Here are some comments on the A-320 crash, official reports, and unofficial speculation. It is truly amazing that official sources attributed the accident to pilot error virtually before the investigation began. A decision seems to have been made to protect Airbus and blame the flight crew no matter what the facts. It was grossly irresponsible to exonerate the aircraft before the flight data recorders were examined, or experts had time to analyse the video tapes and other data. There are several questions that many people have not asked that are critical to an understanding of this accident. If the aircraft was indeed only at 30 feet of altitude, why was it that low? Did the pilot intend to descend to that height? What was the minimum altitude authorized for the low pass? What was the actual airspeed, the pilot-commanded/desired airspeed, and the minimum authorized airspeed? Observers claimed that they heard the engines spool-up too late. The conclusion is that the pilots did not allow for the spool-up delay. Such a delay is NOT specific to the A-320 but is rather a characteristic of all turbo-jet engines. Why would an experienced crew have delayed adding power, or even throttle back to low idle, when a high-speed idle would have made engine response much quicker. When did the crew command a power-increase? Was it several seconds BEFORE witnesses heard the engines START to spool-up? Some maintain that the "computer was turned off". This is an interesting concept for an aircraft that flies completely by electronic controls. There are no direct manual controls of the primary flight surfaces or engine controls. Some auto-matic features may have been de-selected. It is of great interest which these were and how the selected systems operated. > The planes automatic escape chutes, which opened as soon as the plane crashed, That's an interesting report. As far as I know, there is no automatic door opening / escape slide deployment mechanism. Slides inflate auto- matically once doors are opened manually. The likely reason that so few lives were lost is that the aircraft contacted the trees in wings level, controlled flight, with the nose up. The lower fuselage structure and wings absorbed much of the impact, and as trees were destroyed they relatively gradually slowed the aircraft. > I believe that manslaughter proceedings may be brought against the pilot. What will be the outcome if we find that an aircraft system was at fault? Do we bring charges against Airbus management, engineers, or software programmers? It is interesting that British Airways is satisfied that the aircraft was not at fault. How could they have made that decision before any data on the accident was released? Every day that their airplanes sit on the ground costs a lot of money in lost revenue, and is negative publicity for their shinny new airplanes. The airlines thus have a proprietary interest in keeping them flying. Officials blame a flight crew that was chosen for its experience and abilities. This crew was extensively trained and passed certification exams on systems and flight of this aircraft. That such a crew could be involved in an accident like this indicates that the aircraft is not immune to accidents, even with it's advanced technology. The A-320 may have been designed to be more safe than older technology craft, but this does not mean that it is. Only operational experience will establish the actual risk. A major concern of systems analysts and pilots is that automated systems may actually increase risk as the pilot is not "in the loop", at the least not to the extent he is in other aircraft. Operational experience has shown us that automation introduces new problems as it addresses some old ones. As of yet, we have no data to show that the highly automated A-320 will be as safe, less safe, or more safe than older aircraft. We may learn a lot about the aircraft from an analysis of this accident. We will certainly not know why the accident occurred or if anyone is to blame until the investigation is complete. Steve Philipson
Given the extensive commenting on the A-320, perhaps these observations will be useful. They're based on my personal knowledge of avionics as it is implemented and practiced in USAF aircraft and in the 757/767. Incidentally Klaus Brunstein quotes the investment in the A-320 as $10 Billion. I wonder whose "billion" he's using; if it's the English billion, that's an investment of $ 10*13 -- lotsa bucks. The USAF F-16 tactical fighter is a fly-by-wire and implements flight control with a quad-redundant analog (YES - analog) computer in the belly of the plane. It is a microcircuit analog implementation to be sure, but nonetheless avoids the software problem in flight control. There are no cables from the cockpit to the control surfaces except for trim tabs. If the quad-redundant machines are lost, the pilot can try to land the plane by manipulating trim tabs. Needless to say, one of the earliest changes to the aircraft was to put protective armor around the flight controllers. There is a separate 65K (as I recall) computer that integrates aircraft functions, delivers signals to the flight control analog system, receives signals from it, talks to the software-controlled heads-up-display, receives digital inputs from the inertial navigator and from manual pilot inputs, manages the radios, receives signals from and sends control signals to the software-controlled radar, transmits pilot inputs to the digital weapons-control subsystem and receives status information from it, receives and logs all fault indications from the entire aircraft and runs diagnostic tests on itself and on other subsystems, AND manages cockpit instrumentation and display. The sytem also monitors for some danger conditions, e.g., wheels up but ground clearance approaching zero. Everything communicates with everything else on a 1 Megabit/sec digital redundant MUX bus. As I recall, pilot intentions (originating by a non-moving pressure- senstive side stick) are communicated directly to the flight control system which then relays them to the digital systems. Thus the pilot could fly the airplane IF the master digital system failed, although he might have no instrumentation (at one time there was a debate about leaving a few "round instruments" in the cockpit as fallback). USAF has experimented with and test flown a digital fly-by-wire system, but I don't know whether it's been implemented in more recent aircraft, or even in the upgraded F-16. Odds are that newer fighters (e.g., F-18s and F-20s) are all-digital. Almost surely the ATF will be all-digital. Even though the analog system actually flys the F-16, it gets inputs and control from the digital systems. In particular, the acclerometers of the inertial nav system report dynamic acceleration and if it's too high, the intent of the pilot is overriden by the software controls to avoid tearing the wings off the plane and blacking out the pilot. In fact pilots have complained about this because they would be willing to risk aircraft damage and/or blackout to escape a pursuer or perform some maneuver. In US commercial aircraft that have "glass