Appendix A

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey

APPENDIX A
METHODOLOGY FOR THE 2019 GENERAL AVIATION
AND PART 135 ACTIVITY SURVEY
Purpose of Survey
The General Aviation and Part 135 Activity Survey (GA Survey) provides the Federal Aviation
Administration (FAA) with information on general aviation and on-demand Part 135 aircraft
activity. The survey enables the FAA to monitor the general aviation fleet so that it can
anticipate and meet demand for National Airspace System (NAS) facilities and services, assess
the impact of regulatory changes on the fleet, and implement measures to assure the safe
operation of all aircraft in the NAS. The data are also used by other government agencies, the
general aviation industry, trade associations, and private businesses to identify safety problems
and to form the basis for research and analysis of general aviation issues.
Background and History
Prior to the first implementation of the annual GA Survey in 1978, the FAA used the Aircraft
Registration Eligibility, Identification, and Activity Report (AC Form 8050-73) to collect data on
general aviation activity. The form was sent annually to all owners of civil aircraft in the United
States and served two purposes: a) Part 1 was the mandatory aircraft registration revalidation
form; and b) Part 2 was voluntary and applied to general aviation aircraft only, asking questions
on the owner-discretionary characteristics of the aircraft such as flight hours, avionics
equipment, base location, and use. The FAA used this information to estimate aircraft activity.
In 1978, the FAA replaced AC Form 8050-73 with a new system. Part 1 was replaced by a
triennial registration program. In January 1978, the FAA implemented a new procedure, known
as triennial revalidation, for maintaining its master file. Instead of requiring all aircraft owners to
revalidate and update their aircraft registration annually, the FAA only required revalidation for
those aircraft owners who had not contacted the FAA Registry for three years. In 2010, the FAA
eliminated the voluntary Triennial Aircraft Registration Report Program and established rules
that require renewal of an aircraft registration every three years and place time-limits on interim
statuses.1
Part 2 of AC Form 8050-73 was replaced by the General Aviation Activity Survey. Conducted
annually, the survey was based on a statistically selected sample of aircraft, and it requested
the same type of information as Part 2 of AC Form 8050-73. The first survey took place in 1978
and collected data on the 1977 general aviation fleet. The 2019 statistics in this report are
based on the 42nd GA Survey, which was implemented in 2020.2

Federal Register Vol 75, No. 138, Tuesday, July 20, 2010, Rules and Regulations, “Re-Registration and
Renewal of Aircraft Registration.”
2 The name of the survey has changed periodically since 1977. In 1993, the survey was entitled “General
Aviation and Air Taxi Activity Survey” to reflect the inclusion of air taxi (on-demand Part 135) aircraft. In
1999, the survey name changed to General Aviation and Air Taxi Activity and Avionics Survey because
questions about avionics were included every year rather than every other year. Since 2006, the survey
has been conducted as the General Aviation and Part 135 Activity Survey.
1

A-1

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
The GA Survey has undergone periodic revisions to content, implementation, and definition of
the GA population in order to remain current with regulations, activity patterns, and aviation
technology. Chapter 1 of this report (“Historical General Aviation and Air Taxi Measures”)
presents statistical estimates of fleet size and activity for a 10-year period.3 Tables A.1 through
A.3 summarize changes in survey content and design, data collection methods, sample and
population definitions that may affect comparability of statistical estimates across surveys.
Table A.1: Changes in Form or Content of Survey Questionnaire, by Survey Year
Year

Change in form or content of survey questionnaire

1993

Added sightseeing and external load to use categories

1996

Added public use (i.e., flights for the purpose of fulfilling a government function) to use
categories

1999

Re-design the survey form to reduce item non-response, add new content, and be compatible
with optical scanning
Added air medical services to use categories
Discontinued the “other” use category as used in previous years
Began collecting avionics data every year, rather than every other year

2000

“Public use” asked as a separate question

2002

Use categories refined to be mutually exclusive and exhaustive and match definitions used by
National Transportation Safety Board for accident reporting

2004

Air medical services was divided into two types to capture air medical flights under Part 135
and air medical flights not covered by Part 135
A more clearly defined “other” use category was reintroduced

2005

Fractional ownership question was changed from yes/no to a percentage of hours flown
Reduced the number of fuel type response categories by removing obsolete options
Average fuel consumption (in gallons per hour) was added
Revised questions about avionics equipment by adding and rearranging items

2007

Location of aircraft revised to ask the state or territory in which the aircraft was “primarily
flown” during the survey year rather than where it was "based” as of December 31st of the
survey year
Percentage of hours flown in Alaska was added
Questions on percentage of hours flown under different flight plans, flight conditions, and
day/night were revised into a single tabular format
Number of types of landing gear systems was expanded
Ice protection equipment was revised and prohibition from flight in icing conditions was added
Questions about avionics equipment were revised

3 Excluding

estimates for the 2011 survey year, which are not available. For 2011 GA data, use the FAA
Aerospace Forecast estimates
(http://www.faa.gov/data_research/aviation/aerospace_forecasts/media/Tables_28-31.xlsx).

