UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

AIRCASTLE LIMITED

(Name of Issuer)

Common Shares, par value $0.01 per share

(Title of Class of Securities)

G0129K104

(CUSIP Number)

Marubeni Corporation

4-2 Ohtemachi 1-Chome

Chiyoda-Ku, Tokyo, 100-8088 Japan

Attention: General Manager

Telephone: 81 3 3282 9621

(Name, address and telephone number of person authorized to receive notices and communications on behalf of filing persons)

October 2, 2013

(Date of event which requires filing of this statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

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Explanatory Statement

This Amendment No. 4 (“Amendment No. 4”) amends and supplements the statement on Schedule 13D filed by Marubeni Corporation (“Marubeni”) on June 17, 2013 (the “Schedule 13D”), as amended by Amendment No. 1 filed on July 12, 2013, Amendment No. 2 filed on August 9, 2013 and Amendment No. 3 filed on September 3, 2013 by Marubeni, Marubeni Aviation Corporation (“MAC”) and Marubeni Aviation Holding Coöperatief U.A. (“MHC” and together with Marubeni and MAC, the “Reporting Persons”) relating to the common shares, par value $0.01 per share (the “Common Shares”), of Aircastle Limited, a Bermuda exempted company (the “Issuer”). Unless otherwise indicated, each capitalized term used but not defined herein has the meaning assigned to such term in the Schedule 13D as previously amended.

This Schedule 13D, as amended, is being filed jointly by the Reporting Persons as described Item 2 of the Schedule 13D and Amendment No.1 thereto, incorporated herein by reference.

Item 5 is hereby supplemented by the addition of the following:

As of October 2, 2013, MHC has purchased an aggregate of 1,647,100 Common Shares pursuant to the Stock Purchase Plan Engagement Agreement between MHC and Merrill Lynch, Pierce, Fenner & Smith Incorporated dated August 7, 2013. Details regarding these purchases are set forth on Exhibit 7.6 and are incorporated herein by reference. After giving effect to these purchases, MHC owns an aggregate of 13,967,100 Common Shares. Based on the 80,780,299 Common Shares reported to be outstanding in the Issuer’s Quarterly Report on Form 10-Q filed with the Commission on August 6, 2013, the number of Common Shares beneficially owned by the Reporting Persons as of August 29, 2013 represents approximately 17.29% of the Common Shares outstanding.

Item 7 is hereby amended to add the following:

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SIGNATURE

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.

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Exhibit 7.6

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