TUESDAY 16 OCTOBER 2001

SQUADRON LEADER ROBERT BURKE

  680. Did I understand from what you just answered that there were occasions on test when the overspeed limiter did not operate as it should have done?

  A. Only when you were testing it on the ground in the midpower range. Because of the nature of the system if you tested it full power and it did not work you would have wrecked an aircraft, let alone damaged it, so you had to test it at an intermediate power setting and it was not a good procedure. I do not think there was very much wrong with FADEC, it was just the test procedures. I think there may have been one or two minor software adjustments. To cure this problem, the cure came quite a long time after the accident, I cannot give you a date, we changed the procedures, in fact I think we had a go at several different procedures. But of all of the faults in the FADEC at that time, this ground test procedure gave rise to more faults than any other and this—because it was your last ditch to stop this full authority system, and the FADEC means full authority system—running away to overspeed the rotor. This was the back-up; the final stop, the bottom line, whatever you like to call it. Because the test procedures for this feature were leading to run aways and over temps themselves the pilots had very little confidence in this particular feature.

  681. What you are describing are the situations which were not flight safety critical?

  A. No, on the ground.

  682. They were all on the ground?

  A. A helicopter on the ground—and I can speak from personal experience, having been in a helicopter on the ground that flipped over on its back—when the rotors are running is effectively airborne. The best way I can describe it to an intelligent layman is we are always in the position of an aircraft just before it takes off. We are on the run way, just before we take off. When the rotors are going round it only requires some very small thing to make the helicopter lift from the ground or, worse, lift on one side and not on the other side. That is the best way I can describe it.

  683. What happens if you have a single jam in the control system, however temporary it is?

  A. It all depends what kind of aircraft you are talking about. To explain it properly on the Chinook, I did give you a piece of paper in response to a question that you put to me about the aircraft having controlled jams flying on a straight level, I included a small explanation in that. If you have a single control jam in an ordinary conventional, fixed wing aircraft it can be fairly innocuous because if you get a jam in roll or a pitch or a yaw it stays in that channel. Because of the way you control a helicopter in flight it becomes much more complex. On a conventional helicopter with a main rotor and a tail rotor you can sometimes get away with a jam in the tail rotor system only and it is limited just to yaw. However, if you have a control jam in the main controls of a helicopter, a conventional helicopter, it becomes much more complex because the system basically relies on all of the control inputs, both manual and from the hydraulic jacks, working correctly so the logic of the other bits of the system works correctly. In the Chinook that is even more so because you only have two main hydraulic jacks for each rotor and a single fault in the controls can lead to quite unpredictable control responses. The Chinook control system is unbelievably complex, it is very difficult to understand, it has two immensely complex mechanically mixing units on the top, let alone all the hydraulic ones that go in, and every bit of it depends on every other bit of it working effectively. That is the best way I can explain it. I have had a control jam on Mark I where the results as far as the pilots are concerned are just the same as the Mark II. This occurred, thankfully, just as I was taking off. I will describe it in detail because it will answer many questions which people might wish to put up. I was taxiing at Odiham as the captain of an aircraft with a co-pilot, whose name I remember, so we can verify this, as we were ground taxiing we got a bit of jolt through the controls, which is not unusual for ground taxiing in that particular dispersal because concrete used to come up regularly and it is fairly bumpy. I discussed it briefly with the co-pilot, I said, "did you touch the controls?", to which he said, "no, we must have gone over a bump". As I came to lift the aircraft off I felt a restriction of some kind or controls not responding properly and the aircraft instead of lifting off straight that way, (indicating) the nose went down and the back end started lifting and the aircraft started rolling slightly. This was in a Mark I Chinook. I stopped the aircraft immediately and shutdown with the fastest procedure you can do for that. As I explained, you do not want the rotors running, even if you are on the ground, if have you a problem with controls. That aircraft was towed back and the ground crew ran it for about a day and a half between the hangers with ground power on it and without the rotors going to try and reproduce the jam and then they asked me to fly it again. I said, "no, let us give it a bit more", because we thought the vibration might have induced something.

