<PAGE>
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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
 
                             WASHINGTON, D.C. 20549
                            ------------------------
                                   FORM 10-K
 
                                   (MARK ONE)
 
  /X/    ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
         SECURITIES EXCHANGE ACT OF 1934
 
                  FOR THE FISCAL YEAR ENDED DECEMBER 31, 1998
                                       OR
 
  / /    TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
         SECURITIES EXCHANGE ACT OF 1934 [NO FEE REQUIRED]
 
        FOR THE TRANSITION PERIOD FROM ______________ TO ______________
 
                         COMMISSION FILE NUMBER 0-20031
                            ------------------------
 
               AMERICAN INCOME FUND I-C, A MASSACHUSETTS LIMITED
                                  PARTNERSHIP
             (Exact name of registrant as specified in its charter)
 
               MASSACHUSETTS                           04-3077437
      (State or other jurisdiction of       (IRS Employer Identification No.)
       incorporation or organization)
  88 BROAD STREET, SIXTH FLOOR, BOSTON, MA                02110
  (Address of principal executive offices)             (Zip Code)
 
       Registrant's telephone number, including area code  (617) 854-5800
 
          Securities registered pursuant to Section 12(b) of the Act  NONE
                            ------------------------
 
                                             NAME OF EACH EXCHANGE ON WHICH
  TITLE OF EACH CLASS                                  REGISTERED
  ----------------------------------------  ---------------------------------
 
Securities registered pursuant to Section 12(g) of the Act:
 
            796,161 UNITS REPRESENTING LIMITED PARTNERSHIP INTEREST
 
                                (Title of class)
 
                                (Title of class)
 
    Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes /X/  No / /
 
    State the aggregate market value of the voting stock held by nonaffiliates
of the registrant. Not applicable. Securities are nonvoting for this purpose.
Refer to Item 12 for further information.
 
                      DOCUMENTS INCORPORATED BY REFERENCE
       Portions of the Registrant's Annual Report to security holders for
                the year ended December 31, 1998 (Part I and II)
 
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--------------------------------------------------------------------------------
<PAGE>
                           AMERICAN INCOME FUND I-C,
                      A MASSACHUSETTS LIMITED PARTNERSHIP
 
                                   FORM 10-K
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                              PAGE
                                                                                                            ---------
<S>         <C>                                                                                             <C>
                                                       PART I
 
Item 1.     Business......................................................................................          3
 
Item 2.     Properties....................................................................................          5
 
Item 3.     Legal Proceedings.............................................................................          5
 
Item 4.     Submission of Matters to a Vote of Security Holders...........................................          5
 
                                                       PART II
 
Item 5.     Market for the Partnership's Securities and Related Security Holder Matters...................          6
 
Item 6.     Selected Financial Data.......................................................................          8
 
Item 7.     Management's Discussion and Analysis of Financial Condition and Results of Operations.........          8
 
Item 8.     Financial Statements and Supplementary Data...................................................          8
 
Item 9.     Changes in and Disagreements with Accountants on Accounting and Financial Disclosure..........          8
 
                                                      PART III
 
Item 10.    Directors and Executive Officers of the Partnership...........................................          9
 
Item 11.    Executive Compensation........................................................................         11
 
Item 12.    Security Ownership of Certain Beneficial Owners and Management................................         11
 
Item 13.    Certain Relationships and Related Transactions................................................         12
 
                                                       PART IV
 
Item 14.    Exhibits, Financial Statement Schedules and Reports on Form 8-K...............................      13-14
</TABLE>
 
                                       2
<PAGE>
PART I
 
ITEM 1. BUSINESS.
 
    (a)  General Development of Business
 
    AMERICAN INCOME FUND I-C, a Massachusetts Limited Partnership, (the
"Partnership") was organized as a limited partnership under the Massachusetts
Uniform Limited Partnership Act (the "Uniform Act") on March 1, 1991 for the
purpose of acquiring and leasing to third parties a diversified portfolio of
capital equipment. Partners' capital initially consisted of contributions of
$1,000 from the General Partner (AFG Leasing VI Incorporated) and $100 from the
Initial Limited Partner (AFG Assignor Corporation). On May 31, 1991, the
Partnership issued 803,454.56 units of limited partnership interest (the
"Units") to 909 investors. Included in the 803,454.56 units are 7,293.56 bonus
units. The Partnership has one General Partner, AFG Leasing VI Incorporated, a
Massachusetts corporation formed in 1990 and an affiliate of Equis Financial
Group Limited Partnership (formerly known as American Finance Group), a
Massachusetts limited partnership ("EFG" or the "Manager"). The General Partner
is not required to make any other capital contributions except as may be
required under the Uniform Act and Section 6.1(b) of the Amended and Restated
Agreement and Certificate of Limited Partnership (the "Restated Agreement, as
amended").
 
