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SUMMARY
Lightning-Warning Systems
for Use by Airports
Cloud-to-ground lightning strokes present a clear and immediate danger for ground per-
sonnel involved in outdoor ramp operations, such as aircraft fueling, baggage handling,
food service, tug operations, and guiding and directing aircraft to their assigned gates.
When this danger presents, airport ramp operations are suspended until the threat has
passed. Airport staff engaged in outdoor activities are also subject to the impact of light-
ning strikes.
Decisions about ground personnel and ramp operations are made by the airports and
airlines, not by the Federal Aviation Administration (FAA). Individual airlines, companies
providing airport workers, and airport management often have very different procedures
and standards for identifying and responding to potential lightning hazards.
Current Industry Practice
The impact of lightning events in the vicinity of, and on, airport operating areas has long
been recognized as both a safety and an operational issue by airport and airline operators.
Both have frequently invested in lightning detection and warning systems that serve to assess
when ramp and outdoor activities should be halted and then resumed without compromis-
ing worker safety. The technology to support such decision making is offered by a number
of commercial vendors, but appears to be effective given the limited reports of lightning-
induced injuries and deaths in the airport setting. These systems combine the acquisition of
lightning strike data from such sources as the National Lightning Detection Network (NLDN)
with on-site electric field mills and other weather data inputs to produce visual and aural
alarms with respect to the impending arrival of thunderstorms and lightning strikes. Airport
and airline staff then broadcast the need for clearing of the ramp and other outdoor airport
operational areas by their personnel. The return to work announcement is also facilitated
by this equipment.
Although the number of aircraft ramp injuries and deaths attributed to lightning
events is thought to be low, there has been no effort to collect such data into a systematic
database. This is because there is no requirement to report such incidents to federal or
state agencies, and most of the known data is derived from anecdotal reports and infor-
mal studies by individuals having an interest in the subject. While it is recognized that
ramp closures affect the flow of aircraft operations and cause passenger delays that can
ripple through the national air transportation system, neither government agencies nor
airport and aircraft operators have compiled closure statistics that are available for pub-
lic information.
The use of lightning detection and warning systems at airports is also dependent on the
meteorological characteristics of the location and the geographical distribution of lightning
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strikes (cloud-to-ground) throughout the United States. Most lightning strikes occur in the
eastern and central regions of the country. Consequently, the decision to install lightning
detection and warning systems is dependent to a large extent on the potential for such
events and their impact on airport and airline operations. Airports located along the west
coast of the United States, for example, frequently question the cost of installing, operat-
ing, and maintaining lightning detection systems. Conversely, several relatively closely
spaced airports in Florida each have their own lightning detection and warning systems in
place.
The key objective and impetus for the installation of lightning detection and warning
systems is worker safety. A secondary and near equivalent basis for the investment in these
systems is the minimization of ramp closures during such events. In this latter regard, it was
determined that the users of these systems employ differing standards with respect to broad-
casting a "clear the ramp" or "return to ramp activity" message. The industry has focused
on distance out and time since last event to establish bases that, respectively, govern stop-
ping and resuming ramp activities. However, the distances and time intervals employed vary
depending on the risk tolerance of the decision maker, which is generally influenced by past
experience at the airport location, including weather characteristics and frontal passage
speeds.
Liability
Another factor limiting the usefulness and standardization of lightning detection and
warning systems is liability. Some airport operators share information that they obtain con-
cerning lightning and other adverse weather phenomena with airlines and other tenants,
while others have expressly avoided this level of cooperation. Those that disseminate infor-
mation do so in one of several ways. Airports may allow tenants to subscribe to a data feed
generated by their lightning detection and warning systems. Those tenants then employ
their individual criteria for ramp closure and re-opening. Other airports broadcast a visual
display--for example, flashing lights that are visible from all areas of the airline ramp--to
warn personnel of a lightning threat. Again, the response from these workers is governed by
their specific work rules and procedures. Alternatively, airports may also opt not to divulge
weather data out of concern that they may overlook a tenant and be held liable in the event
of injury or loss of life.
Individual airlines and airport tenants that have invested resources in their own weather
monitoring technologies, including lightning detection and warning systems, use the data
collected for their own decision making. In practice, the dominant airline at the airport
where the threat of lightning events warrants the implementation of such systems typically
sets the lead that other airlines may choose to follow. Ramp workers monitor the actions of
their colleagues at other airlines, and they typically vacate and return to the ramp in unison.
