Letter to the Airline Pilots Security Alliance regarding their "security-alert", "Reports of Laser Beams Targeting Aircraft", and subsequent correspondence.

On Januray 1, 2005, the Airline Pilots Security Alliance webpage posted a "security alert" warning pilots about the recent spate of incidents involving lasers being directed at aircraft. This so called "security alert" is so full of undocumented facts, fallacious statements, and erroneous conclusions that I felt it necessary to call them on it. First, I have quoted the contents of this security alert as it appeared on their website on January 14, 2005, the day I first learned of the alert. Second is my letter to David Mackett, the president of the APSA, emailed on Jan 15, 2005. A response was received on January 16, 2005 from David Mackett. Added my reply of January 17, 2005. Added response of January 25, 2005 plus FAA .pdf Report on Laser Pointers. Added my reply of January 25, 2005. Added reply from APSA of January 26, 2005. Reports of Laser Beams Targeting Aircraft

The Airline Pilots Security Alliance has confirmed 8 very recent reports of aircraft cockpits being illuminated by steady or pulsing laser beams in flight in multiple locales in the United States.  We have three additional unconfirmed reports.  The reports range from pilots reporting lasers shining into the skies near their aircraft but not actually shining in the pilots eyes, to a beam near CLE reported in the cockpit and appearing to track with the aircraft, for 15-20 seconds, and damaging the pilot’s eyes, while the aircraft flew at 8500 feet, 15 miles from the airport.  A Cessna 172 pilot suffered temporary blindness when his inboard port wing and cockpit were illuminated by a very bright green light last month.  Among the unconfirmed reports are 3 NWA aircraft reporting laser hits on 12/15/2004.  The FBI is investigating some of the reports, but is not clear they are aware of all of them as yet. The lasers are reported to emanate from the ground, and appear as a green beam when shining into the sky past an aircraft, or as an extremely bright, small green dot in the far distance (up to 30 miles, estimated) when viewed straight on.  Incidents have been reported near CLE (altitude 8500’, 15 miles from airport, 250 kts., 20 second illumination, laser tracking with the aircraft, pilot injured); SLC (Sep 2004, 5 miles from airport on approach, pilot possibly injured);  DAB (C172, altitude 1200’ portion of aircraft illuminated, pilot injured); DEN, IAH, TEB, and DET (3 NWA aircraft reporting [unconfirmed]). Some media have suggested pranksters playing with laser pointers given as Christmas gifts may be responsible.  However, some of the incidents happened well before Christmas and we have not experienced similar activity during past Holiday Seasons, even when laser pointers were first marketed.  More importantly, some of these reports (particularly where the laser hit an aircraft at altitudes of several thousand feet) are not consistent with low powered, “pen-lasers” or laser pointers, which have a range of only 1600 feet and would have great difficulty being held on an aircraft.  These reports imply a much more powerful “industrial” laser or an anti-personnel laser designed to be a weapon, possibly with tracking and/or sighting equipment attached (if the reports of the laser moving with the aircraft are correct).  Both of these lasers are much more sophisticated and expensive and generally not possessed by average citizens. In the CLE incident, the laser was reportedly fired from a point perpendicular to the aircraft’s flight path, requiring the beam to track the aircraft from the side as it traveled at roughly 290 mph. The damage a laser is capable of doing varies with the power and sophistication of the laser.  A laser pointer, with limited range and a pencil thin beam is usually only a nuisance to aircraft and may cause eye damage only when flashed at persons within a few hundred feet).  An industrial laser of the type used in the construction industry, especially if it is augmented for use as a weapon, is powerful enough to cause retinal burns and immediate or delayed temporary loss of vision to a pilot from great distances and at intermediate altitudes.   During critical phases of flight, a properly targeted industrial laser could obviously be catastrophic to the flight’s safety if it blinds the pilot(s). A military-grade anti-personnel laser is designed to blind pilots and other targets instantly.  The beam may be enlarged to encompass the entire cockpit, lazing both pilots simultaneously.  These lasers typically use robust targeting and tracking capabilities to keep them locked on a target, and are of a size that may be mounted in a cargo van or hotel room window near an airport.  A few years ago, an American intelligence pilot shadowing a Russian ship received substantial eye damage due to a laser (possibly a laser rangefinder) being shined at him from the ship’s deck. The human eye is most sensitive to green laser light and less so to red light, therefore a green laser is more dangerous at a given power than a red one.  Some lasers operate in non-visible spectrums like infrared, meaning the pilot cannot even know a laser is targeting him/her until he experiences eye pain and/or vision deterioration.  