    (b)  Financial Information About Industry Segments
 
    The Partnership is engaged in only one industry segment: the business of
acquiring capital equipment and leasing the equipment to creditworthy lessees on
a full payout or operating lease basis. Full payout leases are those in which
aggregate undiscounted, noncancellable rents equal or exceed the acquisition
cost of the leased equipment. Operating leases are those in which the aggregate
undiscounted, noncancellable rental payments are less than the acquisition cost
of the leased equipment. Industry segment data is not applicable.
 
    (c)  Narrative Description of Business
 
    The Partnership was organized to acquire a diversified portfolio of capital
equipment subject to various full payout and operating leases and to lease the
equipment to third parties as income-producing investments. More specifically,
the Partnership's primary investment objectives were to acquire and lease
equipment that would:
 
    1.  Generate quarterly cash distributions;
 
    2.  Preserve and protect Partnership capital; and
 
    3.  Maintain substantial residual value for ultimate sale.
 
    The Partnership has the additional objective of providing certain federal
income tax benefits.
 
    The Closing Date of the Offering of Units of the Partnership was May 31,
1991. Significant operations commenced coincident with the Partnership's initial
purchase of equipment and the associated lease commitments on May 31, 1991. The
acquisition of the equipment and its associated leases is described in Note 3 to
the financial statements included in Item 14, herein. The Restated Agreement, as
amended, provides that the Partnership will terminate no later than December 31,
2002. However, the Partnership is a Nominal Defendant in a Class Action Lawsuit,
the outcome of which could significantly alter the nature of the Partnership's
organization and its future business operations. See Note 8 to the accompanying
financial statements.
 
    The Partnership has no employees; however, it is managed pursuant to a
Management Agreement with EFG or one of its affiliates. The Manager's role,
among other things, is to (i) evaluate, select, negotiate, and consummate the
acquisition of equipment, (ii) manage the leasing, re-leasing, financing, and
refinancing of equipment, and (iii) arrange the resale of equipment. The Manager
is compensated for
 
                                       3
<PAGE>
such services as provided for in the Restated Agreement, as amended, described
in Item 13 herein, and in Note 5 to the financial statements included in Item
14, herein.
 
    The Partnership's investment in equipment is, and will continue to be,
subject to various risks, including physical deterioration, technological
obsolescence and defaults by lessees. A principal business risk of owning and
leasing equipment is the possibility that aggregate lease revenues and equipment
sale proceeds will be insufficient to provide an acceptable rate of return on
invested capital after payment of all debt service costs and operating expenses.
In addition, the leasing industry is very competitive. The Partnership is
subject to considerable competition when equipment is re-leased or sold at the
expiration of primary lease terms. The Partnership must compete with lease
programs offered directly by manufacturers and other equipment leasing
companies, including limited partnerships and trusts organized and managed
similarly to the Partnership, and including other EFG-sponsored partnerships and
trusts, which may seek to re-lease or sell equipment within their own portfolios
to the same customers as the Partnership. Many competitors have greater
financial resources and more experience than the Partnership, the General
Partner and the Manager. In addition, default by a lessee under a lease may
cause equipment to be returned to the Partnership at a time when the General
Partner or the Manager is unable to arrange for the re-lease or sale of such
equipment. This could result in the loss of anticipated revenue.
 
    Revenue from major individual lessees which accounted for 10% or more of
lease revenue during the years ended December 31, 1998, 1997 and 1996 is
incorporated herein by reference to Note 2 to the financial statements in the
1998 Annual Report. Refer to Item 14(a)(3) for lease agreements filed with the
Securities and Exchange Commission.
 
    EFG is a Massachusetts limited partnership formerly known as American
Finance Group ("AFG"). AFG was established in 1988 as a Massachusetts general
partnership and succeeded American Finance Group, Inc., a Massachusetts
corporation organized in 1980. EFG and its subsidiaries (collectively, the
"Company") are engaged in various aspects of the equipment leasing business,
including EFG's role as Manager or Advisor to the Partnership and several other
direct-participation equipment leasing programs sponsored or co-sponsored by EFG
(the "Other Investment Programs"). The Company arranges to broker or originate
equipment leases, acts as remarketing agent and asset manager, and provides
leasing support services, such as billing, collecting, and asset tracking.
 
    The general partner of EFG, with a 1% controlling interest, is Equis
Corporation, a Massachusetts corporation owned and controlled entirely by Gary
D. Engle, its President, Chief Executive Officer and sole Director. Equis
Corporation also owns a controlling 1% general partner interest in EFG's 99%
limited partner, GDE Acquisition Limited Partnership ("GDE LP"). Mr. Engle
established Equis Corporation and GDE LP in December 1994 for the sole purpose
of acquiring the business of AFG.
 
    In January 1996, the Company sold certain assets of AFG relating primarily
to the business of originating new leases, and the name "American Finance
Group," and its acronym to a third party. AFG changed its name to Equis
Financial Group Limited Partnership after the sale was concluded. Pursuant to
terms of the sale agreements, EFG specifically reserved the rights to continue
using the name American Finance Group and its acronym in connection with the
Partnership and the Other Investment Programs and to continue managing all
assets owned by the Partnership and the Other Investment Programs.
 
    (d)  Financial Information About Foreign and Domestic Operations and Export
Sales
 
    Not applicable.
 
