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MiG-21: Much Maligned!

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The service history of the MiG-21 in the IAF and HAL has been superbly and accurately narrated in this article. The author, Wg Cdr K. Suresh, retired recently, (after 17 years) from HAL. Inter-alia, he was involved with flight safety aspects of the MiG-21, embracing design, construction, overhaul, field maintenance and flying operations. Comments and views expressed below are largely for reader interest. There has been adverse comment in recent times by the PAC and the public on the safe operation of the MiG-21. With every MiG aircraft crash (21, 23, 27M, 29, 25), the outcry from an uninformed public (sometimes based on incorrect media reports), has got louder, reaching a crescendo with the tragic crash at Jalandhar on 03 May 02. Quite rightly, the IAF has temporarily suspended flying training on aircraft (not committed to operational alert) pending investigation of suspect aircraft systems. The outcry that the aircraft is unsafe to fly, to put it bluntly, is nonsense. One needs to remember that MiG-21 variants, by the hundreds, have been safely operated since April 1963. The BIS variant entered the IAF in 1977; license production (220 aircraft) by HAL ended in 1988. Aside from performance improvement, safety features were introduced e.g. ‘blown-flaps’ enabling a slower landing-approach, better view of the runway and slower touch-down; recovery to level flight (roll and pitch channel auto pilot) in the event of disorientation at night/in cloud; ground level ejection. Regrettably, the cockpit layout and external view remained a ‘nightmare’. A large number of BIS aircraft are relatively new; only half their technical life (3000 hours) has been expended. About 125 aircraft are to be upgraded to a MiG-21-93 standard (see Indian Aviation 09 Feb 01). HAL overhauls variants of the MiG-21 (airframe, engine, accessories, components); first and second line servicing are done by the IAF. It is essential that materials/components  (indigenous or imported) installed/supplied by HAL are to specification and dimension, especially for engine, fuel and hydraulic components; that overhaul/ maintenance procedures are rigidly observed by HAL/IAF. No aircraft anywhere in the world can be considered airworthy unless the aforesaid is done. I flew and had close contact with the Gnat/Ajeet and the MiG-21 for 25 years. The former came to the IAF, undeveloped; the latter after being fully proven. As one might expect, the former was more difficult to operate safely. All this is history, but necessary to know if one’s conclusions are to be rational.

                                                                                                             -  Air Marshal M.S.D Wollen  



The unfortunate accident on May 03, 2002 near Jalandhar involving a MiG-21-BIS aircraft could not have come at a worse time. In this accident, it is reported that the pilot experienced engine failure and ejected. The aircraft crashed into a building and eight people were killed on the ground. It is learnt that, after this accident, training flying has been suspended on this variant of the MiG-21. Chief of the Air Staff (CAS) stated on TV that the flying has been suspended on MiG-21-BIS fitted with the R-25 engine, pending investigation to establish the cause of engine failure.

In the recent past, there has been so much adverse publicity on the airworthiness of MiG-21 aircraft. It has become a major topic of conversation among all sections of people and many have also voiced their opinion in the media. At the outset, heartfelt condolences to the families of those who lost their lives in Jalandhar.  Condolences also to the families of pilots who lost their lives in flying accidents; recognizing that the lives are irreplaceable. MiG-21 and its accident proneness must be looked at dispassionately, although explanations of any kind are not likely console the grief of those families who lost their kin. An attempt has been made in the succeeding paragraphs to analyze the MiG-21 problems to put the entire issue in the proper perspective.

It has been reported in the magazine “Indian Aviation” that the Public Accounts Committee (PAC) in its 29th report to the Parliament on 21 March 2002 has called for immediate phasing out of the MiG-21 fleet of the Indian Air Force (IAF). With all due regards to the PAC, it is not clear as to what prompted the honorable members to come to this conclusion.  It is also reported that the PAC has pointed out with concern that between 1991-2000, 221 MiG-21 aircraft worth Rs 238.49 crore were lost with 100 pilots getting killed. Similar reports also appeared in some of the national dailies. Prior to discussion on the accident proneness or otherwise of the MiG-21 aircraft, the figures of loss of 221 aircraft and 100 pilots during the period 1991-2000 appear to be incorrect. During this period, 221 MiG-21 were never lost nor 100 pilots lost their lives in MiG-21 accidents. The figures as reported perhaps are the total loss of IAF aircraft involving all the types operated by the service. It is also possible that the figures were wrongly reported in the press.