There is no evidence an anti-personnel laser has fallen into the wrong hands. A laser burn occurs in .001 seconds, while it takes the human eye .25 seconds to blink, making it unlikely a pilot may avoid damage by looking away or blinking if the laser hit is direct (we would make the point that looking away from a very bright light is still recommended, since the hit may not be direct – certainly do not look toward a very bright, ground-based light while flying – even if the light appears very far away).  The damage a laser is capable of is limited to visual interference.  There is no evidence such lasers have the ability to damage the aircraft structure, fuel systems or instrumentation. Existing protection against lasers usually involves laser goggles. But, since the goggles’ protection is wavelength-specific, they are of little use if the wavelength of the offending laser is not known.  Laser detection is being developed now.  Optra, Inc., a Boston technology firm, has developed a laser detector not unlike an automobile radar detector.  The unit sits on the instrument panel of an aircraft and alarms if a laser is present.  It then provides GPS data of the hit, general beam origin, wavelength, exposure time and whether the laser is dangerous.  Currently, this detector costs $2500 per unit and can be deployed to an airline within 6 months.  The unit has not been deployed to any airlines yet.  Optra, Inc. expects to sell the detector for $500 per unit within a few years. APSA is very concerned some of these incidents appear deliberate and may involve sophisticated equipment.  We recommend pilots immediately adopt a policy of never looking directly at bright, ground-based lights (no matter what the distance) during flight, and look away and operate by instruments if they observe a laser directed at the aircraft and include this information in crew briefings. If you have been involved in a lazing experience, please report it immediately to Air Traffic Control and advise us at David_Mackett@secure-skies.org.

Jan 15, 2005 To: David Mackett, President APSA re: "Reports of Laser Beams Targeting Aircraft" as posted at http://www.secure-skies.org/Security_Alert.asp  I happened to come by your "security alert" from a message posted in a laser related internet newsgroup. After reading, it was painfully obvious to me that there are crucial pieces of information in this "alert" that are unfounded, unsubstantiated, and just plain erroneous.  I am taking the time to write this email to provide some factual information in an effort to prevent an inappropriate knee-jerk reaction to these incidents.  I am in no way attempting to minimize the seriousness of the incidents. Shining a laser indiscriminately at anyone is a foolish thing to do. If the perpetrators of these incidents can be caught, they should be punished to the fullest extent of the law.  However, as a laser enthusiast, I don't want to see my hobby adversely affected due to the actions of a few bad apples. Please don't throw out the whole barrel. As an experienced hobbyist, I am very aware of the dangers of lasers to vision. I am also becoming increasingly aware of the amount of erroneous information that is being spread about lasers. My fear is that this erroneous information will be used to make poor decisions about the availability of lasers and their use.  I would like to address these fallacious errors by providing hard numbers and facts to prove that in at least two of the incidents, the ones being given the most attention, that it was impossible for the pilots eyes to have been injured by the laser itself. I will then offer an alternative explanation.  You cite several incidents in your "security alert", but only give any useful information for two, the altitudes of the aircraft, 8500 and 1200 feet. Since we do not know from what distance the laser actually was, I'll assume a worse case scenario and accept those distances as the actual distance to the aircraft. I am also forced to make the assumption that this altitude was AGL and not MSL.  Laser beams do not go straight. Although they start out very small, a couple of millimeters typically, they do spread out. This is properly called divergence, and is an important quality of a laser that is stated by the manufacturers. The divergence is stated in units of radians and typically a laser has a divergence on the order of milliradians.  A simple explanation of a radian is that 1 radian means for X distance traveled by the light, it will diverge X amount. That is, if the divergence was 1 radian (which is approximately 57 degrees), at 1 foot from the laser the beam will have spread in size to 1 foot in diameter. Since the best lasers have divergences approaching 1 milliradian, I will assume a best case and use 1 milliradian as the divergence. 1 mR means that at 1000 foot distance, the beam will be 1 foot in diameter.  In the two cases, that means the beam diameters at the plane would be 8.5 feet and 1.2 feet, respectively. The laser light would be spread out in an approximately circular area of these diameters. The area is an important fact here. For these two cases, the areas are:    8500 ft - 8.5 ft = 102 inches = 8171.28 square inches    1200 ft - 1.2 ft = 14.4 inches = 162.86 square inches  The fully dilated human eye, as a pilot might have flying at night, has a pupil diameter of 7 mm, or about .276 inches. This is an area of about 0.0598 square inches.  