Saving the Chetaks of the IAF

This is a very personal story of my involvement with flight safety, eight years after retiring from the Indian Air Force (IAF). I believe that I helped save a few Chetak helicopters from disaster. This must rate as my most important contribution to flight safety.

But first have a quick look at a bit of personal history relevant to this story. I attended a one-year course at the test pilots school in the UK in 1956 and then did nothing other than test flying for sixteen years. Of these, I spent six and a half years on deputation in Egypt working on Messerschmitt’s last design, the HA-300 - his first supersonic aircraft. In May 1967 the Chief of Air Staff (CAS), Air Chief Marshal Arjan Singh, visited Egypt where I acted as his staff officer for a few days. The very first thing he told me was that my career in IAF was over unless I got back to India, and soon. I asked him why he could not post me back to an IAF unit. After all, he was the all-powerful CAS. He explained the political implications of my working on a very expensive aircraft project in a friendly country. He was right of course; I did have to leave the IAF prematurely in 1976.

There were two unfortunate things involved in my departure. The first was that I was sent to attend the National Defence College (NDC), for which I shall be eternally grateful. A promotion board was held while I was still at the NDC and I was superseded. Since no confidential reports were raised there, my deficiencies were already known to IAF. Yet I was detailed for the one-year study. On completion of NDC, I was posted as Director Flight Safety (DFS) at Air Headquarters (Air HQ).

The second even more unfortunate feature was the decision of IAF to post a superseded officer as DFS. This said a lot about ideas then prevailing about flight safety. By definition, a person who has been bypassed for promotion is likely to be quite demoralised and unable to do justice to the job unless, of course, nothing is expected of him anyway. The IAF later confirmed its disdain for the job of DFS by retiring one incumbent after denying him promotion. Even worse, another superseded officer was posted to the same job. Hopefully, the IAF would not repeat such placements of unwanted officers to a post which really should contribute to enhancing flight safety in IAF.

My only regret on leaving IAF was that I had not been able to contribute to flight safety of operations in the service. But I had no hesitation in requesting premature retirement and then joining a defence agency as its technical executive. Once when I was visiting Bangalore on the agency’s business, I called on Chairman Hindustan Aeronautics Ltd (HAL), Air Marshal LM Katre. I had known him since 1950, immediately after being commissioned, when he was an instructor to convert us to Spitfires and Tempests. As I entered his office and wished him the time of the day, he stood up from his chair and said that before sitting down I should hear what he had to say.

Air Marshal (A/M) Katre’s words surprised me. He said, “We were bloody so and so-s (he used an un-printable word) to let you out of the Air Force”. I told him that it was seven years since I had retired and there was no point in talking about it. He disagreed and told me that if I were still in service he would have inducted me into HAL. This surprised me even more and I asked him what job he wanted me for. He explained that since the fatal accident on the first Ajeet Trainer, he was himself trying to monitor flight testing to ensure that no avoidable risks were being taken. Apparently, many of my friends and ex-colleagues had recommended my name to him for this task. Eventually, I joined HAL in end-March 1984 as Executive Director (Flight Operations & Safety), though the post was then known as Group Executive and abbreviated as GE (FOS). Currently a General Manager (GM (FOS)) holds the post. On promotion he should take over as ED (FOS).

Excitement was not long in coming. While I was busy monitoring the flight test programme of Ajeet Trainer, the Chairman summoned me to his office in mid-June 1984. He described two incidents of force landings in Chetak (Alouette III) helicopters at 17,000 feet above sea level. Lt Gen Bhupinder Singh, General Officer Commanding-in-Chief Central Command, was on a visit to Himalayan mountains of UP in his area of responsibility. The Chetak carrying him suddenly had serious instability. The resulting vibrations caused the helicopter to force land. Another Chetak came to his rescue. Immediately after getting airborne this also force landed due to a similar problem and suffered considerable damage. Fortunately no one was injured. One could easily guess that the Lt Gen must have been quite shaken and very unhappy. A/M Katre said that since I was in charge of flight safety and the Chetaks were of HAL manufacture, I had to do something about this pair of incidents.

Back in my office, I decided that there was no point in my looking at the details of the incidents, as IAF would surely do a thorough job of enquiring into them. I decided to sit back and look at the broader picture. In a period of ten years there had been eleven accidents, including fatal ones, and four incidents of serious instability, sometimes with spacing cable failures, before the two new cases involving the Lt Gen.

Routine Maintenance on a Cheetah
An airman works on the Rotor hub of a HAL Cheetah. The spacing cables can clearly be seen connecting one blade of the rotor to another.

One of these two aircraft also had broken spacing cables. A startling fact immediately struck me. Spacing cables were said to have no function in flight. They only helped to ensure that rotor blades were roughly equidistant during start-up, hovering close to the ground, and switch-off. This ensured that the centre of gravity of the rotor system did not shift to one side. An asymmetric shift could result in severe resonance and perhaps lead to an accident. In IAF spacing cables were fitted on all helicopters of the Chetak and Cheetah (Lama SA-315) types. Yet there were no reports of any instability or cable failures on the Cheetas. For quite a while before the latest incidents, the Indian Army had been operating Cheetahs even in the Himalayas in summer, though IAF personnel seconded to Army units carried out their maintenance. There were no similar problems on the Chetaks operated in substantial numbers by the Indian Navy. Even IAF’s Helicopter Training School (HTS) had never experienced an incident of this type on its Chetaks.