This practice can extend to airport employee decisions to stop and resume outdoor work ac-
tivities. There can be instances when such "follow the leader" tactics are not observed, such
as when relatively large distances separate airline ramp operations areas, and one airline con-
tinues to operate while others have suspended ramp activity, creating a situation that can be
confusing to passengers of those airlines.
One airline, Southwest Airlines, has adopted special practices at certain airports to
deplane passengers when the aircraft arrives at the gate and a ramp work shutdown is in
effect due to lightning. The aircraft is marshaled to the passenger loading bridge position
by the ramp supervisor, who is positioned in a vehicle with lights that indicate left/right of
the lead-in centerline to the pilot during the taxi-in activity. Passengers are thus not exposed
to the lightning threat and are allowed to deplane. Baggage handling activities are not
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conducted until the ramp is cleared for such activity. This has avoided the need to keep pas-
sengers on board the aircraft and engines engaged while the ramp shutdown is in effect.
More airlines may adopt this and similar practices and procedures as a means of minimiz-
ing inconvenience to their passengers.
Standardization
Opinions varied on the value of standardizing technologies for lightning detection and
warning system and their implementation. A majority of airports and airlines contacted
expressed that a single system serving all users at an airport could be viable and might be
funded through lease terms and conditions. Yet they also noted that stop/resume activity
decisions could not be uniformly applied. Furthermore, liability issues would likely govern
any decision for industry standardization.
It is said that lightning does not strike twice in the same place. This can also apply to the
use and implementation of lightning detection and warning systems at airports. No two
airports are alike, and a "one size fits all" approach does not appear to be viable. Airport
geographical settings, weather phenomena characteristics, airport facilities layout, airline
business models and operating procedures, labor union agreements, liability issues, and
cost allocation processes are just some of the primary factors that do not lend themselves to
standardization.
Operational Cost Analysis
An evaluation of the financial and operational impacts on the national air transportation
system resulting from ramp closures associated with lightning strikes was conducted as part
of this research study. The expectation was that incremental cost savings from modified or
enhanced lightning detection and warning systems or from improved operator procedures
could be achieved. Because reliable records on ramp lightning closures at airports are not
available, lightning strike data from NLDN was obtained. This enabled the construction of
a synthetic closure history for an airport based on a strict imposition of the "30/30" rule,
which recommends that outdoor activities be curtailed following a cloud-to-ground lightning
strike within 6 statute miles (corresponding to 30 sec of time delay between the visible light-
ning strike and the sound of the thunder) and not resumed until 30 min after the last light-
ning strike within six statute miles is observed. Based on the sequential time and location
history of nearby lightning strikes, it is possible to calculate the distance of each stroke from
the airport reference point and determine closure and all-clear times. Two airports were sub-
jected to this exercise--Chicago O'Hare International and Orlando International. Chicago
represents a high activity airport located in the upper Midwest in an area of large spring and
summer storms. Orlando represents a medium activity airport in the southeast, near the
climatological maximum for U.S. lightning activity. The number of affected aircraft and the
diurnal pattern of flight operations at each airport were estimated from aircraft activity
measures available from online resources (www.flightaware.com).
The cost analyses were aided by earlier research conducted for the FAA and summarized
in Table S-1. There may be additional direct costs to airlines depending on whether they
need to pay the ramp workers overtime and whether fuel is expended in planes waiting on
the ramp for a gate position to become available. A second cost category evaluates the "ripple
effect" caused downstream. These may include additional opportunity costs (passenger time)
caused by missed connections and direct costs (flight time) of repositioning planes for the
next day. The analyses were also conducted based on the use of an aircraft commonly used
in passenger transport, the Boeing 737-500.
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Table S-1. Standard economic values.
Item Value ($)
Value of Human Life 3.0 million
Average Labor Cost Ramp Rate 13.03/hr
Hourly Cost of Aircraft Delay 1,524/hr/aircraft
Rate of Delay Per Aircraft (fuel, etc.) 2,290/hr/aircraft
Rate of Labor Delay 814/hr
Value of Passenger Time 28.60/hr
SOURCE: Economic Values for FAA Investment and Regulatory Decisions, A Guide.
FAA, 2007 (27).
A series of equations were modeled to quantify the "per minute" cost savings that could
accrue through the use of improved decision making with respect to the timing of ramp
closures and re-openings. These equations were applied to the synthesized lightning and
aircraft activity levels at Chicago O'Hare International and Orlando International airports
due to a shortening of the duration of each ramp closure event by 10 minutes. The savings
represent those for a yearly period of activity and reflect the number of lightning events and
aircraft delay statistics. As indicated in Table S-2, the potential savings from a ten-minute
improvement in delay time during peak operating hours at Orlando is approximately
$2.8 million, compared to the $6.2 million calculated for Chicago.