  So we ran it for about another hour and I should think it had done about eight hours' running by this time and at last they reproduced the jam on the ground. You will have to examine the technical records of exactly what went wrong but they found a problem with one of the hydraulic jacks. The records for that will be somewhere in Swanton Morley and I can give you the name of the RAF co-pilot but, as I did not take off, it is not in my logbook. I think that particular incident was 1987 or 1988. On the question of hydraulic jams, the Chinook Mark II hydraulics were modified so there was an anti-jam system. There had been a problem in the Mark I where a dormant fault was found when one hydraulic jack jammed the controls and another had a dormant fault and it suddenly became apparent. However a mechanical jam below where you got mechanical inputs into the two sets of hydraulics, could have exactly the same results depending on how the jam occurred. Would you like me to go back to the balance spring and the insert pulling out? Is that what you are ultimately getting at, sir? Do you want me specifically to look at that?

  684. Yes

  A. I will explain in aircraft engineering terms how critical loose components are in flying control systems. If on an RAF aircraft we lose a washer or a nut the size of my little finger nail in an engineering procedure, that aircraft is grounded until the component that big (indicates) is found, even slightly smaller than that, or the most thorough engineering examination, often lasting about three days, is carried out before that aircraft is allowed to fly again. I have explained the problems with control jams in helicopters. They tend to be by nature much more complex than in fixed-wing aircraft. But that is how we treat loose articles in the controls. The spring and its mounting point in the Chinook broom cupboard which became detached on one end is about that long (indicates) and then it has got a bit about that big on the end of it. The possibility of that getting jammed in the control closet—and I gave you a picture of what the control closet looked like—it is about that round and that tall and in that I do not know how many bellcranks and levers there are, I guess about 100, and there could not be a worse place to have a loose article than that.

  685. That is the broom cupboard?

  A. In the broom cupboard. I gave you a picture from the aircrew manual just showing the mass of controls there are in there.

  686. Yes, we have seen it. We all went to look at one.

  A. That is really all I can say on jams.

  687. There were two occasions when the control pallet became detached.

  A. Not the pallets, the insert.

  688. But that resulted in the pallet coming adrift from the fixings. They both resulted in stiffness of controls, change of feeling in the controls?

  A. It probably is one of the controls only.

  689. And it was suggested to us that therefore a detachment was not a serious proposition.

  A. What I have said already probably gives you an idea of how seriously the RAF take loose articles. I think you have seen copies of those RAF documents. You may have seen the second one with comments by Group Captain Verdon. I gave you a copy of the first one as well and this is from the Squadron Engineering Officer, so you could not have a more authoritative document than that. I have suffered a number of control failures in various kinds of aircraft, in fact probably more in the Puma than the Chinook, I might say.

  690. Squadron Leader, could we turn to the question of engine fail captions.

  A. It was a well-aired and minor problem. I just happened to find a set of flip cards of about that era of the crash and I think already we had got that in there. They were faults, there was a drill laid down, they were not fully understood at that time. The problem with getting a failure caption, especially if you are flying low level or are under any kind of pressure, is to start with you have to treat it as real because things do happen incredibly quickly in the air. I have had two accidents and about 50 times as many serious incidents as most pilots because of the nature of the job I was in and until you have a really serious incident, particularly if you are close to the ground and to a certain extent more if it happens in a helicopter, you do not realise just how quickly things can go wrong. The first thing you do with an engine failure caption, whatever it says in the book, is you treat it as real and you take a finite length of time to check dials and gauges and confirm to yourself it is not real.

  691. How long would it normally take to check in fact it was a bogus caption?

  A. Difficult to say. It all depends on the circumstances you are in. If you are flying straight and level and you are not doing very much else at the time, both pilots, I would think something between five and ten seconds probably. If you are in a manoeuvre at the time and you have got to take an aircraft out of manoeuver and you get a failure caption of some kind on an aircraft, the first thing that is drilled into you time and time again as a pilot is the safety of the aircraft. You generally roll your wings level and get it into a gentle climb and then try and sort out what the problem is. There have been numerous cases in aviation of pilots getting obsessed and going to a completely useless warning light and looking at that and forgetting about flying the aircraft. So the first thing you do is get the aircraft in a position where its wings are level and probably in a slight climb and then look at it and look round the gauges.

