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Lasers and aviation safety

By Wikipedia,
the free encyclopedia,

http://en.wikipedia.org/wiki/Lasers_and_aviation_safety

Under certain conditions, laser light or other bright lights (spotlights, searchlights) directed at aircraft can be a hazard. The most likely scenario is when a bright visible laser light causes distraction or temporary flash blindness to a pilot, during a critical phase of flight such as landing or takeoff. It is far less likely, though still possible, that a visible or invisible beam could cause permanent harm to a pilot's eyes. Although laser weapons are under development by the military, these are so specialized, expensive and controlled that it is essentially impossible for non-military lasers to cause structural damage to an aircraft.

Aviation hazards from bright light can be minimized or eliminated in two primary ways. First, users on the ground can exercise caution, to prevent or minimize any laser or other bright light being directed in airspace and especially towards aircraft. Second, pilots should have awareness of laser/aviation hazards and knowledge of basic recovery procedures in case of laser or bright light exposure.

Pointing a laser at an aircraft can be hazardous to pilots and has resulted in arrests, trials and jail sentences. It also results in calls to license or ban laser pointers. Some jurisdictions such as New South Wales have restricted laser pointers as a result of multiple incidents.

Lasers and bright lights

Although this article concentrates on lasers, it should be noted that other bright directional lights such as searchlights and spotlights can have the same dazzling/distracting/flashblinding effects. Searchlight/spotlight operators should take the same basic precautions as laser users. Similarly, pilots and safety officials should keep in mind that a reported "laser" incident may be caused by a non-laser bright light.

Lasers in airspace

There are many valid reasons that lasers are aimed into airspace. Lasers are used in industry and research, such as in atmospheric remote sensing, and as "guide stars" in adaptive optics astronomy. Lasers and searchlights are used in entertainment; for example, in outdoor shows such as the nightly IllumiNations show at Walt Disney World's EPCOT Center. Laser pointers are used by the general public; sometimes they will be accidentally or deliberately aimed at or near aircraft. (Of course, no unauthorized person should deliberately aim any type of laser at or near an aircraft.)

Lasers are even used, or proposed for use, with aircraft. Pilots straying into unauthorized airspace over Washington, D.C. can be warned to turn back by shining eye-safe low-power red and green lasers at them. At least one system has been tested that would use lasers on final approach to help line up the pilot on the proper guideslope. NASA has tested a Helicopter Airborne Laser Positioning System. The FAA has tested laser-projected lines on airport runways, to increase visibility of "hold short" markings.

Because of these varied uses, it is not practical to ban lasers from airspace. This would unduly restrict legitimate uses, it would not prevent accidental illumination incidents, and it would not stop someone who deliberately, out of malice or ignorance, targeted aircraft. For this reason, practical laser/aviation safety is based on informed users and informed pilots.

Primary hazards of lasers and bright lights


FAA flight simulator showing distraction where the light does not obscure vision but can distract the pilot. Light intensity 0.5 μW/cm²; for example, a legal 5 mW laser pointer at 3,700 feet (1,130 m).
FAA flight simulator showing distraction where the light does not obscure vision but can distract the pilot. Light intensity 0.5 μW/cm²; for example, a legal 5 mW laser pointer at 3,700 feet (1,130 m).

FAA flight simulator showing veiling glare where it is hard to see through the light to the background scene. Light level 5.0 μW/cm²; for example, a legal 5 mW laser pointer at 1,200 feet (365 m).
FAA flight simulator showing veiling glare where it is hard to see through the light to the background scene. Light level 5.0 μW/cm²; for example, a legal 5 mW laser pointer at 1,200 feet (365 m).

Simulation of temporary flash blindness where the image takes from a few seconds to a few minutes to fade away, depending on how much light entered the eye. Light level 50 μW/cm²; for example, a legal 5 mW laser pointer at 350 feet (107 m).
Simulation of temporary flash blindness where the image takes from a few seconds to a few minutes to fade away, depending on how much light entered the eye. Light level 50 μW/cm²; for example, a legal 5 mW laser pointer at 350 feet (107 m).

