The problem is not the purchase of the system. Its quite clear now that American government has no problem in selling EMALS, AAG or PLS for Indian future aircraft carrier. The issue is that these systems are not ready yet and their failure rate is quite high. You have to keep in mind that a failure rate of this kind during high sea duty would be catastrophic.
See the following reports from two authoritative sources:
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U.S. GAO - Defense Acquisitions: Assessments of Selected Weapon Programs
"Deficiencies affecting water twister components—used to absorb energy when arresting aircraft—of the advanced arresting gear (AAG) technology continue to disrupt the system's development. Recent water twister redesign proved unsuccessful in testing last year. The Navy resolved problems with the redesign and is planning for concurrent testing.......
http://www.dote.osd.mil/pub/reports/FY2013/pdf/other/2013DOTEAnnualReport.pdf
Aircraft compatibility testing continued in 2013. Approximately 400 aircraft launches are being conducted using EA-18G, F/A-18E, F/A-18C, E-2D, T-45, and C-2 aircraft. The Navy has also conducted an additional 1,200 dead-load launches (non-aircraft, weight equivalent, simulated launches). Approximately 55 percent of the EMALS government furnished equipment (GFE) has been delivered to the shipyard.
At the Lakehurst, New Jersey, test site, over 1,967 launches have been conducted and 201 chargeable failures"¦. approximately 240 Mean Cycles Between Critical Failure"¦ where a cycle represents the launch of one aircraft. Based on expected reliability growth,
the failure rate is presently five times higher than should be expected.
"¦.Testing to date has demonstrated that AAG should be able to recover aircraft planned for the CVN-78 air wing, but as with EMALS, AAG's reliability is uncertain. At the Lakehurst, New Jersey test site, 71 arrestments were conducted earlier this year and 9 chargeable failures occurred. The Program Office estimates that
AAG has approximately 20 Mean Cycles Between Operational Mission Failure"¦. 248 times higher than should be expected."
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It is possible that by the time Indian requirements are firmed up, these three systems would be mature enough to be ready to install. However, if they are not, it would be wise for IN to go for a mix of two steam catapults and two EMALS to minimize the risk. But there is no doubt that INS Vishal will have to be a catobar carrier of minimum 80-85000 ton full load displacement with nuclear propulsion. That class of carriers will give IN the heft for out of area/expeditionary operations.