A-2

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Year

Change in form or content of survey questionnaire

2009

Two questions about avionics equipment were revised:
“Air Bag/Ballistic Parachute” was asked as two items—“Air Bag” and “Ballistic
Parachute”
“ADS-B (Mode S)” was separated into two questions—“ADS-B (Mode S) Transmit
Only (Out)” and “ADS-B (Mode S) Transmit and Receive (In)”

2010

Removed the skip instruction in the mail survey based on responses to Part 121/129
operations
Added “Specify” option if reason not flown was “Other”

2013

Added “Specify” option if fuel type was “Other”
Added response categories for reason not flown (“Under maintenance or repair,” “Parted
out/salvaged,” and “In storage”)
The text “Corporate/Executive Transportation” was removed from the description of this use
category and replaced with “Business Transportation – (with a paid flight crew).” The
definition of this use is unchanged.

2014

Added response category for kind/grade of fuel primarily used (”Propane/LP Gas”)

2016

The following questions on the 2016 full survey form underwent additions, deletions, and text
changes:
• Reason not flown
• Percentage of total hours flown under fractional ownership
• Percentage of total hours flown under filed flight plans
• Fuel type
• Avionics.
Other questions and response categories were re-ordered. Data end-users should consult the
survey documents in Appendix B of the current and previous year’s survey report.

2019

Eliminated non-mutually exclusive transponder selection options in “Installed
Transponder/Surveillance Equipment” section of avionics questions

A-3

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Table A.2: Changes in Data Collection Methodology, by Survey Year
Year

Change in data collection methodology

1999

Non-respondent telephone survey conducted to adjust active aircraft and hours flown
estimates4

2000

Discontinued non-respondent telephone survey Added Internet response option

2003

Added a reminder/thank-you postcard between the first and second mailings

2004

Introduced “large fleet” summary form for owners/operators of multiple aircraft Initiated
telephone follow-up effort to contact owners/operators of multiple aircraft who had not
responded.

2010

Introduced end-of-field-period follow-up postcard to owners/operators of single aircraft that
participated the previous survey year but had not yet completed the current year’s survey

2014

Introduced use of email to invite sampled aircraft owners/operators to complete the survey

Table A.3: Changes in Sample Design or Definition of Survey Population, by Survey Year
Year

Change in sample design or survey population

1993

Number of aircraft types classified by the sample was expanded from 13 to 19

1999

Sample design revised to stratify by aircraft type and FAA region

2003

Aircraft with known incorrect addresses and identified as “Postmaster Return” status on the
Registry were retained in the definition of the survey population and eligible for sample
selection

2004

Aircraft listed on the Registry as “registration pending” or “sold” (if sold status less than five
years ago) were retained in the definition of the survey population and eligible for sample
selection. Sample design revised to stratify by aircraft type, FAA region, and whether the
aircraft is certified to fly Part 135. Introduced 100 percent samples of turbine aircraft,
rotorcraft, on-demand Part 135, and Alaska-based aircraft

2005

Introduced light-sport aircraft as an aircraft type sampled at 100 percent. Light-sport included
aircraft with special or experimental airworthiness as well as aircraft for which airworthiness
was not yet final.

2006

Sample design simplified to fewer aircraft types and included 100 percent sample of aircraft
manufactured in the past five years

2008

100 percent sample of light-sport aircraft was limited to special light-sport aircraft.
Experimental light-sport and light-sport without completed airworthiness sampled at a rate
less than 1.0.

2010

Aircraft excluded from the survey population if “sale reported” or “registration pending” more
than 12 months. These aircraft no longer eligible for sample selection due to implementation
of the re-registration rule.

2012

5

Aircraft excluded from the survey population if registration was expired. These aircraft no
longer eligible for sample selection because they do not have valid registrations due to
implementation of the re-registration rule.
Unmanned aerial vehicles are excluded from the survey population.

4

Telephone surveys of non-respondents also were conducted in 1977, 1978, 1979, 1997, and 1998.
Please refer to the 1999 GA Survey report for a full discussion of the telephone survey of nonrespondents.
5 Before 1999, the sample was stratified by aircraft type and state/territory.

A-4

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Survey Population and Survey Sample
The survey population for the 2019 General Aviation and Part 135 Activity Survey includes all
civil aircraft registered with the FAA that are based in the US or US territories and that were in
existence, potentially active between January 1 and December 31, 2019, and had a valid
registration. This includes aircraft operating under:
•

Part 91: General operating and flight rules

•

Part 125: Certification and operations: Airplanes having a seating capacity of 20 or
more passengers or a maximum payload capacity of 6,000 pounds or more (but not
for hire)

•

Part 133: Rotorcraft external load operations

•

Part 135: On-demand (air taxi) operations

•

Part 137: Agricultural aircraft operations.

