The Su-30 MKI’s aerodynamic construction is an unstable longitudinal tri-plane that confers its unprecedented agility. Like most modern jet fighters, this highly unstable platform is manoeuvred by computer-controlled FBW system. Multi-layered backup systems are necessary as without the FBW, the aircraft cannot be manually controlled by the pilots.
Source:
Front-line fighter Su-30 MKI flies with flaws | Page 5
A brief explanation of the standard quad redundancy FBW-FLCS is here...
JF-17 Thunder Multirole Fighter [Thread 6] | Page 234
To ensure near-ultimate safety, the Su-30 MKI’s FBW system is endowed with quadruple redundancy. If one of the FBW channels becomes faulty, it automatically gets disconnected from the system, suitably warning the crew to take appropriate actions.
Does not get 'disconnected' but voted out.
A level-1 failure does not jeopardise the mission,...
No, it does not. But it will -- or should -- create a cockpit level warning.
Under the Western design philosophy, the faulted (not faulty) channel is never disregarded. Not selected for voting is put into standby mode and its parameters are still monitored. If at any time those parameters came within specs, the faulted channel will be 'un-faulted' and is eligible for voting again. This is
NOT a design flaw since there could be many reasons for a channel to become faulted. The only time the FLCC will flag a cockpit level warning is when a channel have a persistent fault.
With a quad channels redundancy design that uses the two-fail operability concept, am guessing that the Russian designers considered a one channel fault to be 'level-1', meaning one channel is voted out and the other three continues to operate the aircraft.
...while a level-2 failure would demand a diversion to the nearest suitable airfield.
This level-2 fault would -- or should -- be a second channel fault.
The system now have only two channels which means no voting is possible. Under the Western design philosophy, one channel will be used as primary signals provider to operate the aircraft. There will be no performance degradation such as auto-g limits. The pilot would still be able to dogfight, drop bombs, etc.
...a level-3 failure would normally be rarer than one in a million possibility which unless quickly rectified could lead to the loss of aircraft.
This is when three out of four channels are faulted.
Speaking for Western design concept, as I came from the F-16, the only time a quad channels FBW-FLCS flies with two channels is combat damages or some kind of non-combat related collisions, aka 'bird strike'. Our training demands that if there is a cockpit level FLCS warning, the pilot must RTB. This is peace time, no need to take unnecessary risk to pilot and equipment.
However, this redundancy philosophy cannot rule out hardware related issues such as manufacturing quality, of which Soviet/Russian gear do not have a good reputation. Either the IndAF have, through their training, discovered a genuine design flaw in the Soviet/Russian design of the FBW-FLCS, or the IndAF is being shafted by the Russians with shoddy remanufactured gear.
Remanufactured hardware is not bad. Basically, everything is reconditioned/remanufactured. But have no doubt the Russians keep records of which hardware go to which customer.
The aircraft crashed when a crucial FBW switch was toggled disabling the flight control system. Was it therefore, a self-inflicted tragedy?
There is no 'disabling' of the FLCS. It is not possible under the FBW concept. Whatever this switch is and what it does, it does not 'disable' the FLCS. There is a miswording here. Until someone among the Indian members here can find and post the image of this switch, this will have to remain a mystery. But there is no possible 'disabling' of the FBW-FLCS.