To evaluate the sensitivity of the predicted economic impact on the interval between the
last lightning strike and a return to normal operations, an additional set of analyses reduc-
ing the "all clear" time from 30 min to 15 min after the last reported lightning strike within
6 mi of the airport was conducted. The reduced time interval may be more common at air-
ports than the "standard" 30 min used for general outdoor activities. This "30/15" analysis
was conducted for the summer months (June-August), when lightning activity is the most
frequent.
The rule change from 30/30 to 30/15 results in a slight increase in the number of events
due to the few cases when the airport would be opened and then quickly closed again under
the 30/15 rule (causing two events instead of one to be recorded), while the airport would
have stayed closed under the 30/30 rule. While this could represent an increased hazard for
ramp personnel, it results in a significant reduction in delay time, totaling 354 minutes at
Chicago and 1,568 minutes at Orlando.
The results for Chicago indicate a potential savings of approximately $3.4 million from
hypothetical implementation of the 30/15 rule for the summer. The results for Orlando
are perhaps more intriguing because the shorter "all-clear" time provides limited openings
in the ramp closures and reduces the number of longer and more costly delays. In this
Table S-2. Lightning events, delay minutes, and savings.
Savings Associated
with a 10-min
Lightning Events Total Annual Reduction in Ramp
Airport (no.) Delay (min) Closure Interval
($)
Chicago O'Hare
International 51 3,064 6,206,310
Orlando International 56 3,243 2,801,372
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hypothetical analysis, this results in a potential savings of $6.3 million at Orlando for the
summer of 2006.
The cost analysis indicates that delay cost impacts are complex. They are a function of
several factors, including the activity levels and mix of aircraft operating at an airport, the
number of lightning events, the timing of the lightning event, the type of lightning event
(local convective or associated with broad-scale flow), the duration of the lightning event
and the rules the airline/airport operators use in issuing the "all clear" signal to resume
ramp activity. The analysis also indicates that the annual value of new technologies or new
procedures that could reduce ramp lightning delays, although varying by airport, could
be substantial. The potential savings produced by a reduction of even a few minutes would
likely be sufficient to more than cover the cost of introducing improved technology or
practices.
Because safety concerns for the ramp workers are paramount, it appears the airlines and
airports will likely err on the side of caution in closing ramp operations. This suggests that
the most likely path to improved operational efficiency is in being able to sound an "all clear"
as quickly as possible after the initial event, as long as it can be done without compromising
safety.
Future System Improvements
There are a number of promising ways to refine and improve lightning detection and
warning systems for airports, airlines, and other tenants. These make better use of all the
currently available weather observations through the development of "smarter" software
and analysis algorithms, and by incorporating new technologies. Relatively more short-term
opportunities for such enhancements and that are strong candidates for additional research
and implementation include the following:
· Intelligent self-monitoring warning systems that check their own performance and evaluate
the adequacy of the specific warning criteria being used.
· Incorporation of additional weather information, such as that available from the currently
deployed Doppler meteorological radars.
· Adoption of total lightning systems that detect and locate both cloud-to-ground and intra-
cloud lightning strikes.
Recommendations
The current state of the industry for airport lightning detection and warning systems
appears to be effective. There are, however, potential ways to further minimize the number
and duration of ramp closure events and enhance decisions involving ramp worker safety.
We recommend the following action items:
1. Refine the warning algorithms and criteria through the use of self-monitoring software. While
this approach is not necessarily guaranteed to shorten ramp closures, it would provide an
objective standard for selecting warning criteria to balance safety and efficiency.
2. Incorporate additional meteorological data sets, primarily meteorological radar data and
other remote sensing information, to better define the spatial and temporal limits of the light-
ning hazard. Using integrated data sets to define the geometrical extent of the lightning cells
and then tracking their evolution and movement should be particularly valuable.
3. Continue demonstrations and tests of total lightning systems to enhance and refine the tech-
nology embedded in current lightning and detection systems.
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4. Conduct research to enable the improved determination of those lightning events that are
most likely to produce short-term (less than 1 min) impacts on ramp activity. This may
include lightning cell tracking and echo movement vector analysis that can serve to minimize
the number and duration of ramp closures.
5. Devise a system of collecting and reporting lightning events and their impact on aircraft
ramp and outdoor activities. This will provide additional data to determine the extent of
such weather impacts on aircraft operations and identify those improvements that are
cost-beneficial.
6. Develop training programs for the use and application of lightning detection and warning
systems that improve the ramp closure/re-open decision-making process.
