As filed with the Securities and Exchange Commission on May 19, 2011

Registration No. 333-169474

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

AMENDMENT NO. 8 TO

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

SPIRIT AIRLINES, INC.

(Exact name of registrant as specified in its charter)

2800 Executive Way

Miramar, Florida 33025

(954) 447-7920

(Address, including zip code, and telephone number, including

area code, of registrant’s principal executive offices)

B. Ben Baldanza

President and Chief Executive Officer

Spirit Airlines, Inc.

2800 Executive Way

Miramar, Florida 33025

(954) 447-7920

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies To:

Approximate date of commencement of the proposed sale to the public:

As soon as practicable after this Registration Statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.    ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

EXPLANATORY NOTE

This Amendment No. 8 to Form S-1 Registration Statement (Registration No. 333-169474) of Spirit Airlines, Inc. is being filed solely to include updated exhibits to the Registration Statement. Accordingly, Part I, the form of prospectus, has been omitted from this filing.

PART II

The following table sets forth the costs and expenses, other than underwriting discounts, payable in connection with the sale and distribution of the securities being registered. All amounts are estimated except the SEC registration fee and the FINRA filing fee. All the expenses below will be paid by Spirit Airlines.

Spirit Airlines, Inc. is a Delaware corporation. Section 145 of the Delaware General Corporation Law authorizes a court to award, or a corporation’s board of directors to grant, indemnity to directors and officers in terms sufficiently broad to permit such indemnification under certain circumstances for liabilities, including reimbursement for expenses incurred, arising under the Securities Act of 1933, as amended. Our amended and restated certificate of incorporation to be in effect upon the completion of this offering permits indemnification of our directors, officers and employees and other agents, in each case to the maximum extent permitted by the Delaware General Corporation Law, and our amended and restated bylaws to be in effect upon the completion of this offering provide for indemnification of our directors, officers, employees and other agents to the maximum extent permitted by the Delaware General Corporation Law. In addition, we have entered into indemnification agreements with our directors, officers and some employees containing provisions which are in some respects broader than the specific indemnification provisions contained in the Delaware General Corporation Law. The indemnification agreements may require us, among other things, to indemnify our directors against certain liabilities that may arise by reason of their status or service as directors and to advance their expenses incurred as a result of any proceeding against them as to which they could be indemnified. Reference is also made to Section 8 of the underwriting agreement to be filed as Exhibit 1.1 hereto, which provides for indemnification by the underwriter of our officers and directors against certain liabilities.

During the last three years, we made sales of the following unregistered securities:

(1) On December 29, 2008, we issued an aggregate of $5.0 million of additional Tranche B Notes to investment funds managed by Oaktree and investment funds managed by Indigo;

(2) Pursuant to the Recapitalization Agreement, we will issue common stock in connection with the closing of this offering in exchange for:

II-1

(3) We have granted equity awards for an aggregate of 1,389,750 shares of our common stock to employees and directors under our 2005 Stock Plan.

The sales of the above securities in paragraph (1) were deemed to be exempt from registration under the Securities Act in reliance upon Section 4(2) of the Securities Act and in paragraph (2) were deemed to be exempt from registration under the Securities Act in reliance upon Sections 3(a)(9) and 4(2) of the Securities Act. The sales of the above securities in paragraph (3) was deemed to be exempt from registration under the Securities Act in reliance upon Rule 701 promulgated under Section 3(b) of the Securities Act as transactions by an issuer not involving any public offering or pursuant to benefit plans and contracts relating to compensation as provided under Rule 701. The recipients of the securities in each of these transactions represented their intentions to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof, and appropriate legends were placed upon the stock certificates issued in these transactions. All recipients had adequate access, through their relationships with us, to information about us.

There were no underwriters employed in connection with any of the transactions set forth in Item 15.

See the Exhibit Index beginning on page II-5, which follows the signature pages hereof and is incorporated herein by reference.

The undersigned registrant hereby undertakes that:

(1) for purposes of determining any liability under the Securities Act, the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective;

(2) for the purpose of determining any liability under the Securities Act, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof;

(3) for the purpose of determining liability of the registrant under the Securities Act to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the

II-2

following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii) the portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv) any other communication that is an offer in the offering made by the undersigned registrant to the purchaser; and

(4) the undersigned will provide to the underwriters at the closing specified in the underwriting agreement, certificates in such denominations and registered in such names as required by the underwriters to permit prompt delivery to each purchaser.

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the registrant pursuant to the provisions described in Item 14, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

II-3

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, we have duly caused this Amendment No. 8 to Registration Statement on Form S-1 to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Miramar, State of Florida, on the 19th day of May, 2011.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Amendment No. 8 to Registration Statement has been signed by the following persons in the capacities indicated below on May 19, 2011.

II-4

EXHIBIT INDEX

II-5

II-6

II-7