EPA-AA-SDSB 79-17
Technical Report
Evaluation of HC Control Strategies for
General Aviation Piston Engines
by
Richard S. Wileox
July 1979
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analysis of
issues using data which are currently available. The purpose in
the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical devel-
opments which may form the basis for a final EPA decision, position
or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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I. INTRODUCTION
In support of the current final rulemaking action for aircraft
emission standards, the cost effectiveness of controlling hydro-
carbon (HC) exhaust emissions from general aviation piston-powered
aircraft (PI) is evaluated. Houtman (1976) previously evaluated
the cost effectiveness of controlling this source for HC and carbon
monoxide (CO). Recent analyses by Jordan (1977) and FAA (1978)
have indicated that these aircraft are not major contributors to
violations of the National Ambient Air Quality Standard for CO
which adversely affect the public health and welfare.
Although HC emissions from general aviation are also small
when compared to many other sources, the oxidant problem is so
widespread that all reasonable controls should be implemented.
Based on this premise, several potentially cost-effective control
strategies for these aircraft are evaluated to determine if reduc-
tions in HC from general aviation piston-powered aircraft are
justified.
II. DISCUSSION
A. Cost Effectiveness
To determine the most cost efficient means of meeting and
maintaining the National Ambient Air Quality Standards (NAAQS),
potential control strategies are evaluated on the basis of their
relative cost effectiveness, i.e., the monetary cost of preventing
one ton of emissions. Unfortunately, cost-effectiveness analyses
have some associated uncertainties. For example, the point at
which a control strategy is not considered to be cost effective has
never been precisely defined. Also, when future control strategies
are being evaluated, it is important to remember that as the most
efficient controls are implemented, each succeeding control incre-
ment will have a higher marginal cost. Because of this expected
price increase, it is not necessarily correct to make decisions
with regard to a potential control strategy by comparing its cost
effectiveness to that of other past or presently considered strate-
gies.
These kinds of limitations prevent cost-effectiveness analyses
from being used as an absolute decision making device in every
instance. Cost effectiveness is most appropriately employed in
decision making along with other information. It is also useful,
however, as a screening mechanism to eliminate those control
strategies whose cost effectiveness is not within the range of
values that are generally accepted to be cost efficient.
In this analysis, cost-effectiveness comparisons are used as a
screening mechanism. Therefore, a decision will be made to further
evaluate HC emission controls for general aviation piston-powered
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aircraft, only if the cost effectiveness of these controls is
reasonably within the range of values for other strategies which
are currently being seriously considered. As shown in Table 1,
current cost-effectiveness values range up to about $950.
Most of the cost-effectiveness figures contained in Table 1
are based on annual costs. Therefore, to maintain the greatest
degree of comparability between those figures and the figures
derived in this analysis, the costs of controlling exhaust emis-
sions from general aviation aircraft are annualized. Also, the
cost-effectiveness figures contained in Table 1, and the costs
which are used throughout this study, are based on 1978 dollars.
The following formula is used to determine the cost-effec-
tiveness values for the control concepts which are reviewed in this
analysis.
(C.Rf) + (LtF.Cf) + M.
Cost Effectiveness = —
Jr Lt
r t
Where: C. = incremental cost to the consumer;
Rf = capital recovery factor based on 10% interest per
annum and 20 year useful life;
L = landing and takeoff cycles (LTO's) per year (250);
F. = increment in fuel consumption in gallons per LTO;
Cf = price per gallon of aviation fuel ($0.97/gal);
P = pollutant reduction per LTO; and
M. = annual maintenance increment.
i
All of the control costs are attributed to HC since it is the only
pollutant being considered for regulation in this study.
