Approach lighting system safety

The current standards and criteria to implement approach lighting systems are based on the number of aircraft operations, the type of airport operations, and the design criteria of runway operations. These criteria do not address issues such as the safety of passengers and rescue personnel after an aircraft accident/incident.

Airports around the world face enormous challenges to protect people and property during regular aircraft operations. Significant encroachment of airports around populated areas has occurred in the past five decades. For the 31 years from 1976-2007, commercial aviation demand – measured in terms of commercial passenger enplanements in the system – has tripled from 238 to 767 million₁.

Approach lighting systems (ALS) provide a critical component of the runway safety systems to allow a pilot to transition from instrument to visual flight during landing. In the United States, there are 2100 runway ends which are equipped with ALS. These systems, while critical for safe landing, also provide a potential issue in the case of an undershoot or overrun on a landing. An aircraft landing in an ALS field is in an environment which has both electrical equipment and structures. There is great potential for damage to the aircraft, injury to passengers and problems for the first responders.

The structures in the United States that are located within the ALS area are required to be frangible according to FAA Advisory Circular AC150/5345-45C. The frangibility of the mounting structures used in various approach lighting systems reduces the potential damage caused by an aircraft collision. Most collisions with the approach lighting system appear to be minor incidents where the system was struck by a low approach aircraft, however since only 40ft of a structure is required to be frangible, if a catastrophic incident occurs where an aircraft impacts the steel support towers, it may pose a significant hazard. It should be noted that the steel tower supports are typically beyond the runway safety area.

While the structures are specified and uni­versal, the electrical control of the systems varies by the type of approach lighting system installed. For example, the ALSF systems (specified in FAA-E-2689a), are wired in a series configuration that allows for minimum impact on the intensity of the individual lights, due to the constant current regulation. However, MALS, specified in FAA-E-2980, have each light bar hooked to a circuit breaker much like lighting in the home is wired. Control of the ALS can be provided through hard wiring from the tower or through radio control. In the case of a catastrophic failure of the system, one where an aircraft damages several components of the system, it is believed that the system will shut down due to operational requirements outside of the system specification, but a specification of this behavior was not found. In this case, passengers escaping from the crash area or first responders approaching the scene will be potentially exposed to a live and damaged electrical system.

Another issue associated with the safety of an ALS, is the divided jurisdiction of ownership and control. In the United States, the ALS is owned and operated by the FAA, while the airport authority operates other components of the airport. In times of critical incidents, this divided jurisdiction may also be an issue.

This project was undertaken by the Virginia Tech Transportation Institute, to investigate the potential issues with the catastrophic failure of the ALS due to a collision and to develop recommendations for dealing with the potential hazards of these systems. The project included a review of crash histories, interviews with airport and FAA officials and then development of recommendations.

Incident review

In order to identify safety risks and hazards, an extensive review of aircraft accidents was undertaken. During the period of analysis between 1975 and 2007, there were 110 accidents with known collisions with approach lighting systems. This translates into an accident rate with approach lighting systems of one per 37 million operations. This metric is remarkable in terms of safety. Recent statistics of aircraft fatal events for modern airlines suggest a fatality every 5.5-10.5 million operations.

Of the 110 accidents identified, the most common accident involved MALSR with 46% of collisions (also the most common approach lighting system). The next highest collision rates where for ALSF systems, which registered 14% of the collisions. The remaining per­centages were equally divided between MALSFs, MALS, Localiser Antennas (8% each) and VASI collisions, totalling 18%. Collision recorded rates for SSALRs were 2%.

The review of the collisions often involved aircraft striking the system, but often without the knowledge of the pilot. The very fact the pilot was unaware of striking the ALS is tribute to the frangibility requirements. Significant collisions often involved severe damage to the aircraft, often striking support structures beyond the RSA. However, these situations often did not specify ALS issues. Given the low frequency of ALS specific events, additional information was sought from airport operations, FAA, and ARFF personnel.

Airport operations review

Current mitigation practices and general techniques were gathered by directly interviewing airport operators, FAA officials, ARFF departments, and mutual aid response groups. The purpose of these interviews was to obtain in-depth, site-specific responses regarding current operational procedures, and to identify best practices that take system and insti­tutional issues into consideration with respect to the mitigation of approach lighting system hazards.

