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Airports Using Terminal Weather Information Systems (26). overtime or whether extra fuel is used by planes waiting on
An analysis of that study found that this approach is more the ramp for a gate to become available.
appropriate for evaluating the impact of thunderstorms The second cost category evaluates the "ripple effect" that
along the flight path, rather than the effect of cloud-to- is caused by downstream delays. These may include addi-
ground lightning strikes in the vicinity of the airport on tional opportunity cost of passenger time caused by missed
ramp operations. connections, as well as direct costs of extra flight time in-
The key issues are the tradeoffs between safety (close ramps curred in repositioning planes for the next day.
as needed to prevent injuries or deaths from lightning) and The best economic estimates we found originate from an
efficiency (minimize ramp closures). Safety is clearly the driv- FAA report (27). The remaining input values would be sensi-
ing factor in airport and airline investment in lightning de- tive to each particular situation, depending on airport and
tection and warning systems, but it is difficult to quantify airline. The estimated values made available in the FAA re-
since there are so few reported deaths and injuries caused by port are presented in Table 2.
lightning. Because our survey did not identify any specific The hourly cost of aircraft delay shown in Table 2 is a
concerns about missed warnings or unsafe working condi- representative value. Costs will vary by aircraft type. Various
tions, we concluded that the basic safety requirements are aircraft and their block hour operating costs as of 2001 and
well met by the current systems and procedures. 2002 are shown in Table 3.
The most appropriate approach is thus to concentrate on
ways to improve efficiency through decreasing ramp closure
Case Studies
times, without compromising safety. To do this, we will
attempt to quantify the actual closure costs, with emphasis Closure costs will always be a function of the amount
on the closure costs "per minute" after the initial ramp shut- of aircraft operations affected, the geographical area and
down. These closure cost estimates will ultimately be used to lightning climatology, and flight schedule. To get a balanced
evaluate any proposed improvements to current lightning de- perspective, we chose two airports for detailed case study
tection and warning systems either to not initiate an unneeded analysis--Chicago O'Hare International Airport (ORD) in
closure or to try to get an airport back into full operation as Illinois, and Orlando International Airport (MCO) in
soon as possible when lightning strikes no longer present a Florida. As shown in Table 4, ORD is a high-activity airport
danger. Given the general unpredictability as to where and located in the upper Midwest in an area of large spring and
when a lightning strike will occur, there will always be a re- summer storms. MCO is a medium-activity airport in the
quired minimum closure time before ramp operations can be southeast, near the climatological maximum for U.S. lightning
resumed safely. This implies that there will always be a signif- activity.
icant cost associated with the initial alarm declaration and the
clearing of the ramp.
Lightning Delay Analysis
Because reliable records on ramp lightning closures at air-
Analysis of Costs
ports are not available, we obtained from Vaisala NLDN
Two main cost categories were segmented for analysis. The lightning strike data within 10 statute miles of both ORD and
first concentrates on the costs at the local airport where the MCO for the calendar year 2006. We then constructed a
lightning is occurring. These costs will include the opportu- synthetic closure history for each airport based on a strict
nity cost of lost passenger time, which are applicable in events imposition of the 30/30 rule. As discussed in Chapter 1,
of any duration. There may also be direct costs to the airline, the 30/30 rule recommends that outdoor activities be cur-
depending on whether they need to pay the ramp workers tailed following a cloud-to-ground lightning strike within
Table 2. Standard economic values.
Item Value ($)
Value of Human Life 3.0 million
Average Labor Cost, Ramp Rate 13.03/hr
Hourly Cost of Aircraft Delay 1,524/hr/aircraft
Rate of Delay Per Aircraft (fuel, etc.) 2,290/hr/aircraft
Rate of Labor Delay 814/hr
Value of Passenger Time 28.60/hr
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Table 3. Aircraft block hour operating costs. from the airport reference point and determined closure and
all-clear times for both airports. The results of this exercise
Block Hour Cost are summarized in Appendix A.
Aircraft Type ($/hr) It should be noted that all data contained in the following
analyses and shown in Tables 5 through 12 were derived using
Commercial Passenger Service the synthetic lightning duration technique employed on the
Vaisala lightning detection data and therefore do not repre-
Airbus 319 1,960 sent actual reported lightning duration delays.