  692. You have told us, I think, about the various problems caused by electrical power interrupts. Taking you through this critique of the Defence Committee could you just explain a little bit more what the engine condition levers are and what the effect of their being disabled. You refer to this.

  A. Yes, the engine condition levers are three-position levers up there at the cockpit and one position is a stop position, one is in ground idle position, where you set the aircraft rotors running on the ground, and one is full throttle. The full throttle is then modified by the FADEC or on the old Chinook by a purely hydro mechanical system to bleed off from full power. The engine is set at full power and it is bled off and whatever kind of computer or fuel control system you are using, adjusts the power of the engines to keep 100 per cent rotor speed. The engine condition levers take you from these particular conditions, stop, ground idle, then full throttle but that is modified by the fuel control system, the FADEC in the case of the Mark II, in response to the rotor speed and how much power you are using. This is the collective or thrust lever.

  693. Is there anything in the over-temperaturing of the engine by the FADEC system? You refer to this but does it produce any serious results at the time?

  A. When the engines are over temped?

  694. You said that several engines had been over-temperatured.

  A. The Ministry of Defence will give you better information on this than me, but I have seen two or three engines which have been over-temped. You have to scrap or completely rebuild the back end, the hot end of the engine.

  695. If they become over-temperatured in flight is that likely to have a serious result?

  A. Yes it is likely to have a serious effect on any jet engine. In fact, because we have engines which are split into two halves, the front half produces a lot of gas going at high speed and that drives another turbine at the back which is connected to the rotors. There is a loss of engine drive to the rotors as well almost straightaway, especially if the things melt or start getting distorted.

  696. You have commented on torque mismatch. Is that when a differential power is produced by each engine?

  A. Yes. One of the functions of the FADEC (and you will find it in my layman's guide to the FADEC) is to match the power between the two engines so they are sharing the power to the rotors. If you get a mismatch of torque it means that one engine is doing no work and the other engine is doing all the work. There might be a good reason for that. One engine may have lost power, malfunctioned or, in the case of a runaway, it might well be producing too much power.

  697. What is the practical effect on the aircraft of a significant torque mismatch?

  A. It all depends whether you are in a benign flight regime or if you are very heavy. Perhaps the one engine that has gone up might well then have reached its limit and it cannot produce any more power or it might go into emergency power or something like that. In a benign flight regime it has really very little effect.

  698. I think you mentioned that large numbers of the Digital Electronic Control Units were returned to the makers for fault investigation, is that right?

  A. Yes, I think it has happened again since. Because I was the unit test pilot involved in maintenance I can remember that we had run out of DECUs, all of the aircraft in the hanger, the ones undergoing overhaul, had been robbed of their DECUs and at some stage the frontline aircraft could not get up to sufficient numbers because we had run out of DECUs. The situation was very bad, this is from personal memory, there were many days at Odiham when we only had one Chinook only available for training, some days when we had none, and the situation got so bad, as far as my memory serves me, when, the final straw was another DECU going down and we had no aircraft available and the Northern Ireland standby aircraft had to be used for the United Kingdom standby commitments.

  699. What was the position, was this a design problem?

  A. Nobody really knows, my Lord, because on most of the ones that went back no fault was found. All the ones that were taken out had something going wrong with them, that is why they were taken out. Part of the problem was that because of the speed at which this aircraft was introduced, the ground technicians were not terribly familiar with the systems and what they did was take out an unserviceable DECU and sometimes swap them across from side to side and, as with any bit of electronic equipment, as soon as you start moving it round the connections start going and you will find that most of the problems on any computer are probably simple electrical connections and the more you move them the more problems you get. I do not know whether the problems persist in that area, and I cannot answer that, but at the time we were desperately short.