Aircraft operating under Part 121 as defined in Part 119 are excluded from the survey
population. Foreign air carriers, which operate under Part 129, are also not part of the survey
population. Civil aircraft that are known not to be potentially active during the survey year are
excluded from the population (e.g., aircraft on static display, destroyed prior to January 1, 2019).
The Aircraft Registration Master File, maintained by the FAA’s Mike Monroney Aeronautical
Center in Oklahoma City, Oklahoma, serves as the sample frame or list of cases from which a
sample of civil aircraft is selected. The Registration Master File (“Registry”) is the official record
of registered civil aircraft in the United States. For the purpose of defining the 2019 survey
population, we used the Registry’s list of aircraft effective through December 31, 2019.6
The Registry, like many sample frames, is an imperfect representation of the survey population.
While it may exclude a small number of aircraft that operate under the FAA regulations
governing the operation of general aviation and on-demand Part 135 aircraft, it also includes
aircraft that are not part of the survey population. Prior to sample selection, the following
ineligible aircraft are removed: Aircraft whose registration has been cancelled or revoked
•

Aircraft based in Europe or registered to a foreign company that has not returned
flight hour reports

•

Aircraft that operate under Part 121

•

Aircraft destroyed or moved to static display prior to January 1, 2019

6 The

Civil Aviation Registry updates the Master file approximately weekly but not on a schedule that
corresponds exactly to December 31st. For the 2019 survey population, we used a Registry Master file
that was made available on January 22, 2020, and reflected records processed through December 30,
2019.

A-5

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
•

Aircraft that are flagged Postmaster Return (known to have incorrect address
information) on the aircraft Registration file prior to 2010 (ten years prior to survey
year).

•

Aircraft that have held interim registration statuses (e.g., “sale reported”) more than
more than 12 months (prior to January 1, 2019)7

•

Aircraft with registrations that expired prior to January 1, 2019

•

Aircraft that are unmanned aerial vehicles.

The Registry Master file used to define the 2019 survey population included 289,755 aircraft.
This represents a decrease of 1.4 percent compared with the Registry file from 2018 (293,841).
After excluding the aircraft described above, 272,554 records remain, which is 94 percent of the
Registry. The 2019 survey population of 272,554 is a decrease of 77 aircraft compared to the
2018 population of 272,631 aircraft.
The 2019 GA Survey Sample
The 2019 survey sample is stratified by aircraft type, FAA region in which the aircraft is
registered, whether the aircraft operates under a Part 135 certificate, and whether the aircraft
was manufactured in the past five years. Aircraft operated under a Part 135 certificate were
identified using the FAA’s Operations Safety System (OPSS) database that was merged with
the Registry by N-number.
Aircraft are classified into FAA regions by the state or US territory of registration. Table A.4
summarizes how states and territories are mapped to region.8

7

The registration rule allows aircraft to be listed as sale reported for a maximum of six months. For the
purpose of defining the survey population, we allow aircraft to hold this status for 12 months because we
cannot consistently differentiate among aircraft that did or did not hold valid statuses for the other six
months of the year. The number of aircraft mistakenly included in the survey population should be small.
The error of including ineligible aircraft has a smaller impact on statistical estimates of activity than
erroneously excluding eligible and potentially active aircraft.
8 The FAA defines the regions at www.faa.gov/about/office_org/headquarters_offices/arc/ro_center.
Statistical estimates reported by region in which an aircraft is primarily flown follow the same mapping
based on the state in which the aircraft is primarily operated.

A-6

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Table A.4: Regions and States/Territories Constituting Region
Region

States/Territories

Alaska

Alaska

Central

Iowa, Kansas, Missouri, Nebraska

Eastern

Delaware, Maryland, New Jersey, New York, Pennsylvania, Virginia, Washington,
D.C., West Virginia

Great Lakes

Illinois, Indiana, Michigan, Minnesota, North Dakota, Ohio, South Dakota,
Wisconsin

New England

Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont

Northwest Mountain

Colorado, Idaho, Montana, Oregon, Utah, Washington, Wyoming

Southern

Alabama, Florida, Georgia, Kentucky, Mississippi, Navassa Island, North
Carolina, Puerto Rico, South Carolina, Tennessee, US Virgin Islands

Southwestern

Arkansas, Louisiana, New Mexico, Oklahoma, Texas

Western-Pacific

American Samoa, Arizona, Baker, Howland, and Jarvis Islands, California, Guam,
Hawaii, Johnston Atoll, Kingman Reef, Midway Islands, Nevada, Palmyra Atoll,
Wake Island