(Note: The photos at right flash because most incidents are of flashes and not of steady illumination. In accidental illuminations there may be just one or a few flashes. Even in deliberate illuminations, it is hard to hand-hold a laser on a moving target, so there will be a series of longer flashes. With helicopters at close range, it is possible to have a more-or-less continuous light.)


There are some subjects which laser/aviation safety experts agree pose no real hazard. These include passenger exposure to laser light, pilot distraction during cruising or other non-critical phases of flight, and laser damage to the aircraft.

The main concerns of safety experts are almost exclusively focused on laser and bright light effects on pilots, especially when they are in a critical phase of flight: takeoff, approach, landing, and emergency maneuvers.

There are four primary areas of concern. The first three are "visual effects" that temporarily distract or block pilots' vision. (For lasers, these effects are only of concern when the laser emits visible light.)

  • Distraction and startle. An unexpected laser or bright light could distract the pilot during a a nighttime landing or takeoff. A pilot might not know what was happening at first. They may be worried that a brighter light or other threat would be coming.
  • Glare and disruption. As the light brightness increases, it starts to interfere with vision. Veiling glare would make it difficult to see out the windscreen. Night vision starts to deteriorate.
  • Temporary flash blindness. This works exactly like a bright camera flash: there is no injury, but night vision is temporarily knocked out. There may be afterimages -- again, exactly like a bright camera flash leaving temporary spots.

The three visual effects above are the primary concern for aviation experts. This is because they could happen with lower-powered lasers that are commonly available. The fourth concern, eye damage, is much less likely. It would take specialized equipment not readily available to the general public.

  • Eye damage. Though it is unlikely, high power visible or invisible (infrared, ultraviolet) laser light could cause permanent eye injury. The injury could be relatively minor, such as spots only detectable by medical exam or on the periphery of vision. At higher power levels, the spots may be in the central vision -- in the same area where the original light was viewed. (This is why one should not look directly straight into the sun or any bright light. Instead, look away or far off to the side.). And most unlikely of all is injury causing a complete and permanent loss of vision. To do this requires very specialized equipment and a desire to deliberately target aircraft. Someone wanting to do this could find far less expensive, and much easier ways to attain their goals. (It should be noted that claims of permanent injuries are not proof of injury. Some laser experts are skeptical of some reported pilot injuries, as the injuries would have required different types or powers of lasers than those reported.)

It is extremely unlikely that any of the four elements above would cause loss of the aircraft, especially if the pilots react properly and work as a team.

Analyzing the hazard

The exact hazard in a specific situation depends on a number of factors.

Laser/bright light factors

  • The power of the laser or bright light. The more light emitted, the brighter and more hazardous it will be.
  • The beam divergence. A low-divergence "tight" beam will be a hazard at greater distances than one which spreads out rapidly.
  • Visibility (wavelength) of the beam. An infrared or ultraviolet laser beam does not present any visual effect risk to pilots, as they cannot see it. However, at high powers it can present an eye damage risk. In some cases, this hazard may be greater since a pilot would not know they were being illuminated.
  • Color of the beam (for visible wavelengths). In general, the eyes of pilots in an illuminated nighttime cockpit are most sensitive to greenish-yellow light (of wavelength around 500–600 nanometers, peaking at 555 nm). A blue or red laser will appear much dimmer -- and thus less distracting -- than a green or yellow laser of equal power (wattage).To give a specific example, a 10-watt continuous-wave YAG laser at 532 nanometers (green), can appear brighter to the eye than an 18-watt continuous-wave argon-ion laser that outputs 10 watts of 514 nm (green-blue) light plus 8 watts of 488 nm (blue) light.
  • Pulsed/continuous nature of the beam. Some laser beams emit their energy in pulses. A pulsed laser presents a greater eye damage risk than a continuous laser of equal (average) power. This is because the power is packed into shorter pulses.

Operational factors

  • Beam movement. If the beam is moving around such as in a laser show, it covers a greater area of the sky and thus has a greater chance to illuminate an aircraft. However, if it did scan across a cockpit, in general the exposure duration would be shorter. (A more precise analysis would look at the relative motion of the beam and aircraft.)
  • Location of the beam relative to airports. The beam must avoid airspace around airports and busy air routes. The FAA has established safety zones around airports, which are described in the "Regulation" section below. It is possible to use beams within the zones, if the beam power is below the FAA limit for the zone.
  • Projector and laser stability. To avoid accidents, the laser projector must be secured with relation to termination points and beam blocks. If a projector slips, or safety software fails, the beam could enter unsafe areas of airspace.