The media gets overexcited whenever there is an accident involving a MiG aircraft of the IAF. There is surely cause for concern for the number of accidents that plague IAF. But all MiG types are labeled "flying coffins" or "widow makers" without bothering to see if common causes or versions of the aircraft are involved. Most often the headlines read, another “MiG-21 crashes -….” Very recently, an accident involving MiG-23 in Rajasthan sector was reported as that of MiG-21.

MiG family in IAF’s inventory include three variants of MiG-21 (FL, M & BIS-training, ground attack & air defence), MiG-23 & 27 (ground attack), MiG-25 (fighter reconnaissance) and MiG-29 (air defence).  Among the MiG-21 variants, the FL and M versions are fitted with R-11 engines and the BIS with the R-25 engine. The FL version was inducted from1966-1970, M version from 1973-1970 and the BIS version from 1977-1985. The causes for accidents vary for each different type of aircraft, but common causes, as elsewhere in the world, are Human Error and Technical Problems. However, in India many aircraft of all types are lost to bird hits, as there is a sharp increase in numbers of large scavenging birds in active flight paths due to rise in population and poor social hygiene.

It is also not realized that over the last several decades, accident rates have come down dramatically. Statistical data presented in the report of Comptroller and Auditor General of India (CAG) released in Jun 2000, confirmed that the accidents rates have indeed shown a steady downward trend.  As per CAG report, the overall accident rate (per 10,000 flying hours) of the IAF for the period 1991-92 to 1996-97 was down from 1.59 to 0.89 and that of the MiG-21 from 3.53 to 1.89. It is reliably learnt that the downward trend has continued. The press and the electronic media were not as vocal about accidents in the past as it is today. This gives the false impression that fight safety is being compromised more than ever before.

It must be mentioned that the accident rates of fighter aircraft, particularly single engine variants, are always higher all over the world. Most of the fighter aircraft are flown by a single pilot unlike, airliners, transport aircraft or helicopters that have a multi-crew element. Every military service, tries to reduce accidents to an irreducible minimum and IAF is no exception. Our country has one of the harshest operational environment, very hot deserts, very humid locations, and the mighty Himalayas. It is the resilience and the adaptability of the IAF (in spite of constraints like lack of ideal infrastructure) that must be appreciated, while judging its capability for safe conduct of operations. IAF uses its aircraft to meet its operational requirements and some of these put the man-machine interface to severe tests. The tendency in some quarters to compare IAF accident rates (say) with those of US Air Force or Royal Air Force is totally unfair.

It is fashionable to allege that MiG-21s are getting old and hence more prone to accidents. MiG-21s are the mainstay of IAF fighter fleet and are flown for the maximum amount of hours. In the words of previous CAS, Air Chief Marshal AY Tipnis, “MiG-21s are most in numbers and in use operationally”. PAC had observed that, in the last decade, 62% of IAF accidents had occurred on the MiG-21. It is seen that the accident rates are in proportion to the fleet strength of MiG-21s, which constitutes 60 % of IAF fighter strength. Infact, the accident rates of the MiG-23 and MiG-27 are higher than that of the MiG-21.

The age of the MiGs is not a real problem as every aircraft is overhauled after a predetermined number of hours. It is accepted for service use only if it fully meets the requirements for brand new planes. Items, which have a limited life, such as rubber parts, are routinely changed well before their useful life is reached. There has not been a single report of any MiG-21 aircraft accident due to airframe fatigue. The fatigue life of MiG-21 fleet has been increased after joint scientific studies by IAF, Hindustan Aeronautics Limited (HAL) and National Aerospace Laboratory and in collaboration with the original Russian manufacturers. Aircraft of mid 1960 vintage, which had completed their stipulated calendar life of 35 years, have all been withdrawn from service. There is no correlation between accidents and ageing.

