1 EXHIBIT 99.6 BK ASSOCIATES, INC. 1295 Northern Boulevard Manhasset, New York 11030 (516) 365-6272 - Fax (516) 365-6287 April 30, 2000 Mr. Tom Ashe AerFi Group plc Aviation House Shannon, County Clare Ireland Dear Tom: In response to your request, BK Associates, Inc. is pleased to provide an update on our opinion regarding the current maintenance adjusted Base Value (BV) as well as the half-time BV as of April 30, 2000, of the aircraft (Aircraft) in the AerCo portfolio (Portfolio). Two months ago we also provided our opinion of the values of the Aircraft. This letter is, to some extent, an update of that appraisal. The Portfolio comprises 33 aircraft and our opinion on their current values is tabulated in the attached Figure 1. The values are expressed in millions of U.S. dollars. It should be understood that BK Associates has neither inspected the Aircraft nor their maintenance records, but has relied upon the information provided by you and in the BK Associates database which includes data on some of the Aircraft that was obtained for previous appraisals we have conducted on the Aircraft. The assumptions have been made that all Airworthiness Directives have been complied with; accident damage has not been incurred that would affect market values; and maintenance has been accomplished in accordance with a civil airworthiness authority's approved maintenance program and accepted industry standards. Deviations from these assumptions can change significantly our opinion regarding the Aircrafts' values. According to the International Society of Transport Aircraft Trading's (ISTAT) definition of base value, to which BK Associates subscribes, base value is the Appraiser's opinion of the underlying economic value of an aircraft in an open, unrestricted, stable market environment with a reasonable balance of supply and demand, and assumes full consideration of its "highest and best use". An aircraft's Base Value is founded in the historical trend of values and in the projection of value trends and presumes an arm's length, cash transaction between willing, able and knowledgeable parties, acting prudently, with an absence of duress and with a reasonable period of time available for marketing, which BK Associates considers to be 12 to 18 months. 2 Mr. Tom Ashe April 30, 2000 Page 2 As the definition suggests, Base Value is determined from historic and future value trends and is not influenced by current market conditions. It is often determined as a function of the original cost of the aircraft, technical characteristics of competing aircraft, and development of new models. For the most part, nothing has occurred since we last appraised the Portfolio that would suggest any changes to the base values. Thus, the half-time base values are generally slightly lower to account for the passage of time and further aging of the aircraft. The adjusted values could be considerably different since they are based on more recent data that you provided. This is especially so when heavy maintenance visits have occurred since the last appraisal. For those values given in Figure 1 that include adjustments to account for the current maintenance status, the adjustments are approximate, based on industry average costs, and normally would include an adjustment for the time remaining to a "C" check, time remaining to a "D" check, time remaining to landing gear overhaul and time remaining to a heavy shop visit on engines. Where the data indicated that a check, overhaul or shop visit was due, or in progress on March 31, 2000, we have assumed it has now been completed. BK Associates, Inc. has no present or contemplated future interest in the Aircraft, nor any interest that would preclude our making a fair and unbiased estimate. This appraisal represents the opinion of BK Associates, Inc. and reflects our best judgment based on the information available to us at the time of preparation and the time and budget constraints imposed by the client. It is not given as a recommendation, or as an inducement, for any financial transaction and further, BK Associates, Inc. assumes no responsibility or legal liability for any action taken or not taken by the addressee, or any other party, with regard to the appraised equipment. By accepting this appraisal, the addressee agrees