msn 414

DHC-6 Twin Otter Series 300

8Q-TAO

msn 414

Ser 300

G-BDHC • N38535 • VQ-TGW • N38535 • DQ-PSD  VQ-TGW  N38535

8Q-TAO

Transglobe Expedition The Aircraft: Twin Otter

In selecting an aircraft for use on the Transglobe Expedition’s Antarctic and Arctic phases several important factors had to be taken into account. The aircraft had to be both mechanically reliable and well proved as it is a single aircraft operation. It also had to be able to withstand landing and take off in far from ideal ground and ice surface conditions.

It had to have sufficient range and payload to resupply the ice group during the crossings on both polar ice caps and, most importantly, the aircraft had to have a short take off and landing capability due to the lack of large flat areas in the regions in which the ice group operated. Taking all these points into consideration, it was decided that the de Havilland of Canada Twin Otter was the ideal aircraft. The Twin Otter is a light twin turbo-prop aircraft, powdered by two Pratt & Whitney PT6A-27 free turbine engines, and has an all up weight of 12,500 pounds (5,700 kgs). In its commuter role the Otter carries 20 passengers and two crew, whereas in the cargo role (as the expedition used it) the usual payload is about 2,000 pounds (900 kgs) depending on the range required. The greater the range, the less payload can be carried and surface conditions in the polar regions also governed take-off weight.

The Twin Otter used by the expedition was owned and was generously loaned by the Chubb Group. It was a 300 series and was the first Twin Otter on the British Aircraft Register, hence the registration G-BDHC. It was repainted red, white and blue, and all top surfaces were painted black to absorb as much heat as possible from the sun and to prevent ice from forming on the aircraft. It is a technique used with success by another operator of Twin Otters in the Antarctic at the time: The British Antarctic Survey. The Twin Otter was equipped in the wheel/ski configuration which means the pilot had the option of landing on wheels on prepared runways, such as the McMurdo ice runway in the Antarctic and during the ferry flight to the Antarctic, or he could select skis for field landings during the polar crossings.

The skis are operated by hydraulics, and a system of hydraulic rams moves the skis up and down around the fixed undercarriage. The undersurfaces of the skis are coated in a teflon-type finish which is designed to prevent the skis from sticking to the ice or snow when parked overnight.

As navigation by compass is difficult in the polar regions, one of the then latest navigation aids had been obtained: The Canadian Marconi “Omega” system, CMA734, which worked essentially on very low frequency global radio transmissions. Several stations throughout the world transmitted signals which were collected in the aircraft and, in conjunction with other information fed into it, the system computed the position of the aircraft. This type of navigational device was essential to enable the aircrew to locate the ice group during their polar crossings.

Another aid for locating the ice group to be carried by the aircraft was a very high frequency (VHF) homer. This was a system for tracking signals transmitted by the ice group when in reasonable proximity. An indicator in the cockpit told the pilot which way to go — left or right.

The two man crew of the aircraft consisted of Giles Kershaw, the pilot, who had been flying in the Antarctic for the previous five summer seasons with the British Antarctic Survey, and was a very experienced pilot on Twin Otters, especially in the ski configuration, and the engineer, Gerry Nicholson, who had just completed three summer seasons in the Antarctic working on Twin Otters. G-BDHC left England in early December, flying via Reykjavic (Iceland), Frobisher Bay (Canada), Toronto (Canada), Miami (USA), South Caicos (Turks & Caicos Islands), Trinidad (Caribbean), Manaus (Brazil), Asuncian (Paraguay), Salta & Mar Del Plata (Argentina), Comodoro Rivadavia (Brazil), Stanley (Falkland Islands), Rothera and Halley (two British Antarctic Survey bases in the Antarctic) and finally to Sanae (a South African base). Here the aircraft met the Expedition’s ship - MV Benjamin Bowring - and the main expedition. The ferry flight of some 12,000 miles (19,200 kms) took eleven flying days.

As the ship started unloading, the aircraft began to fly the expedition’s equipment and provisions to Borga where the party was to overwinter. Once these flights were completed and the base camp established the aircraft returned to England via the ferry route to go on charter in March 1980.

Later in the year as the Antarctic winter gave way to summer the aircraft returned to the Antarctic by the end of October 1980, ready to assist the ice group on its 2,600 mile (4,160 kms) journey to Scott Base on the Ross Ice Shelf via the South Pole. The aircraft was used for resupply of food and fuel and also to find alternative routes when obstacles confronted the ice group.

The resupply work was either done by landing near the ice group or, when no suitable areas were available, the stores were air dropped. During the crossing the aircraft operated first from Borga and then when the ice group neareed the South Pole it flew via the South Pole, to McMurdo on the Ross Ice Shelf from where it covered the second half of the crossing from Williams Airfield.

The base party from Borga travelled with the aircraft on this flight and established a new radio link at McMurdo. Once the ice group arrived the aircraft prepared to return to UK via South Pole, Rothera to via New Zealand and Australia to allow for visits to the trade exhibitions in these countries. On arrival back in the UK the aircraft again went on charter.

The next and last phase of the expedition which required air support was in the Arctic in early February 1982. Positioning the aircraft for this means a flight from the UK to Iceland, Labrador, Toronto, Winnipeg, Yellowknife, Resolute and finally to the base camp at Alert in Northern Canada. From Alert support was provided while the ice group travelled over the sea ice to the North Pole and then on to Spitsbergen. The pilot for this phase of the Expedition was Karl Zberg. As the ice group progressed from the North Pole towards Spitsbergen so the aircraft and the base camp crew changed to Cape Nord, Greenland and eventually to Longyearbyen, in Spitsbergen, to cover the last part of the ice group’s journey. During the crossing of the North Pole the Expedition’s ship sailed to the Spitsbergen area and then gather the ice group from the edge of the sea ice and returned to England. Once the ice group was safely aboard the ship the aircraft returned to the United Kingdom via Bodø in Norway, to await the ultimate arrival of the expedition team.