Since the amount of light entering the eye is all that is important, we can calculate how much of the laser actually enters the eye. Since we have calculated the areas of the laser beams and the area of the pupil, it is simply a matter of dividing one into the other. For the two cases this is:    8500 ft - .276 divided by 8171.28 = about 0.00338%    1200 ft - .276 divided by 162.86 = about 0.16947%  Now that we know what percentage of light enters the eye we can determine how much power actually enters the eye. If we assume a good laser pointer putting out the maximum legal limit of 5 milliwatts:    8500 ft - 5 mW x 0.00338% = 169 nanowatts (nW)    1200 ft - 5 mW x 0.16947% = 8.4735 microwatts (uW)  Now that we know how much laser energy is entering the eye we can then refer to the appropriate regulations to determine the classification and safety of this power level. This regulation is 21CFR1040 and is available from the CDRH on the FDA's website at, http://www.fda.gov/cdrh/radhlth/summary.html  From this document it can be found that a Class I laser for visible wavelengths is defined as having less than 390 nanowatts of power for 10,000 seconds duration. Class I is described as "levels of laser radiation are not considered to be hazardous." This is the lowest classification of lasers by the CDRH.  We can conclude that if the laser was a typical green laser pointer that it is impossible for there to have been any eye damage to the pilots.  However, it is possible that the laser was more powerful than this. We can work the calculations backwards from the point that would cause eye damage and determine the power of the laser at the source. The classification where lasers become an acute viewing hazards is Class IIIb. The power levels for visible Class IIIb lasers ranges from 5mW to .5 watt. Since the minimum is 5mW we will use that value.  Working backwards means we must calculate backwards assuming 5mW of laser power is entering the eye. We've already calculated above what percentage of the beam enters the eye, so we just do the math in reverse.    8500 ft - 5mw / 0.00338% = 147.9 watts    1200 ft - 5mw / 0.16947% = 2.95 watts  For these two cases it has been determined that the laser for the 8500 foot distance must be about 150 watts, and for the 1200 foot distance, can be about 3 watts. The most powerful 532nm (green) lasers that are readily available rarely exceed 50 watts. 3 watts is very doable but still not common to the average person. A used 3 watt 532nm laser still costs several thousand dollars. Also, this is not even in the realm of modified laser pointers and lower cost laser modules.  There are other types of lasers that are greenish in color such as an argon laser. However, these lasers are extremely bulky, weigh hundreds of pounds, require 3 phase 440v power at 70 amps/leg, and several gallons of water per minute for cooling. Not exactly something some prankster is going to be lugging around. The DPSS 532nm laser is much more compact and more efficient power wise.  Another factor to consider is that a 3 watt laser shining up into the sky is going to be visible to anyone on the ground for at least five miles. I would be curious to know if during these incidents anyone on the ground saw the laser. Until such a story could be confirmed I find it unlikely then that a high powered laser was used.  Also, I assumed a best case scenario of 1 milliradian divergence. Most lasers have a higher divergence, which would mean the beam spreads out even faster and would require an even higher powered lasers. If we double the divergence to 2 mR, the power required for the same power at the given distances quadruples. For the two cases this translates to 592 watts and 12 watts. The first has maybe only been seen in the lab, and the second is possible, but even more expensive and difficult to use.  I think another answer to the pilots "injuries" is more likely. I think it is much more likely that some stupid person was showing off their laser pointer and tried aiming it at an aircraft. The pilot was startled by the light, a light bright enough to cause an afterimage. The pilot then starts rubbing their eyes. After images don't go away quickly so the pilot keeps rubbing their eyes until they become irritated and sore. They may even cause slight corneal abrasions. It feels like they have sand in their eyes. The pilot then concludes that the laser caused eye damage.  True retinal damage from a laser is unfelt and usually unnoticed. The burn spot is very small and will affect only a tiny part of one's vision. The blind spot caused by this damage is quickly adjusted for by the brain and becomes unnoticeable under ordinary circumstances. It takes an opthamologist experienced with laser eye injuries to detect the retinal burn, if it can be detected at all.  