Situational factors

  • Day vs. night. Almost all concern is over nighttime illumination. The three visual effects listed above (distraction, glare and flash blindness) are minimized during the day since the eye is not dark adapted, and since visible lasers are not often used outdoors in daytime.
  • Motion and speed of the aircraft. A slow aircraft is at greater risk than a fast one (relative to travel across the viewer's line of sight). Helicopters are at greatest risk because they can hover, presenting a relatively stationary target.
  • Distance to the aircraft. A low-flying aircraft is at greater risk. Again, helicopters are vulnerable due to their close ground proximity.
  • Direction relative to the aircraft and cockpit. A beam aimed directly at an incoming aircraft gives the greatest risk to pilots. One aimed across the aircraft's travel gives less risk, partially because the light enters through the side windows, and partially because it is harder to keep the beam aimed exactly at the cockpit area. A beam aimed straight up gives the least risk, although it is still possible for the beam to illuminate the cockpit during a banking turn.

Pilot/aircrew factors

  • Flight phase. The risk is greatest when the exposure comes during a time of high workload: takeoffs, critical or emergency maneuvers, and landings.
  • Pilot awareness and response. Ideally, pilots will be aware of laser and bright light hazards, and will know how to recover in case of an incident. Conversely, a pilot can make the situation worse if he or she overreacts, stares at the light to try to locate its source, or takes immediate unnecessary evasive maneuvers.

The U.S. FAA has studied some of these factors . They conducted research using pilots in flight simulators to determine the effects of laser exposure on pilot performance; results were released in August 2003 and June 2004.

Accidental vs. deliberate exposure

Laser users must take appropriate precautions to avoid accidents. (Some steps are outlined below in the section "Reducing the hazard".) In most cases, an accidental exposure is likely to be one or a few brief flashes, as the aircraft moves through a stationary beam, or as a hand-held beam sweeps over the cockpit.

There have been cases of deliberate intent, where someone through ignorance or malice deliberately aimed a laser at an aircraft. Note that no one should ever deliberately aim a laser at an aircraft. It can result in pilot distraction, and may well result in searches by authorities to find the source. There have been a number of cases reported where laser pointer users were arrested and tried; a few have even gone to jail. Such incidents also can lead to calls to license or ban laser pointers.

Whether an accidental or deliberate exposure, any pilot seeing a flash should avoid looking in the direction of the light, since it may be quickly followed by additional flashes.

Example laser safety calculations


Graphic illustrating how laser pointer hazards are most serious when the laser is close to the aircraft
Graphic illustrating how laser pointer hazards are most serious when the laser is close to the aircraft

The graphic at right shows many important laser/aviation safety concepts.For example, it shows that the areas of most concern -- eye damage, flash blindness and glare -- occur relatively close to the aircraft. The distraction risk covers the longest hazard distance, but fortunately also presents the least concern. The photos in the graphic also give an idea of what the visual effect looks like to the pilot, at various distances.

Note that while the distances given are exact ("52 feet", "262 feet"), the laser's brightness is in fact falling off slowly. It is not as if at 51 feet the laser is an eye hazard and at 53 feet it is eye safe. Effects diminish continuously with increasing distance.

Also, the weaker effects are part of any stronger effect. Even if a laser does not cause eye damage at 25 feet, it can still cause flash blindness, glare and a distraction.

For any given laser, the relative distances shown here may change. For example, an invisible (infrared) laser can be an eye hazard for hundreds of feet, but presents no flash blindness, glare or distraction hazard. Because of this, each laser must be analyzed individually.

To give another example, here are calculations of a more powerful laser -- the type that might be used in an outdoor laser show. A 6-watt green (532 nm) laser with a 1.1 milliradian beam divergence is an eye hazard to about 1,600 feet (488 meters), can cause flash blindness to about 8,200 feet (1.5 mi/2.5 km), causes veiling glare to about 36,800 feet (7 mi/11.2 km), and is a distraction to about 368,000 feet (70 mi/112 km).

