Indian Air Force

Problems With Sukhoi-30 MKI Engine

Earlier, an article was made on the availability of Sukhoi-30 MKI aircraft, where it was stated that there is less operational availability (Around 55%) of the Sukhoi-30 MKI fleet. Here, we are going in a bit depth of it, one of the problems which cause less operational availability i.e. Problems with the Sukhoi-30 MKI Engine.

The engine is the main heart and powerplant of any aircraft. At times, engines are considered the base and aircraft designed and manufactured around and according to it. Because the engine is unable to fit or unable to power the aircraft properly, then the aircraft won’t be able to perform at its optimal levels and safety will also remain a concern.

The Sukhoi-30 MKI has a reputation in both ways, as a successful aircraft and an expensive logistical and maintenance nightmare. So, discuss a bit over here,

Problems With Engine

We all know that Sukhoi-30 MKI is powered by the Russian AL-31 FP Turbofan engine. It is one of the members of the AL-31 Family of Engines. This engine generates a thrust of almost 123 KN. Each Sukhoi-30 MKI carries 2 AL – 31 FP engines. This engine also comes with the TVC (Thrust Vectoring Nozzles), which can pitch from -15 to +15 Degree. This gives an edge to these fighters in maneuverability in many ways.

Problem No. 1

One of the problems of the Sukhoi-30 MKI Engine is very Susceptible to FOD (Foreign Object Damage), which means that it is very delicate in terms of foreign particles which include dust, sand, etc. In India, we know that such weather is very common, and due to this, there were many problems found.

The Solution to this was provided by Russians to use the Titanium mesh grills at intakes. It is not at all clear whether IAF is using it or not. Most of the time, the intake of engines are always closed for the same reason. Redcaps are generally used at intake.

Problem No. 2

The other Problem with the Sukhoi-30 MKI engine is that it’s not Modular. Modular means in an engine, if a certain part gets damaged, then that part is directly replaced. The whole engine doesn’t have to go for repair. This doesn’t happen in the 31 series Engine (Non-Modular). But in 41 series (Used in SU-57) the Engine is modular. So a certain faulty part can directly be replaced.

Problem No. 3

Between January 2012 and December 2014, it is said that 69 Problems with the Sukhoi-30 MKI engine were detected. 11 Vibration Issues (Failure of bearings), 8 failures of friction between moving parts (Lubricating Oil issue), and 33 Failures of Impure fuel (Chips in Oil) were the cause behind engine trouble.

Here, problems improved after Russian gave 9 Modifications on it and all of them will be implemented in other engines, during the overhauls.

The Bearing issue was that, since the aircraft are used to operate under severe conditions, the bearing used to wear out very faster or even get damaged totally at times, causing failures. Along with fatigue loading caused the failure. This was solved by making new and better bearings fit and using more superior quality of the oil.

In the Lubricating Oil issue, the pressure was not properly developed for the lubrication. Meaning there was an issue in the pressure ratio of the Lubricant Tank. Which was again due to improper characteristics of fuel pressure nozzles. It was solved by arranging a better lubrication system and which also decreased wear and tear.

While for Impure Fuel, it is said that most of the Soviet fighters can fly on any kind of oil. But here it changed as it indirectly contaminated the fuel, as there were sludge deposits in it. Sukhoi-30 MKI & Mirage same Fuel was used and Sukhoi-30 MKI has problems while Mirage has almost no issues. Seems like, AL – 31 was very Prone to FOD, as this issue was only found in this series of Engine. The issue was solved easily by using high-quality fuel.

Problem No. 4

This is one of the main problems with the Sukhoi-30 MKI engine i.e. the Overhaul time. It was not about the duration of the overhaul, it was about the frequency of an overhaul.

Here, the Titanium Nozzles require the Overhaul every 500 hours. And the MBTO (Mean time between overhaul) of the engine was 1000 hours. The TTL(Total Technical Life) of engine AL – 31 FP is 2000 hours (Note that in many articles it is 3000 hours but in the official site of HAL it is actually 2000 hours).

Before 2015, many cases were found where MBTO came to 500 hours and at times even less than 300 hours. This was a real alarming stage. It is said many Sukhoi-30 MKI had a mid-engine failure (Single engine fail) during flights. So Su-30 had to land on a single-engine (They are designed in a way that it can land on single-engine, but can’t perform Operations). After those 9 improvements, the MBTO was reached up to 900 hours (Still less than rated 1000 hours).

