This is how Hickman described it;
MR RAWLINSON: The fuel system was to be limited to 50 psi. How was that to be checked? For instance, what is the system on board the Nimrod to ensure that the pressure does not exceed 50 psi?
GP CAPT HICKMAN: We’re not talking about these checks which are done at 50 psi.
MR RAWLINSON: (overspeaking) under which is …?
GP CAPT HICKMAN: Okay, every 30 days the fuel system is pressurised through the refuelling probe, so that we pressurise the whole system. That’s done using a fuel (inaudible) at 50 psi.
THE CORONER: With the tanks full or empty?
GP CAPT HICKMAN: Yes, with the tanks full. So, we refuel so we refuel the aircraft through the probe, filling
THE CORONER: So, all the tanks are full?
GP CAPT HICKMAN: Filling all the tanks up and then so the system is pressurised.
THE CORONER: Are all the tanks full when you carry out your pressure test?
GP CAPT HICKMAN: Yes, yes.
THE CORONER: Have you had a blow off yet?
GP CAPT HICKMAN: No.
MR RAWLINSON: As a matter of interest, when you carry out the tests, do you ensure that the aircraft is flat enough and not declined or anything like that?
GP CAPT HICKMAN: Yes, we’ve learned from we certainly learned from that instrument report that you referred to earlier that if the aircraft is in a nose down attitude, then that causes problems. So, no, we make sure that they are at least level.
THE CORONER: What do you test, just as a matter of interest? The fuel comes into the tanks; how do you test the system that transfers fuel from one tank to another? The fuel-transfer system; is that tested at 50 psi. How do you do it, do you open everything, all valves?
GP CAPT HICKMAN: It’s the use of booster pumps for pressurising. They’re also turned on to make sure that both the refuel and the fuel feed systems are pressurised.
THE CORONER: So, every pipe that is connected to a fuel tank is pressurised to 50 psi?
GP CAPT HICKMAN: Yes.
THE CORONER: Except those feeding the engine?
GP CAPT HICKMAN: Yes.
THE CORONER: And this is done when all tanks are full?
GP CAPT HICKMAN: Yes.
THE CORONER: So it’s in fact a hydraulic test?
GP CAPT HICKMAN: It’s the aim is to look for leaks. We’re looking for leaks from fuel couplings.
THE CORONER: Yes. If you fill a system to its maximum so all the tanks are full, so you have a complete system full of fuel, then if you pressurise that you are, in effect, conducting a hydraulic test, is that right? Of the system.
GP CAPT HICKMAN: Well, as you’ve heard before, we’re not going to see those sorts of pressures throughout the fuel system.
THE CORONER: No, we’re talking about the test referred to. If you fuel the tanks and every fuel system in the refuel gallery and the transfer gallery, you fill that up so all those tanks are full and then you conduct your pressure test, would you simply fill it 50 psi and watch for leaks? That’s what I am trying to understand. What do you do?
GP CAPT HICKMAN: Well, we … what we’re doing is we will refuel the aircraft completely so that it would start off empty and then it will end up full. During that refuel, we will look for leaks.
THE CORONER: That is your pressure test?
GP CAPT HICKMAN: Yes.
THE CORONER: So you don’t do anything else other than that?
GP CAPT HICKMAN: No.
THE CORONER: So you just refuel normally and watch. You refuel at 50 psi and you expect, therefore, that all components of the refuel system to be at 50 psi? It is an important piece of evidence and it is important to understand exactly what it is you test. Are you testing the system as part of a hydraulic test of the system, or are you simply refilling the aircraft and watching for leaks, knowing that the fuel going in is at 50 psi, and if there are no leaks by the time the aircraft is full, then the system must be able to withstand a filling pressure of 50 psi?
GP CAPT HICKMAN: Yes. I mean, it’s an attempt to it’s certainly an attempt to reproduce what the aircraft will experience during air to air refuelling, by refuelling through the probe, and using the aircraft booster pumps to responsibility and pressurise the fuel feed system as well.
THE CORONER: So you are trying to recreate the system in flight?
GP CAPT HICKMAN: Yes.
THE CORONER: It is not a hydraulic test, then, is it?
GP CAPT HICKMAN: No.
MR RAWLINSON: Forgive me; the purpose of recreating the actual refuelling conditions is what AAR is now planning?
GP CAPT HICKMAN: Yes, it was introduced when air to air refuelling was still instated, but because the system was still in the aircraft, we’re continuing to check that part of the system.
THE CORONER: To put it clearer, you refuel the aircraft using the air to air refuelling probe?
GP CAPT HICKMAN: Yes.
THE CORONER: That is all you do?
GP CAPT HICKMAN: Yes.
THE CORONER: And if there are no leaks, that is your pressure test.
MR RAWLINSON: How do you check for leaks?
GP CAPT HICKMAN: The aircraft is depanelled, as far as possible, and then it’s inspected by the tradesmen.
THE CORONER: What equipment is used for this refuel? Is it the same ground refuel system, only adapted an attachment for the probe at the nose?
GP CAPT HICKMAN: That test equipment was already in existence, the ability to refuel through the probe, so that part of the system could be tested. So we’ve simply introduced we’ve just adapted that maintenance procedure that was already in existence. Because when a component in a fuel system is replaced, it’s normal to pressure test it using this MP, and we’ve just pulled up that MP as a way of pressure testing.
THE CORONER: You can see the subtle difference between pressure testing, which is a natural test of withstanding pressure, and refuelling an aircraft and seeing if it leaks?
GP CAPT HICKMAN: Yes.
THE CORONER: What you do, if I understand it, is refuel the aircraft and watch to see if it leaks.
GP CAPT HICKMAN: Yes.
THE CORONER: So it is not really fair to describe it as a pressure test.
GP CAPT HICKMAN: It’s the same test that we would conduct if we replaced a component in that system.