Exhibit 10.4 6-1162-GOC-044 March 21, 1997 CONTINENTAL AIRLINES, INC. 2929 Allen Parkway Houston, Texas 77019 Subject: Letter Agreement No. 6-1162-GOC-044 to Purchase Agreement No. 1783 - Application of Advance Payments Gentlemen: This Letter Agreement amends Purchase Agreement No. 1783 dated March 18, 1993 (the Agreement) between THE BOEING COMPANY (Boeing) and CONTINENTAL AIRLINES, INC. (Buyer) relating to Model 757-224 aircraft. All terms used herein and in the Agreement, and not defined herein, will have the same meaning as in the Agreement. If the foregoing accurately reflects your understanding of the matters treated herein, please indicate your acceptance by signing below. Boeing has received and is holding advance payments for Model 737 aircraft to be delivered to Buyer under Purchase Agreement No. 1951 (Advance Payments). In order to complete the delivery of Model 757 aircraft designated as Tab Block ND318, Manufacturer's serial number 27560, on March 21, 1997, (Aircraft ND318) and in consideration of Buyer's commitment to pay the balance due at the time of delivery, Boeing may apply [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.] of the Advance Payments against the balance due on Aircraft ND318. Buyer agrees to reimburse Boeing on March 24, 1997, the amount of [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.] plus interest on that amount for the period between March 21 and March 24, 1997, with the interest to be calculated as described in paragraph 5 of Letter Agreement 6-1162- WLJ-375R4. Very truly yours, THE BOEING COMPANY Original signed by: By Gunar O. Clem Its Attorney-In-Fact ACCEPTED AND AGREED TO this Date: March 21, 1997 CONTINENTAL AIRLINES, INC. Original signed by: By Jeffery M. Smisek Its Executive Vice President and General Counsel