that BK Associates, Inc. shall bear no such responsibility or legal liability. This appraisal is prepared for the use of the addressee and shall not be provided to other parties without the express consent of the addressee. Sincerely yours, BK ASSOCIATES, INC. /s/ John F. Keitz John F. Keitz JFK/kf President Attachment ISTAT Certified Senior Appraiser 3 FIGURE 1 AerCo PORTFOLIO CURRENT VALUES BASE VALUE # TYPE REGIST SERNUM DoM ENGINE 1/2 TIME MT. ADJ. -------- ------- ------ ------ ----------- -------- -------- 1 B757-2Y0 B-2831 26153 Aug-92 RB211-535E4 40.850 41.100 2 B737-3Y0 B-2539 26068 Jun-92 CFM56-3C1 24.300 25.350 3 A300B4-203 VT-EVD 240 May-83 CF6-50C2 13.050 14.500 4 B737-3Y0 EI-BZF 24465 Aug-89 CFM56-3B1 19.750 20.200 5 B737-3Y0 EI-BZJ 24677 Mar-90 CFM56-3B1 20.150 20.950 6 B737-48E HL7227 25764 Jun-92 CFM56-3C1 25.850 25.800 7 B737-48E HL7228 25765 Jul-92 CFM56-3C1 25.850 26.100 8 MD83 B28023 49952 Dec-91 JT8D-219 22.750 22.950 9 A320-211 EI-CTD 85 Feb-90 CFM56-5A1 22.600 23.750 10 B737-4Y0 EC-EVE 24685 May-90 CFM56-3C1 23.350 24.500 11 B767-3Y0ER EC-FCU 24999 Feb-91 PW4060 57.800 56.200 12 MD83 EC-FXY 49627 Apr-89 JT8D-219 19.850 19.500 13 MD83 EC-FCZ 49790 Oct-89 JT8D-219 20.400 20.050 14 B757-2Y0 G-OOOX 26158 Feb-93 RB211-535E4 41.900 41.650 15 A320-212 G-JGFW 299 Apr-92 CFM56-5A3 29.850 28.800 16 A320-231 G-YJBM 362 Nov-92 V2500-A1 30.100 29.900 17 B737-4Y0 G-OBMF 23868 Oct-88 CFM56-3C1 19.850 20.250 18 A320-212 G-MONW 391 Feb-93 CFM56-5A3 30.400 30.400 19 B737-3Y0 HA-LED 24909 Apr-91 CFM56-3C1 22.600 22.800 20 B737-4Y0 TC-AFJ 23979 Jan-89 CFM56-3C1 20.400 19.850 21 B737-3Y0 TC-SUP 24908 Mar-91 CFM56-3C1 22.600 23.900 22 B737-4Y0 TC-JDE 24904 Feb-91 CFM56-3C1 23.400 23.900 23 B737-4Y0 TC-JDZ 26066 Jun-92 CFM56-3C1 26.350 25.500 24 F100 PT-MRX 11341 Aug-91 TAY650 13.500 13.550 25 F100 PT-MQB 11350 Apr-92 TAY650 14.550 14.750 26 F100 PT-MRF 11351 Sep-91 TAY650 13.500 13.650 27 B767-3Y0ER CC-CEY 24947 Mar-91 PW4060 57.800 58.350 28 B757-2Y0 EI-CEY 26152 Aug-92 RB211-535E4 40.850 40.500 29 A320-211 C-FNVU 403 Dec-93 CFM56-5A1 30.600 29.600 30 DC8-71F N823 46064 Apr-69 CFM56-2C1 13.200 13.430 31 B747-283B N622 22496 Oct-81 JT9D-7Q 30.500 33.700* 32 DC8-71F N872 46040 May-69 CFM56-2C1 13.200 12.250 33 B737-5Y0 PT-MNH 26067 Jun-92 CFM56-3C1 17.900 19.150 * replaced by scrap value 4 BK ASSOCIATES, INC. 1295 Northern Boulevard Manhasset, New York 11030 (516) 365-6272 - Fax (516) 365-6287 May 4, 2000 Mr. Tom Ashe AerFi Group plc Aviation House Shannon, County Clare Ireland Dear Tom: In response to your request, BK Associates, Inc. is pleased to provide an update on our opinion regarding the half-time Base Value (BV) and the maintenance adjusted BV as of April 30, 2000, of the aircraft (Aircraft) in the AerFi/Indigo portfolio (Portfolio). The Portfolio comprises 35 aircraft and our opinion on their current values, expressed in millions of U.S. dollars, is tabulated in the attached Figure 1. We previously appraised most of these Aircraft for you in January 2000. However, the composition of the Portfolio has changed since that time and you have also provided current maintenance status information. It should be understood that BK Associates has neither inspected the Aircraft nor their maintenance records, but has relied upon the information provided by you and in the BK Associates database which includes data on some of the Aircraft that was obtained for pervious appraisals we have conducted on the Aircraft. The assumptions have been made that all Airworthiness Directives have been complied with; accident damage has not been incurred that would affect market values; and maintenance has been accomplished in accordance with a civil airworthiness authority's approved maintenance program and accepted industry standards. Deviations from these assumptions can change significantly our opinion regarding the Aircrafts' values. According to the International Society of Transport Aircraft Trading's (ISTAT) definition of base value, to which BK Associates subscribes, base value is the Appraiser's opinion of the underlying economic value of an aircraft in an open, unrestricted, stable market environment with a reasonable balance of supply and demand, and assumes full consideration of its "highest and best use." An aircraft's Base Value is founded in the historical trend of values and in the projection of value trends and presumes an arm's length, cash transaction between willing, able and knowledgeable parties, acting prudently, with an absence of duress and with a reasonable period of time available for marketing, which BK Associates considers to be 12 to 18 months. 