Air Commodore Jasjit Singh in his article on the MiG-21, published in the Indian Express (Sunday Apr 07, 2002) had highlighted the following:

  1. MiG-21 has not only been one of the most successful designs but also one of the most widely used.

  2. MiG-21 has great advantage because of low accident rate, low costs, outstanding maneuverability, and easy maintenance making it the most affordable fighter.

He has also brought out that China has modified and upgraded the MiG-21 aircraft under the nomenclature F-7 and later F-7MG. A large number of these (150) Chinese built MiG-21s (F-7P) are in use with the Pakistan Air Force. China and Pakistan are expected to continue to use the MiG-21 in the coming decades. Jasjit has briefly touched on our interest  (in late 1950s), in the US built F-104 Starfighter. A few salient points concerning this are discussed in the paragraph below.

In the late 1950s, there was a great clamor to acquire the F-104 Starfighter from the Americans who had already supplied this aircraft to Pakistan. The deal did not go through due to various political reasons and then India took the Soviet offer and inducted the MiG-21. In retrospect, American refusal to supply the F-104 Starfighter was a blessing in disguise. We would not have been able to afford, operate and maintain this aircraft with our infrastructure that existed then. Most importantly, Americans held the key and were in a position to stop supply of essential spares at any time, which in turn would seriously affect the availability of aircraft.

MiG-21 thus became the mainstay of the IAF since mid 1960s and has done yeomen service. The aircraft has enriched the IAF by providing invaluable flying experience to a very large number of its pilots. These aircraft have flown the maximum number of hours in India compared to anywhere else in the world. IAF has also exploited this aircraft with a lot of innovation, which surprised even the Soviets.

Last year, politicians took up this issue with the Government. Expressing grave concern over continuing high incidence of crashes of Indian Air Force jets leading to loss of precious lives of young pilots, 126 Members of Parliament (MPs) from all political parties petitioned Prime Minister (PM) Atal Behari Vajpayee and the then Defence Minister Jaswant Singh, demanding immediate induction of Advance Jet Trainer (AJT) into the force. However, the available data do not fully support the theory that accidents were mostly caused due to poor training in the absence of the AJT.

The Russians used this occasion to hit back at the IAF, holding it mainly responsible for the high rate of accidents. Perhaps for the first and only time in a relationship going back four decades; they blamed India for the frequent crashes of its MiG fighter aircraft and "delivering a heavy blow to MiG's reputation around the world". A senior MiG executive, Vladimir Zhukovsky, accused India of "creating conditions for frequent crashes by buying low quality spares" from Ukraine and East European countries. "At times, it even buys spares that have outlived their utility," he is reported to have told media persons at the MAKS-2001 International Air show at a Moscow suburb.

Many in the country fell for the Russian allegation and some sections of the press went hammer and tongs to emphasize that all accidents were a result of poor quality of spares. Unfortunately, neither Air HQ nor MoD refuted these to state that there was no correlation between quality of spares and accidents. But the Russian allegations did not go completely unchallenged, as retired officers are not restricted in their access to the press.

IAF faced a critical spare parts crunch after the collapse of USSR when Air Chief Marshal SK Kaul was the CAS. Now retired, he dismissed the Russian outburst as “an old MiG ploy. MiGs were crashing even when the USSR was supplying spares. They never admit that the design is bad, and quickly blame crashes on bad maintenance”. Air Chief Marshal Kaul also questioned the need to make so many modifications in the MiG-21, the mainstay of the IAF, "if there were no design problems". His successor, Air Chief Marshal (Retd) S K Sareen singled out MiG-27 ground-attack aircraft for "design inadequacies".  Air Chief Marshal Sareen disclosed that India was forced to look elsewhere when the "Russians started taking us for a ride by overcharging up to four times. This forced India to shop for spares in the East European market. "They had the same kind of weapon systems as ours, had reduced their forces almost overnight by half, and had surplus spares to offer," he recalls. Some of the parts were made available by cannibalizing aircraft. "But these were purchased after stringent quality control checks," Unofficially, the former Chiefs must have viewed the Russian outburst as a "desperate sales pitch".