We define 15 aircraft types to execute the sample design. The classification distinguishes
among fixed wing aircraft, rotorcraft, experimental aircraft, light-sport, and other aircraft. Within
the major categories of fixed wing and rotorcraft, we differentiate aircraft by type and number of
engines (e.g., piston, turboprop, turbojet, turbine, single- and two-engines). Experimental aircraft
are subdivided by amateur-built status and airworthiness certification, and we classify “other”
aircraft as gliders or lighter-than-air. Light-sport is subdivided into special and experimental
based on airworthiness certification. Light-sport aircraft for which airworthiness certificates are
not yet final are included with experimental light-sport.
Aircraft Sampled at 100 Percent
The 2019 survey sample includes several types of aircraft that are sampled at a rate of 1.0.
Because of the FAA’s interest in better understanding the operation of these aircraft, all such
aircraft listed in the Registry are included in the survey sample to ensure a sufficient number of
responses to support analysis and provide more precise estimates of fleet size and aircraft
activity. These include:
•

100 percent sample of turbine aircraft (turboprops and turbojets)

•

100 percent sample of rotorcraft

•

100 percent sample of special light-sport aircraft

•

100 percent sample of aircraft operating on-demand Part 135

•

100 percent sample of aircraft registered in Alaska

•

100 percent sample of aircraft manufactured within the past five years (since 2015
inclusive).
A-7

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Aircraft sampled at 100 percent account for 59,124 observations in the 2019 survey sample.
Aircraft Sampled at Less than 100 Percent
Aircraft that are not part of a 100 percent sample are selected based on sampling fractions
defined for each cell in the sample design matrix. Flight hours is the primary measure needed
by the FAA. Sample fractions for each sample strata are defined to optimize sample size to
obtain a desired level of precision for an estimate of flight activity. Data from the previous survey
year on average hours flown, variability in hours flown by region and aircraft type, and response
rates are used to set precision levels and target sample sizes for each stratum. Aircraft are
randomly selected from each cell in the matrix, subject to the desired sample size. Strata where
the desired sample size exceeds the population are examined and the sample size is adjusted
to include all observations.9 The 2019 survey sample includes 25,870 aircraft that are selected
at a rate of less than 1.0, which is a decrease from 2018 when 26,707 aircraft were sampled.
The 2019 GA Survey sample included 84,994 aircraft. Table A.5 summarizes the population
counts and sample sizes by aircraft type.

9

In 2019, an additional six strata were sampled at 100 percent to meet precision requirements (1,406
aircraft).

A-8

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Table A.5: Population and Survey Sample Counts by Aircraft Type

Population

Sample Size

Sample as
Percent of
Population

179,881

31,380

17.4

1 engine, 1–3 seats

50,605

6,898

13.6

1 engine, 4+ seats

113,369

15,314

13.5

2 engines, 1–6 seats

11,269

6,332

56.2

2 engines, 7+ seats

4,638

2,836

61.1

Fixed Wing - Turboprop

11,064

11,064

100.0

1 engine

5,537

5,537

100.0

2 engines, 1–12 seats

3,917

3,917

100.0

2 engines, 13+ seats

1,610

1,610

100.0

Fixed Wing - Turbojet

15,985

15,985

100.0

Rotorcraft

12,197

12,197

100.0

Piston

4,133

4,133

100.0

Turbine (1 engine)

5,904

5,904

100.0

Turbine (multi-engine)

2,160

2,160

100.0

7,181

2,113

29.4

Glider

2,742

851

31.0

Lighter-than-air

4,439

1,262

28.4

Experimental

43,202

9,211

21.3

Amateur

32,796

5,248

16.0

Exhibition

3,033

1,448

47.7

Experimental light-sport*

6,251

1,485

23.8

Other experimental

1,122

1,030

91.8

3,044

3,044

100.0

272,554

84,994

31.2

Aircraft Type
Fixed Wing - Piston

Other Aircraft

Special light-sport
Total

* Includes light-sport aircraft with experimental airworthiness and light-sport aircraft for which airworthiness
certification is not final

Weighting the Survey Data
Data from completed surveys are weighted to reflect population characteristics. The weights
reflect the proportion of aircraft sampled from the population in each sample strata and
differential response as well as adjustment for aircraft that are not part of the survey population.

