Forum attic item #14

[Chris H]

I have just returned from the Mawsons Huts Foundation (MHF) expedition to Commonwealth Bay and am writing up my reports when I came across this forum and its interest in the search for Mawsons air tractor. Perhaps I can shed some light on this years expedition, since the Air Tractor search was my responsibility.

I am a 59 year old doctor, with degrees in engineering and science as well as medicine. Previous experience includes doing science in environments as challenging as Antarctica. This is my second Antarctic trip, first being to Casey base.

I am partial to small aeroplanes, having spent 10 years - and a lot of flying time - as a remote area doctor. I never got a licence, but had a great time in the passenger seat.

My prime position on the 8 person team was Medical Officer - though the trip was without any health problems. Among my numerous other duties was the search for the Air Tractor, for which I used Ground Penetrating Radar (GPR - made by Mala in Sweden). Mapping software was sponsored by Golden Software in Colorado.

The GPR was unsuccessful in locating the plane, though the equipment functioned without problem during the expedition, being used to make contour maps in the ice down to 4metres. It was also used for bathymetry on two ice lakes and to map within the 600mm of ice on the floor of Mawsons Hut.

The doctor on the previous years' 2007-8 expedition, a pilot, initiated the search but did not have the appropriate equipment to pursue it. There will be another attempt to find the plane in this years (2009-2010) expedition, using a different approach based on my findings from this year.

Here are some facts from this years search:

1) We dug two holes, 1.7m and 2.7m. The first - based on the previous doctors' position - was too close to the sea. GPR showed a promising shape, which turned out to be a hard ice layer at 1.5m.

2) After the first hole came up empty I went back to the original pictures of the Air Tractor, taken by Campbell in 1931 and Young in 1976. From these I constructed 3 transit lines based on good, easily visible, well separated (about 120 deg) points. When taken into the field, all 3 lines met at one spot, and all were sensitive to translation and therefore useful. I am pretty sure that this is the spot where the fusillage has rested since at least 1931 and possibly 1913.

3) I also had pictures of a big melt in 2002, where a lot of rock was exposed. With the help of a professional photographer, we photographed the landscape from the same positions and superimposed the pictures. This established that the Air Tractor was sitting over a melt creek, and not on rock previously visible.

4) Pictures from 1931 and 1976 confirm that the ice in the shore area is not glacial, so the frame has not gone into the sea with ice movement.

5) From the pictures, where the ice level is similar, it can also be estimated
that the plane was sinking at the rate of about 30mm per year. This would put it now at about 900mm below the 1976 level. Measurements of todays rock levels show that this years ice level is about 800mm higher than 1976, so the frame should be about 1700mm below the surface. The GPR was capable of reaching to about 4m below the surface, and should pick up a tubular steel frame 6m long by about 1m wide.

6) Two overlapping scans were done, each of 17m radius over the spot where the frame was estimated to lie. A significant feature was seen at 2.5m in the place estimated for the plane, and a 3m x 1m trench was cut down to 2.7m. The hard ice layer at 1.5m was found, and another at 2.5m. A metal detector was used in the hole but no signal returned. The dig was abandoned.

7) The floor of the trench was surveyed and found to be at high tide level, and ice containing seaweed fragments was found at this depth. This means that liquid water was present at some time, and that it was likely to be seawater. A study of the temperature records from Dumont D'Urville (DDU), the French base 200km away, show a significant rise in summer temperature to well above freezing in the 70s and 80s with a peak in about 1980. Comparison between DDU records and those taken by MHF expeditioners suggest that DDU temperatures are a degree or two lower, but otherwise follow a similar pattern.

8) The Air Tractor seat was found about 100m away on rocks at the other side of the bay. This was a home made seat in addition to the two existing seats in the plane. It was clear from the photographs of the abandoned frame that the third seat had been cut from the frame, so its discovery does not imply any movement of the main frame.

My conclusions are that an appropriate search was done, using GPR, of an area where it is highly likely that the plane rested for at least 45 years between 1931 and 1976 (and probably 64 years since 1913). The fact that the plane was not found this year suggests either that GPR is not the right technology to use, or that the frame has moved since 1976.

a) If another technology is better, then it is likely that a magnetometer would be a preferred option. I don't know anything about magnetometers, and if someone does then please let me know.

b) If the frame has moved then it is unlikely to have gone anywhere but down and/or into the sea (which is about 30m N this year). It is possible that a big melt exposed the frame to liquid water, and that it sank to the bottom of the harbour. It may therefore be useful to survey the bay (called Boat Harbour) which is about 6m deep, using divers.

If anyone has comments on the above, and any more ideas or facts to help with the search, please post them here. The Air Tractor is an intriguing story, and I think its down there somewhere.....

[Catfish]

Hello Chris H. !

Thanks a lot for posting this ! I indeed believe a ground radar is not as effective as a iron-detecting device, like a magnetometer, but this should be very sensitive, having to work at least through a depth of one meter of ice, or better more -
Since i'm a geologist i belive there might be some other devices that might work, but weight and complexity may limit their use. Is the underground (bedrock) magnetic in any way (thinking of magnetite, or other iron-bearing rock) ?
Thanks and greetings,
Catfish

P.S: at M.Fra: Huh ?