B. Baseline Exhaust Emissions
The present standards (promulgated in 1973) were directed
predominantly at controlling CO; therefore, the HC standard was set
by EPA at a lenient level to preclude HC-CO tradeoffs by some
possible control technologies. A review of the baseline (uncon-
trolled) emissions from these aircraft found that the fleet-
weighted average emissions were the same as the present standard of
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Table 1
Cost Effectiveness of Strategies for HC Control
(1978 Dollars)
Cost
Control Strategy Effectiveness
with Control Increment $/Ton
Degreasing 0-40% -230 a/
Gravure 0-98% -60 aj
Gas Terminal 0-67% 0 aj
Acrylonitrile 0-35% 0 aj
Polyethylene 0-95% 0 aj
Charcoal 0-99% 0 aj
Miscellaneous Chemicals 0-35% 0 aj
Dry Cleaning 0-80% 10 aj
Industrial Finishing 0-75% 10 aj
Carbon Black 0-95% 10 aj
Formaldehyde 0-95% 20 aj
Refining 0-67% 10 aj
Arch. Coatings 0-100% 20 aj
GHDV Evap. 5.8-0.5 gm/mi 20 aj b/
Open Burning 0-25% 20 aj
Ethylene Oxide 0-95% 20 aj
Acrylonitrile 36-99% 40 aj
Ethylene Dichloride 0-95% 40 aj
Paint & Varnish 0-70% 60 aj
Degreasing 41-90% 100 aj
Industrial Finishing 76-97% 110 aj
Gasoline Handling 16-50% 110 aj
Cyclohexanone 0-95% 140 aj
Metal Decorating 0-90% 160 aj
Miscellaneous Chemicals 35-53% 220 aj
Gasoline Distribution 67-99% 300 aj
Coke Ovens 0-80% 490 aj
LDV Exhaust 0.9-0.41 gm/mi 530 aj
Foundries 0-60% 560 aj
Letterpress & Lithography 0-90% 790 aj
Gas Handling 51-91% 780 aj cj
HDV Gas 90% of baseline 300 d/
HDV Diesel 90% of baseline 162 d/
LDV I/M 955 e/
LOT 1.7-0.8 gm/mi 139-201 f/
a/ DOT (1976).
b/ A more recent EPA analysis which supports a regulation yet to
be published as a proposal, yields numbers in the range of $70
to $250 per ton.
c/ Agrees reasonably well with a more recent EPA analysis.
d/ EPA (1978).
e/ EPA (1979a).
f/ EPA (1979b).
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0.0019 HC Ibm/ rated power/cycle. Therefore, the level of control
must be more stringent to effectively reduce HC emissions from this
source.
The fleet-weighted baseline exhaust emissions per LTO cycle
are shown in Table 2.
C. Control Strategies Using Fuel Schedule Enleanment
When the present promulgated standards were issued, EPA
identified fuel schedule enleanment as the most practical control
technology for these airplane engines. As shown in Figure 1, the
fuel-air ratio which is necessary to meet the CO standard is below
the fuel-air ratio which is required to attain the HC standard.
Therefore, by meeting the CO standard, additional reductions in HC
were achieved. The most stringent potential HC reduction reviewed
in the analysis of fuel enleanment concepts, is the level of HC
control that would result if the present CO standard was attained.
(The potential HC reductions attributable to each of the control
concepts which are reviewed in this analysis are hereafter referred
to as "the HC reduction criteria.")
The fleet-weighted reductions in fuel consumption and gaseous
emissions for the most stringent enleanment HC reduction criteria
are shown in Table 3. Two enleanment concepts are reviewed:
fuel metering tolerance reductions and automatic fuel scheduling.
a) Fuel Metering Tolerance Reduction
The simplest and least expensive control concept is to modify
the existing fuel system so that the fuel-air mixture of each
engine is calibrated at or near the production lean limit. Specif-
ically, this modification would result in reducing the fuel meter-
ing orifice tolerances of the carburetor or fuel injectors. FAA
recertification of the engine or airframe would not be required.
The cost of this modification has been estimated by one engine
manufacturer to be $150 to $200 per engine, excluding the cost of
engineering and development (Avco 1977). There is no maintenance
increment associated with this hardware.
For the purposes of this analysis, the total incremental cost
of the hardware to the consumer is $200. It is unlikely that the
hardware could be less expensive after amortizing the costs of
engineering and development over the expected production volume;
therefore, this is considered the "best case" control cost.
The fuel metering tolerance reduction control technique is
incapable of fully attaining the most stringent potential HC
reduction which has been identified (Table 3). It is, however,
capable of a significant reduction in HC, the level of which can be
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Table 2
Baseline Piston Aircraft Emissions
Engine HC Emissions
Model (Ibs/bhp per LTD)
IO-320D
IO-360-B
0-320-D
0-200-A
10-5 20-D
Tiara G 285-B
GTSIO-520-K
TSIO-360-C
Weighted Average
0.00120
0.00160
0.00159
0.00220
0.00220
1.00140
0.00140
0.00470
Promulgated Standard
Fraction Weighted
of Fleet HC Emissions
0.055 0.00007
0.159 0.00025
0.121 0.00019
0.285 0.00063
0.129 0.00028
0.141 0.00020
0.072 0.00010
0.036 0.00017
0.00189
0.00190
Source - Data Derived From Deimen (1977).
