MiG-21: design flaw could be the culprit

In fact, HAL and MiG’s manufacturers in Russia are already working on modifying the flame tubes. ‘‘The flame tube catches fire which, at times, results in an engine flame out. The flame tube has been redesigned,’’ sources added. It is in the flame tube that the fuel and air get mixed to power the engine and temperatures are as high as 3,500 degrees Celsius, according to a former MiG-21 pilot.

The re-designed flame tubes are yet to be fitted into the R-25 engines since they are still undergoing a series of tests in Russia. ‘‘But we are not flying unsafe aircraft. HAL and IAF have taken certain measures to ensure that in-house improvisation results in sorting out the problem,’’ the official said. Air Chief Marshal S. Krishnaswamy, chief of air staff (CAS), ordered the immediate grounding of the fleet on May 3, when two aircraft were lost within a month due to engine flame out.

The Public Accounts Committee report tabled in Parliament on March 21 mentions the flame tube burning problem and the joint efforts undertaken by HAL and IAF to sort it out. Defence analysts say while a design deficiency is a serious issue, there is no reason to panic, since these engines continuously undergo improvement and upgradation.

Air Marshal (retd) Denzil Keeler, former inspector general flight safety, concurs.

‘‘We had a major problem with the MiG-21 engines in the late ’80s too. There were a number of crashes. We grounded the entire fleet and carried out checks and found a defect in the routing of pipelines,’’ he said. ‘‘There was chaffing of oil, fuel and hydraulic pipe due to the routing of the pipeline. There was also the problem of vibration of the engine due to a lack of proper alignment, resulting in the engine touching the fuselage. The IAF is very efficient in sorting out the problem along with the competent personnel at HAL. They did it in the past and within a month they can do it again,’’ added Keeler. The IAF will re-assess the situation on Monday after the preliminary report is submitted, official sources said.