Further on in your "security alert" you make the statement,    "An industrial laser of the type used in the construction     industry, especially if it is augmented for use as a weapon,     is powerful enough to cause retinal burns and immediate or     delayed temporary loss of vision to a pilot from great     distances and at intermediate altitudes." I presume you are referring to the lasers used on construction sites as levels and survey lines. These lasers are Class II lasers, a lower class that laser pointers. I would also like to know how they can be "augmented for use as a weapon." It is not possible except in certain cases to take a laser and increase its power to any great extent. The most likely case of an "augmented" laser is a modified green laser pointer. This is only possible because the laser was capable of the higher powers to begin with and turned down to the legal limit during calibration. Even so, these 'modded pointers' are still of insufficient power to cause eye injury in the cases cited.  Another statement,    "A military-grade anti-personnel laser is designed to blind     pilots and other targets instantly." The problem is that although possible, there just aren't any "anti- personnel lasers." Such weapons have been banned by treaty. The closest possibility would be laser range finders, which are available on the surplus market, but these all operate in the infrared and are thus invisible to the eye.  Yet another,    "A laser burn occurs in .001 seconds, while it takes the human eye    .25 seconds to blink, making it unlikely a pilot may avoid damage    by looking away or blinking if the laser hit is direct" What is your evidence for this statement? How do you know how long it takes for a laser to burn the retina?  It is all highly dependent on how much power there is. An extremely high powered laser could do damage in milliseconds, but a lower powered laser might take seconds.  I would have to conclude that after reading your "security alert" and the fallacious statements, undocumented facts, and erroneous conjectures, that this "security alert" is nothing more than an attempt to create a state of unfounded fear regarding lasers.  Again, I do not mean to belittle the seriousness of lasers being pointed at aircraft. These incidents, if found to be true and accurate, need to be dealt with. However, to imply such things as laser "augmented for use as a weapon" and to state that pilots have sustained eye damage when the facts simply do not support such a conclusion is irresponsible at best.  It is in the best interest of all involved that any reactions to these incidents be based upon the facts once they have been verified.  I request that this "security alert" be retracted due to these errors can be corrected.

Response received Jan 16, 2005. (sorry for the formatting, I just cut & pasted out of my email. I did at least change it from blue text to black) Brian -   Thank you for your very well-presented email.  Obviously, you have a wealth of knowledge about lasers that could be helpful in evaluating laser incidents involving aircraft.  I hope we can call on you to assist us in areas where we have questions about lasers or their capabilities.  The security alert on our site was developed after consultation with the manufacturer of a line of sophisticated green lasers, the senior engineer at a niche firm that manufactures the industry's first laser detector (which garnered a best new product award from AvWeek, and from an FAA bulletin about the capabilities and concerns about the capabilities of lasers used against aircraft, and, finally, from the bulletin the FBI issued to alert crews to terrorists interest in using lasers against aircraft.   Let me address your main points:     > >   I would like to address these fallacious errors by providing hard > numbers and facts to prove that in at least two of the incidents, the > ones being given the most attention, that it was impossible for the > pilots eyes to have been injured by the laser itself. I will then offer > an alternative explanation.   In two of the incidents the pilots were removed from flight status, examined at the hospital and diagnosed with retinal burns by a physician.  They were not diagnosed with corneal abrasions. You cannot get retinal burns by rubbing your eyes. > >   Laser beams do not go straight. Although they start out very small, a > couple of millimeters typically, they do spread out. This is properly > called divergence, and is an important quality of a laser that is stated > by the manufacturers.   Yes, we're familiar with divergence.   > > > >   Now that we know what percentage of light enters the eye we can > determine how much power actually enters the eye. If we assume a good > laser pointer putting out the maximum legal limit of 5 milliwatts:   The "legal limit" you refer to concerns only lasers manufactured in the U.S.  Much more powerful and sophisticated lasers can be imported legally.  Lasers of 50mW are easily obtained on the internet for several hundred dollars. > >     >   We can conclude that if the laser was a typical green laser pointer > that it is impossible for there to have been any eye damage to the > pilots.   First, we don't know if the laser was a "typical green laser pointer" and the fact is there WERE retinal burns to two pilots' eyes.  Second, retinal burns are not our primary concern.  Our concern (eye damage or not) is a laser causing temporary blindness to a pilot during a critical phase of flight (as happened several nights ago in BUR when a SWA airplane was lazed very close to the airport, blinding the pilot).  