A-9

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Initially, each aircraft for which we receive a completed survey is given a weight that reflects
sampling fraction and differential response. That is:
WEIGHT = (Population Nijkl/Sample Nijkl) * (Sample Nijkl/N Respondentsijkl)
where i, j, k, and l represent the four sample strata of aircraft type, FAA region, Part 135 status,
and whether an aircraft was manufactured in the past five years.
The weight is subsequently adjusted to reflect information about non-general aviation aircraft.
Survey responses that indicate an aircraft is not part of the survey population—e.g., destroyed
prior to January 1, 2019; displayed in a museum; or operated primarily under Part 121 or 129—
are used to remove aircraft from the sample and the population. The procedure assumes that
ineligible aircraft occur similarly among survey respondents and non-respondents. To the extent
that ineligible aircraft are less likely to receive and complete a survey, this approach will
underestimate the adjustment for aircraft that are not part of the general aviation population.
Errors in Survey Data
Errors associated with survey data include sampling and non-sampling errors. Sampling errors
occur because the estimates are based on a sample of aircraft rather than the entire population
and we can expect, by chance alone, that some aircraft selected into the sample differ from
aircraft that were not selected.
Non-sampling errors include a) errors that arise from difficulties in the execution of the sample
(e.g., failing to obtain completed interviews with all sample units), and b) errors caused by other
factors, such as misinterpretation of questions, inability or unwillingness to provide accurate
answers, or mistakes in recording or coding data.
Sampling Error
The true sampling error is never known, but in a designed survey we can estimate the potential
magnitude of error due to sampling. This estimate is the standard error. The standard error
measures the variation that would occur among the estimates from all possible samples of the
same design from the same population.
This publication reports a standard error for each estimate based on survey sample data. An
estimate and its standard error can be used to construct an interval estimate (“confidence
interval”) with a prescribed level of confidence that the interval contains the true population
figure. In general, as standard errors decrease in size we say the estimate has greater precision
(the confidence interval is narrower), while as standard errors increase in size the estimate is
less precise (the confidence interval is wider). Table A.6 shows selected interval widths and
their corresponding confidence.

A-10

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Table A.6: Confidence Interval Estimates
Approximate
confidence
that interval includes
true population value

Width of interval
1 Standard error

68%

2 Standard error

95%

3 Standard error

99%

This report presents a “percent standard error” for each estimate, which is the standard error
relative to the mean. The percent standard error is the ratio of the standard error to its estimate
multiplied by 100. For example, if the estimate is 4,376 and the standard error is 30.632, then
the percent standard error is (30.632/4,376) x 100 = 0.7. Reporting percent standard errors
makes it possible to compare the precision of estimates across categories.
Estimates and percent standard errors reported in Table 2.1 in Chapter 2 ("Population Size,
Active Aircraft, Total Flight Hours, and Average Flight Hours by Aircraft Type") provide an
example of how to compute and interpret confidence intervals. To obtain a 95 percent
confidence interval for the estimated number of total hours flown for twin-engine turboprops in
2019, where the total hours flown is estimated to be 1,178,429 and the percent standard error of
the estimate is 1.8, the following computation applies:
Lower confidence limit: 1,178,429 – 1.96(1.8/100)(1,178,429) = 1,136,854
Upper confidence limit: 1,178,429 + 1.96(1.8/100)(1,178,429) = 1,220,004
In other words, if we drew repeated samples of the same design, 95 percent of the estimates of
the total hours flown by twin-engine turboprops would fall between 1,136,854 and 1,220,004.
Non-sampling Error
Sampling error is estimable and can be reduced through survey design (e.g., by increasing
sample size), but it is difficult, if not impossible, to quantify the amount of non-sampling error.
Although extensive efforts are undertaken to minimize non-sampling error, the success of these
measures cannot be quantified.
Steps taken to reduce non-sampling error include strategies to reduce non-response and efforts
to minimize measurement and coding errors. The 2019 GA Survey incorporated the following
steps to maximize cooperation among sample members:
•

Two methods for completing the survey (Internet, paper-pencil mail form) and three
methods of inviting survey participation (mail, email, and telephone).

•

Three mailings of the survey, reminder letters and postcards, and end-of-field-period
follow-up postcard or email.

•

Cover letters accompanying each survey mailing explained the purpose of the survey
and the endorsement (organizational logos) of several aviation associations.
A-11

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
•

Cover letters assured owners of the confidentiality of their responses and informed
them: “Names of individuals are never associated with responses. There is an
identification number on your survey only so [survey contractor] knows who should
receive the letter.”

•

Use of additional sources to obtain updated contact information and help ensure the
mail survey reaches the sample member (e.g., National Change of Address).

•

Use of a toll-free telephone number and email address to respond to questions.

•

Collaboration with aviation organizations and industry groups to raise awareness of
the survey and encourage cooperation.

•

Telephone follow-up to owners or operators of multiple aircraft who had not yet
responded.

The survey efforts minimize measurement error by increasing the likelihood that respondents
share a common understanding of survey questions and reducing errors in data coding. These
efforts include:
•

Close collaboration with the FAA, other federal agencies, and aviation groups to
refine question wording and definitions to questions. The questionnaire is reexamined regularly to identify ambiguities or revisions necessary to remain
consistent with aviation regulations and definitions.

•

Periodic re-design of the survey questionnaire and pre-testing significant revisions
with a sample of aircraft owners or operators.

•

Comprehensive editing and verification procedures to ensure the accuracy of data
transcription to machine-readable form.

•

Manual review and verification of a subset of single-aircraft mail surveys throughout
the field period.