A detailed analysis of MiG-21 accidents reveals that the main cause factors are:

  1. Human Error (Aircrew).

  2. Technical Defects.

  3. Bird Strikes.

Human Error (Aircrew) constitutes about 40 % of all accidents in the MiG-21 and this percentage is not high at all and almost all Air Forces in the world have about the same percentage of Pilot Error accidents.  In the words of ACM Tipnis, “MiG-21 is a high demand aircraft”. It certainly is a quantum jump for an inexperienced pilot who has just finished his training on sub-sonic jet trainers like Kiran or Iskra. IAF is using the MiG-21 in the AJT role, which is neither optimal for training nor cost effective. (See appendix 1 about Flying Training)

MiG-21, although a high demand aircraft, is docile and has no aerodynamic vices. It has excellent handling characteristics and has served to provide very valuable flying experience to a large number of IAF pilots. Some like the previous and the present CAS swear by the aircraft. It is the docility of the aircraft that not only generates a good bit of confidence but also encourages forays into exceeding the limits of the stipulated flight envelope. In air combat maneuvers, many inexperienced pilots have got into trouble without realizing it. At high angles of attack, the induced drag increases sharply and unless the angle of attack is quickly reduced, the aircraft develops a high rate of descent, which cannot be arrested with the power available (even with reheat). Added to this, there is no protest from the aircraft like severe shudder, wing rocking. etc, prevalent in other types of aircraft. This gives a feeling of well-being and a number of pilots did not recognize the danger in time to take recovery action or eject.

The training of pilots is under constant review with procedures being updated regularly and creating the required level of awareness. IAF has very strict norms during each stage of training and only those who have the capability are posted to fly fighters. Even with the finest of filters there is always someone who would get through various stages without showing any weakness. Some of these individuals get in to trouble, fail to recover from difficult situations and sometimes they compound a simple emergency. This is a human failing and is no different in any other part of the world and Indians alone cannot be singled out for it. One particular CAS (in mid 80s) is on record to have stated that “I would rather lose a pilot in an error type of accident than in actual combat, for those who survive the rigors of peace time would be really combat ready”. While this is one way of viewing an accident, the proper way would be to consider even “One accident as One too many”. It is very difficult particularly for the families of those who lost someone close to accept error or error of judgment on the part the individual. It must be appreciated that the best of professionals make mistakes, be it Tendulkar, Tiger Woods or Pete Sampras.  A fighter pilot has no chance like these top sportsman who are firmly on ground (not having challenged gravity) and are able to play the next innings or the next match.

A correspondent writes in Times News Network (Sunday, September 02, 2001) “The MiG-21s are arguably the most difficult to fly. Compare it to Mirage-2000 which has the fly-by-wire technology, making it very easy to fly”. Such off the cuff statements leads to all kinds of inference by the general public. Correspondents should use a lot of restraint while writing on complex technical matters. A-320 accident at Bangalore in 1990 is a case in example where fly-by-wire did not help when the pilots failed to manage energy properly.

Technical Defect accidents occur due to interplay of a complex set of factors. Technical defects leading to an accident could be either due to an inherent or an induced problem. The primary factors are:

  • Design inadequacies                            Inherent

  • Manufacturing/Overhaul Quality             Induced

  • Maintenance                                      Induced

  • Operational Factors                             Induced

It is seen that every technical defect accident has to be analyzed and investigated thoroughly to be able to take appropriate remedial measures. IAF has a well-established system of accident investigation. The investigation team has experts drawn from the manufacturers, scientists from Defence R&D Organization and National Laboratories, besides specialists from IAF. While every effort is made to try and establish the exact cause, sometimes it is not possible to correlate the sequence of events with the available material evidence. Hence, a set of probable causes is worked out and remedial measures taken. The absence of full-fledged Flight Data Recorders (FDR) in the older types of aircraft is a serious limitation. In aircraft fitted with FDR and Cockpit Voice Recorders (CVR) the job is much easier, but even here in some cases interpretation of recordings poses a great challenge.

MiG-21 has had its share of technical defects falling under all the categories but the situation is not one where every other aircraft is falling out of the sky. There were some design deficiencies - mostly engine related. These have been corrected with the help of original designers and indigenous industry viz. HAL. Treating them as limitations and modifying operating or maintenance procedures where necessary have tackled one or two areas that were difficult to redesign and would not have been cost effective. Jalandhar accident will also be tackled in similar steps.