This capability is within that of a sophisticated green laser pointer. > >   However, it is possible that the laser was more powerful than this. We > can work the calculations backwards from the point that would cause eye > damage and determine the power of the laser at the source. The > classification where lasers become an acute viewing hazards is Class > IIIb. The power levels for visible Class IIIb lasers ranges from 5mW to > .5 watt. Since the minimum is 5mW we will use that value.   Why would you not use the max value instead of the mininmum? > > >   For these two cases it has been determined that the laser for the 8500 > foot distance must be about 150 watts, and for the 1200 foot distance, > can be about 3 watts.   Again, this is the minimum value, according to your calculations.  The laser's power has not been determined.   he most powerful 532nm (green) lasers that are > readily available rarely exceed 50 watts. 3 watts is very doable but > still not common to the average person. A used 3 watt 532nm laser still > costs several thousand dollars. Also, this is not even in the realm of > modified laser pointers and lower cost laser modules.   We agree.  Our Security Alert pointed to the use of sophisticated lasers in the cases where the pilots' eyes were medically damaged.  Doesn't change the fact that flash blindness, not eye damage is our primary concern and THAT can (and apparently has ) been done with a green laser pointer. > >   There are other types of lasers that are greenish in color such as an > argon laser. However, these lasers are extremely bulky, weigh hundreds > of pounds, require 3 phase 440v power at 70 amps/leg, and several > gallons of water per minute for cooling. Not exactly something some > prankster is going to be lugging around. The DPSS 532nm laser is much > more compact and more efficient power wise.   We have not suggested these incidents are caused by "pranksters" any more than someone shooting at passing cars from an overpass is a "prankster." > >   Another factor to consider is that a 3 watt laser shining up into the > sky is going to be visible to anyone on the ground for at least five > miles. I would be curious to know if during these incidents anyone on > the ground saw the laser. Until such a story could be confirmed I find > it unlikely then that a high powered laser was used.   We have no reports of neighbors seeeing lasers shining into the sky.  There are two reports of pilots seeing lasers shining in the sky near their aircraft.  We don't believe 3 watt lasers were used. > >  > >   I think another answer to the pilots "injuries" is more likely. I think > it is much more likely that some stupid person was showing off their > laser pointer and tried aiming it at an aircraft.   Clearly that is a primary possibility in some of the events, particularly AFTER the story made headlines.   The pilot was startled > by the light, a light bright enough to cause an afterimage. The pilot > then starts rubbing their eyes. After images don't go away quickly so the > pilot keeps rubbing their eyes until they become irritated and sore. > They may even cause slight corneal abrasions. It feels like they have > sand in their eyes. The pilot then concludes that the laser caused eye > damage. > >   True retinal damage from a laser is unfelt and usually unnoticed. The > burn spot is very small and will affect only a tiny part of one's > vision. The blind spot caused by this damage is quickly adjusted for by > the brain and becomes unnoticeable under ordinary circumstances. It > takes an opthamologist experienced with laser eye injuries to detect the > retinal burn, if it can be detected at all.   A doctor detected retinal burns in two events. > >   Further on in your "security alert" you make the statement, > >     "An industrial laser of the type used in the construction >      industry, especially if it is augmented for use as a weapon, >      is powerful enough to cause retinal burns and immediate or >      delayed temporary loss of vision to a pilot from great >      distances and at intermediate altitudes." > > I presume you are referring to the lasers used on construction sites as > levels and survey lines. These lasers are Class II lasers, a lower class > that laser pointers. I would also like to know how they can be > "augmented for use as a weapon."   We were referring to powerful industrial lasers with robust tracking equipment attached.   It is not possible except in certain > cases to take a laser and increase its power to any great extent. The > most likely case of an "augmented" laser is a modified green laser > pointer. This is only possible because the laser was capable of the > higher powers to begin with and turned down to the legal limit during > calibration. Even so, these 'modded pointers' are still of insufficient > power to cause eye injury in the cases cited.   Our information is that a 50mW laser can, in fact, cause eye injury, but, again, that's not our primary concern. > >   Another statement, >     "A military-grade anti-personnel laser is designed to blind >      pilots and other targets instantly." > > The problem is that although possible, there just aren't any "anti- > personnel lasers." Such weapons have been banned by treaty. The closest > possibility would be laser range finders, which are available on the > surplus market, but these all operate in the infrared and are thus > invisible to the eye.   