                                       4
<PAGE>
ITEM 2. PROPERTIES.
 
    Incorporated herein by reference to Note 3 to the financial statements in
the 1998 Annual Report.
 
ITEM 3. LEGAL PROCEEDINGS.
 
    Incorporated herein by reference to Note 8 to the financial statements in
the 1998 Annual Report.
 
ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.
 
    None.
 
                                       5
<PAGE>
PART II
 
ITEM 5. MARKET FOR THE PARTNERSHIP'S SECURITIES AND RELATED SECURITY HOLDER
  MATTERS.
 
    (a)  Market Information
 
    There is no public market for the resale of the Units and it is not
anticipated that a public market for resale of the Units will develop.
 
    (b)  Approximate Number of Security Holders
 
    At December 31, 1998, there were 863 record holders in the Partnership.
 
    (c)  Dividend History and Restrictions
 
    Pursuant to Article VI of the Restated Agreement, as amended, the amount of
cash distributions to be declared and paid to the Partners is determined on a
quarterly basis. Each quarter's distribution may vary in amount and is made 95%
to the Limited Partners and 5% to the General Partner. Generally, cash
distributions are paid within 30 days after the completion of each calendar
quarter.
 
    Distributions in 1998 and 1997 were as follows:
 
<TABLE>
<CAPTION>
                                                                                            GENERAL     LIMITED
                                                                                TOTAL       PARTNER     PARTNERS
                                                                             ------------  ---------  ------------
<S>                                                                          <C>           <C>        <C>
Total 1998 distributions...................................................  $    634,306  $  31,716  $    602,590
Total 1997 distributions...................................................       792,883     39,644       753,239
                                                                             ------------  ---------  ------------
      Total................................................................  $  1,427,189  $  71,360  $  1,355,829
                                                                             ------------  ---------  ------------
                                                                             ------------  ---------  ------------
</TABLE>
 
    Distributions payable were $158,577 at both December 31, 1998 and 1997.
 
    There are no formal restrictions under the Restated Agreement, as amended,
that materially limit the Partnership's ability to pay cash distributions,
except that the General Partner may suspend or limit cash distributions to
ensure that the Partnership maintains sufficient working capital reserves to
cover, among other things, operating costs and potential expenditures, such as
refurbishment costs to remarket equipment upon lease expiration. Liquidity is
especially important as the Partnership matures and sells equipment, because the
remaining equipment base consists of fewer revenue-producing assets that are
available to cover prospective cash disbursements. Insufficient liquidity could
inhibit the Partnership's ability to sustain its operations or maximize the
realization of proceeds from remarketing its remaining assets. In particular,
the Partnership must contemplate the potential liquidity risks associated with
its investment in commercial jet aircraft. The management and remarketing of
aircraft can involve, among other things, significant costs and lengthy
remarketing initiatives.
 
    Although the Partnership's lessees are required to maintain the aircraft
during the period of lease contract, repair, maintenance, and/or refurbishment
costs at lease expiration can be substantial. For example, an aircraft that is
returned to the Partnership meeting minimum airworthiness standards, such as
flight hours or engine cycles, nonetheless may require heavy maintenance in
order to bring its engines, airframe and other hardware up to standards that
will permit its prospective use in commercial air transportation. Individually,
these repairs can cost in excess of $1 million and, collectively, they could
require the disbursement of several million dollars, depending upon the extent
of refurbishment. In addition, the Partnership's equipment portfolio includes an
interest in three Stage 2 aircraft having scheduled lease expiration dates of
December 31, 1999. These aircraft are prohibited from operating in the United
States after December 31, 1999 unless they are retro-fitted with hush-kits to
meet Stage 3 noise regulations promulgated by the Federal Aviation
Administration. The cost to hush-kit an aircraft, such as the Partnership's
Boeing 737s, can approach $2 million. Although the Partnership is not required
to retro-fit its aircraft with hush-kits, insufficient liquidity could
jeopardize the re-marketing of these aircraft and risk their disposal at a
depressed value at a time when a better economic return would be realized
 
                                       6
<PAGE>
from refurbishing the aircraft and re-leasing them to another user.
Collectively, the aggregation of the Partnership's potential liquidity needs
related to aircraft and other working capital requirements could be significant.
Accordingly, the General Partner has maintained significant cash reserves within
the Partnership in order to minimize the risk of a liquidity shortage,
particularly in connection with the Partnership's aircraft interests.
 
    Finally, the Partnership is a Nominal Defendant in a Class Action Lawsuit
described in Note 8 to the accompanying financial statements. A preliminary
settlement agreement will allow the Partnership to invest in new equipment or
other activities, subject to certain limitations, effective March 22, 1999. To
the extent that the Partnership continues to own aircraft investments that could
require capital reserves, the General Partner does not anticipate that the
Partnership will invest in new assets, regardless of its authority to do so.
Until the Class Action Lawsuit is adjudicated, the General Partner does not
expect that the level of future quarterly cash distributions paid by the
Partnership will be increased above amounts paid in the fourth quarter of 1998.
In addition, the proposed settlement, if effected, will materially change the
future organizational structure and business interests of the Partnership, as
well as its cash distribution policies. See Note 8 to the accompanying financial
statements.
 