Now, here thing is each Aircraft had 2 engines, think about the time which it has to remain in the overhaul, and what if both the engines are not on the same cycle. The time for the overhaul will be astronomical. Also, every 500 hours a definite overhaul because of Titanium Nozzles. So over a period of a single-engine, it has to go 4 Overhauls. And for a single aircraft 8 overhauls (In the worst case, if engines are not following the same cycle).

It is said that the Life of the Airframe of Sukhoi- MKI is 6000 hours. After that, it has to go for an overhaul. So till that time, Sukhoi-30 MKI would have gone 3 Engine change and with that minimum 12 overhauls and maximum 24 overhauls. And along with this, the engine rarely completes its full technical life, normally it becomes unusable before that only.

The above all can be verified by a simple number also. India had a designed fleet of Sukhoi-30 MKI 272 Aircraft so IAF would require 1632 Engines. And in an interview (on 1st Aug 2020) of Air Marshal Raghu Nambiar with Livefist, he mentioned that “Till date 930 engines of Sukhoi-30 MKI have been Produced”. Looking this way that 930 Engines for 272 Aircraft. Now this is till 2020, and we still have at least a decade minimum with these aircraft, so this all calculation is proved to be true.

Really this is a costly adventure in both ways, making the engines and overhauling it 4 times over its TLL. And this is for a single-engine consider it for the whole fleet. Well, the figures might be really too large and CAG would be needed to bust it. The above problem has no solution as of now.

Current Status

At once, there was a proposed solution that at a mid-life overhaul of Sukhoi-30 MKI, the Super Sukhoi would come in the picture to upgrade it with the latest avionics and Radars. Here it was planned that AL-41F-1S (117S) turbofan engine with thrust vector control. Which is installed on the Su-35 type aircraft can generate 142 kN of thrusts with its afterburners which is just 19 kN of extra thrusts.

But According to recent updates, this proposal of the engine is dropped as even this new engine has its own problems and MTBO is not increased (Remains around 1000 hours and TTL of 4000 Hours). Along with this overall cost of Super Sukhoi would Shoot up. So IAF decided just to go for the High powerful AESA Radar and to upgrade avionics and electronic warfare systems.

Just to put into perspective and comparing it with others, the GE ( General Electric) Turbofan engines are much better than Russian Engines. According to many articles, the GE 404 ( which is being used in Tejas Mk I) has the MBTO of a maximum of 4000 Hrs (Note this is MBTO, the TTL could be more).

When Sukhoi-30 came out in 1996, it was offered with the AL-31 FU engine. This engine had a thrust of 145 KN and along with that, it came with Pitch and Yaw Thrust Vectoring Control of -15 to +15 Degree. But nobody knows what happened and how it got changed to the AL-31 FN engine in the production phase. Here, one can also say that Russian actually didn’t give us the Superior Technolgy.

Along with there, the Radar of Sukhoi-30 MKI has the MTBO of 100 hours only. There is also a Sensor Fusion issue of Sukhoi-30 MKI (Here, there many speculations that the Sub-systems of Sukhoi-30 MKI don’t talk to each other). And mainly due to this only, the Super Sukhoi Upgrade is taken seriously. Because here, the Radar will be changed and New Avionics will also be added.

Earlier, the engines used to go for overhaul at Russia, now they are overhauled at HAL, Koraput. Also, the reason their non-operationality along with this is the premature fail rate and delivery of Spare’s issue. The Russian hasn’t shared many parts of technology with Indian private vendors for the reasons best known to them. It is said that actually Russians earn very good money by supplying new spare parts at solid profit margins, but are always reluctant to quickly make repairs at 25 percent of the cost of new items. Deals mare made with Russia to get these parts on an urgent basis and HAL has also stocked them for faster service.


Having said all these, none of these defects stop the Su-30MKI to be the best multirole air superiority fighter in the South Asian subcontinent. Even with these defects, when this Majestic Beast is airborne, Even the PAF and PLAAF fear of it. Thanks to the robust logistics & supply chain as well as the ground maintenance crew whose upkeep keeps the flanker flying & combat-ready. The aircraft in spite of Such controversies have shown its capabilities even keeping the Radar Off in many of the Wartime Exercises. And without any doubt, it is the Most potent fighter in the Arsenal of IAF.

Nirav Kotak

A Mechanical Engineer and a Defense Enthusiast wanting to share knowledge and learn more from others as well.

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