Incorrect.  The chinese ZM-87 (or similar; don't have the designate in front of me at the moment) is a military anti-personnel laser currently deployed.  Additionally, anti-personnel lasers are currently in use against our troops in Iraq, treaty or no.  There ARE in fact antipersonnel lasers and these are exactly what terrorists are interested in buying or converting (as reported by FBI). > >   Yet another, >     "A laser burn occurs in .001 seconds, while it takes the human eye >     .25 seconds to blink, making it unlikely a pilot may avoid damage >     by looking away or blinking if the laser hit is direct" > > What is your evidence for this statement? How do you know how long it > takes for a laser to burn the retina?   FBI.   > >   I would have to conclude that after reading your "security alert" and > the fallacious statements, undocumented facts, and erroneous > conjectures, that this "security alert" is nothing more than an attempt > to create a state of unfounded fear regarding lasers.   Brian, let me get emotional for just a second.  There is not one fallacious statement, undocumented fact or erroneous conjecture in our alert.  We are not attempting to create a state of unfounded fear.  We have pilots who suddenly went blind after seeing a bright light on the ground during critical approach phases of flight, endangering the flight's success.  We have pilots who were taken off flight status and diagnosed with retinal burns by a doctor.  In one case, the pilot simply saw the light on the horizon, didn't rub, didn't blink, didn't think anything of it.  Then, he woke up with a puffed up, bloodshot eye the next morning.  33 aircraft have been lazed in the past few weeks.  I would expect many copycats once the news got out, and each copycat has the ability to endanger a flight.  What concern about the above do you think is unfounded? > >   Again, I do not mean to belittle the seriousness of lasers being > pointed at aircraft. These incidents, if found to be true and accurate, > need to be dealt with. However, to imply such things as laser "augmented > for use as a weapon" and to state that pilots have sustained eye damage > when the facts simply do not support such a conclusion is irresponsible > at best.   The phrase, "converted for use as a weapon" comes directly from an FBI bulletin.  The "facts" are that doctors report pilots have sustained eye damage. > >   It is in the best interest of all involved that any reactions to these > incidents be based upon the facts once they have been verified.   The facts were verified before the alert went out. > >   I request that this "security alert" be retracted due to these errors > can be corrected.   No sir.  We represent 25,000 pilots whose health and safety depend on having the information vital to their and their passengers' safety.  There are no errors in the alert. > > > > >

Jan 17, 2005 To: David Mackett, President APSA David,  Thank you for your response to my email.  First, an error in my calculations has been brought to my attention. I had used a wrong number in figuring out what percentage of light enters the eye. Here are the corrected calculations with the original erroneous results in brackets:    assuming 1 mR divergence    8500 ft - 8.5 ft = 102 inches = 8171.28 square inches    1200 ft - 1.2 ft = 14.4 inches = 162.86 square inches    fully dilated human pupil    7mm = .276 = .0598 square inches    percentage of light entering eye    8500 ft - .0598 divided by 8171.28 = 0.000732% [0.00338%]    1200 ft - .0598 divided by  162.86 = 0.036719% [0.16947%]              ^^^^^              This is the error, I originally used the diameter .276              instead of the area .0598. I need to divide the areas.    power of light entering the eye from assumed 5mW laser    8500 ft - 5mW x 0.000732% = 36.6 nanowatts [169 nW]    1200 ft - 5mW x 0.036719% = 1.84 microwatts [8.4735 uW]    reverse calculated laser power assuming 5mW enters the eye    8500 ft - 5mW / 0.000732% =  683 watts [147.9 watts]    1200 ft - 5mW / 0.036719% = 13.6 watts [2.95 watts]  As you can see, the error actually works in favor of my argument that it would take a very powerful laser to cause retinal burns in these cases. My original results were off by a factor of about 4.6.  Also, something I forgot to address in my first email. I had used the altitude of the aircraft as the distance from the laser. In reality, this distance would have to have been greater, perhaps twice as much, due to the angle required to get the laser to shine through the cockpit windows and into the pilots eyes. Even when an aircraft is on approach in a nose down attitude, a laser source straight on would still be some distance from the ground position of the aircraft. The effect of this is more divergence and less laser power in the pilots eyes, necessitating a more powerful laser to reach damage threshold.  I would like to clarify that I am fully aware of the danger to an aircraft from even a low powered laser causing temporary flash blindness to the flight crew. The laser would not have to be of sufficient power to cause damage to be a hazard to operations of an aircraft during a critical phase of flight. Among my many interests I am also an aviation enthusiast. Unfortunately I've never had the opportunity to get my wings. I certainly wouldn't want any bright light, laser or not, shining at my aircraft while I was attempting a night landing.  