Airbus 320 2,448
ATR 72 1,401 O'Hare International Airport
Beach 1900 676 The results for ORD indicate there would have been
Boeing 727-200 2,887 68 ramp closures in 2006, with a total closure time of
Boeing 737-100/200 2,596 70.8 hours, or approximately 1% of the time. Figure 18 pres-
Boeing 737-300/700 2,378 ents the full histogram of the length (time duration) of each
Boeing 737-500 2,271 ramp closure based on this simulation. The synthetic closure
Boeing 737-800 2,201 distribution is strictly based on the 30/30 rule in a hypothet-
Boeing 757-200 3,091
ical system without electric field mills.
Table 5 shows the distribution of synthetic lightning in-
British Aerospace 146 2,776
duced ramp closures for ORD stratified by time of day and
Canadair CRJ-145 1,072
season of the year. When events overlapped a time period,
Canadair CRJ-200 864
the event was assigned to the time period it most affected.
Dehavilland Dash 8 970 Table 5 indicates a slight preference for lightning events to
Embraer 120 Brasilia 861 occur in the late afternoon. As would be expected, lightning
Embraer ERJ-145 996 events are most frequent in the summer and least frequent in
Fokker 100 2,406 the winter. We caution, however, that this analysis contains
Jetstream 31/32 544 only 1 yr of data, so it may not be generally representative of
Jetstream 41 759 the long-term diurnal duration climatology. Nonetheless,
McDonnell Douglas 9-30 (DC 9-30) 2,280
based on NOAA's 2006 climate summary and 30-yr normals
for thunderstorm events, 2006 was a relatively normal year,
McDonnell Douglas 80 (MD-80) 2,630
with 42 thunderstorm events compared with a normal of
McDonnell Douglas 87 (MD-87) 2,300
40 events. This suggests that the 68 lightning-induced ramp
closures at ORD that we deduced from the data are consistent
General Aviation--Corporate and Air Taxi with the climatological record of thunderstorms for the area.
As illustrated in Figure 18, a majority of the closures are
Small Business Jet 500 estimated to have been for 45 min or less, with only 14 clo-
Mid-Size Business Jet 750 sures exceeding 90 min and only 3 closures exceeding 3 hr.
Large Business Jet 1,000 The data also indicate several days when there was more than
one closure because of recurring lightning events. We con-
General Aviation--Private clude that these results indicate that occurrences of long-
duration delays that could potentially cause en route delays
and ground holds in the National Airspace System are infre-
Single-Engine Piston 100
quent, but may occur. It is important to note, however, that
Multi-Engine Piston 200
in most cases these extreme events will be caused by large
Multi-Engine Turboprop 300
mesoscale convective systems that are either stationary over
Rotorcraft 250 the airport, extend over large areas, or generate repeated
lines of storms across the airport. These events will gener-
6 statute miles (corresponding to 30 sec of time delay ally result in en route and terminal airspace delays irre-
between the visible lightning strike and the sound of the spective of their effect on ramp operations. Because these
thunder) and not resumed until 30 min after the last light- events are infrequent and are likely to be associated with a
ning strike within 6 mi. general disruption of the National Airspace System, these
Based on the sequential time and location history of nearby costs are more appropriately addressed in an analysis of
lightning strikes, we calculated the distance of each stroke thunderstorms along the flight path rather than lightning
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Table 4. Aircraft operations levels at selected airports.
Airport Operations/Day
Chicago-O'Hare International Airport, IL (ORD) 2,662
Dallas-Ft. Worth International Airport, TX (DFW) 1,915
Denver International Airport, CO (DEN) 1,603
Phoenix-Sky Harbor International Airport, AZ (PHX) 1,494
Charlotte-Douglas International Airport, NC (CLT) 1,421
Orlando International Airport, FL (MCO) 977
Tampa International Airport, FL (TPA) 716
Pittsburgh International Airport, PA (PIT) 649
Note: Operations/day includes those operations conducted by air carrier, air taxi,
general aviation, and military aircraft. An aircraft operation is either a takeoff or a
landing.
strikes in the vicinity of the ramps, and thus were not in- 7 a.m. Hourly operations levels remain in the 80 to 100 range
cluded in our cost analysis. throughout the day until approximately 10 p.m., when activity
Table 6 summarizes the per-minute values used to estimate declines rapidly. The number of aircraft affected at ORD was
the closure costs resulting from lightning events. Using these estimated at 90 planes per hour based on the typical daily
values, we calculated per-minute cost values for a sample short operation statistics shown FlightAware's graphics for ORD.
