)
Abridged info on RISKS (comp.risks)

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Date: Sat, 19 Jun 1999 03:05:01 +0300
From: Diomidis Spinellis <dspin@aegean.gr>
Subject: Resetting the A320 computer

I was travelling from Athens to Munich on Lufthansa flight LH 3425 on 16 Jun
1999.  Shortly before taxiing for takeoff, our A320 plane left the runway
and moved aside.  The captain immediately informed us that we were having a
slight technical problem that they would try to rectify and that we would be
given further information in a short while.  About five minutes later the
following announcement was made:

  "Ladies and Gentlemen this is your captain again.  We had to reset two
  of our computers and now it is looking real fine again."

During the flight the crew kindly allowed me to talk to the first officer
about the incident.  My prepared list of questions concerned the problem
domain, its criticality, frequency of occurrence, and reporting procedures.
According to the captain, the problem occurred on a flight control computer
(ELAC1) and involved erroneous position monitoring of the right elevator.
The officer assured me that the problem was not critical, occurred on only
one of four different reports and although it was part of a ground checklist
it would not have been a problem during the flight.  I was told that such
problems sometimes do occur and that the problem had already been reported
by telex to the airline's maintenance base.

Here is a verbatim - I hope - transcription from a printed log I was shown:

  F/CTL servo fault
  R Elevator POS MON XDLR

(Disclaimer: I am not an aviation expert; the report is my - perhaps
limited - understanding of the captain's answers.)

The risks?  As far as I know modern flight-control computers do not need a
reset before takeoff*, nor should a reset be needed after a human operator
error.  Obviously a software or hardware fault had caused the computers to
malfunction.  Since resetting a computer does not typically isolate and
correct faults (otherwise Windows would long have reached a 0% defect rate),
we were flying on a plane with a known and demonstrated software fault.
Although the problem manifestation was on a non-critical area, we all know
that the underlying cause could well result in more serious side-effects
since it occurred on a critical flight control component.  More worryingly,
this appeared not to be a singular event.

[*] Interestingly the Space Shuttle software does need to be reloaded
between different flight phases.  A fascinating description can be found in
Gene D. Carlow. Architecture of the space shuttle primary avionics software
system. Communications of the ACM, 27(9):926-936, September 1984.

Diomidis Spinellis, University of the Aegean

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End of RISKS-FORUM Digest 20.46 
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