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Table 3
Fleet Weighted Emission Factors (Ib/LTO)
CO HC NOx Fuel
Baseline 15.4 0.32 0.04 0.69
Controlled 8.8 0.21 0.20 0.57
Percent Change -43% -34% +400% -17%
Source: Houtman (1977).
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estimated from information contained in a document prepared by the
Avco Corporation (Avco 1977). It is stated that disregarding the
obvious variation of the fuel schedules from model to model, the
control technique could reduce the baseline CO emissions from the
best 0-320 engine tested by 28 percent (from the mean engine
setting to the lean limit). As previously stated, enleanment
reduces CO and HC together; therefore, for the purposes of this
simplified analysis, this same proportion of control is applied to
the baseline fleet-weighted average HC emissions.
As shown in Table 3, a 1.0 percentage point reduction in CO
corresponds to a 0.79 percentage point change in HC (34/43 = 0.79).
Therefore, the 28 percent reduction in CO is equivalent to a 22
percent reduction in baseline HC (28 x 0.79 = 22). Based on Table
3, this would mean a reduction in HC of 0.07 Ibm per LTO and a
reduction in fuel consumption of 0.08 Ibm per LTO. The cost
effectiveness is approximately $2,300 per ton of HC reduced. This
control technique is not reasonably within the range of costs that
have been calculated for other mobile and stationary source control
strategies (Table 1).
b) Automatic Fuel Scheduling
Recent information indicates that an engine power control
system which automatically schedules the fuel-air ratio may come
quite close to achieving the currently promulgated CO standard
(Scott 1978). Developed by Woodward Governor Company, Beech
Aircraft Company, and Teledyne Continental Motors, the system is
referred to as the single lever power control. It has been FAA
certified in a Beechcraft Bonanza airframe equipped with a Con-
tinental 10-520 engine. Presently, the fuel control is used in
conjunction with a constant speed propeller and a continuous fuel
injection system. The unit could also be used on turbocharged
engines and possibly be adapted to carbureted engines as well
(Liseon 1978).
The power control system automatically regulates the fuel
schedule above 1500 rpm. During takeoff, the fuel-air ratio is
leaned to just slightly rich of "best power." For climbout, the
mixture is leaned to "best power," and for approach it is near
"best economy." (The corresponding fuel-air ratios for these
conditions are shown in Figure 1.) The power control unit also
compensates for changes in ambient conditions and altitude.
Industry representatives were unable to state the actual cost
of this unit to the consumer. They did comment, however, in the
context of statements made previously by Helms (1977) regarding the
cost of achieving the current EPA standards. Scott (1978), Liseon
(1978), and Norsworth (1978) generally agreed that in limited
production quantities, i.e., 500-1000 units, the cost of the single
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lever power control may be close to or greater than the $1,500 to
$3,000 as cited by Helms (1977). If the unit were widely used as
emission control hardware, there was agreement that the price would
be reduced, perhaps by 33 percent.
To evaluate the cost effectiveness of this hardware, the "best
possible" emission control case will be examined. Although no
emission tests have been conducted (Wilkinson 1978), it is assumed
that because the power control unit might nearly achieve the
existing CO standard, it will achieve the suggested HC reduction
criteria (a 34 percent reduction from baseline emissions). Also it
is assumed that if the unit was widely used for pollution control,
the incremental cost to the purchaser of a new aircraft would be
$1,000 per engine with no accompanying maintenance penalty.
By using the emission and fuel reduction information contained
in Table 3, the cost effectiveness is calculated to be over $8,000
per ton of HC reduced. This is significantly greater than the
currently accepted range of values for other control strategies
(Table 1).
D. Other Control Strategies
It has been demonstrated that fuel schedule modifications are
not cost effective for reducing HC exhaust emissions alone. A
variety of other control techniques for light airplane piston
engines have been evaluated by NASA and EPA contractual efforts,
and will now be considered.