duration (less than 60 min), medium duration (61 to 135 min) In our analysis, we assumed there would be no direct op-
and long duration (greater than 136 min) event. The number erating costs to the airlines for short duration events because
of affected aircraft and the diurnal pattern of flight operations they should be able to catch up without incurring additional
were estimated from the material available on the FlightAware costs. For medium and long duration events, the direct local
website (www.flightaware.com). The pattern consists of mini- airport costs were obtained by multiplying the number of
mal operations activity (an operation is defined as a takeoff or planes affected times the number of ramp workers per plane
a landing) between the hours of 12 a.m. and 5 a.m. Then there times the overtime rate of ramp workers times one-half of
is an increase in operations, reaching approximately 100/hr by the delay. The reason for using one-half of the delay was to
Duration
30
27
25
20
Count
15
12
10
6 6 6
5
5
3 3
0
0
30 31-45 46-60 61-75 76-90 91-120 121-150 151-180 181+
Duration, min
Figure 18. Duration of lightning delays at ORD during 2006.
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Table 5. ORD lightning event frequency stratified by time
of day and season of year.
Hour Dec-Feb Mar-May Jun-Aug Sep-Nov Total
0-3 2 1 1 4
3-6 3 4 7
6-9 1 3 1 5
9-12 2 2 2 2 8
12-15 3 1 3 3 10
15-18 4 4 5 13
18-21 3 6 3 12
21-24 3 4 3 10
Total 5 16 26 22 69
Table 6. ORD per-minute cost values.
Cost Item
(Based on Boeing 737-500) Value
Passengers per plane $100
Value of passenger time $0.478/min
Passenger time ripple effect 1.5 times local airport passenger effect
Ramp workers standard pay rate $13.03/hr
Ramp workers overtime pay rate $19.55/hr
Average ramp workers per plane 6
Operating cost for Boeing 737-500 $2,271/hr
Aircraft repositioning time 0 for short duration
1 hr for medium duration
2 hr for long duration
Note: The typical duration of an event was deduced from the ORD 2006 NLDN data.
account for the fact that airlines would be able to catch up by multiplying the operating cost of the Boeing 737-500 times
somewhat faster after a delay without occurring the full the number of planes affected times the repositioning time
duration of delay in overtime cost. The above factors are pre- (as shown in Table 6).
sented in the following equation:
REDC = N(OCOPN NPIRN) RT
DLAC = 1/2(NPA NRPP ORRW DD)
where
where
REDC = ripple effect direct cost,
DLAC = direct local airport costs, N = number of aircraft affected of type N,
NPA = number of planes affected by delay, OCOPN = hours operating cost of aircraft type N, and
NRPP = number of ramp workers per plane, RT = repositioning time.
ORRW = overtime rate of ramp workers, and
DD = duration of delay. The local airport opportunity costs were calculated as the
per-minute value of passenger time multiplied by the num-
The ripple effect direct costs are caused by the added end- ber of passengers per aircraft times the number of aircraft
of-day cost of repositioning planes. This cost was calculated affected by the delay times the duration of delay. Based on
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information contained in the ATC-291 report (26), the rip- relatively infrequent, occurring only 16 times during 2006, as
ple effect cost or opportunity ripple factor applied for pas- shown in Table 7.
senger time was assumed to be 1.5 times the local airport Medium and long duration events present higher incre-
effect, as shown in the equation below: mental per-minute potential savings because more costs
come into play and more aircraft and people are affected.
LAOC = VPT NOPID DD However, short duration events are more frequent. The po-
tential delay reduction is likely not correlated to the duration
where of the event. Using the 2006 data, we estimated the potential
savings of a 10-min reduction in delay for each duration
LAOC = local airport opportunity cost, lightning event. It should be noted that we did not include in
VPT = value of passenger time, this analysis lightning events between the hours of 10 p.m.
NOPID = number of passengers incurring delay, and and 7 a.m. because operations during those hours are much
DD = duration of delay. less than during the core 7 a.m. to 10 p.m. local time. Reduc-
tion in lightning delays during these "off" hours should pro-
The ripple effect opportunity cost may be determined from vide minimal cost savings.
the following equation: The potential minutes saved for each duration event were
calculated by multiplying the number of events times the as-
REOC = LAOC ORF
sumed 10-min savings. As shown in Table 8, the total poten-
where tial savings over a period of 1 yr (using 2006 as the proxy)
would be slightly over $6 million.