There have been a number of specialist committees that have looked into some of the MiG-21 technical problems, the latest being Dr Kalam Committee. These teams make a number of recommendations of general nature like, “if you have a balanced diet, exercise, avoid stress, alcohol and tobacco you are likely to lead a healthy life”. The media and a number of self- styled experts start to believe that implementation of recommendations of a Committee is the panacea for all ills. The most important point to note is that no committee is able to address a specific problem. The specifics have to be tackled by catching the bull by the horn by the Operator, Maintainer, Designers and Engineers from the industry, IAF and HAL in our case. Only effective operator and industry interface can produce desired results. In the case of MiG-21, a number or technical problems have been successfully solved jointly by IAF and HAL. In some cases, the Russians did not have the answers or did not co-operate with us. They also tended to insinuate that the problem was only in India not elsewhere. It is also to the credit of Indians that the Russians admitted to some of the problems when they were confronted with solid scientific data.

IAF starting with acquisition of Jaguar aircraft in late 1979, inducted 15 different types of aircraft besides radar and missiles in a span of six to seven years. The best of technicians, engineers and pilots went on to new types.  Besides, the MiG-21 aircraft were also relocated in forward bases with minimum infrastructure. Although, Air HQ may not admit, this did disturb skill levels.

There have been technical defect accidents due to lapses both during manufacturing and maintenance, human element being predominant. In the case of MiG-21, these are not of such large magnitude as to sow all kinds of suspicious seeds. The industry and the maintenance engineers are seized of the problems and are constantly taking measures to minimize lapses. Operational lapses leading to technical defects are rare and these pertain mainly to engine handling for which there are adequate procedures. Some of the technical defect and measure taken are discussed below:

In mid 80s, there were a loss of few aircraft due to fire consequent to hydraulic leaks and the fluid coming in contact with the hot engine zone. The cause was identified and eliminated with improved maintenance actions and adequate care during manufacture /overhaul. One of the primary causes was the shift of engine alignment, which resulted in uneven heating of fuselage causing hydraulic leaks.  Improved locking of engine tie rods was devised to ensure that the alignment did not shift after engine installation. Further, young design engineer Mr. Nadgir from HAL Nasik Division devised a simple easy to install additional heat shield which not only reduced the zonal temperature but also made the system more tolerant. This modification was appreciated very much by the original Soviet designers.

There were a number of failures of dowel bolts in R-11 engines. These bolts are used to attach the bevel gears (in the gear train) that receive the main drive from the engine. Most of the failures occurred on ground during starting but two aircraft were lost due to failure in air. The cause was identified as a due to a lapse during overhaul and corrective actions were taken.

R-25 engine had a problem of seizure of oil pump and while one aircraft was lost the other managed to land back. The cause was identified as due to lack of lubrication of pump drive shaft, which had a grease pack. Although the Russians had introduced forced oil lubrication three years earlier the information had not been passed on to India and we learnt at the cost of an aircraft, luckily the pilot had ejected. All engines were subsequently modified. (See Appendix 2: Flame Tube Burning : R-25 Engines)

There have engine failures due to loss of drive, either to main gearbox or to the main fuel pump. Most of these cases were due to lapses during overhaul and corrective actions have been taken.

Engine Flame Out as it is called is nothing but an engine failure due to extinguishing of combustion inside the engine. This occurs when of air fuel ratio is upset resulting in engine surge. The disruption of air or fuel supply could also be due to mechanical reasons, ingestion of foreign object like bird etc. Flameouts due to mechanical reasons like blade failure and foreign object damage are relatively easy to establish during post accident investigation. The cause(s) of flameouts that occur without any mechanical damage, which are a result of very complex interplay of various control systems, are very difficult to establish. The absence of a full-fledged FDR is a major handicap and the investigation is an uphill task. In such cases, the most probable cause is listed and measures taken. Interestingly, in 1985 Air HQ proposed fitment of FDR on all MiG-21-BIS aircraft. It is learnt that the proposal was turned by MoD Finance, as too expensive and a suggestion was made that IAF could fit these recorders to one in five aircraft. Finally, it did not see the light of the day as the proposal got linked with the aircraft upgradation program.