The two previous examples illustrate that the cost effective-
ness of any HC control strategy for this source is very sensitive
to the total cost of the system. Therefore, in considering other
control techniques, a low cost will be the primary concern. All of
the remaining control techniques are able to provide a significant
degree of HC control.
a) Air Injection System
Renzy (1976) has ranked various control concepts based on a
variety of criteria as shown in Table 4. Air injection ranks first
as the least expensive, and since it is also known to be very
effective in reducing HC emissions from piston engines, it will be
evaluated for its cost effectiveness. It should also be pointed
out that air injection was ranked fourth in overall utility as a
control concept (Table 5).
Air injection exhaust after treatment has been well defined as
an automotive emission control device. It works by injecting air
into the engine exhaust port which, as it mixes with the hot
exhaust, oxidizes a portion of the HC and CO remaining in the
exhaust stream. The additional air is typically supplied by an
engine-driven air pump.
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Table 4
Concept Rank Ordering Versus Criteria Importance
Criteria
Improved Cooling Combustion Chamber*
Improved Fuel Injection Systems
Air Iniection
Multiple Spark Discharge System*
Ultrasonic Fuel Atomization, Autotronic
Variable Timing Ignition System*
Thermal Fuel Vaporization, Ethyl
Hydrogen Enrichment, JPL
Texaco CCS
2-Stroke Diesel, McCulloch*
Ford Proco
Variable Camshaft Timing
Honda CVCC
4-Stroke Diesel, Open Chamber
Dominant
E
M
I
S
S
I
0
N
S
Q
3
4
14
12
13
11
1
5
7
6
10
2
8
S
A
F
E
T
Y
1
2
5
3
4
6
7
14
8
11
9
13
12
10
P
E
R
F
0
R
M
A
N
C
E
6
1
8
5
9
3
10
7
12
2
13
4
11
14
C
0
0
L
I
N
G
1
14
9
7
11
8
13
4
2
6
3
10
12
5
W
E
I
G
H
T
&
S
I
Z
E
1
2
5
3
5
4
7
8
10
13
11
9
12
14
F
U
E
L
E
C
0
N
0
M
Y
6
5
14
12
10
11
9
1
2
4
3
13
8
7
C
0
S
T
6
7
1
2
4
5
3
12
10
13
9
8
11
14
Secondary
R
E
L
I
A
B
I
L
I
T
Y
3
A
5
6
1
7
2
8
12
9
11
14
13
10
T
E
C
H
N
0
L
0
G
Y
2
1
3
4
5
7
6
9
13
11
14
8
10
12
0 C
P H
E A
R R
A A
T C
I T
0 E
N R
A I
L S
•T
I
C
S
1
6
3
2
5
9
4
12
10
13
11
8
7
14
M a
A n
I d
N
T M
A A
I I
N N
A T
B E
I N
L A
I N
T C
Y E
1
2
5
3
4
6
7
8
13
9
14
10
11
12
Minor
I
N
T
E
G
R
A
T
I
0
N
6
4
2
1
10
3
9
7
11
13
12
5
8
14
M
A
T
E
R
I
A
L
S
3
2
6
1
4
5
7
14
13
12
9
8
10
11
P
R
0
D
U
C
I
B
I
L
I
T
Y
2
7
1
5
4
6
3
8
11
13
12
9
10
14
A
D
A
P
T
A
B
I
L
I
T
Y
4
6
1
2
7
3
5
8
11
14
12
9
10
13
o
I
* Not considered an HC control concept in this analysis.
Source: Rezy (1976).
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Table 5
Concept Ranking for Emissions
Rank Concept
1 Hydrogen Enrichment, JPL
2 Honda CVCC
3 Improved Fuel Injection Systems
4 Air Injection
5 Texaco CCS
6 Ford Proco
7 2-Stroke Diesel, McCulloch a]
8 4-Stroke Diesel, Open Chamber
9 Improved Cooling Combustion
Chamber aj
10 Variable Camshaft Timing
11 Thermal Fuel Vaporization,
Ethyl
12 Ultrasonic Fuel Atomization,
Autotronic
13 Variable Timing System aj
14 Multiple Spark Discharge System a/
a/ Not considered an HC control technique in this analysis.
Source: Rezy (1976).