REOC = ripple effect opportunity cost, The savings for each duration are calculated by multiply-
LAOC = local airport operating costs, and ing the per-minute costs (savings) for each duration by the
ORF = opportunity ripple factor. minutes saved. The total minutes saved and the total dollar
savings are then obtained by adding the savings for each du-
The monetary per-minute cost calculations are shown in ration. The average per-minute savings is then calculated by
Table 7. The last column indicates the per minute cost and is dividing the total dollar savings by the total per minute sav-
calculated as: ings. In equation form, this is
TPMSA = (SDMS SDV + MDMS MDV + LDMS LDV)
PMC = TC/DD /(SDMS + MDMS + LDMS)
where where
PMC = per minute cost, TPMSA = total per minute savings,
TC = total cost of delay, and SDMS = short duration minutes saved,
DD = duration of delay. SDV = short duration per-minute value,
MDMS = medium duration minutes saved,
These results indicate the per-minutes costs increase with MDV = medium duration per minute value,
the duration of delay. Fortunately, medium and long dura- LDMS = long duration minutes saved, and
tion delays during the period 7 a.m. to 10 p.m. at ORD are LDV = long duration per-minute value.
Table 7. Typical monetary values for various duration events during the core
7 a.m. to 10 p.m. period at ORD.
Typical No. of Local Airport Cost ($) Ripple Effect ($) Per
Type of Duration Aircraft Total Minute
Event (min) Affected Direct Opportunity Direct Opportunity Cost ($) Cost ($)
Short 30 45 0 64,350 0 96,525 160,875 5,362
Medium 120 180 21,109 1,029,600 408,780 1,544,400 3,003,896 25,032
Long 210 315 55,409 2,702,700 715,365 4,054,050 7,527,524 35,845
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Table 8. Estimate of potential savings from a 10-min improvement
in lightning delays during the 7 a.m. to 10 p.m. core period at ORD.
Total Annual
Type of Event Number of Total Annual Potential Annual Per-Minute Potential
Events Minutes Delay Minutes Saved Cost ($) Savings ($)
Short 35 1,275 350 5,362 1,876,700
Medium 13 1,258 130 25,032 3,254,160
Long 3 531 30 35,845 1,075,350
All 51 3,064 510 12,169* 6,206,210
*Weighted average, calculated with Total Annual Potential Savings divided by Potential Annual Minutes Saved.
Orlando International Airport peak period for storms at ORD is 3 p.m. local time, the peak
period for storms at MCO is 6 p.m. to 9 p.m. local time. These
Paralleling our analysis for ORD, we analyzed 2006 NDLN differences are probably the result of the different climate
data from Vaisala to produce a synthetic ramp closure data zones for two airports. ORD is in a continental climate, af-
set for MCO using the same process as described for ORD. The fected more frequently than MCO by synoptic type storms,
synthetic delay information for MCO is presented in Ap- whereas MCO is affected by more local weather factors, such
pendix A. The results of the Orlando lightning event duration as summertime sea breeze convergence zones.
analysis for 2006 are shown in Figure 19. As would be expected MCO reports approximately 33% of the daily flight oper-
because of the location in the most active lightning region in ations that ORD reports, with MCO averaging approximately
the U.S., Orlando (MCO) had almost twice as many lightning 40 flight operations per hour between the hours of 7 a.m. and
events as ORD (126 compared with 68). The total minutes of 8 p.m., with a rapid decline in operations after 8 p.m. Mini-
delay were also higher (143 hr for MCO compared to 71 hr for mal activity is seen overnight, and flight operations begin to
ORD). The duration pattern of MCO, summarized in Table 9, increase at approximately 5 a.m.
indicates a tendency for longer duration events than occur at As shown in Table 10, 52 of the 2006 lightning events
ORD. At ORD, 66% (45/68) of 2006 lightning events were less occurred overnight between the hours of 9 p.m. and 6 a.m.
than 1 hr in duration, whereas MCO reported 60% (75/126) Because flight operations are very limited during these hours,
of the lightning events in 2006 were less than 1 hr. approximately 41% (52/126) of the synthetic 2006 lightning
There is also a higher frequency for summertime lightning delays would have resulted in minimal economic costs to the
events at MCO (62%) compared with ORD (38%). While the airport and airlines.
Duration
40
35
35
30
26
25
Count
20
15
15 14
11
10
10
6 6
5 3
0
30 31-45 46-60 61-75 76-90 91-120 121-150 151-180 180+
Duration (min)
Figure 19. Duration of lightning delays at MCO during 2006.