    Cash distributions consist of Distributable Cash From Operations and
Distributable Cash From Sales or Refinancings.
 
    "Distributable Cash From Operations" means the net cash provided by the
Partnership's normal operations after general expenses and current liabilities
of the Partnership are paid, reduced by any reserves for working capital and
contingent liabilities to be funded from such cash, to the extent deemed
reasonable by the General Partner, and increased by any portion of such reserves
deemed by the General Partner not to be required for Partnership operations and
reduced by all accrued and unpaid Equipment Management Fees and, after Payout,
further reduced by all accrued and unpaid Subordinated Remarketing Fees.
Distributable Cash From Operations does not include any Distributable Cash From
Sales or Refinancings.
 
    "Distributable Cash From Sales or Refinancings" means Cash From Sales or
Refinancings as reduced by (i)(a) amounts realized from any loss or destruction
of equipment which the General Partner determines shall be reinvested in similar
equipment for the remainder of the original lease term of the lost or destroyed
equipment, or in isolated instances, in other equipment, if the General Partner
determines that investment of such proceeds will significantly improve the
diversity of the Partnership's equipment portfolio, and subject in either case
to satisfaction of all existing indebtedness secured by such equipment to the
extent deemed necessary or appropriate by the General Partner, or (b) the
proceeds from the sale of an interest in equipment pursuant to any agreement
governing a joint venture which the General Partner determines will be invested
in additional equipment or interests in equipment and which ultimately are so
reinvested and (ii) any accrued and unpaid Equipment Management Fees and, after
Payout, any accrued and unpaid Subordinated Remarketing Fees.
 
    "Cash From Sales or Refinancings" means cash received by the Partnership
from sale or refinancing transactions, as reduced by (i)(a) all debts and
liabilities of the Partnership required to be paid as a result of sale or
refinancing transactions, whether or not then due and payable (including any
liabilities on an item of equipment sold which are not assumed by the buyer and
any remarketing fees required to be paid to persons not affiliated with the
General Partner, but not including any Subordinated Remarketing Fees whether or
not then due and payable) and (b) general expenses and current liabilities of
the Partnership (other than any portion of the Equipment Management Fee which is
required to be accrued and the Subordinated Remarketing Fee) and (c) any
reserves for working capital and contingent liabilities funded from such cash to
the extent deemed reasonable by the General Partner and (ii) increased by any
portion of such reserves deemed by the General Partner not to be required for
Partnership operations. In the event the Partnership accepts a note in
connection with any sale or refinancing transaction, all payments subsequently
received in cash by the Partnership with respect to such note shall be included
in Cash From
 
                                       7
<PAGE>
Sales or Refinancings, regardless of the treatment of such payments by the
Partnership for tax or accounting purposes. If the Partnership receives purchase
money obligations in payment for equipment sold, which are secured by liens on
such equipment, the amount of such obligations shall not be included in Cash
From Sales or Refinancings until the obligations are fully satisfied.
 
    "Payout" is defined as the first time when the aggregate amount of all
distributions to the Limited Partners of Distributable Cash From Operations and
Distributable Cash From Sales or Refinancings equals the aggregate amount of the
Limited Partners' original capital contributions plus a cumulative annual
distribution of 11% (compounded quarterly and calculated beginning with the last
day of the month of the Partnership's Closing Date) on their aggregate
unreturned capital contributions. For purposes of this definition, capital
contributions shall be deemed to have been returned only to the extent that
distributions of cash to the Limited Partners exceed the amount required to
satisfy the cumulative annual distribution of 11% (compounded quarterly) on the
Limited Partners' aggregate unreturned capital contributions, such calculation
to be based on the aggregate unreturned capital contributions outstanding on the
first day of each fiscal quarter.
 
ITEM 6. SELECTED FINANCIAL DATA.
 
    Incorporated herein by reference to the section entitled "Selected Financial
Data" in the 1998 Annual Report.
 
ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
  OF OPERATIONS.
 
    Incorporated herein by reference to the section entitled "Management's
Discussion and Analysis of Financial Condition and Results of Operations" in the
1998 Annual Report.
 
ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA.
 
    Incorporated herein by reference to the financial statements and
supplementary data included in the 1998 Annual Report.
 
ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
  FINANCIAL DISCLOSURE.
 
    None.
 
                                       8
<PAGE>
PART III
 
ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE PARTNERSHIP.
 