The IAF had set up a committee to enquire into the causes of instability and spacing cable failures. It concluded that drag dampers, which reduce the movement due to lead and lag of rotor blades, were not functioning properly. The committee reduced the time between overhauls from 800 hours to 400. But the instability, sometimes accompanied with cable failures, did not stop.

Concerned with the spate of such cases, IAF asked for help from Aerospatiale, the original designer-cum- manufacturers of the Alouette III, which were produced under license by HAL and named Chetak by IAF. Its teams visited India in 1979 and 1983 and examined maintenance and operating practices of several Chetak units. They were extremely critical of IAF’s handling of the helicopters including poor blade tracking, systems maintenance, etc. They also found fault with operations as according to them IAF was doing too many auto-rotation practices which they perceived to be overloading the main rotor assemblies. HAL’s facilities at Barrackpore were found inadequate. After these were improved, HAL teams toured Chetak and Cheetah units and conducted maintenance workshops. The IAF took corrective action to incorporate the designers’ and HAL’s suggestions. But as was clearly shown by Lt Gen Bhupinder Singh’s experience, the failures did not stop.

Chetak over Hyderabad.
A HAL Chetak flying low trailing the IAF ensign. The Spacing cables can be seen clearly near the Hub.

Armed with these initial inputs, I visited HAL’s overhaul shop where drag dampers were being serviced. To my surprise I found several of them already defective even after only 400 hours of operation. Yet they had not been involved in cases of dangerous instability. I decided that the root cause lay elsewhere.

The fact that the Indian Navy never had even one case of instability was surprising. The Navy’s servicing of Chetaks may well have been as good as IAF’s, if not better. But all the same, some incidents should have occurred on Naval Chetaks if the causes were common with IAF. On the other hand, HTS being an IAF unit would have had maintenance practices of the same standard as other units of the service. And it would have practiced any number of auto-rotations. Yet it had no similar failures. The Indian Army’s example was the clinching argument. If you were a good IAF officer you deputed your worst technicians to the Army. Jokes aside, there was no way that the Army’s Cheetahs were being maintained in any remarkably better manner than IAF’s Chetaks. My conclusion was that despite Aerospatiale’s critical conclusions, auto-rotations and poor maintenance were not guilty of causing instability or spacing cable failures. This left operating methods as the most likely cause.

The history of all seventeen aircraft involved in serious instability cases soon brought out a possible link. All Chetaks, which experienced instability with or without spacing cable failure, had extensively operated in the Himalayas. This included even the one, which had an accident near Nagpur, when Air Chief Marshal IH Latif was said to have been on board. Fortunately for IAF, he was not injured. Operating Chetaks in the Himalayas had to be the root cause. This was confirmed by pilots experienced in flying Chetaks in the hot and high environment of the mountains. They explained that whereas the maximum permissible transient collective pitch was 1.05, in almost every single take off it had to be taken to its maximum of 1.10. This was mostly due to all up weight being higher than the helicopters were capable of lifting easily. Turbulence made it even worse. Europeans do not often realise that in the Himalayas in the summer, sunshine can raise the temperature to 40°C or more above the international standard for the concerned altitude. Thus the Chetaks were operating above their declared ceiling, at higher than desired weight and at excessively high density-altitudes, often in the presence of unpleasant turbulence.

I remembered that IAF had evaluated the SA-315 for hot and high operations. In fact an IAF test pilot set a high altitude world record in it. IAF obviously selected the aircraft with a view to operating it in the hostile Himalayan environment. Yet it was the Chetak, which was being used. Armed with some statistical calculations I faced the Chairman. I informed him that the chances were very slim that the problem was anything other than use of Chetaks in the Himalayas in conditions for which it was not suited. Operations under these adverse conditions were over-straining the main rotor assembly, hence the failures. Spacing cable failures were the symptom and not the cause of the problem. I suggested to him that above a density altitude, which I specified, Chetaks should not be used and should be replaced by Cheetahs. Air Marshal Katre was convinced and decided to take up the solution with IAF.

Soon after returning from a visit to Delhi, the Chairman told me that the idea to replace Chetaks with Cheetahs had been rejected outright by the Air Officer Commanding-in-Chief of Central Air Command. His problem was that he would have lost all his assets of helicopters with no Cheetahs available to him in a hurry. A/M Katre told me that he would bide his time. In September 1984, he took over as CAS.

Within a few days of assuming charge as CAS, Air Chief Marshal Katre summoned me to Air Headquarters (Air HQ ). He told me that he had placed the Assistant Chief of Air Staff (Flight Safety) ((ACAS (FS)) directly under himself, at least for a while. He asked me to visit the ACAS (FS) and help him issue a suitable air staff instruction to implement my suggestion. After completing this job I returned to Bangalore. A few more days passed and I was summoned to Air HQ again. This time the CAS said to me, ”You will be glad to know that your recommendations have been implemented: I immediately replied,” Sir, you will be glad to know that you have lost your last Chetak to this problem”.

I was almost right. I heard rumours that two Chetaks were sent to Siachin Glacier and failed to return. Apparently this must have been an unavoidable operational need and the exact cause of their loss is not known to me. But since then, for the last eighteen years or so, not a single case of instability or spacing cable failure has been encountered. This was my greatest flight safety triumph. I sincerely believe that I helped save a few Chetaks from disaster. Now that we have new types of helicopters, much better suited to operating in the Himalayas especially in the summer, we are unlikely to see a Chetak coming to grief attributable to this problem.