Regarding the perforation of the aircraft by bullets, and the supposed gradual depressurization that "should" occur, it might be worth remembering the disaster of the world's first fleet of jet passenger aircraft, the British "Comet". In the early 1950s they were falling out of the sky in some numbers. Very inconvenient. This was some 5 years before Boeing came out with its 707.
Stress cracking caused a single, small window (about the same size as normal side windows) that the plane had on the top of the cabin, to begin to weaken. At some point the window began to crack and then suddenly gave way. The result was that nearly the entire contents of the cabin were explosively sucked through the open window. It took years to understand what had happened since all they could find was plane wreckage (usually under water) with bodies and seats scattered over an improbably large area. The result is that until the problem was found some years later, and corrected, the aircraft was taken out of service. It was this that allowed Boeing with its 707 (and shortly later, Douglas with its DC8) to catch up and dominate the market at the time. Suggesting that the only problem with bullet holes is that the pressurization system couldn't keep up with the air leakage, is therefore rather simplistic. The real problem is what happens when a window is hit and the pressure differential takes over causing explosive decompression. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: Gregg Kervill [mailto:[email protected]] Sent: May 6, 2002 9:42 AM To: [email protected] Subject: RE: Stun Guns on Aircraft - summary and comments GK Dear All, Many thanks for your comments - I think it may be worth making some comments in summary: 1- Lightning has the same effect. Disagree - lightening is an external effect - Physics 101 and the "Ice Pail" experiment. If anyone doubts the difference go and visit the Munich Science Museum where every day (I think they still do it) a volunteer climbs into a metal 'pod' and is winched between two electrodes (about 20 feet apart) and becomes part of the discharge path. Seeing it sure beat reading about it at school. Any discharge on the inside of the "Ice Pail" is transferred 'instantaneously to the outside surface - this is, after all, the principle upon which the Van de Graff(sp?P generator is based. (Note the volunteer does NOT wave out of the window!!!) 2- Holes in structure versus hole and carriers in semiconductor substrates (yes it was a pun). I agree with those who preferred the idea of perforated eardrums (depressurization) to perforated electronics. 3- Dead Pilot versus Dead Electronics. Neither is ideal - but many (most) commercial aircraft are fly be wire - One of my clients make Simulators - and I flew (for the first time ever) and Air Bus (simulator) from London Heathrow to London Gatwick - Landed (ON THE RUNWAY) and taxied (the most difficult part) to the airport. I had full control of the simulator and was flying by instruments. The controls are ALL electronic and if there had been multiple (i.e. non-random) fails then even a pilot would not have been able to move the control surfaces. 4- Testing - at 50kV????? any comments from ESD engineers out there????? 5- TASER versus Stun gun - thanks for correcting my misunderstanding - Two comments - First - if the stun gun is discharged through the airframe there will be an induced potential in local electronic systems. Second - if I must turn off my tape recorder (powered but a single AA cell) because it may affect systems then how is discharging 50k considered to be safe and OK??? 6- Design of interfaces to cope - some of the prototype systems that I did safety and reliability work on in (1995)uses surface mount components to provide lightening protection - these devices would not provide Creepage distances of more than a couple of millimeters. 7- Ground computers - I agree that this is worrying - the UK has even more out of date equipment and then the new system (that will control air traffic in the South of England) used equipment (and software) purchased in the late 80's early 90's. I just hope that it still works when they take it out of the box. The point is that RANDOM failures exist and there procedures have been developed (and practiced) to deal with them. Anything that induces non-random and multiple failures is - I suggest - another ball game. 8- The chances are low - I agree - I was flying back from the west coast the morning of 9-11 and I did not get a warm fuzzy feeling about probability when I watched the news footage - but I have made many flights since and it will not stop me from flying. I am grateful for the fact that Europe and the middle East are sharing their security experiences with the US. Security is a cultural thing and the US has a long way to go before it provides the same level of security from officials AND MORE IMPORTANTLY from passengers. These are Gregg's four pointers to improve security at ZERO cost: Security guards most NOT walk around together. ALL alarms must be investigated by security (a telephone call saying OK - is negligence). ALL unattended baggage MUST be treated as a bomb. ANYONE asking me to "keep and eye" on their baggage will be told to take it with them or I will report it as a bomb. Security is the responsibility of everyone that flies - Please help to keep me safe and I will do my best for everyone else. Best regards Gregg ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