    (a-b) Identification of Directors and Executive Officers
 
    The Partnership has no Directors or Officers. As indicated in Item 1 of this
report, AFG Leasing VI Incorporated is the sole General Partner of the
Partnership. Under the Restated Agreement, as amended, the General Partner is
solely responsible for the operation of the Partnership's properties. The
Limited Partners have no right to participate in the control of the
Partnership's general operations, but they do have certain voting rights, as
described in Item 12 herein. The names, titles and ages of the Directors and
Executive Officers of the General Partner as of March 15, 1999 are as follows:
 
DIRECTORS AND EXECUTIVE OFFICERS
  OF THE GENERAL PARTNER (SEE ITEM 13)
 
<TABLE>
<CAPTION>
NAME                                                      TITLE                          AGE              TERM
------------------------------------  ---------------------------------------------      ---      ---------------------
<S>                                   <C>                                            <C>          <C>
 
Geoffrey A. MacDonald                 Chairman and a member of the Executive                      Until a successor is
                                      Committee of EFG and President and a Director               duly elected and
                                      of the General Partner                                 50   qualified
 
Gary D. Engle                         President and Chief Executive Officer and
                                      member of the Executive Committee of EFG               50
 
Gary M. Romano                        Executive Vice President and Chief Operating
                                      Officer of EFG and Clerk of the General
                                      Partner                                                39
 
James A. Coyne                        Executive Vice President of EFG                        38
 
Michael J. Butterfield                Senior Vice President, Finance and Treasurer
                                      of EFG and Treasurer of the General Partner            39
 
Sandra L. Simonsen                    Senior Vice President, Information Systems of
                                      EFG                                                    48
 
Gail D. Ofgant                        Senior Vice President, Lease Operations of
                                      EFG                                                    33
</TABLE>
 
    (c)  Identification of Certain Significant Persons
 
    None.
 
    (d)  Family Relationship
 
    No family relationship exists among any of the foregoing Partners, Directors
or Executive Officers.
 
    (e)  Business Experience
 
    Mr. MacDonald, age 50, is a co-founder, Chairman and a member of the
Executive Committee of EFG and President and a Director of the General Partner.
Mr. MacDonald was also a co-founder, Director, and Senior Vice President of
EFG's predecessor corporation from 1980 to 1988. Mr. MacDonald is President of
American Finance Group Securities Corp. and a limited partner in Atlantic
Acquisition Limited Partnership ("AALP") and Old North Capital Limited
Partnership ("ONC"). Prior to co-founding
 
                                       9
<PAGE>
EFG's predecessors, Mr. MacDonald held various executive and management
positions in the leasing and pharmaceutical industries. Mr. MacDonald holds a
M.B.A. from Boston College and a B.A. degree from the University of
Massachusetts (Amherst).
 
    Mr. Engle, age 50, is President and Chief Executive Officer of EFG and sole
shareholder and Director of its general partner, Equis Corporation and a member
of the Executive Committee of EFG and President of AFG Realty Corporation. Mr.
Engle joined EFG in 1990 as Executive Vice President and acquired control of EFG
and its subsidiaries in December 1994. Mr. Engle is Vice President and a
Director of certain of EFG's subsidiaries and affiliates, a limited partner in
AALP and ONC and controls the general partners of AALP and ONC. Mr. Engle is
also Chairman, Chief Executive Officer, and a member of the Board of Directors
of Semele Group, Inc. ("Semele"). From 1987 to 1990, Mr. Engle was a principal
and co-founder of Cobb Partners Development, Inc., a real estate and mortgage
banking company. From 1980 to 1987, Mr. Engle was Senior Vice President and
Chief Financial Officer of Arvida Disney Company, a large-scale community
development company owned by Walt Disney Company. Prior to 1980, Mr. Engle
served in various management consulting and institutional brokerage capacities.
Mr. Engle has a MBA from Harvard University and a BS degree from the University
of Massachusetts (Amherst).
 
    Mr. Romano, age 39, became Executive Vice President and Chief Operating
Officer of EFG, and Secretary of Equis Corporation in 1996 and is Secretary or
Clerk of several of EFG's subsidiaries and affiliates. Mr. Romano joined EFG in
November 1989, became Vice President and Controller in April 1993 and Chief
Financial Officer in April 1995. Mr. Romano assumed his current position in
April 1996. Mr. Romano is also Vice President and Chief Financial Officer of
Semele. Prior to joining EFG, Mr. Romano was Assistant Controller for a
privately held real estate development and mortgage origination company that he
joined in 1987. Previously, Mr. Romano was an Audit Manager at Ernst & Whinney
(now Ernst & Young LLP), where he was employed from 1982 to 1986. Mr. Romano is
a Certified Public Accountant and holds a B.S. degree from Boston College.
 
    Mr. Coyne, age 38, is Executive Vice President, Capital Markets of EFG and
President, Chief Operating Officer and a member of the Board of Directors of
Semele. Mr. Coyne joined EFG in 1989, remained until May 1993, and rejoined EFG
in November 1994. In September 1997, Mr. Coyne was appointed Executive Vice
President of EFG. Mr. Coyne is a limited partner in AALP and ONC. From May 1993
through November 1994, he was employed by the Raymond Company, a private
investment firm, where he was responsible for financing corporate and real
estate acquisitions. From 1985 through 1989, Mr. Coyne was affiliated with a
real estate investment company and an equipment leasing company. Prior to 1985,
he was with the accounting firm of Ernst & Whinney (now Ernst & Young LLP). He
has a BS in Business Administration from John Carroll University, a Masters
Degree in Accounting from Case Western Reserve University and is a Certified
Public Accountant.
 