•

Programmed logic checks for web surveys to identify illogical, unusual or
inconsistent data.

•

Analysis of preliminary data to identify unusual or illogical values and place follow-up
inquiries with participants to verify or correct responses.

We undertake extensive effort to reduce measurement error, particularly where we can
anticipate systematic or repeated error on the part of survey respondents, but it is impossible to
eliminate all measurement error. Survey participants may misunderstand questions or misreport
flight activity in ways that cannot be anticipated or prevented through survey design. Where
survey reports appear nonsensical or contradict FAA regulations, we manually verify that the
data were processed accurately. Instances in which a small number of illogical reports occur
may be suppressed and are indicated in table notes. No additional steps are taken to cleanse
the data of apparently illogical reports or assign them to other categories. To do so would
introduce additional and systematic error that would be misleading and would affect other uses
of the data.

A-12

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Imputation of Missing Data
Imputation of missing data is important for stabilizing the estimates of aircraft activity and
equipment. Values are imputed for variables if the survey response is incomplete, the survey
form did not include the question, or the Registry data field is blank. Table A.7 lists the variables
for which values are imputed, describes the imputation procedure, and shows the percentage of
cases with imputed data. The table shows rates of imputation among active aircraft that
received the full survey form (first column of numbers) and rates including active aircraft that
completed the short form (last column).10 Asterisks note the questions not asked on the short
form.
Table A.7: Variables with Imputed Values, Imputation Procedure, and Percentage Imputed
Among Active Aircraft
Percent
Imputed
(full
survey
form only)

Percent
Imputed (incl.
short form)

0.8

2.2

Variable

Imputation Procedure

Hours by use (e.g.,
personal, business
transport)

Mean values by aircraft type

Fractional ownership
hours11

Nearest neighbor by aircraft type
by make model series

23.9

18.0

Hours rented/leased *

Nearest neighbor by aircraft type
by make model series

1.7

37.2

Public use hours

Nearest neighbor by aircraft type
by make model series

1.5

6.7

Hours by flight
plans/flight conditions *

Mean values by aircraft type

2.9

38.0

Airframe hours *

Nearest neighbor by aircraft type
by hours flown

5.5

39.6

Number of landings

Nearest neighbor by aircraft type
by make model series by age

2.4

8.5

Landing gear *

Nearest neighbor by aircraft type
by make model series

2.5

37.7

Fuel type *

Nearest neighbor by aircraft type
by make model series

2.5

37.6

Fuel burn rate

Nearest neighbor by aircraft type
by make model series

3.5

5.5

The “full” and “short” forms of the survey are described below in the section “Data Collection Methods.”
Beginning with the 2016 survey, fractional ownership was no longer asked on the full survey form,
thereby increasing the imputation rate among full survey returns.
10
11

A-13

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Percent
Imputed
(full
survey
form only)

Percent
Imputed (incl.
short form)

Variable

Imputation Procedure

Avionics equipment *

Nearest neighbor by aircraft type
by make model series by age

9.1

39.7

State primarily flown

Assign state of registration from
Registry

2.2

14.0

Year of manufacture
(Registry data field)

Nearest neighbor by aircraft type
by make model series

0.6

1.5

Percentages are based on unweighted survey responses among active aircraft (total 30,591).12
* Question not asked on the abbreviated survey form administered to owners/operators of multiple aircraft.

In 2019, rates of imputations for most variables are 1 to 5 percent for aircraft that completed the
full survey form. Item non-response on key activity variables is low—hours flown by use (0.8
percent), rented or leased hours (1.7 percent), and year of manufacture (0.6 percent).
Survey Content
The 2019 GA Survey questionnaire requests the aircraft owner or operator to provide
information on flight activity, flight conditions, where the aircraft was flown, and aircraft
characteristics. Variables derived from the survey responses include:
•

Number of total hours flown in 2019, hours flown by use, and total lifetime airframe
hours

•

The state in which the aircraft was primarily flown

•

Hours flown by filed flight plan, including flight under Visual Flight Rules (VFR),
Instrument Flight Rules (IFR), and without flight plans

•

Hours flown as part of a fractional ownership program (short form only), rented or
leased, or used to fulfill a government function

•

Type of landing gear and number of landings in 2019

•

Fuel type and average fuel burn rate

•

Avionics equipment installed in the aircraft.

12

In previous survey years, the imputation rates were calculated based on all survey responses (active
and inactive aircraft). The rates shown here will not be comparable to those reported in previous years.