Reducing the hazard

There are a number of ways that laser users, regulators and pilots reduce the potential hazard from outdoor laser use. These measures include:

Police enforcement

Police have begun using helicopters to patrol and seek out people using lasers to disrupt aviation.

User hazard reduction measures

  • Using the lowest power necessary for the task.
  • Increasing the beam divergence. The beam spreads out faster, so at any given distance, the amount of light entering the eye or a cockpit windscreen will be less (e.g., lower irradiance).
  • Keeping beams away from areas with many aircraft, such as airports and flight paths.
  • Terminating beams on buildings, dense trees, etc. to prevent laser light from entering protected airspace. This is a common protection measure for outdoor laser shows, if there are structures available for termination.
  • Using spotters to watch for aircraft. This is commonly done for laser shows which tend to be short-duration (around an hour) and infrequent (nightly shows are rare).
  • Using automated detection systems such as radar or sky cameras. These are used for long-duration (all night) and frequent (nightly) applications, such as laser guide stars used at astronomical observatories.
  • Developing and following policies for outdoor laser operations, such as the ANSI standard "Safe Use of Lasers Outdoors"or NASA's "Use Policy for Outdoor Lasers".

Regulatory hazard reduction measures

  • Restricting the sale or use of laser devices. This is done in some jurisdictions. For example, in April 2008 New South Wales, Australia banned laser pointer possession, except by special permit, in an effort to reduce the number of laser illuminations of aircraft. In October 1997 in the United Kingdom, laser pointers were restricted to less than 1 milliwatt output, for similar reasons. In the U.S., the Congressional Research Service notes that a ban could "pose significant challenges because these devices are widely available at low cost and are used in a variety of applications such as laser pointers, laser levels and laser gun sights."
  • Requiring review or approval of outdoor laser uses. This is discussed in the Regulation and control section below.
  • Amending existing laws, or enacting new ones, to try to discourage irresponsible laser use. One U.S. federal effort in this direction is the "Securing Airplane Cockpits Against Lasers Act of 2005", discussed in the History section below.

Pilot/aircrew hazard reduction measures

  • Fixed laser installations (e.g., guidestars from observatories) may be marked on aeronautical charts so pilots are aware of potential beams along their flight path. Temporary uses (laser shows) may be described in pre-flight information. For example, in the U.S., laser uses submitted to the FAA are often listed in NOTAMs for pilots.
  • Education and training. The SAE G-10T Laser Hazards Subcommittee is working on Aerospace Recommended Practice document 5598, "Laser Visual Interference - Pilot Operational Procedures." This will provide information for pilots on recognizing and recovering from a laser or bright light incident. Articles in aviation publications also have provided helpful information, such as "Laser Illuminations: The Last Line of Defense - The Pilot!".

Active hazard reduction (proposed measures)

Some measures have been proposed to protect aircrews including goggles and windscreen filters. These may work in theory (especially against known wavelengths) and may be useful in some situations such as military operations. However, these measures may not be suitable, practical or recommended for widespread civil air operations.

  • Laser safety goggles. Laboratory-type laser safety goggles are not well suited for pilot operation. "The 20% transmission ratio of laboratory laser eyewear would probably have disastrous effects on a cockpit crew who must read instruments while flying at night.... The optical quality of such systems also becomes a factor because slight amounts of distortion or haze which may be of no concern in the laboratory may be a major concern to pilots flying at low altitudes and high speed." Also, there may be a variety of laser wavelengths/colors that may need to be defended against. If all wavelengths are protected, the goggles essentially are opaque. There are also issues with the discomfort of wearing goggles routinely, given that laser incidents are relatively rare.
  • Active "smart" goggles which can detect laser light and then activate a blocking/dimming process based on the power and wavelength. It is not known if these are in production or use; if so, it is likely that these are used only in military applications.
  • Glare shields that can be pulled down over a windscreen to reduce all incoming light.
  • Laser event detectors/recorders that can sense a laser illumination and record information about the wavelength and power. This does not provide protection but does give information about an illumination which may be useful for later analysis or legal action.