5 Mr. Tom Ashe May 4, 2000 Page 2 As the definition suggests, Base Value is determined from historic and future value trends and is not influenced by current market conditions. It is often determined as a function of the original cost of the aircraft, technical characteristics of competing aircraft, and development of new models. For the most part, nothing has occurred since we last appraised the Portfolio about one year ago that would suggest any changes to the base values. Thus, the base values are generally lower to account for the passage of time and further aging of the aircraft since the January appraisal. The maintenance adjusted values are, of course, changed to reflect the current maintenance status. BK Associates, Inc. has no present or contemplated future interest in the Aircraft, nor any interest that would preclude our making a fair and unbiased estimate. This appraisal represents the opinion of BK Associates, Inc. and reflects our best judgment based on the information available to us at the time of preparation and the time and budget constraints imposed by the client. It is not given as a recommendation, or as an inducement, for any financial transaction and further, BK Associates, Inc. assumes no responsibility or legal liability for any action taken or not taken by the addressee, or any other party, with regard to the appraised equipment. By accepting this appraisal, the addressee agrees that BK Associates, Inc. shall bear no such responsibility or legal liability. This appraisal is prepared for the use of the addressee and shall not be provided to other parties without the express consent of the addressee. Sincerely yours, BK ASSOCIATES, INC. /s/ John F. Keitz John F. Keitz President ISTAT Certified Senior Appraiser JFK/kf Attachment 6 FIGURE 1 AERFI/INDIGO PORTFOLIO BASE VAL. TYPE OPERATOR REGIST S/N DoM 1/2 TIME MT. ADJ ---- -------- ------ --- --- -------- ------- 1 A320-211 Air France FGJVC 204 Jul-91 27.350 27.350* 2 A320-211 Air France FGJVD 211 Jul-91 27.350 27.350* 3 A320-231 Flying Colours Airlines G-BVYA 354 Oct-92 30.100 31.200 4 A320-231 Flying Colours Airlines G-BVYC 411 Apr-93 30.800 31.450 5 A320-232 British Midland G-MIDZ 934 Jan-99 39.000 40.300 6 A320-214 China Northwest B-2211 1041 Jul-99 40.750 40.750* 7 A321-200 British Midland G- 1207 Apr-00 51.000 51.000 8 B737-347 Delta Airlines N304WA 23345 Jul-85 14.200 13.200 9 B737-3S1 Varig PP-VPF 24834 Jun-90 21.550 22.050 10 B737-3S1 Frontier Airlines N311FL 24856 Aug-90 21.700 22.550 11 B737-3M8 Virgin Express Ireland EI-TVP 25041 Mar-91 22.645 23.450 12 B737-3Y9 China Southern N999CZ 25604 Nov-92 25.070 24.550 13 B737-3L9 Frontier Airlines N310FL 26440 Mar-92 23.450 24.550 14 B737-3U3 Air New Zealand ZK-NGE 28733 Dec-97 34.650 35.400* 15 B737-3U3 Frontier Airlines N309FL 28734 Dec-97 34.650 35.200* 16 B737-3L9 Frontier Airlines N313FL 26442 May-92 23.650 23.250 17 B737-3M8QC Aeropostale F-GIXP 24021 Nov-88 20.650 20.550 18 B737-405 Virgin Express OO-VEK 24270 May-89 21.750 21.450 19 B737-405 Virgin Express OO-VEJ 24271 Jun-89 21.750 22.250 20 B737-4K5 Blue Panorama Airlines EI-CUA 24901 May-90 23.050 23.850 21 B737-4S3 LOT SP-LLH 25594 May-92 25.985 26.800 22 B737-4K5 Blue Panorama Airlines D-AHLS 27074 Apr-92 25.765 26.550 23 B737-505 Braathens LN-BRD 24651 Apr-90 16.250 17.450 24 B737-58E Asiana HL-7233 25768 May-95 22.000 21.400 25 B737-505 British Airways G-GFFB 25789 Feb-92 18.200 19.600 26 B737-505 Xiamen Airlines B-2592 27153 Aug-93 20.000 19.500 27 B737-505 Xiamen Airlines B-2593 27155 Mar-93 19.650 18.200 28 B757-231 Trans World Airlines N718TW 28486 May-99 52.150 52.150 29 F100 TAM PT-MRC 11320 Apr-91 13.000 13.000 30 F100 TAM PT-MRD 11322 Jun-91 13.000 13.050 31 MD82 Spainair EC-GTO 49570 Feb-88 17.050 17.750 32 MD82 Finnair OH-LMW 49905 Oct-90 21.200 20.350 33 MD82 Reno Air N831RA 49931 Aug-90 21.200 20.400 34 MD82 Reno Air N822RA 49932 Sep-90 21.200 21.200 35 MD82 Finnair OH-LMH 53245 Apr-92 22.900 22.400 * excluded