cockpits" (as the CRT displays are called), flight control has continued to be traditional direct cable linkage for the most part although hydraulic boost is almost always needed. There are aircraft in which the stick motions control only a hydraulic system which is the only linkage to the surfaces. There usually is an all-digital system called by some such name as "Flight Director" that does or helps with navigation (especially on inertial-nav equipped aircraft), controls the aircraft trajectory in conjunction with an autopilot or other nav inputs, might support fuel management, might handle the aircraft through Cat III (blind-landing) procedures, controls the descent from flight altitude to minimize fuel consumption, handles the throttles to conserve fuel consumption, etc. Without a lot of technical details, one cannot know how the A-320 designers implemented their software and distributed the functionality across one or more computers. Odds are that the flight control is in a separate and redundant set of machines for safety. If the designers were astute, the redundant machines are powered from separate power sources and through individual circuit breakers. [There is a recorded instance in a commercial aircraft of the pilot losing an important instrument because it was powered through a circuit breaker that also happened to control some inconsequential other thing -- such as lighting.] So any comment about "shutting off the computer" (in the A-320) must refer to the flight management system, not to flight control. Airlines are forever interested in optimizing cost of operation, and who knows what flight-profile or flight-maneuvers may have been incorporated into the A-320 systems? Who knows what combination of danger situations have been programmed in -- and the flight crew blundered into? Who knows whether the aerodynamically possible and economically desired flight envelope has been built into the software -- and the flight crew accidentally violated? One can easily imagine a software requirement that says something like: IF engines throttled back AND wheels down AND altitude less than ..... AND rate of descent equal to .... AND speed less than ..... THEN aircraft is landing and adjust angle of attack to .....; also check for proper fuel-flow conditions for landing, check flap position, ...... In spite of what has been said, I personally am not yet ready to conclude that a software anomaly lurks in the A-320. Personal opinion of course, but it sounds suspicious to me. There is one other observation about glass cockpits that my friends in the business have told me. Round instruments not only indicate some parameter but they also convey rate-of-change information. Glass instruments evidently have been implemented to convey only the parameter value, not the derivative of the parameter. If true, one can imagine that in some circumstances the flight crew is denied helpful and possibly critical information about events. Willis Ware
When considering the safety of a fly-by-wire system compared to a "normal" system, you must consider whether the overall safety of the system is improved. Granted there are failure modes in fly-by-wire that would not otherwise exist, but there are also a lot of things you can do with fly-by-wire that you would not be able to do with a "normal" system. If the overall safety of the system is improved, then it is a better system. [But don't forget that if the aircraft is designed to be aerodynamically unstable (i.e., without the computer) -- as are some high-performance planes -- overall safety can be nonexistent under certain conditions. At the IEEE COMPASS '88 this week, John Cullyer noted that in a fully fly-by-wire plane such as the planned Eurofighter, the pilot will have at most two seconds in which to decide whether to eject, after which it may generally be too late. (The Experimental Aircraft Project is developing a plane that will be -12% (un)stable. John described the VIPER effort, which is being subjected to extensive formal proofs, and which is being designed for the EAP.) PGN]
There was a video on German TV Newsshows (ARD, ZDF, SAT1) indicating that the Airbus plane 1. was 10 meters above the ground 2. in a position making the pilot unable to see the trees at the end of the runway (which was too short for landing an Airbus) 3. engines got power far to late to get back into secure hights. Seeing the video one will get the impression that the whole thing (going to a small, badly equipped airfield and doing demonstrations) was a very risky PR manoeuver. There might be some serious problems with this Airbus plane (see B. Littlewoods comments) but I guess this time it was the pilot's fault. H.L. Hausen
From the Los Angeles Times, June 29, 1988: PENTAGON COMPUTER SYSTEM CALLED A $40-MILLION FAILURE The Pentagon's latest effort to unscramble its tangled foreign military sales accounts has been a $40-million failure, the House Government Operations Committee said Tuesday. It said a costly new computer system for straightening out the botched program was two years behind schedule, had thousands of unresolved problems and ultimately could cost $75 million without performing well. As a result, the committee said, the Defense Department cannot say why there is an unreconciled $1-billion difference between cash on hand in a special trust fund and total payments by foreign countries that purchase U.S. military equipment through the foreign military sales program. "The [foreign military sales] trust fund system is in shambles," Committee Chairman Jack Brooks (D-Tex.) said.... The new accounting system, developed by the SAGE firm of Rockville, Md., for the military, was supposed to be ready in October, 1986. Now the completion date has been postponed until next October, or two years behind schedule.
Path: sq!utfyzx!utgpu!utzoo!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!rutgers!orstcs!mist!budd From: email@example.com (Tim Budd) Newsgroups: comp.lang.misc Subject: Re: What makes a language "easy" to program in? Date: 17 Jun 88 20:31:42 GMT Organization: Oregon State Universtiy - CS - Corvallis, Oregon No, I'm not sure you want a ``do what I want'' command. The following story is true, I've just forgotten some of the less important details. There was a Lisp system once that had something called DWIM (do what I mean). If you typed an expression, if it didn't make sense, it would try various techniques to see if something close to it made sense, and do that. Now a friend of mine was using this system and kept having amazingly slow programs. It turned out he was saying things like (CAR ...) when the system wanted (car ...). It would not recognize CAR, go through some analyzing, discover that a probable meaning was car, then do it. Problem was there was no feedback - no indication he was doing anything wrong, it produced the right answer, just slowly. So there are dangers in ``do what I want'' systems even when (and this is a big if) they can exactly figure out what it is that you want. [Forwarded to Risks by Mark Brader] [That was Warren Teitelman's INTERLISP environment. PGN]
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