A-14

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Data Collection Methods
Collecting Data from Owners/Operators of a Single Aircraft
Appendix B presents the materials used to conduct the 2019 survey. The survey form
administered to owners/operators of a single aircraft is shown in Figure B.1. The postcard
invitation to the Internet component and the reminder/thank-you postcard are shown in Figures
B.2 and B.3. Surveys sent to aircraft owners who started, but did not complete, an Internet
survey included a special insert (Figure B.4). Surveys mailed to Alaskan addresses included an
insert with the endorsement of Alaska aviation associations encouraging owners to participate
(Figure B.5). Each of the three mailings for the survey was accompanied by a cover letter,
shown respectively in Figures B.6, B.7, and B.8. The data collection effort for the 2019 survey
also included an end-of-field-period postcard or email (Figure B.9).
The survey data were collected from owners and operators of the sampled aircraft through two
modes—the Internet and mailings of the questionnaire. We implemented the Internet
component before the mailing portion to maximize the number of responses collected
electronically. We first sent the owners/operators of sampled aircraft a postcard (mailed on
February 21, 2020) or email (sent February 24, 2020) inviting them to complete the survey on
the Internet. All single-aircraft surveys received through July 20 (on-line or by mail) were
processed and included in analysis.
We mailed survey questionnaires to owners/operators of sampled aircraft three times during the
field period as well as a reminder/thank-you postcard between the first and second mailings and
an end-of-field-period follow-up postcard. With the exception of the final postcard, each mailing
was sent to owners or operators who had not yet responded to the survey at that time or had
not been assigned a final disposition. The final postcard was sent only to owners/operators that
had participated in the 2018 survey but had not yet completed a 2019 survey by the end of May.
We mailed the first questionnaire on March 20, 2020, followed by the reminder/thank-you
postcard on April 17, 2020. The second mailing was sent April 24, 2020. The final postcard was
mailed on May 29, 2020, prior to the third mailing, which was sent June 5, 2020.
Collecting Data from Owners/Operators of Multiple Aircraft
The 2019 GA Survey continued the effort initiated in 2004 to increase cooperation among
respondents who own or operate multiple aircraft. The 2019 survey employed data collection
tools and methods similar to those introduced in 2004, including telephone contact with
owners/operators of multiple aircraft to encourage participation among non-responders after the
first mailing. The survey forms, cover letters, and reminder letter are presented in Appendix B,
Figures B.10–B.14.
The responses of multiple-aircraft owners or operators are important for accurately estimating
general aviation activity. Because of the increased burden of reporting for multiple aircraft, there
was a concern that these operators were less likely to respond to the survey. After selecting the
sample, we identify groups of aircraft belonging to the same operator using several resources:
FAA’s OPSS, databases available from aviation associations, and the Registry.
Owners or operators of multiple aircraft receive an abbreviated survey form to minimize the
reporting burden. The form, developed in cooperation with several aircraft operators and
aviation associations, allows an operator to report a summary of activity for a group of aircraft of
a similar type instead of requiring the operator to complete a separate and longer questionnaire
A-15

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
for each individual aircraft. This survey form (Figure B.10) collects data on key variables for
major classes of aircraft (e.g., hours flown, how flown, fuel consumption, fractional ownership,
and number of landings). The form does not collect data on flight plans, fuel type, landing gear,
or avionics.
Data collection for owners or operators of multiple aircraft followed similar timing as that for
single aircraft. We programmed an Internet survey that matched the hard-copy survey form and
the on-line survey remained open throughout the field period. We mailed survey questionnaires
three times during the field period and sent a reminder letter between the first and second
mailings. Each mailing was sent to owners or operators of multiple aircraft who had not yet
responded to the survey and had not been assigned a final disposition. The first survey mailing
was sent February 21, 2020, followed by a reminder letter on March 27, 2020. The second and
third mailings were sent April 3, 2020, and June 5, 2020, respectively. All large fleet surveys
received through July 20 were processed and included in analysis.
To maximize survey response, we placed follow-up telephone calls to multiple-aircraft owners or
operators who had not responded. The telephone effort began March 16, 2020 and continued
through the field period. The calling effort focused on encouraging survey participation and
ensuring that survey mailings were reaching the appropriate person in the organization, but
surveys were completed by telephone when necessary.
The alternate survey form for owners or operators of multiple aircraft has reduced respondent
burden and improved representation of activity among high-end and high-use aircraft. In 2019,
31.2 percent of all completed surveys followed this data collection track.
Response Rate
The response rate is calculated conservatively following guidelines published by the American
Association for Public Opinion Research (AAPOR), a professional association that establishes
standards, best practice guidelines, and a code of ethics for professional survey researchers
and research firms.13 Specifically, the response rate is computed as the number of completed
and partial surveys returned divided by the total number of eligible aircraft in the sample using
the following formula.
RR = (C + P) / (C + P) + (NR + INS + REF + PMR + UNK)
Where
RR = Response Rate
C = Completed survey
P = Partial survey
NR = No response

13

The American Association for Public Opinion Research. 2016. Standard Definitions: Final Dispositions
of Case Codes and Outcome Rates for Surveys. 9th edition. AAPOR.