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Air injection systems were considered to be a potential
control technology at the time Federal emission standards for this
source were originally proposed. Bendix (EPA 1973) evaluated this
concept on a Continental 0-200 engine and concluded that it could
meet or exceed the Federal standard for HC and CO emissions. Areas
in which further development work was necessary were also identi-
fied.
Unlike automotive engines, aircraft piston engines use fuel-
air mixtures which are much richer than stoichiometric over most of
the flight regime. This means that the exhaust from these engines
contains a large quantity of potential energy in the form of HC and
CO. Under some conditions, if too much air is injected into the
exhaust, overheating of the exhaust manifold could result in its
failure. This problem can be alleviated by correctly sizing the
injection air flow and installing a thermal sensor to prevent
overheating. Under normal operating conditions, the added heat
from the exhaust may adversely affect engine cooling. This may
require double-wall construction of the exhaust system or a rede-
sign of the engine cooling shroud. It is expected that the air
injection pump will fit into the existing engine cowling config-
uration, however.
Specific HC emission reduction figures for this control
concept have been reported by Bendix (EPA 1973) and Renzy (1977)
which are based on actual engine tests. Bendix (EPA 1973) tested a
Continental 0-200 engine and found that the HC emissions were 67
percent below the existing Federal standard. It was also pointed
out that because of the abnormally long residence time of the
exhaust before it was sampled, the HC reduction was somewhat
inflated. Renzy (1976) tested a Continental 0-200 and applied the
results to Continental IO-520-D. For this engine, HC emissions
were 35 percent below the standard.
For the purposes of this simplified analysis, a "best case"
condition is considered where injection reduces the fleet-weighted
HC emissions to a level between the values reported by Bendix (EPA
1973) and Renzy (1977). Hence, the reduction criteria is assumed
to be 50 percent of the existing HC Federal standard. Since it has
already been demonstrated that the fleet-weighted baseline HC
emissions are equivalent to the existing Federal standard (Table
2), the assumed reduction criteria can be directly applied to these
baseline values. Therefore, a reduction of 0.16 Ibm of HC per LTO
is used in the cost-effectiveness formula.
The literature which was reviewed as part of this analysis
contained only one reference to the cost of installing an air
injection system on an aircraft piston engine. Northern Research
(1971) reported that the new engine price increment would be $200.
This price may seem somewhat high when current automotive experi-
ence is considered as a benchmark. In a document prepared for the
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EPA (Lindgren 1978), the price of an automotive air injection
system is $32.
There are several factors which would increase the system
price for a light piston aircraft. These include: 1) higher
pass-through costs since more corporate entities are involved
(i.e., a minimum of hardware, engine, and airframe manufacturers);
2) FAA certification costs for the engine and airframe; 3) develop-
ment costs for a larger number of engine families; 4) a lower
economic volume over which to amortize nonrecurring expenses; and
5) added costs due to additional cooling and over temperature
safety control considerations. If the above factors are con-
sidered, a cost of $200, in 1978 dollars, does not appear to be
unreasonable.
Other costs will be incurred by this control technique
throughout its useful life in addition to the first cost. Although
automotive air injection systems do not require maintenance during
the useful life of the car (5 years or 50,000 miles), it is con-
ceivable that some direct and indirect maintenance will be required
by the aircraft system because its useful life is much longer (20
years). Operating the air injection system will also increase fuel
consumption slightly by absorbing a small amount of horsepower from
the engine to drive the pump. Northern Research (1971) estimated
that these costs would average a total of $30 per year. This cost
is equivalent to about $45 in 1978 dollars.
The cost effectiveness of the air injection system can now be
calculated by inserting into the formula: (1) $200 as the incre-
mental cost to the consumer, and (2) a yearly expenditure of $45
for added maintenance and increased fuel consumption. This control
concept requires $3,000 to reduce one ton of HC; it is much more
expensive than any cost-effectiveness value that has been calcu-
lated for other control strategies (Table 1).
E. Remaining Concepts
Since air injection has a very high cost-effectiveness value
and it is ranked as the least costly control concept (Table 4), as
well as one of the better HC emission reduction techniques (Table
5), all other potential control concepts can be eliminated from
further consideration since they will be even less cost effective.