I am still not convinced of the reality of retinal damage to the pilots eyes. I have discussed this matter with a few people who are familiar with laser eye injuries. Retinal burns are very difficult to detect. It requires an exam by an opthamologist experienced in retinal laser damage, and often times the examination is inconclusive. You mention that the pilot's condition was determined by "a physician." Unless this "physician" is experienced in diagnosing laser eye damage I would be very dubious of the diagnosis. Everyone I know would be very keen to read the medical reports.  In your reply you state,    "We have pilots who were taken off flight status and diagnosed     with retinal burns by a doctor.  In one case, the pilot simply     saw the light on the horizon, didn't rub, didn't blink, didn't     think anything of it.  Then, he woke up with a puffed up,     bloodshot eye the next morning." I'll let the words of someone with first hand experience than I reply,    "I know of cases (in the company where I work) of people receiving     an exposure to a laser (visible) and thinking nothing further of     it until a retinal burn was found at the next eye exam (anyone     working directly with lasers has to be examined for retinal burns     every 2 years), no soreness, no bloodshot eyes, no puffiness.     Corneal damage would cause the symptoms they describe, not (only)     a retinal burn."  In response to why I used the minimum value instead of the maximum for Class IIIb lasers as the basis for my calculations, it was because this was the lowest power expected to cause damage. Remember, this was in the part where I was calculating backwards to find the minimum power of the source laser. If I were to have used the maximum power in those calculations, the result would have been a higher powered laser, which would have worked in favor of my argument. I was attempting to determine the minimum power required under those circumstances that might begin to cause eye damage.  In response to my question about witnesses on the ground seeing the laser, you said you were aware of none. This would be an important piece of information to find out. If people on the ground were able to see the laser shining in the sky, especially from a distance, then that would mean the laser was of significant power. Lower powered lasers are very difficult to see from an any significant angle. They are practically invisible except when they are directed toward the viewer. With all the attention given these incidents, I am surprised no one has come forward to say "I saw a laser in the sky" to the authorities or especially the media. People love to be the center of attention and a chance to be on TV would be tempting. Since only the pilots have seen the laser, I'm tempted to think the lasers were of lower powers.  Regarding anti-personnel lasers, I was unaware of the Chinese device you mentioned. As far as I am aware, there is a treaty signed by most respectable nations banning such devices as being inhumane. It is of no surprise to me that some countries wouldn't care. However, I think we can both agree that it is highly unlikely one of these devices is being used. From my knowledge of lasers, an anti-personnel laser would best be infrared. Not only does it make it invisible to the target, it is also much easier to obtain the higher powers necessary to do retinal damage.  As to this FBI bulletin, would it be possible to obtain a copy of it for examination? If it's online somewhere, a URL would suffice. It would also be helpful having more detailed information for these laser incidents. The only information floating around so far is the altitude of the aircraft. This leads to too much guessing. What is the possibility of seeing copies of the incident reports? Also, although I doubt the possibility of seeing the medical reports themselves, further more specific information about the eye exams would be of interest as well. All of this information would be of interest to the laser community at large and I would like to be able to share it with them. In a sense the laser community has a vested interest in this problem.  My request for a retraction of your security alert should probably be restated as a request for something less embellished. I agree that pilots should be aware of the potential danger to flight operations and to know how to react should they become a target. However, I still feel that it is unnecessary to include statements about lasers "augmented for use as weapons", "anti-personnel lasers", and possible tracking systems. Until there is evidence of such, this is just speculation. Speculation if not qualified can lead to rumor and rumors have a way of taking on a life of their own.  I thank you for taking the time to have this dialog with me. With more information on these incidents, I and my fellow laserists will have a better understanding of the issue. Because of our combined knowledge of lasers, with the information currently available, we are very doubtful of the accuracy of these reports.

