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Research group of Prof. Peter B. Ladkin, Ph.D.
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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 3, Issue 79

Sunday, 12 October 1986


o China Air incident... the real story
Peter G. Trei
o Air-Traffic Control Spoof
Peter G. Neumann
o Aviation Accidents and Following Procedures (RISKS-3.77)
Matthew Waugh
o DC-9 crash again
Peter Ladkin
o Info on RISKS (comp.risks)

China Air incident... the real story

Mon 13 Oct 86 01:04:22-EDT
     Excerpted from 'Tumbledown Jumbo', an article in the Oct 86' issue of
     FLYING magazine, concerning the China Airlines 006 incident of Feb 86.
     ellipses and contractions in [square brackets] are mine.
        At one point the autothrottle brought the engines back to about zero 
     thrust. the throttles came forward again, the number-four engine did
     not respond. The flight engineer ... told the captain that the engine 
     had flamed out.
        Maximum restart altitude is 30,000 feet [the plane started at 41,000].
     The captain told the first officer to request a lower altitude. He then
     told the engineer to attempt a relight, even though the plane ... was still
     at 41,000. The restart attempt was unsuccessful.
        The captain ... released the speed and altitude hold on the autopilot. The
     autopilot was now programmed to maintain pitch attitude and ground track. The
     airplane continued to lose speed gradually ... and the captain eventually 
     disengaged the autopilot completely and pushed the nose down.
        At the same moment, the airplane yawed and rolled to the right. The
     captain's attitude indicator appeared to tumble [as did two backups].
     The airplane had now entered the clouds. At the same time ... the other three
     engines quit.
     [paragraph omitted, describing speed varying between Mach .92 and 80 knots,
     as crew attempts recovery under up to 5G accelerations.]
        After ... more than two minutes, the 747 emerged from the clouds at 11,000
     feet and the captain was able to level it by outside reference. Coincidentally,
     he felt that the attitude indicators 'came back in' at this point. [engines
     1,2, & 3 restart themselves, and 4 responds to a checklist restart].
     Initially the captain decided to continue ... [but it was noticed
     that] the landing gear was down and one hydraulic system had lost all
     its fluid. ... the captain decided to land at San Francicso. The plane operated
     normally during descent, approach and landing.
         [Later analysis showed that engine four had NOT flamed out, but just stuck
     at low thrust due to a worn part. The others were also responding to the 
     throttles very slowly, a common problem at 41,000 feet. The NTSB inquiry
     concluded that...] the captain had become so preoccupied with the dwindling
     airspeed that he failed to note that the autopilot, which relied on ailerons
     only, not the rudder, to maintain heading, was using the maximum left control-
     wheel deflection available to it to overcome the thrust asymmetry due to the 
     hung outboard engine. When the right wing nevertheless began to drop, ...
     the captain didn't notice the bank on the attitude indicator ... . When he
     did notice it, he refused to believe what he saw. At this point, ... the
     upset had begun and the captain and first officer were both spatially 
         Once the erroneous diagnosis of a flameout had been announced, ... the
     captain placed excessive reliance on the autopilot.... When he finally
     disengaged it, and put himself 'back into the feedback loop' it was at a
     critical moment, and he could not adjust quickly enough to the unexpected
     combination of control feel and instrument indications to prevent the upset.
          The rest of the article is devoted to RISKS-style analysis of use
     of automatic systems. To give a more down-to-earth (pun intended)
     analogy, suppose your car was equipped with an AI 'drivers assistant',
     which handled all normal highway driving. Suppose further, at night,
     with you drowsy and at 60 mph, the right front wheel blows out. The AI
     blasts the horn to alert you, and applies substantial left torque to
     the steering wheel to keep it straight. You realize your in trouble,
     grab the wheel, and turn off the AI. The wheel immediatally jumps out
     of your hands to the right (you didn't know how much torque the AI was
     applying), and the car swerves off the road...
         The use of automated systems to handle routine operations of critical
     systems, with dangerous situations suddenly dumped in the hands of human
     operators, presents a new Risk... that they may not fully understand the
     ramifications of the problem during the critical transition time.
         A co-worker of mine who has worked in both the Navy and civilian
     nuclear programs tells me that Navy reactor systems are designed to keep
     humans in the loop. The only thing the automated systems can do without
     a person is 'scram' or shut down the reactor. Changes in power level,
     opening and shutting valves, pulling control rods, operating pumps, etc,
     must be performed by the people constantly tending the reactor. Thus, the
     system cant very easily spring surprises on the operators.

Air-Traffic Control Spoof

Peter G. Neumann <Neumann@CSL.SRI.COM>
Sat 11 Oct 86 20:03:57-PDT
     Some of you may have missed a recent set of rather serious breaches of the
     integrity of the air-traffic control system.  It is another important
     instance of a masquerading spoof attack typified by the Captain Midnight
     case (although via voice rather than digital signals).  [Again note the
     October 86 issue of Mother Jones noting similar vulnerabilities and the ease
     of performing attacks.]
       Washington Post, 8 October 1986
       MIAMI -- A radio operator with a ``bizarre sense of humor'' is posing as
       an air traffic controller and transmitting potentially dangerous flight
       instructions to airliners, and pilots have been warned about it, an
       Federal Aviation Administration spokesman said.  Two fake transmissions
       have occurred in the last week, and one caused a premature descent, said
       Jack Barker of the FAA's southern region in Atlanta.  ``There have been no
       dangerous incidents, but the potential for danger is there.  It's more an
       annoyance than a safety problem,'' Barker said from an FAA meeting in
       Washington.  Barker said the operator uses two frequencies that air
       traffic controllers use to tell pilots how to approach Miami International
       Airport.  The transmissions began Sept. 25, and the last was Friday [3
       Oct], he said.

Aviation Accidents and Following Procedures (RISKS-3.77)

Fri, 10 Oct 86 11:50:44 PDT
     The accident report involving a British Airways 737 at Manchester Airport
     was released recently. The aircraft suffered an engine compressor failure on
     take-off. The aircraft instruments indicated something else (I'm a little
     hazy about exactly what, I think it was a tire burst), and standard
     operating procedure was to turn clear of the runway, basically I believe to
     clear the runway for other traffic. This the pilots did, bringing the wind,
     which had been dead ahead to blow from the now burning engine and wing, onto
     the fuselage. Multiple lives were lost, etc.
     It would appear from this that had the pilots performed an abort and
     maintained the runway, all that would be required for safety reasons, the
     deaths could have been reduced or avoided. However the operating procedure,
     for operational (not safety) reasons mandated otherwise and worsened an
     otherwise pretty terrible situation.
     UUCP   : {ihnp4|mtuxo}!naples!mjw	Matthew Waugh
     ATTMAIL: attmail!mjw			AT&T IS, Lincroft, N.J.
                             		Telephone : (201) 576-3362

DC-9 crash again

Peter Ladkin <ladkin@kestrel.ARPA>
Fri, 10 Oct 86 14:50:49 pdt
     Danny Cohen's point about accuracy is well taken. The incident I was trying
     to refer to was the crash of Eastern 212, a DC-9, in Charlotte, N.C. I
     apologise to Risks readers for not confirming this before posting.
     Danny and I have exchanged letters on the issue of *deliberate override*.
     Danny considers the action of turning off the LAAS to be both non-deliberate
     and not an override.  I still consider it both deliberate and an override.
     It seems to hinge on whether habitual actions can be described as
     deliberate, and on whether not following prescribed procedure upon receipt
     of a warning can be considered an override.
     Peter Ladkin

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