UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G/A

Under the Securities Exchange Act of 1934

(Amendment No. 6)*

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO RULES 13d-1(b), (c) and (d) AND AMENDMENTS THERETO FILED

PURSUANT TO RULE 13(d)-2(b)

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

x Rule 13d-1(c)

¨ Rule 13d-1(d)

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

Page 1 of 12 Pages

Ste 111

Memphis, TN 38132

This Schedule 13G/A is filed on behalf of The Pabrai Investment Fund II, L.P., an Illinois limited partnership (“PIF2”), Pabrai Investment Fund 3, Ltd., a British Virgin Islands corporation (“PIF3”), Dalal Street, LLC, a California limited liability company (“Dalal Street”) and general partner of PIF2 and sole investment manager of PIF3, Harina Kapoor, and Mohnish Pabrai, managing member of Dalal Street and a shareholder and president of PIF3 (collectively, the “Reporting Persons”), pursuant to a Joint Reporting Agreement dated May 10, 2012, filed by the Reporting Persons as Exhibit A to this Schedule 13G/A.

1220 Roosevelt

Suite 200

Irvine, CA 92620-3667

PIF2 is an Illinois limited partnership. PIF3 is a British Virgin Islands corporation. Dalal Street is a California limited liability company. Mohnish Pabrai and Harina Kapoor are United States citizens.

(a) and (b).

This Schedule 13G/A shall not be construed as an admission that any Reporting Person is, either for purposes of Section 13(d) or 13(g) of the Exchange Act of 1934, as amended (the “Act”) or for other purposes, is the beneficial owner of any securities covered by this statement. By virtue of the relationships between and among (i) Dalal Street in its capacity as the General Partner and Investment Manager of PIF2 and PIF3, respectively,

(ii) Mohnish Pabrai, in his capacity as the managing member of Dalal Street and (iii) the other Reporting Persons, as further described in Item 2(a), each of the Reporting Persons may be deemed to be the beneficial owner of all or a portion of the shares of Common Stock held by the other Reporting Persons. Because of the relationships described in Item 2(a), the Reporting Persons may be deemed to constitute a “group” within the meaning of Rule 13d-5 under the Act, and as such, each member of the group would be deemed to beneficially own, in the aggregate, all the shares of Common Stock held by members of the group. The Reporting Persons disclaim membership in a group and disclaim beneficial ownership of any of the shares of Common Stock except as follows.

‡ All percentages in this table are based on the 19,127,691 shares of Common Stock of Pinnacle Airlines Corp. issued and outstanding as of November 1, 2011, as reported in the Form 10-Q for the quarterly period ended September 30, 2011 filed by Pinnacle Airlines Corp. with the Securities and Exchange Commission on November 4, 2011.

(c) Dalal Street and Mohnish Pabrai, in his capacity as managing member of Dalal Street have the shared power to vote or to direct the vote and the shared power to dispose or to direct the disposition of the shares of Common Stock set forth opposite the name of each of PIF2 and PIF3 in the table above. Dalal Street and Mohnish Pabrai disclaim beneficial ownership of any such shares of Common Stock except to the extent of their pecuniary interest therein, if any. Harina Kapoor, in her capacity as account holder, and Mohnish Pabrai, in his capacity as husband and advisor, have the shared power to vote or to direct the vote and the shared power to dispose or to direct the disposition of the shares of Common Stock held by Harina Kapoor, and Mohnish Pabrai disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any.

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 10, 2012

THE PABRAI INVESTMENT FUND II, L.P.

By: Dalal Street, LLC, Its General Partner

PABRAI INVESTMENT FUND 3, LTD.

DALAL STREET, LLC

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