III. SUMMARY AND CONCLUSION
The cost effectiveness of alternative strategies for control-
ling HC exhaust emissions from piston-powered aircraft ranges from
$2,300 to $8,000 per ton. These values were based primarily on
industry supplied data. Although EPA considers the cost infor-
mation to be reasonably representative, the actual expense of
pollution control may be somewhat lower if a rigorous independent
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analysis were made. The costs, however, would have to be signifi-
cantly reduced to bring the cost-effectiveness values for these
aircraft within the range of other implemented or planned control
strategies, A reduction of that size seems unlikely based on the
information which is currently available. Therefore, controlling
the HC emissions from piston-powered aircraft is not considered to
be cost effective at this time. In the future, however, as the
marginal costs of controlling air pollution increase, this source
may again be considered for control.
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IV. REFERENCES
Avco Corporation. 1977. The Past Development and Future
Development of the Avco Lycoming Aircraft Piston Engines for
Reductions in Exhaust Emissions. Avco Lycoming Williamsport
Division, Williamsport, Pa.
Bastress, E.K., R.C. Baker, C.F. Robertson, R.D. Siegal, and
G.E. Smith. 1971. Assessment of Aircraft Emission Control
Technology. Northern Research and Engineering Corporation.
Report No. 1168-1. EPA Contract No. 68-04-0011.
Datwyler, W.F., A. Blatter, and S.T. Hassan. 1973. Control of
Emissions from Light Piston-Engine Aircraft. The Bendix
Corporation. EPA Report No. APTD-1521.
Deimen, J.M. 1977. Aircraft Emissions at Selected Airports
1972-1985. TSR AC77-01. Emission Control Technology Divis-
ion, EPA, Ann Arbor, MI.
Department of Transporation, Interagency Task Force on Motor
Vehicle Goals Beyond 1980. 1976. Air Quality, Noise and
Health.
Environmental Protection Agency. 1978. Proposed Gaseous
Emission Regulations for 1983 and Later Model Year Heavy-Duty
Engines: Draft Regulatory Analysis. Emission Control Tech-
nology Division, EPA, Ann Arbor, MI.
. 1979a. Cost Effectiveness of Portland I/M
Program. Memo from Catherine O'Rourke to Janet Becker.
Emission Control Technology Division, EPA, Ann Arbor, MI.
. 1979b. Gaseous Emission Regulations for
1983 and Later Model Year Light-Duty Trucks. F.R. 44(135):
40784-40839.
Federal Aviation Administration. 1978. General Aviation
emission measurements at Lakeland, Florida. Memo from Chief,
High Altitude Pollution Staff, FAA, to Director, Environmental
Quality.
Helms, J.L. 1976. Summary of the General Aviation Manufac-
turers' Position on Aircraft Piston Engine Emissions. Pre-
sented at the 1976 Aircraft Piston Engine Exhaust Emission
Symposium, NASA Lewis Research Center. NASA CP-2005.
Houtman, W.H. 1976. Development of EPA Aircraft Piston Engine
Emission Standards. Presented at the 1976 Aircraft Piston
Engine Exhaust Emission Symposium, NASA Lewis Research Center.
NASA CP-2005.
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IV. REFERENCES (cont'd)
. 1977. Reevaluation of the Need for Aircraft
Piston Engine Emission Standards. TSR AC77-03. Emission
Control Technology Division, EPA, Ann Arbor, MI.
Jordan, B. C. 1977. An Assessment of the Potential Air
Quality Impact of General Aviation Emissions. Office of Air
Quality Planning and Standards, EPA, Research Triangle Park,
N.C.
Lieson, P. Woodward Governor Company. 1979. Telephone
Communication with R. S. Wilcox, Emission Control Technology
Division, EPA, Ann Arbor, MI.
Norsworthy, J. Woodward Governor Company. 1979. Telephone
Communication with R. S. Wilcox, Emission Control Technology
Division, EPA, Ann Arbor, MI.
Rezy, B. 1976. TMC Aircraft Piston Engine Emission Reduction
Program. Presented at the 1976 Aircraft Piston Engine Exhaust
Emission Symposium, NASA Lewis Research Center. NASA CP-2005.
Scott, 0. W. Beech Aircraft Corporation. 1979. Telephone
communication with R. S. Wilcox, Emission Control Technology
Division, EPA, Ann Arbor, MI.
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