30 April 2015 © David Eyre
On 22 April 2015, a special visitor arrived in Perth for a two-week geophysical survey contract.
The aircraft, registered in Canada as C-FTGX, is a turboprop conversion of the famous Douglas DC-3, known as a Basler Turbo BT-67.
Manufactured during World War Two in 1944, it was built as a military version of the DC-3, initially designated as a C-47B for the US Army Air Force, but was instead allocated to the US Navy as a Douglas R4D-6. It served the Navy for over 20 years, later being redesignated as a C-47J.
In the late 1960s, it was sold to a civilian owner and registered N2566B in 1972, based in Alaska. It was re-registered as N56KS in 1977.
In 2004, N56KS was sold to Basler Turbo Conversions at Oshkosh, Wisconsin, and in August 2010 was converted to a BT-67 and sold later that year to Alci Aviation, operated by Bell Geospace.
Basler began in the late 1950’s as FBO Basler Flight Service and Basler Airlines. With years of experience flying the DC-3, they decided to improve and modernise the aircraft. The resulting conversion is called ‘Basler BT-67’, the first of which was converted in 1990. Old DC-3 airframes are re-engined with Pratt and Whitney PT6A-67R five-bladed turboprop engines, the fuselage lengthened by 4 feet ahead of the wing, strengthened airframe, leading edge and wing-tip modifications, plus modern avionics, fuel, hydraulic and electrical systems. Compared to the standard DC-3, the BT-67 has a 35% increase in cabin volume, 43% increase in payload, 24% more speed, 76% more productivity, up to 100% more fuel capacity, lower stall and approach speeds.
Bell Geospace are based in Houston, Texas and are one of the few companies that acquire gravity gradiometry data for geophysical surveys. Gravity gradiometry is used to measure the density of the subsurface rock, to locate oil, gas and mineral deposits. The aircraft has permanently installed Full Tensor Gravity Gradiometer (FTG) (hence the registration C-FTGX), manufactured by Lockheed Martin, and a tail-mounted magnetometer ‘stinger’. The FTG needs to be powered continuously, using twin generators to provide mains power while the aircraft is parked on the ground.
Survey flights are challenging for the crew as it must fly at a height of around 80 metres, using precise navigation to remain within a 15 metre ‘box’, vertically and laterally. If it goes out of the box, it must be brought back in the box within one kilometre, or the whole survey line has to be abandoned and flown again. The equipment is sensitive to turbulence, so flights are usually flown at times when calm conditions are forecast, such as early morning or later afternoon. The aircraft is crewed by two pilots and one or two survey technicians. The pilots take turns, with one pilot flying with reference to a bulls eye and on instruments, whilst the other pilot keeps an eye outside for obstructions, birds or other aircraft. Survey flights last about 4 – 8 hours per day.
HISTORY OF C-FTGX:
|43-48508||US Army Air Force||C-47B-1-DK||Built by Douglas at Oklahoma City, Oklahoma, USA. Original Manufacturer’s Serial Number was 14324. Not taken up by USAAF|
|17266||US Navy||26 AUG 1944||R4D-6Z||New Manufacturer’s Serial Number 25769 assigned.|
|15 FEB 1966||Sold at NAF Litchfield Park, Arizona|
|N2566B||R.J Heady||JUN 1972||DC-3C||Based in Alaska|
|N56KS||Kachemak Seafoods||21 JUN 1977||Based in Alaska. Stored at Anchorage in Oct 1978.|
|Sea Bear Air Transport||15 SEP 1980|
|2 JUN 1981||Substantially damaged in incident at Togiak Airport, Alaska.On a flight from Dillingham, Alaska to Togiak, the aircraft undershot the runway on final approach to land at 16:40 hours.The main gear hit ground ruts and the runway edge. No fatalities. NTSB report ANC81DA061:|
|Roger W Brooks||27 JUL 1984|
|Galaxy One Inc||23 JUL 1986|
|Corporate Express (registered to IFL Group Inc)||SEP 1988|
|K & K Aircraft Inc||11 APR 1990||Based at Bridgewater, Virginia, used as a sprayer.|
|Dynamic Aviation||OCT 2000|
|Eastern Mennonite University||12 MAY 2004|
|Basler Turbo Conversions LLC||2 DEC 2004||Stored at Oshkosh, Wisconsin.|
|Basler Turbo Conversions LLC||AUG 2010||BT-67||Converted to BT-67 – conversion number 55.|
|Bell Geospace Aviation Inc||10 NOV 2010|
|C-FTGX||Bell Geospace Aviation Inc (registered to ALCI Aviation Ltd)||17 NOV 2010||Modified for geophysical survey work with Full Tensor Gravity Gradiometer (FTG)|