    Mr. Butterfield, age 39, is Senior Vice President, Finance and Treasurer of
EFG and certain of its affiliates and is Treasurer of the General Partner and
Semele. Mr. Butterfield joined EFG in June 1992, became Vice President, Finance
and Treasurer of EFG and certain of its affiliates in April 1996 and was
promoted to Senior Vice President, Finance and Treasurer of EFG and certain of
its affiliates in July 1998. Prior to joining EFG, Mr. Butterfield was an Audit
Manager with Ernst & Young LLP, which he joined in 1987. Mr. Butterfield was
employed in public accounting and industry positions in New Zealand and London
(UK) prior to coming to the United States in 1987. Mr. Butterfield attained his
Associate Chartered Accountant (A.C.A.) professional qualification in New
Zealand and has completed his CPA requirements in the United States. He holds a
Bachelor of Commerce degree from the University of Otago, Dunedin, New Zealand.
 
    Ms. Simonsen, age 48, joined EFG in February 1990 and was promoted to Senior
Vice President, Information Systems of EFG in April 1996. Prior to joining EFG,
Ms. Simonsen was Vice President, Information Systems with Investors Mortgage
Insurance Company, which she joined in 1973.
 
                                       10
<PAGE>
Ms. Simonsen provided systems consulting for a subsidiary of American
International Group and authored a software program published by IBM. Ms.
Simonsen holds a BA degree from Wilson College.
 
    Ms. Ofgant, age 33, is Senior Vice President, Lease Operations of EFG and
certain of its affiliates. Ms. Ofgant joined EFG in July 1989, was promoted to
Manager Lease Operations in April 1994, and became Vice President of Lease
Operations in April 1996. In July 1998, Ms. Ofgant was promoted to Senior Vice
President of Lease Operations. Prior to joining EFG, Ms. Ofgant was employed by
Security Pacific National Trust Company. Ms. Ofgant holds a BS degree in Finance
from Providence College.
 
    (f)  Involvement in Certain Legal Proceedings
 
    None.
 
    (g)  Promoters and Control Persons
 
    See Item 10 (a-b) above.
 
ITEM 11. EXECUTIVE COMPENSATION.
 
    (a)  Cash Compensation
 
    Currently, the Partnership has no employees. However, under the terms of the
Restated Agreement, as amended, the Partnership is obligated to pay all costs of
personnel employed full or part-time by the Partnership, including officers or
employees of the General Partner or its Affiliates. There is no plan at the
present time to make any officers or employees of the General Partner or its
Affiliates employees of the Partnership. The Partnership has not paid and does
not propose to pay any options, warrants or rights to the officers or employees
of the General Partner or its Affiliates.
 
    (b)  Compensation Pursuant to Plans
 
    None.
 
    (c)  Other Compensation
 
    Although the Partnership has no employees, as discussed in Item 11(a),
pursuant to Section 9.4(c) of the Restated Agreement, as amended, the
Partnership incurs a monthly charge for personnel costs of the Manager for
persons engaged in providing administrative services to the Partnership. A
description of the remuneration paid by the Partnership to the Manager for such
services is included in Item 13, herein and in Note 5 to the financial
statements included in Item 14, herein.
 
    (d)  Compensation of Directors
 
    None.
 
    (e)  Termination of Employment and Change of Control Arrangement
 
    There exists no remuneration plan or arrangement with the General Partner or
its Affiliates which results or may result from their resignation, retirement or
any other termination.
 
ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT.
 
    By virtue of its organization as a limited partnership, the Partnership has
outstanding no securities possessing traditional voting rights. However, as
provided in Section 10.2(a) of the Restated Agreement, as amended (subject to
Sections 10.2(b) and 10.3), a majority interest of the Limited Partners has
voting rights with respect to:
 
1.  Amendment of the Restated Agreement;
 
2.  Termination of the Partnership;
 
                                       11
<PAGE>
3.  Removal of the General Partner; and
 
4.  Approval or disapproval of the sale of all, or substantially all, of the
    assets of the Partnership (except in the orderly liquidation of the
    Partnership upon its termination and dissolution).
 
    As of March 1, 1999, the following person or group owns beneficially more
than 5% of the Partnership's 803,454.56 outstanding Units:
 
<TABLE>
<CAPTION>
                                         NAME AND                          AMOUNT          PERCENT
        TITLE                           ADDRESS OF                     OF BENEFICIAL         OF
       OF CLASS                      BENEFICIAL OWNER                    OWNERSHIP          CLASS
----------------------  -------------------------------------------  ------------------  -----------
<S>                     <C>                                          <C>                 <C>
Units Representing      Old North Capital Limited Partnership
Limited Partnership     88 Broad Street                              124,065.23 Units         15.44%
Interests               Boston, MA 02110
</TABLE>
 
    Messrs. Engle, MacDonald and Coyne have ownership interests in ONC. The
general partner of ONC is controlled by Gary Engle. See Items 10 and 13 of this
report.
 