Bird Strikes are a major problem in India which affects both military and civil aviation. In a MiG-21, being single engine aircraft, bird strike particularly into the engine is critical. This leads to surge, stagnation of engine and flame out and depending on the phase of flight, the pilot may not even have time to eject. Entry of a bird into air intake, causes disturbance of airflow and since the fuel schedule is maintained as selected by the engine control lever, a mismatch results and leads to flame out. In the engines fitted on the MiG-21, the first stage itself is a rotating assembly, unlike some engines, which have a set of static guide vanes. This increases the vulnerability to mechanical damage consequent to a bird strike. In a number of bird strike cases, people on the ground have observed unusual flame behind the aircraft and this is one of the reasons for reporting that the aircraft caught fire. Fire is the consequence of and not the cause.

In order to combat the bird menace, IAF has had to modify all flying profiles. The Government has set up Airfield Environment Management Committees in all States to control unauthorized constructions, garbage disposal, location of slaughter-houses etc. It is sad but true that in most states these committees are not functioning and there is no real will to tackle bird menace. In the coming years unless there is concerted action by all the Government agencies, the bird strike threat would take gigantic proportions.

IAF accidents must be looked at in the Indian context and efforts being made to contain these must be given due credit. It is unfortunate that the MiG-21 has got maligned unnecessarily and become a victim of media trial - that too by people with very little knowledge of the complexities of an aircraft accident. The approach is usually to sensationalize particularly on TV where the anchor speculates about the cause even before the fire in the wreckage has been put out. Many self-styled experts pronounce their instant verdict on an accident that takes days and even months to painstakingly investigate. This only compounds the confusion. A prime example of such a case was the accident of MiG-21 at Palam in Oct 1999, due to engine failure, consequent to a bird hit. This accident was sensationalized on TV as engine failure due to mechanical reasons even before the official word was out from Air HQ. The media tends to play on emotions or typically takes the audit view of measuring loss in terms of money. Both these approaches cannot help establish the cause of an accident where only a rational approach is called for.

“Today’s headlines are not News tomorrow”. Hence by the time the actual cause of an accident is established the same media, which sensationalized the whole thing, has totally forgotten the event. The trauma of those families who lost someone in an accident can never be eliminated. Therefore it is necessary for the media to be more objective and for Air HQ and MoD to be more transparent, in sharing correct information without compromise on security. After the Jalandhar accident, two different TV channels had each called an Air Vice Marshal (AVM) as an expert. It must be mentioned that one of the AVM had no flying experience on the MiG-21 and the other was not a pilot. The media persons, who tend to exhibit knowledge on all subjects, believe that all air force officers are like them and have a view on all topics. One only wished they had called someone like Denzil Keelor, Tarlochan Singh or Jasjit to talk about the MiG-21. During Kargil conflict, the daily media briefing was appreciated by one and all. It is suggested that a similar media briefing be done post accident and officially give out correct available information. This is the only way to put an end to all the speculation.

IAF realising the potential for continued utilization of the MiG-21 rightly decided to upgrade 125 MiG-21-BIS aircraft with Russian assistance. Upgrade program has commenced at Nasik Division of HAL and the program likely to be completed by 2005. Essentially, the features of upgrade are, Multimode Pulse Doppler Fire Control Radar (Kopyo), RLG based Inertial Navigation system with GPS, HUD, MFD, Helmet mounted sight, Weapon Aiming Computer, ECM, Mission Planning and Retrieval, CVR & FDR and flexible architecture of digital bus interface. MiG-21-BIS upgrade program is behind schedule and has faced inordinate delay due to various reasons, importantly instability of Russian Industry. These upgraded aircraft with plenty of airframe hours would serve the designated operational slot for at least a decade and a half.

The last word in India on MiG crashes belonged to the then Minister of Defence, Mr Jaswant Singh. He expressed his dislike for sensational reporting of the problem. He was replying to a question in the Lok Sabha on its last day of the monsoon session. With frequent accidents involving MiG –21s, these fighter aircraft were being termed by some as "Flying Coffins". Defence Minister Jaswant Singh said, "Government does not agree with this kind of sensationalising of security-related issues. These aircraft remain fully airworthy and continue to carry out all the tasks, as planned during their first induction".

