Orpheus Mod 113 & Its Aftermath

Excitement after emergency was over!
By Gp Capt Kapil Bhargava (Retd)

During my deputation to HAL as a test pilot, I had several incidents which could have been a lot worse that they turned out to be. One of these was on Gnat IE 1073 on January 23, 1960. The incident itself was not much to write home about. But its consequences are well-worth recounting.

Let me first describe a bit about the background to this little tale. My first flight in a Gnat was on November 24, 1959 on the first HAL assembled Gnat. Prior to the rather exciting flight which is the main subject of this anecdote, I had a grand total of 8hrs 55mts of production test flying on several Gnat aircraft. I completed eight flights adding up to five hours on IE 1073 in clean configuration till the aircraft and all its system were working satisfactorily. I cleared it for installation of the drop tanks for its final flight to get it ready for delivery to IAF.

Meanwhile one of my initiatives was to record several parameters of each aircraft which were not part of the production test schedule. My idea was to collect all possible statistical data of the fleet to validate the performance figures of the Flight Manual. The record would have also generated other information which was not given in it. This would have helped identify any aircraft which did not perform to the same level as the rest of the fleet. A pertinent reason for the need of such data was that extra fuel tanks were about to be installed on the aircraft. But no flight tests were planned by HAL or advised by Folland for a revision of the Flight Manual.

My fateful flight on the IE 1973 with drop tanks went well in excellent weather. I got a few extra performance figures for my record. The final point was to note the maximum level speed at full throttle at 20.000 feet. As soon as the drop tanks were empty, I opened full throttle to accelerate to the maximum speed roughly over Kolar airfield. A few seconds after the speed stopped increasing, the engine wound down to idling with no warnings of any kind. My immediate reaction was to pull up and gain maximum possible height until the speed dropped to about 170 knots. I had already turned towards home and was sure I could land the aircraft back at the HAL airfield. My next action was to consider if there was anything else I could do to get the engine working again. It was still running at idling rpm but did not respond to throttle movements. An attempt to relight was no help. Of course, unlike the Vampire, there was no isolation switch in the aircraft. There was nothing I could do except plan my approach and landing. I kept the drop tanks on with the thought that I could jettison them if I needed a last minute stretch of the glide. By about 1700 feet amsl. I told myself that ejection was ruled out and that I was committed to the landing.

As it turned out, I landed exactly on the initial part of old 09 runway (now relegated to a taxi tack). With normal braking and the parachute, I stopped comfortably in about 800-900 yards and turned off to stop at the normal spot from where we used to operate the aircraft. I switched off the aircraft and got out. I had warned you at the beginning of my tale that the incident did not generate much excitement. But some fun was soon to begin.

As I got a few yards away from the aircraft, I saw that much fuel was draining out of the aircraft as the engine rpm was dying. A Bristol Siddeley engineer watching me come in, ambled over and said to me, “I see that you are a victim of Orpheus Mod 113.” In some surprise, I asked what this mysterious mod was. He still very casually told me that one of the fuel pipelines of the engine must have broken. I asked him how and why would such a thing happen. He said the the pipelines were all steel and they often cracked and broke due to fatigue. This was a shock and I explained that the aircraft had just done a few minutes over five hours and perhaps the engine would have run another couple of hours on the test bed during production. Did that mean that fatigue failure could occur in well under ten hours of operation? Still very casually, he said, “Oh, we have had failures on the test bed itself some times in less than two hours of operation. That’s why Orpheus Mod 113 replaces the steel pipelines with rubber ones. The engine on your aircraft has not been modified.” This was the big shock of the day and asked him rather rudely, “How the hell, have you cleared the engine for flight?” The calm Brit engineer just shrugged his shoulders.

I got back to my office, changed into my uniform and charged off to send an official telegram to Air Headquarters. It basically said that the Orpheus engines as installed on the aircraft were dangerous and the last few words said. “All Gnats are grounded till Orpheus Mod 113 is introduced.” I do not remember where Wg Cdr Roshan Suri the Chief Test Pilot was, away or what. But I did not wait for him since I perceived the risk to be too great and unnecessary. The engine failure could occur during take off, leading to a certain fatality. The reaction from Air Headquarters was almost instantaneous by a telegram addressed to Flt Lt Kapil Bhargava. It informed me that I had absolutely no authority to ground the fleet of Gnats. This privilege rested only with the Defence Minister and the Chief of Air Staff. I responded with an abject apology for my lack of knowledge of the protocol but added, “However, no Gnat should be flown till Orpheus Mod 113 is implemented. The risk of a major accident without it is excessive”. Authority or no authority, that did ground all Gnats.

Obviously Air Hq was in a hurry to get the fleet back in the air. I soon got a letter from a Wg Cdr Tech (Eng) advising me what I should do to restart flying the aircraft without waiting for the mod to be carried out. Basically the letter said that I should check the engine before every flight and if it was satisfactory, I could resume flying. I replied to the Wg Cdr that I was not an engineer and hence did not know how to check the engine. I also said that I was not clear what instructions to give to the technical staff on how to check it. I mentioned that the incident was caused by the servo pipeline cracking due to fatigue. This controlled the stroke of the fuel pump and its failure had led to the pump going to its idling stroke. Since there were many steel pipelines, I would be unable to identify which one would fail next. Besides my visual inspection would not indicate if a pipeline was about to fail due to fatigue. I asked if we should do dye-penetrant tests or x-ray for all the steel pipelines. I requested the Wg Cdr to come and show us the methods suggested by hin or Air Hq could please send another engineer on a short TD to HAL to show us how to do the visual and other checks to clear the engine for each flight. I never got a reply to this polite mail and at least in HAL all Gnats remained grounded till Orpheus Mod 113 was implemented on each aircraft.

The epilogue of this tale was not related to the Gnat. AVM AM (Aspy) Engineer (Later CAS) then Managing Director HAL phoned me on hearing about the successful retrieval of the Gnat. After congratulating me, he said, “Even though you do not want to be the number two on the HF-24 project, you are now detailed for it”. The order meant that I made three flights on the HF-24 Glider. Luckily, I was soon pulled out of HAL for the Avro project in the UK. My reluctance was due to the fact that I had been convinced that the HF-24 would fail to get airborne with Roshan Suri flying it on its maiden flight. I had offered bets on this of a bottle of scotch to many people in HAL but no one took me up on it. As it turned out, my fear was too prophetic, to everyone’s sorrow. But flying the Gnat in HAL and the errors on the HJF-24 project helped me a great deal to handle Messerschmitt’s HA-300 prototype in Egypt. It was mostly a case of avoiding the errors committed on these two projects, and forestall any new ones. But I did succeed in getting the control system of the HA-300 to feel almost completely like the Gnat, but without its pitfalls. The aircraft became quite a pleasure to fly with control movements and forces very similar to our Gnats.