    The ownership and organization of EFG is described in Item 1 of this report.
 
ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS.
 
    The General Partner of the Partnership is AFG Leasing VI Incorporated, an
affiliate of EFG.
 
    (a)  Transactions with Management and Others
 
    All operating expenses incurred by the Partnership are paid by EFG on behalf
of the Partnership and EFG is reimbursed at its actual cost for such
expenditures. Fees and other costs incurred during the years ended December 31,
1998, 1997 and 1996, which were paid or accrued by the Partnership to EFG or its
Affiliates, are as follows:
 
<TABLE>
<CAPTION>
                                                                                  1998        1997        1996
                                                                               ----------  ----------  ----------
<S>                                                                            <C>         <C>         <C>
Equipment management fees....................................................  $  113,260  $  166,417  $  140,227
Administrative charges.......................................................      68,052      63,870      40,295
Reimbursable operating expenses due to third parties.........................     386,856     136,800     151,051
                                                                               ----------  ----------  ----------
      Total..................................................................  $  586,168  $  367,087  $  331,573
                                                                               ----------  ----------  ----------
                                                                               ----------  ----------  ----------
</TABLE>
 
    As provided under the terms of the Management Agreement, EFG is compensated
for its services to the Partnership. Such services include acquisition and
management of equipment. For acquisition services, EFG is compensated by an
amount equal to 2.23% of Equipment Base Price paid by the Partnership. For
management services, EFG is compensated by an amount equal to 5% of gross
operating lease rental revenue and 2% of gross full payout lease rental revenue
received by the Partnership. Both acquisition and management fees are subject to
certain limitations defined in the Management Agreement.
 
    Administrative charges represent amounts owed to EFG, pursuant to Section
9.4(c) of the Restated Agreement, as amended, for persons employed by EFG who
are engaged in providing administrative services to the Partnership.
Reimbursable operating expenses due to third parties represent costs paid by EFG
on behalf of the Partnership which are reimbursed to EFG at actual cost.
 
    All equipment was purchased from EFG, one of its affiliates or from
third-party sellers. The Partnership's acquisition cost was determined by the
method described in Note 2 to the financial statements included in Item 14,
herein.
 
    During 1997, the Partnership and certain affiliated investment programs
sponsored by EFG exchanged their ownership interests in certain vessels for
aggregate consideration of $11,565,375. The Partnership's share of such
consideration was $1,203,062 consisting of common stock in Semele valued at
 
                                       12
<PAGE>
$313,146, a note receivable from Semele of $459,729 and cash of $430,187. For
further discussion, see Note 4, "Investment Securities--Affiliate / Note
Receivable--Affiliate to the financial statements included in Item 14 herein and
Item 10.
 
    All rents and proceeds from the sale of equipment are paid directly to
either EFG or to a lender. EFG temporarily deposits collected funds in a
separate interest-bearing escrow account prior to remittance to the Partnership.
At December 31, 1998, the Partnership was owed $50,767 by EFG for such funds and
the interest thereon. These funds were remitted to the Partnership in January
1999.
 
    During 1996, the Partnership received payment in full from EFG of a note and
accrued interest thereon which was beneficially assigned to the Partnership in
1994 by a former affiliate of AFG as partial consideration for the exchange of
certain intermodal cargo containers.
 
    Certain affiliates of the General Partner own Units in the Partnership as
follows:
 
<TABLE>
<CAPTION>
                                                                NUMBER OF     PERCENT OF TOTAL
AFFILIATE                                                      UNITS OWNED    OUTSTANDING UNITS
-------------------------------------------------------------  ------------  -------------------
<S>                                                            <C>           <C>
Atlantic Acquisition Limited Partnership.....................       16,536             2.06%
Old North Capital Limited Partnership........................   124,065.23            15.44%
</TABLE>
 
    Atlantic Acquisition Limited Partnership ("AALP") and Old North Capital
Limited Partnership ("ONC") are both Massachusetts Limited Partnerships formed
in 1995 and affiliates of EFG. The general partners of AALP and ONC are
controlled by Gary Engle. In addition, the limited partnership interests of ONC
are owned by Semele Group, Inc. ("Semele"). Gary D. Engle is Chairman and CEO of
Semele.
 
    (b)  Certain Business Relationships
 
    None.
 
    (c)  Indebtedness of Management to the Partnership
 
    None.
 
    (d)  Transactions with Promoters
 
    See Item 13(a) above.
 
                                       13
<PAGE>
PART IV
 
ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K.
 
<TABLE>
<S>        <C>        <C>                                                                              <C>
(a)        Documents filed as part of this report:
 
           (1)        Financial Statements:
 
                      Report of Independent Auditors.................................................          *
 
                      Statement of Financial Position at December 31, 1998 and 1997..................          *
 
                      Statement of Operations for the years ended December 31, 1998, 1997 and 1996...          *
 
                      Statement of Changes in Partners' Capital for the years ended December 31,
                      1998, 1997 and 1996............................................................          *
 
                      Statement of Cash Flows for the years ended December 31, 1998, 1997 and 1996...          *
 
                      Notes to the Financial Statements..............................................          *
 
           (2)        Financial Statement Schedules:
 
                      None required.
 