A total of 15 airport locations were visited by the research team, which included primary, reliever, general aviation facilities. The airport locations were chosen based on size, whether they possessed an ATC tower, approach lighting system hardware, and previous overrun or undershoot incidents.

Facility size appears to play a significant role with regard to current procedures, in addition to the required certification₂. The majority of facilities, both large and small, had not considered the impact of approach lighting system hazards, or potential hazards with respect to their current emergency response plan. Furthermore, few facilities had considered the implications of a compromised approach lighting system with respect to the walking wounded from an aircraft incident, as well as the emergency response personnel.

Smaller facilities, which did not have the same resources as some larger facilities, often relied on common sense and any electrical training that the response team (e.g., ARFF) might have. A common method used to de­activate the electrical field when ATC assistance was not available, is manually shutting down the electric vault. These scenarios often involved obtaining access to those locations containing the electrical vault. However, specific procedures, often unwritten, included deactivating the electrical vault through throwing a switch. Specific instructions on which switch to throw were often not known. In most cases the FAA-owned equipment was only accessible with FAA permission and keysets. When asked about post-incident risks, response personnel often highlighted that the electrical field was of concern for both the responding agencies and the evacuating passengers. For the response personnel (ARFF or mutual aid), a major concern was the con­tinued risk of ignition sources and the resulting risk of additional fires.

The larger facilities have the benefit of ATC tower support, to aid in the possible mitigation strategy for approach lighting system hazards. Most often, for those facilities that contained an ATC tower, the immediate response upon an incident would be to ask ATC to shut down the approach lighting system. Inter­estingly, for some of the larger facilities, additional risks were identified that also played a dominant role in the potential threat to evacuating passengers and rescue personnel. Depending on location, the environmental terrain may impede rescue efforts or enhance the poten-tial dangers. Those facilities located near water, that also had approach lighting systems extend into the waterway, out­- lined the structural issues and also the electrical/water interaction.

Finally, other risks identified included weather, wildlife, deactivating the approach lighting system and continuous power equipment risks, the interactions of de- energising the lighting on one runway, and the effect that de-energising the lighting on one runway has on other runways (e.g., approach lighting system power connections).

Mitigation recommendations

A number of mitigation techniques were recommended after the interview process. A set of common mitigation strategies appeared to be consistent for both smaller and larger airport facilities and these techniques are highlighted.

Group or committee review

In an effort to establish a foundation to mitigate potential approach lighting system hazards, the research effort suggests that a small group of airport operations, emergency response (on-site ARFF or off-site mutual aid emergency response personnel) and FAA personnel (as appropriate to the size/classification of the airport) be convened to examine and discuss potential ALS hazards. Establishing a group with members from a variety of organisations will provide the depth and knowledge to handle the broad discussion points. In addition, it was suggested a yearly review of potential approach lighting system hazards be conducted, in order to update and discuss emergency response planning and procedures.

The group approach to mitigation planning provides input from a variety of sources that includes those agencies responsible for att­ending to a potential incident, and also those agencies that own and maintain the equipment.

Cross-training

Another solution to implement was the establishment of some level of cross-training between airport operations, FAA, and agency response personnel. An effort to familiarise or cross-train personnel on how the approach lighting system functions, so that they are knowledgeable on system operations and shutting down the system during a potential incident, was considered essential.

The cross-training effort should include conducting walk-through training as needed, in order to confirm that personnel who might be involved in responding to an approach lighting incident know how to de-energise the system (including any emergency power sources to the system), as well as how to confirm that the approach lighting system equipment is de-energised at the scene. It is recommended that walk-through training on communications is conducted between emergency response personnel, responsible for an incident outside the airport boundary, and those responsible for de-energising the system. Also, it is recommended that a walk-through of access points to the approach lights under various hypothetical situations is conducted, in order to confirm access routes and that any desired alternate routes are acceptable.