It is once again reiterated that the design philosophy of the MiG-21 must be respected the aircraft manufactured/overhauled as per technology, operated and maintained as per instructions to minimize chances of accidents. One is confident that IAF with relentless efforts would surmount the problems. It would indeed be very sad if the MIG-21 were withdrawn from service. If that happens, one can only say that we are a “Developing country with very Rich habits”.

Appendix 1: Flying Training

It is reported that training flying on one of the MiG-21 variants has been suspended pending investigation. This needs elaboration, as in some sections of the press it has been presumed that the training halted pertains to that of AJT role being performed by the MiG-21.

Flying training in the IAF starts with Stage I-on piston engine HPT-32 aircraft. Thereafter, Stage II – on subsonic jet trainer, Kiran. After this stage, the cadets are commissioned    and those selected for fighters train Stage IIA-on Kiran/Iskra. After this stage, they train on the MiG-21 FL version at MiG Operational Flying Training Unit (MOFTU). This training is essentially that of AJT type ie, basics of tactical flying. On completion of MOFTU, pilots are posted to operational squadrons equipped with different types of aircraft.

In the squadrons, a pilot first undergoes conversion on the type of aircraft and then follows what is called the “Operational Flying Training Syllabus” laid down for that particular type of aircraft to attain “Fully Operational” status by day and night. Now as a front line pilot, he is required to maintain laid down standards of proficiency and for this purpose, pilots of every fighter squadron train regularly for which syllabus is laid down. This training is a day-to-day affair, where tactical exercises are done to realistic conditions consistent with safety. Fighter pilots need this training to maintain good form just like a top athlete or a sportsman. It is this squadron training that has been temporarily stopped by the IAF on MiG-21-BIS pending investigation of the recent accident.

Appendix 2: Flame Tube Burning : R-25 Engines

Sunday (12 May 2002) Indian Express has carried a report by one its correspondents titled “MiG-21 Crashes may be due to Design Deficiency”. Quoting an Air Force source he has stated that “ design deficiency is suspected to have caused two air crashes in less than a month. Flame tube burning is feared to be one of the reasons”. It must be brought out that such reports are highly speculative when investigations are still in progress.

R-25 engines fitted on the MiG-21-BIS aircraft like most jet engines have a combustion chamber with ten interconnected flame tubes. This is where controlled combustion of fuel takes place and the heat energy generated (hot gases) drives the turbines. In these engines, burning of `interconnectors' and some adjacent areas of the flame tubes has been observed. It is learnt that 50% of the engines that come back for normal overhaul (without any defect reported) have some amount of flame tube burning. These are repaired during overhaul. In some cases, pieces of `interconnectors' are found in the jet pipe and the engine is withdrawn then for repairs.

Russians initially stated that the flame tube problems were peculiar to Indian operation and went to the extent of casting suspicion on the type of fuel being used in India. They accepted that the flame tube problem was prevalent in other countries too, only after they were confronted with data and facts. Russians have taken up the work of design improvements to the flame tubes after number of rounds of technical discussions. The whole process of redesign and testing does take time.

Flame tube design is such that the actual flame is contained and the temperature controlled by three layers of out flowing cooling air. The aerodynamic arrangement is such that while cooling air can get in to flame tubes, the flame cannot escape out of the tube, due to what is called “Eductor” effect. It must be mentioned that the phenomena of flame tube burning has not caused any accident so far. However, a number of engines have been withdrawn for repairs. Accidents involving the flame tube area (not due to burning) are, one case due to faulty workmanship during overhaul-improper locking of one of the burners, two cases in late 80s, involving engines of Russian origin due to dislodgment of `swirler' (from inside the flame tube). The process of fitment of 'swirler' on to flame tubes stands modified.

Flame tubes are the stomach of the engine and the present problem of burning on R-25 engines is like a benign tumor, which is being treated. The present state of flame tubes is one of tolerable design and the IAF is managing by carrying out additional inspections.  


This article first appeared in the magazine Indian Aviation and has been reproduced here with the permission of the author

Last Updated on Wednesday, 25 November 2009 02:25  

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