Sent small note January 24, 2005 re lack of response.

Received January 25, 2005. Yes, I did get it.  Sorry, we've been swamped.  As to your calculations, it is clear you're much more knowledgeable on laser capability than I am, so I won't attempt to debate.  What's really important about the laser events (and the lasers used ) is they have caused diagnosable damage to pilots' eyes and interfered dramatically with their ability to safely pilot an aircraft, endangering themselves, their careers and their passengers. Whatever power they were (visible or not visible to witnesses, sophisticated or amateur, powerful or not) the lasers used were dangerous to aircraft.  I would like to believe (and said in interviews) these were probably sophisticated lasers costing hundreds of dollars.  I don't want to see overregulation of a hobby either.  Accepting they are lower power and STILL capable of interfering with flight, leads down a path to increased regulation on even small lasers, which we don't think is supportable right now. I agree there's no evidence a ZM-87 was used in any of these incidents. But, at least in two incidents (SLC, A/C 5 miles from airport; eye damage to pilot and exposure for several seconds while the aircraft moved, and CLE, A/C 15 miles from airport at 8500 MSL; eye damage to pilot), the reports by professional pilots suggest (as you allude) a very powerful laser (powerful enough to cause eye damage at great range) with the capability to track the aircraft for 15-20 seconds.  The only way to avoid that conclusion is to discount the accuracy of these reports, which we don't have the luxury of doing.  In these cases, a laser was deliberately used as a weapon and had the capability of being so used.  The timing and scope of these incidents, combined with a very recent FBI report suggesting their possibility, made the allusion to "weaponized lasers" prudent. I am trying to get permission to share the FBI bulletin.  If I receive it, it will be posted on our site.  I am attaching a copy of an FAA bulletin regarding laser dangers to pilots. [click to read PDF file] We also are expecting two 50mW lasers soon for testing.  We'll have more information when it's complete. Additionally, our security alers expire four weeks after the last confirmed report on their content.

Jan 25, 2005 To: David Mackett, President APSA David, I think we can both agree that any laser of any power is a hazard to air traffic. Also, thank you for the document from the FAA and thank you for the effort to share the FBI memo. I realize that you are a busy person, but I would like to continue our dialog focusing on the issue of pilots receiving eye damage. I'm sure you can understand that from our point of view having a knowledge of lasers, we find it difficult to believe that there has in fact been any actual eye damage. I and my fellow laserists would really appreciate any help in obtaining more detailed information on the diagnoses. To be blunt, I guess we need proof. I am hoping you are in a position to help. If in fact there has been verifiable eye damage from a laser, then this implies that these incidents may represent a concerted effort by someone to target aircraft with malicious intent as opposed to someone playing around negligently. But until we see some evidence that there is laser induced eye damage, we are hard pressed to accept this conclusion knowing what it would take to accomplish. I see your group is going to do some testing. I would appreciate being informed of the results and being able to share it with my fellow laserists. Once again, I thank you for your time.

Received January 26, 2005 Brian - I have only the information I received, which is that several pilots in the early incidents had medically diagnosed eye damage and were removed from flight status.  It's well-beyond my purvue to see their medical records and I rely on reports from their airlines, the FAA and, in one case, first hand reporting. The reason our bulletin was worded the way it was is that we were (and remain) very concerned that the early incidents were NOT consistent with amateurs playing with laser pointers and may have been something more.  The fact that police have made two arrests in the subsequent incidents has led the public to believe this was all an amateur prank.  That's just not consistent with the information we have about the first incidents in their entirety. I also believe a malicious laser attack would take a very sophisticated and concerted effort - almost beyond the realm of beliveability.  But, if you'd told me on September 10, terrorist teams would hijack multiple airliners, fly them into buildings and collapse the WTC with them, I would have laughed in your face.