Regulation and control


The U.S. FAA Laser Free Zone extends horizontally 2 NM (3,700 m) from the centerline of all runways (two dark lines in this diagram) with additional 3 NM (5,560 m) extensions at each end of a runway. Vertically, the LFZ extends to 2,000 feet (610 m) above ground level.
The U.S. FAA Laser Free Zone extends horizontally 2 NM (3,700 m) from the centerline of all runways (two dark lines in this diagram) with additional 3 NM (5,560 m) extensions at each end of a runway. Vertically, the LFZ extends to 2,000 feet (610 m) above ground level.

The U.S. FAA Critical Flight Zone extends horizontally 10 NM (18.5 km) around the airport, and extends vertically to 10,000 feet (3,050 m) above ground level. The optional Sensitive Flight Zone is designated around special airspace needing bright-light protection.
The U.S. FAA Critical Flight Zone extends horizontally 10 NM (18.5 km) around the airport, and extends vertically to 10,000 feet (3,050 m) above ground level. The optional Sensitive Flight Zone is designated around special airspace needing bright-light protection.

In the United States, laser airspace guidelines can be found in Federal Aviation Administration Order JO 7400.2 (Revision "G" as of April 2008), Procedures for Handling Airspace Matters, Part 6, Chapter 29, "Outdoor Laser Operations". Bright light airspace guidelines are in Chapter 30, "High Intensity Light Operations".

In the United Kingdom, CAP 736 is the "Guide for the Operation of Lasers, Searchlights and Fireworks in United Kingdom Airspace."

For all laser users, the ANSI Z136.6 document gives guidance for the safe use of outdoor lasers.While this document is copyrighted by ANSI and is relatively costly, a flavor of its recommendations can be seen in NASA's Use Policy for Outdoor Lasers.

Airspace zones

The U.S. FAA has established airspace zones. These protect the area around airports and other sensitive airspace from the hazards of safe-but-too-bright visible laser light exposure:

  • The Laser Free Zone extends immediately around and above runways, as depicted at right. Light irradiance within the zone must be less than 50 nanowatts per square centimeter (0.05 microwatts per square centimeter). This was set at "a level that would not cause any visual disruption."
  • The Critical Flight Zone covers 10 nautical miles (NM) around the airport; the light limit is 5 microwatts per square centimeter (μW/cm²). This "was determined to be the level at which significant glare problems can occur."
  • The optional Sensitive Flight Zone is designated by the FAA, military or other aviation authorities where light intensity must be less than 100 μW/cm². This might be done for example around a busy flight path or where military operations are taking place. This "was identified as the level of exposure at which significant flash blindness and afterimages could interfere with a pilot's visual performance."
  • The Normal Flight Zone covers all other airspace. The light intensity must be less than 2.5 milliwatts per square centimeter (2500 μW/cm²). This is about half of the Class 3R power level, and is not considered hazardous for a brief exposure.

For non-visible lasers (infrared and ultraviolet), the irradiance at the aircraft must be eye-safe -- below the Maximum Permissible Exposure level for that wavelength. For pulsed visible lasers, the irradiance at the aircraft must be both eye-safe and must be at or below any applicable FAA laser zone.

In the UK, restrictions are in place in a zone that includes a circle 3 NM (5.5 km) in radius around an aerodrome (airport) plus extensions off each end of each runway. The runway zones are rectangles 20 NM (37 km) in total length and 1000 meters (3280 feet) wide, centered about each runway.

Reporting

In the U.S., those persons operating outdoor lasers are requested to file reports with the FAA at least 30 days in advance, detailing their laser power(s). They must reference their operation location with respect to local airports and describe the laser power emitted within the Sensitive, Critical and Laser Free zones. Note that it is possible to use lasers whose output exceeds the limits of these zones, if other control measures are in place. For example, spotters could be used to watch for aircraft, and turn off the laser if a potential conflict is sighted. (This raises separate issues about the number, training and effectiveness of the spotters; the FAA must be satisfied that these issues are answered for the particular operation.)

FAA Advisory Circular 70-1 "Outdoor Laser Operations" contains two forms plus instructions. One form is a "Notice of Proposed Laser Operations", the other is a "Laser Configuration Worksheet" which is filled out for each laser or each different laser configuration. The FAA will review the report, and will either send a letter of objection or will send a letter of non-objection. The language is important; the FAA does not "approve" or "disapprove" as this implies a higher level of regulatory authority which the FAA does not have.

