Dude I understand what you are saying. This used to happen in older aircraft. But modern aircraft production uses concurrent engineering. Even F35 follows concurrent engineering if I remember correctly. I am simply telling you what is being done in LCA.
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Bengaluru: Amidst the ongoing ‘controversy and confusion’ over whether the Indian Air Force (IAF) is keen to go ahead with the home-grown Light Combat Aircraft (LCA) Tejas programme beyond the first and second blocks of 20 each, the sixth series production
english.mathrubhumi.com
Ok, clearly you have misunderstanding about concurrent engineering. It is not making the change during the production stage based on customer's feed back.
The main concept of concurrent engineering is not only making every sub-system contractor to start his part of R&D simultaneously, but bring all other department (i.e procurement, maintenance, factories, airforce, etc) to participate the design work from very beginning. So, these departments can start to design their part of procedure along with designing team, as the result, they can save their time. On the other hand, the design team can receive their feedback immediately and incorporate these into their blueprint before the "final product". So, it can
reduce the time-consuming and expensive design change in IOC.
In other words, one of major purpose of concurrent engineering is to minimize the modification after IOC.
If someone blames the modification after IOC for the delay of the project, the concurrent engineering approach didn't work as it is supposed to be in this project.