...
In the course of six months, the modification of a DC-3 takes place in three major areas: airframe, engines and props. The airframe is returned to its original specification. The radial engines are replaced with new Pratt & Whitney Canada PT6A-67R turboprop engines, certified to FAR Part 33, Amendment 10. Less maintenance is required for these engines, because overhaul time is at 6,000 hours versus 1,200 for the radial engines. Hartzell five-blade metal propellers replace the three-bladed props. Basler-converted airframes are “zero-time,” with respect to mandated inspections.

The company inserts a 40-inch plug in the fuselage, forward of the wing. This increases the airframe’s volume by 35 percent, and moves the cabin bulkhead forward five feet. Without this plug, the new props would be right outside the pilot’s window.

“We didn’t think it was a good idea to have the ice shields in line with the cockpit,” said Tom Weigt, president of Basler Turbo Conversions.

“A fully loaded BT-67 has a slower approach speed than a comparably loaded DC-3. At 10,000 feet, the PT6A 67R engines pull the BT-67 along at 230 mph, and burns 150 gallons per hour of jet fuel,” said Weigt.
...
“On the old DC-3, the wing stalls as a whole, and you lose aileron control,” explained Weigt. “Adding a wing cuff (a leading edge droop) increased the wing area effect. The cuff causes the outer wing to stall last, and keeps airflow over the aileron, which improves stall behavior.”
...
The basic BT-67 aircraft costs $4.5 million, and an aircraft equipped with maximum capability would run $13-plus million. Such an aircraft is classified, but it would probably contain search radar, infrared, intelligence of some level, listening devices, secure communications, night vision compatibility, an on-board oxygen generation system and probably a gun capability.

“Every year we make some changes,” said Weigt. “Most of them come from our customers who ask, for example, ‘Can you build a glass cockpit?’ ‘Can you take some weight out of the aircraft?’ ‘Can you improve the performance?’ ‘Can you give us a military flight manual?’ they’ll ask. The good thing is we can respond to them. When the request comes in, we take action.”
...