Establishment of an in-house reference guide

Establishing a reference guide for facility per­sonnel appears to be beneficial for mitigating approach light system hazards. The reference guide provides picture references for all buildings, including those designated specifically for approach lighting systems. The reference guide is used to orient personnel on the approach lighting system and other buildings/ equipment within and around the airfield.

In addition to the reference guide, it is suggested that a list of names, phone numbers (home, mobile, pager) and work schedules be compiled for all those who might be involved in responding to an aircraft/approach lighting system incident. This list can be included in the reference guide above and also placed in a convenient location for emergency purposes.

Approach Lighting System access planning

In addition to the cross-training mitigation suggestions, the research team also found that access to specific areas to de-energise the approach lighting system was required for response personnel. Establishing a means for response personnel to access areas to de-energise an ALS should be considered.

Additional recommendations were also developed that take into account facility size, facility location, and other resources. These recommendations and additional techniques can be found in the Airport Cooperative Research Programme report, available online₃.

Conclusion and recommendations

A number of interesting results were obtained regarding current approach lighting system specifications, previous incident records, on-site practices and issues, and a culmination of hazard types. With the information given, the report proposed hazard identification techniques and mitigation strategies.

Approach lighting systems are well-engineered and consist of various failure mode mechanisms that allow for continuous power during severe weather situations. However, despite these failure modes, the literature review revealed some oversights in the construction of the systems themselves. The incident database showed that undershoot situations that involve collisions with the approach lighting system, were more frequent than overrun collisions with the approach lighting system. However, the reports associated with these types of events lack specific details regarding the interaction of the approach lighting system with the aircraft involved in the incident. The reports often only state that the approach lighting system was struck, but there is no evidence that the system played a major role in the outcome of the situation, or if it hindered or caused further safety concerns. The reporting process should allow for specific information to be entered regarding the approach lighting system, with respect to details about damage, whether the system shut down or tripped breakers, whether the system functioned as operationally intended after the incident, or if other complications were identified. These additional details can help determine how the system interacted with the incident aircraft and if the approach lighting system posed additional risks after the incident.

The interview information gathered during the site visits proved to be a valuable addition to the information gathered from the literature and incident review. To begin, most of the airport facilities had not considered the impact an approach lighting system had on incidents and the additional risks to rescue personnel when a system was compromised. The research team also identified that the relationship between airport facilities and other agencies varied greatly between each facility. The procedural mitigation techniques suggested require a high degree of collaboration between airport operations and other agencies.

Future research

Additional research is required in order to identify potential technology needed to de-energise the approach lighting system when a valid incident occurs. During the interview process, the research team asked about technological solutions and respondents voiced concern about how a system would identify a valid incident situation. Further research is required to investigate what a valid incident situation consists of and also what technology would need to be incorporated on current systems to allow for a system to de-energise. Multiple testing techniques will be required, to ensure that systems do not deactivate unintentionally. The adoption of technological shut-off mechanisms may be considered in the future; however, extensive research regarding how the system detects an incident and what elements are shut down needs greater exploration.

Finally, additional research is required to identify appropriate warning mechanisms for response personnel during incidents involving approach lighting systems. A thorough human factors review of warning types (e.g., visual, auditory, etc.) should be considered, in order to warn response personnel when an approach lighting system has been deactivated. Pre­liminary assessment of warning types suggests a two-point approach that incorporates both visual and auditory warning mechanisms. These warning efforts can be incorporated into future research regarding automated de-energisation of systems that may be employed in the future.

References

1. Federal Aviation Administration, Terminal Area Forecast (TAF), Software version 2006.
2. Federal Aviation Regulations, Title 14, Code of Federal Regulations (CFR), Part 139. 2004. Available online: http://www.faa.gov/airports_airtraffic/airports/airport_ safety/part139_cert/, Accessed December 2009.
3. Gibbons, R.B., Edwards, C.J., and Trani, A (2009). Guidance for Identifying and Mitigating Approach Light System Hazards (Airport Cooperative Research Program: Report RRD 6). Online: http://144.171.11.107/Main/ Blurbs/ Contractors_Final_Report_for_ACRP_RRD_6_Guidance_f_162283.aspx