There is no iota of doubt that the LCA is a world-class fighter, the cutting-edge technology employed in the overall design of the fighter is contemporary and LCA Tejas in its current form will not go obsolete for decades.
The reasons are many, Tejas has an Air-frame designed for strength and stiffness under specified loads in extreme environment with durability and damage tolerance. The fighter incorporates a highly reliable quadruplex digital Fly-By-Wire (FBW) Flight Control System to ease handling by the pilot. The digital FBW system of the Tejas employs a powerful digital flight control computer (DFCC) comprising four computing channels, each with its own independent power supply and all housed in a single Line Replaceable Units (LRU). The new generation glass cockpit comprises Multi Function Displays (MFD), Head Up Display (HUD) and Stand by Instrumentation System driven by Open Architecture Mission and Display Computer. The computer interfaces with pilot display systems like the MFD is through the MIL-STD-1553B multiplex avionics data buses and RS-422 serial links. MIL-STD-1553 is a military standard published by the United States Department of Defense that defines the mechanical, electrical, and functional characteristics of a serial data bus.
So why was IAF earlier opposing the induction of the Tejas in its fleet, some of the the main reasons are as follows:
Firstly, the lack of Active Electronically Scanned Array (AESA) radar solution. The inherent advantages of AESA radar are the obvious inertia-less scanning and the minimal feeder loss as no lengthy feeder cables are involved. Unlike in the MSA radar, the AESA radar has the impudence to perform even with failure of some of its radiating elements. The AESA radar helps build substantially compact radar systems resulting in low weight, minimal aerodynamic drag, and relatively smaller radar cross-section (RCS), all of which are of vital importance operationally for the Tejas aircraft. Besides, the AESA radar provides enhanced beam agility with higher reliability. The latest AESA sensor further helps track air and sea-targets simultaneously while maintaining the routine scan over the operational area.
DRDO has already built a ground based AESA radar, though the technology has been developed it is still in the process of miniaturizing the technology to be fitted into the Tejas's radome, this radar is called the UTTAM.
The Tejas fighter now incorporates the Israeli EL/M-2032 advanced pulse Doppler, multimode planar array fire-control radar which has a maximum range of around 150 km. HAL has also integrated the Israeli Derby and Python air-to-air missiles, and a data link that digitally interconnects between all the hardware elements.
The need of the hour is to hasten the Uttam development or look for an import substitute as a stop-gap arrangement, Elta's own EL/M 2052 AESA radar could be a viable option for the Tejas. The EL/M-2052 is based on a fully solid-state active phased array technology which has a longer detection range, high mission reliability and a multi-target tracking capability of up to 64 targets. In Air-to-ground missions, the radar provides very high resolution mapping (SAR), surface moving target detection and tracking over RBM, DBS and SAR maps in addition to A/G ranging.
Apart from Elta India has the option to choose from several other manufacturers such as Northrop Grumman, Raytheon (US based), Thales, Euroradar, Selex, Ericsson (European based), Toshiba, Phazotron & Tikhomirov NIIP (Russian based). But right now Elta looks like the ideal choice since it was reported that HAL was also looking to upgrade all the squadrons of Jaguars & Mirage fighters with these radars.
Secondly, HAL has also undertaken to equip the Tejas with air-to-air refueling and a electro-optic Electronic Warfare (EW) sensor suite under its wing as these capabilities are lacking in the first-cut Mk-1 version.
Lastly, Janes Defense Weekly reported that HAL envisages the Mk 1A as being around 1,000 kg lighter than the Mk 1, which weighs 6,500 kg. It aims to achieve this weight loss by shedding 200-300 kg of ballast secured in the aircraft's nose to stabilise it and another 700-800 kg by reducing its heavy and 'over-engineered' landing gear. The platform would also be fitted with Israeli firm ELTA Systems' active electronically scanned array (AESA) radar, replacing the heavier and less capable 'hybrid' version of ELTA's EL/M-2032 lightweight multi-mode radar, which was developed jointly with DRDO.
In the final analysis an AESA radar whether it is of Indian or foreign origin will be the most important upgrade and will make the Tejas an effective air-defence fighter. It is also worthy to note here that both China and Pakistan does not have this capability yet.