Iroquois Turbine Rotation
By the time you read this, the last 2008 rotation of No. 3 Squadron personnel and the two Iroquois helicopters, should be safely back home in New Zealand after a very successful 18 month deployment to Timor Leste.
Taking the rotorblade off
The deployment operated two UH-1H Iroquois helicopters, and worked with the International Stabilisation Forces in support of the government of Timor Leste. This is one of the many stories that happened in the background, requiring close liaison and work between deployed and home units, to ensure that both aircraft were kept in a constant state of readiness.
Our team of 31 aircrew, ground crew and support staff arrived at the end of October 2007, for the third rotation of No 3 Squadron detachment in Dili, Timor Leste. We were located close to the township in a location known as the HPOD (Helicopter Point of Departure). The ANZAC camp was small but well established, with hard standing air conditioned accommodation, excellent food and medical facilities, and nice open hangars to work from.
This story started with a phone call on Friday 16 November 2007 at 1130 local time – 1530 Kiwi time – when everyone back home was starting to tidy up their workspace and thinking about heading down to the Mess for the usual Friday exchange of ideas and problem solving. Staff at Ohakea Technical Support Unit (OTSU) had been going over some recent engine performance data – a test carried out on a routine basis. They found that the vibration limits had been exceeded and some urgent work needed to be done to allow the aircraft to remain flying.
By the time we had looked at the records and spoken to the Maintenance Flight Commander (MFC) at No. 3 Squadron, it was well after knock off-time back home. It had been determined that the N2 power section of the Iroquois engine, which have a vibration limit of 2.3” IPS (peak), had been recorded at 2.39” during the previous Performance Engine Analysis Test (PEATS). This meant the engine was not running as balanced as it should. It was decided to carry out another PEATS flight to recheck the N2 vibrations.
The aircraft was towed into the hangar, where our small and dedicated team of aircraft and avionics technicians had the PEATS kit installed by mid-afternoon. A test flight was carried out, confirming that the engine was indeed vibrating above limits at 2.45” IPS. After more discussions with MFC3, our options were simple – we could either change the engine, or attempt to rotate the turbines inside the engine to adjust the balance and reduce the vibrations.
An engine change was our preferred (if not drastic) option and would only take two days. A turbine rotation however could stretch out over three to four days, due to the checks required in this process. MFC3 conferred with fellow engineers at home and, in consultation with the Director of Aeronautical Configuration (DAC), decided that the engine was safe to fly until the next scheduled Phase servicing in 60 hours time. The proviso was that another N2 vibration flight was to be carried out at the mid-point, in about 30 hours time, to see if the vibration was getting worse.
What the home team was balancing was a trade-off between the extra time taken to hopefully achieve a successful turbine rotation, the limited pool of serviceable engines, and the option of returning the engine to Singapore for a warranty claim. At our remote location, we could only imagine the ‘heavy’ discussions that would have been carried out between DAC, No. 3 Squadron and the engine specialists!
The hours rolled by fast for NZ3808, and by 24 November 2007, we were ready to install PEATS again for another N2 vibration flight. The result this time was 2.46” IPS – a fraction worse, but the average vibration readings had dropped. The all clear was given to allow the aircraft to proceed to Phase.
The next major decision was in the hands of the engineering staff at Ohakea – to attempt turbine rotation or change the engine. After much discussion and research, it was decided to send CPL ‘Poly’ Tavave from the Helo Bay, with some specialist tooling needed to disassemble the turbine section.
Our aircraft flew the remaining hours off in just under two weeks and was brought into the hangar to fit PEATS and prepare the aircraft for turbine rotation. The maintenance team disassembled the engine as far as they could until the point where the specialist tooling was required. CPL Tavave arrived in-theatre on Friday, 7 December 2007 and, after a quick orientation, was straight into work, with most of the maintenance team helping or looking on.
For the technical amongst you, the power shaft was rotated 180 degrees, with the N2 turbines remaining stationary. The theory being that the power shaft and turbines had been reassembled, after overhaul, with the heavy sides together. Rotating the power shaft should balance out any weight-induced vibrations.
By late afternoon, 08 was ready for its first post-rotation flight. Many breaths were held as it took off for the short flight, and many cheers were heard when post-flight results were advertised – 0.8” IPS! The first rotation had worked, meaning no other rotations were needed. The (ginger) beers were broken out and the message passed back to MFC that the engine was good to go.
Apart from the days saved in further rotations, the fix had also averted an engine change – saving the Air Force many thousands of dollars, and ensuring our spare engine remained just that. CPL Tavave now had a few days up his sleeve and, when not helping out on the Phase servicing, was able to enjoy the company of detachment personnel and the occasional sightseeing ride around town. He departed the following Tuesday, on one of the two C-1 30 Hercules, involved in OP GYRO rotation changeover. We thank you for your help and expertise, CPL Tavave.
NZ3808 went on to have a contingency Phase servicing in record time.
One week later, she was outside ready to start the usual post-phase engine runs and adjustments. The spare engine was used a few weeks later on the other aircraft. But that’s another story…