Mountain weather can easily fool you

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image: Copyright Civil Aviation Safety Authority

by Gilbert Griffith, a Flight Safety Australia reader

I had taken my ultralight thruster single seat aircraft out for a short trip of less than an hour around the local area.

I have been flying here regularly since 1974, starting in hang gliders, then flying trikes, ultralights, gliders, paragliders, GA, and even model helicopters, multicopters (drones) and model aircraft. I got my PPL at 17 years of age at Moorabbin airport in 1968. First solo was in a Victa Airtourer 100 at Civil Flying School in late 1967.

The thruster is aluminium framed with a dacron covered high wing and engine on the front of the single tube fuselage. It has full width ailerons and a normal tail empennage with large control surfaces. Elevator trim is an adjustable bungee cord. I had also made a modification to adjust a small amount of flap by lowering both ailerons with a car handbrake handle. I had also removed the fibreglass cockpit (after a crash demolished it), so apart from a windscreen attached to two down tubes, everything was open.

The local grass strip is at Porepunkah in north-east Victoria and runs north-south a couple of kilometres east of Mount Buffalo.

I was flying about ten kilometres east of the strip, over Wandiligong at 7500 feet when I decided to return to the strip and land.

The weather was overcast with cloud down to about 8500 feet but to the west was a line of darker cloud having a roll shape aligned almost north-south. Nothing particularly unusual and no bad weather was expected.

As I began the return leg I was hit suddenly by strong turbulence and a strong headwind. The turbulence was strong enough to tip my plane well over 90 degrees both ways in roll. I was concerned enough to tighten my full harness lap and shoulder straps, but I let the turbulence do what it wanted without fighting it and maybe over stressing the aircraft. It also started to rain fairly heavily, so my legs, shorts and lower body were soaked in seconds. The windscreen protected my head and face well. I was expecting to be rolled inverted at any moment.

I had to increase power to maintain any sort of headway or ground speed and even with full throttle of the twin carburettor, twin cylinder, 45HP Rotax two stroke engine, I was losing altitude at about 2000 feet per minute. I was worried about running out of fuel. I could not turn far enough around with the harness so tight so I could not see the fuel gauge on the tank behind my seat. At normal cruise power settings there would have been plenty of fuel, but at full throttle the engine was very thirsty.

While I was thinking about whether I would have enough altitude to clear the ridge between me and the airstrip I was still a couple of kilometres from the 1500-foot ridge and down to about 3000 feet myself. The airstrip was a further two kilometres past the ridge. It was still hellishly turbulent, but the rain stopped after a couple of minutes.

I had my eye on an emergency landing area or two in case I ran out of fuel or couldn’t make the intervening ridge. There was the Bright golf course, which I had force landed on once before in a different aircraft after the spark plugs had oiled up and the engine stopped. That was the second forced landing in that particular two seat thruster that I had had. Anyway, surprisingly, I observed that there was no sign of wind at ground level. The sewerage farm ponds immediately north of the golf course was dead still. All the surrounding trees were also showing no signs of any wind at all. So, I knew that a landing there would be a non-event.

Fortunately, the engine restored my faith in Rotax, as it didn’t even miss a beat with the heavy rain wetting it down (the rear flywheel is open to the elements and the points inside are readily accessible through the holes in the flywheel face). And as I had a plan B in mind for an easy forced landing, the fuel amount ceased to be a worry.

The headwind was slacking off a bit, and it looked like I would easily clear the ridge by a few hundred feet and leave me with a straight run to the airport, but it was still rocking and rolling until I cleared the ridge.

I have spent years flying this particular ridge in hang gliders from about 1974 in the first gliders to be produced in Victoria. I had made hundreds of flights in most conditions and had a few crashes as well, so I knew as much as one could about what the wind could do there.

Once over the ridge everything smoothed out with no turbulence and no headwind. Conditions were back to what they were just 15 minutes before and just like they had been all morning. Except for the fact that all the hangar doors along the strip were now closed, where they had been fully open with people milling around outside. Now there was no sign of people. It turned out that they had had to rush to close all the hangars as the doors were almost blown off by the gusts estimated to be around 90 to 100 kilometres per hour.

I overflew and joined downwind to the south at about 800 feet which was normal for ultralights. I did a normal base turn and final and rolled to a stop in front of the hangar. People were coming out of the hangars and running towards me as I shut down the engine. As I climbed out a couple of close friends ran up and hugged me with the most common comment being, ‘We thought you were dead.’

Quite a few pilots have died in the area over the years, thanks to dodgy weather that can appear suddenly. There is a lot of hang gliding, paragliding, ultralights, a few local GA pilots, and at times many visiting glider pilots. It’s a great place for recreational mountain flying, with good thermals and some good take-off sites.

In summary, mountain weather can easily fool you. And at the time there was no internet with access to radar maps that are so useful now. Also, I should have had more fuel on board. The tank holds 80 litres, but I have never filled it completely. Usually I have 20 to 40 litres which is plenty for an hour or two of flight. I had started with just over 25 litres and landed with about 8 litres remaining. On this engine there is a big difference between half throttle cruise and full throttle fuel consumption.

3 COMMENTS

  1. A well written & thoughtful article Gilbert.

    Checking out the area on Google Earth, having a strip tucked so closely into the lee of the Mount Buffalo plateau must mean you get a lot of ‘exciting’ circuit flying!

    Looking back, was deviating the approach to the North to fly over the town (and thus avoid the ridge altogether) a possibility which you didn’t get to fully consider due to the critically bad flying conditions?

    • Sorry for the delay in replying Cam.

      Circuits are most interesting when it is hot and there are many thermals.
      One incident I had involved an invisible willy willy in the middle of the strip which turned me 90 degrees causing me to hit a tree. Compound tib and fib fracture. That’s another complete story though.

      Re deviating to the north, over the town. I had time to consider it. Time was pretty telescoped! I am lucky in that I have never had occasion to panic when confronted with an emergency situation. But a forced landing in the town was not a good prospect. As it was I was within gliding distance to suitable paddocks the whole time, even with a probable negative L/D if the engine stopped. Two strokes do this often enough that I have come to expect it rather than the reverse. I have had two Rotax engine failures with forced landings, but not with this particular engine.

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