A-16

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
INS = Insufficient complete; a partial survey that is not sufficient to count as a complete
REF = Refused
PMR = Postmaster Returned, no new address
UNK = Unknown eligibility
The numerator is comprised of completed surveys and partial surveys that provide enough
information to be used for analysis. Partial surveys must include information on hours flown to
be analyzed.
In addition to completed and partial surveys, the denominator includes cases for which no
response was received, insufficiently completed surveys, refusals, surveys returned as
undeliverable by the US Postal Service, and cases of unknown eligibility. The last category
includes aircraft in which the owners cannot be identified or cannot report about aircraft activity
(e.g., owner is deceased, and the survivors cannot report on the aircraft activity, survey recipient
does not own the aircraft listed).
The denominator includes aircraft that were sold or destroyed during the survey year. The
survey collects data on flight activity for the portion of the year the aircraft was eligible to fly, and
data collection efforts attempt to identify and mail surveys to new owners.
The denominator excludes aircraft known not to be part of the general aviation fleet or known
not to be eligible to fly during the survey year. These are aircraft that were destroyed prior to the
survey year, operated primarily as an air carrier, operated outside the US, or exported overseas.
Table A.8 shows the final response rate by mailing and overall, along with the number of
completed surveys. The number of completed surveys shown here excludes duplicate surveys
after cleaning the returned survey data to retain the form with the most complete information.
The overall response rate for the 2019 GA Survey was 41.4 percent. Over 72 percent of
responses were received on the Internet and 17 percent were received from the first mailing.
The second and third mailings had lower response, but these rates are calculated
conservatively. For example, the Mail 3 response rate is the proportion of sampled aircraft that
returned that hard-copy survey. If a third mailing was sent, but the survey was later completed
on-line, then the response is recorded as “Internet.”
Table A.8: Response Rate by Mailing
Mailing

Completes

Response
Rate

% Total
Response

Internet

25,123

29.9%

72.2%

1st Mailing

5,724

6.8%

16.5%

2nd Mailing

2,521

3.0%

7.2%

3rd Mailing

1,424

1.7%

4.1%

34,792

41.4%

100.0%

Overall

A-17

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
The response rate calculation retains all non-responding surveys, sampled units with bad
addresses, and sampled aircraft of unknown eligibility in the denominator. In the 2019 survey
the survey sample included about 754 aircraft that could not be contacted because their status
was “Sale Reported,” “Registration Pending,” or the address was known to be incorrect based
on the Registry status.
Table A.9 shows response rates by aircraft type. The overall response rate in 2019 is 41.4
percent. Participation is highest among experimental amateur aircraft (54 percent), multi-engine
turbine rotorcraft (53 percent), and experimental light-sport aircraft (52 percent). Piston rotorcraft
have the lowest rates of participation (32 percent).

A-18

Appendix A: Methodology for the 2019 General Aviation
and Part 135 Activity Survey
Table A.9: Response Rate by Aircraft Type
Sample

Invalid
Sample14

Completes

Response
Rate

31,380

231

13,510

43.4%

1 engine, 1–3 seats

6,898

39

2,905

42.4%

1 engine, 4+ seats

15,314

57

7,143

46.8%

2 engines, 1–6 seats

6,332

75

2,503

40.0%

2 engines, 7+ seats

2,836

60

959

34.5%

11,064

118

4,076

37.2%

1 engine

5,537

18

2,325

42.1%

2 engines, 1–12 seats

3,917

83

1,126

29.4%

2 engines, 13+ seats

1,610

17

625

39.2%

Fixed Wing - Turbojet

15,985

285

5,087

32.4%

Rotorcraft

12,197

138

5,175

42.9%

Piston

4,133

35

1,315

32.1%

Turbine: 1 engine

5,904

55

2,747

47.0%

Turbine: Multi-engine

2,160

48

1,113

52.7%

2,113

11

974

46.3%

851

2

424

49.9%

1,262

9

550

43.9%

9,211

72

4,529

49.6%

Amateur

5,248

36

2,791

53.5%

Exhibition

1,448

12

570

39.7%

Experimental light-sport*

1,485

8

761

51.5%

Experimental Other

1,030

16

407

40.1%

3,044

17

1,441

47.6%

84,994

872

34,792

41.4%

Aircraft Type
Fixed Wing - Piston

Fixed Wing - Turboprop

Other Aircraft
Glider
Lighter-than-air
Experimental

Special light-sport
Total

* Experimental light-sport includes aircraft with experimental airworthiness certification and light-sport
aircraft for which airworthiness certificates are not final.

14

We remove non-GA aircraft from the population before the sample is selected, but some surveys are
returned indicating that the aircraft should not be part of the survey population (e.g., the aircraft was
destroyed or salvaged, placed on static display, used only in ground maintenance school training). The
Invalid Sample represents such aircraft, which are excluded from response rate calculations.

A-19