If the laser use is for a show or display in the U.S., there is a more stringent regulatory process. In the U.S., any use of lasers in a show or display requires pre-approval from the FDA Center for Devices and Radiological Health. This is required both for the laser equipment, and separately for the show itself (site, audience configuration, beam effects, etc.). As part of the CDRH's show approval ("variance") process, the CDRH will require a letter of non-objection from the FAA. Without this, the laser show cannot legally proceed.

In the U.S., laser activity in a given area is communicated to pilots before their flight via a NOTAM. Pilots exposed to a laser or bright light during flight should follow Advisory Circular 70-2 "Reporting of Laser Illumination of Aircraft".

UK laser operators report outdoor laser, searchlight or firework operations at least 28 days in advance, using the Notification Form found in annex A of the CAP 736 document.

Regulatory and standards development

A key group inside the U.S. working on laser/aviation safety is the SAE G-10T, Laser Safety Hazards Subcommittee. It consists of laser safety experts and researchers, pilots and other interested parties representing military, commercial and private aviation, and laser users. Their recommendations have formed the basis of the FAA laser and bright light regulations and forms, as well as standards adopted in other countries and by the ICAO.

The ANSI Z136.6 standard is the "American National Standard for Safe Use of Lasers Outdoors."The Z136.6 committee has worked closely with SAE G-10T and others, to develop recommended safety procedures for outdoor laser use.

History

Until the early 1990s, laser and bright light aviation incidents were sporadic. In the U.S., NASA's Aviation Safety Reporting System showed only one or two incidents per year. The SAE G-10T subcommittee began meeting around 1993 as the number of incidents grew. Almost all of the incidents were known or suspected to be due to outdoor laser displays. Almost all of the concern was over potential eye damage; at the time visual effects were felt to be a minor consequence.

In late 1995, a number of illumination incidents occurred in Las Vegas due to new outdoor laser displays. Although the displays had been approved by the FDA as eye-safe for their airport proximity, no one had realized that the glare/distraction hazard would adversely affect pilots. In December 1995 the FDA issued an emergency order shutting down the Las Vegas shows.

Within the SAE G-10T subcommittee, there was some consideration about cutting back or banning laser shows. However, it became apparent that there were a large number of non-entertainment laser users as well. The focus shifted to control of known laser users, whether shows or industry/research. New policies and procedures were developed, such as the FAA 7200 Chapter 29, and Advisory Circular 70-1. Although incidents continued to occur (from January 1996 to July 1999, the FAA's Western-Pacific Region identified more than 150 incidents in which low-flying aircraft were illuminated by lasers)[1], the situation seemed under control.

Then in late 2004 and early 2005, came a significant increase in reported incidents linked to laser pointers. The wave of incidents may have been triggered in part by "copycats" who read press accounts of laser pointer incidents. In one case, David Banach of New Jersey was charged under federal Patriot Act anti-terrorism laws, after he allegedly shone a laser pointer at aircraft.

Responding to the incidents, the Congressional Research Service issued a study on the laser "threat to aviation safety and security." Because there was no federal law specifically banning deliberate laser illumination of aircraft, Congressman Ric Keller introduced H.R. 1400, the "Securing Airplane Cockpits Against Lasers Act of 2005." The bill was passed by the U.S. House and Senate, but did not go to conference and thus did not become law.In 2007, Keller re-introduced the bill as H.R. 1615. It passed the House in May 2007 but as of April 2008 has not been voted on in the Senate.

On March 28 2008, a "coordinated attack" took place using four green laser pointers aimed at six aircraft landing at the Sydney (New South Wales) Australia airport. . As a result of this attack plus others, a law was proposed in mid-April 2008 in NSW to ban possession of handheld lasers, even "harmless classroom pointers". The Australian state of Victoria has reportedly had a similar ban since 1998, but press reports state that it is easy to buy lasers without a permit.

On February 22 2009, a dozen planes were targeted with green laser beams at Seattle-Tacoma International Airport.An FAA spokeswoman said there were 148 laser attacks on aircraft in the U.S. from January 1 2009 to February 23 2009.

See also




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Published - July 2009














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