           (3)        Exhibits:
 
                      Except as set forth below, all Exhibits to Form 10-K, as set forth in Item 601
                      of Regulation S-K, are not applicable.
</TABLE>
 
<TABLE>
<CAPTION>
   EXHIBIT
   NUMBER
-------------
<C>            <S>
 
          4    Amended and Restated Agreement and Certificate of Limited Partnership included as Exhibit A to the
               Prospectus, which is included in Registration Statement on Form S-1 (No. 33-35148).
 
         13    The 1998 Annual Report to security holders, a copy of which is furnished for the information of the
               Securities and Exchange Commission. Such Report, except for those portions thereof which are
               incorporated herein by reference, is not deemed "filed" with the Commission.
 
         23    Consent of Independent Auditors.
 
         99(a) Lease agreement with Gearbulk Shipowning Ltd. was filed in the Registrant's Annual Report on Form10-K
               for the year ended December 31, 1995 as Exhibit 99 (c) and is incorporated herein by reference.
 
         99(b) Lease agreement with General Motors Corporation was filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1996 as Exhibit 99 (d) and is incorporated herein by reference.
 
         99(c) Lease agreement with Southwest Airlines, Inc. was filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1996 as Exhibit 99 (e) and is incorporated herein by reference.
</TABLE>
 
------------------------
 
*   Incorporated herein by reference to the appropriate portion of the 1998
    Annual Report to security holders for the year ended December 31, 1998 (see
    Part II).
 
                                       14
<PAGE>
<TABLE>
<CAPTION>
   EXHIBIT
   NUMBER
-------------
<C>            <S>
         99(d) Lease agreement with Southwest Airlines, Inc. was filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1996 as Exhibit 99 (f) and is incorporated herein by reference.
 
         99(e) Lease agreement with Southwest Airlines, Inc. was filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1996 as Exhibit 99 (g) and is incorporated herein by reference.
 
         99(f) Lease agreement with Finnair OY was filed in the Registrant's Annual Report on Form 10-K for the year
               ended December 31, 1997 as Exhibit 99 (h) and is incorporated herein by reference.
 
         99(g) Lease agreement with Finnair OY was filed in the Registrant's Annual Report on Form 10-K for the year
               ended December 31, 1997 as Exhibit 99 (i) and is incorporated herein by reference.
 
         99(h) Lease agreement with The Helen Mining Company was filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1997 as Exhibit 99 (j) and is incorporated herein by reference.
 
         99(i) Lease agreement with Reno Air, Inc. is filed in the Registrant's Annual Report on Form 10-K for the
               year ended December 31, 1998 and is included herein.
 
         99(j) Lease agreement with Trans Ocean Corporation, Inc. is filed in the Registrant's Annual Report on Form
               10-K for the year ended December 31, 1998 and is included herein.
</TABLE>
 
(b)  Reports on Form 8-K
 
    None.
 
                                       15
<PAGE>
                                   SIGNATURES
 
    Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed below on behalf of the registrant and in the capacity and
on the date indicated.
 
<TABLE>
<S>                             <C>  <C>
                                AMERICAN INCOME FUND I-C,
                                a Massachusetts Limited Partnership
 
                                By:  AFG Leasing VI Incorporated,
                                     -----------------------------------------
                                     a Massachusetts corporation and the
                                     General Partner of the Registrant.
</TABLE>
 
<TABLE>
<S>        <C>                                        <C>        <C>
By:        /s/ GEOFFREY A. MACDONALD                  By:        /s/ GARY D. ENGLE
           ----------------------------------------              ----------------------------------------
           Geoffrey A. MacDonald                                 Gary D. Engle
           CHAIRMAN AND A MEMBER OF THE EXECUTIVE                PRESIDENT AND CHIEF EXECUTIVE OFFICER AND
           COMMITTEE OF EFG AND PRESIDENT AND A                  A MEMBER OF THE EXECUTIVE COMMITTEE OF
           DIRECTOR OF THE GENERAL PARTNER                       EFG (PRINCIPAL EXECUTIVE OFFICER)
 
Date: March 31, 1999                                  Date: March 31, 1999
 
By:        /s/ GARY M. ROMANO                         By:        /s/ MICHAEL J. BUTTERFIELD
           ----------------------------------------              ----------------------------------------
           Gary M. Romano                                        Michael J. Butterfield
           EXECUTIVE VICE PRESIDENT AND CHIEF                    SENIOR VICE PRESIDENT, FINANCE AND
           OPERATING OFFICER OF EFG AND CLERK OF THE             TREASURER OF EFG AND TREASURER OF THE
           GENERAL PARTNER (PRINCIPAL FINANCIAL                  GENERAL PARTNER (PRINCIPAL ACCOUNTING
           OFFICER)                                              OFFICER)
 
Date: March 31, 1999                                  Date: March 31, 1999
</TABLE>
 
                                       16