The Flying Bulls’ Douglas DC-6

The DC-6 undergoes a complete eight-week-long maintenance check every year. In addition to this standard procedure, many hundreds of working hours were invested in an avionics retrofit at the beginning of 2020 to equip the aircraft, which was built in 1958, with new technology.

The rare and special jewel of the Flying Bulls has always been well-equipped, but the latest upgrade means a further enhancement of technical equipment. In terms of instrument flight capability, the DC-6 is now on a level comparable to a modern aircraft. Dozens of drawings and circuit diagrams were prepared for this project, new instrument panels were manufactured, and a total of around 4 km of new cable was routed. The most frequently used cable has an outer diameter of only 1.27 mm. All cables are required to comply with aviation approved specifications.

Installation of a New Navigation System

The primary objective of the retrofit was to install two new navigation devices, which were integrated into the existing avionics system. The navigation devices rely on GPS, but can also receive and process classic (ground-based) navigation signals. Likewise, two new Digital Air Data Computers (DADC), which measure dynamic pressure, ambient pressure, and ambient temperature to feed this information digitally to the navigation devices, were also installed. This increases the accuracy and integrity of the navigation equipment.
While the DC-6 has always met all technical requirements, this has opened up new approach procedures for pilots at various airports in international air traffic.

Installation of a New Transponder

A transponder system is an absolute must-have in every aircraft. In European airspace, the so-called “ADS-B Out” is becoming mandatory for an increasing number of aircraft categories. Via this system, the aircraft transmits its position and other data via the transponder every 1-2 seconds.

Furthermore, these new transponders are also “ADS-B In” capable, which means they can receive the “ADS-B Out” signals of other aircraft and visualise them on a display for the crew. This state-of-the-art system makes it possible to see where other aircraft are heading, and at what altitude, at all times. The “traffic” is displayed on the electronic map of the navigation devices, enabling pilots to quickly visually identify other aircraft by means of geographical references.

It is regarded as part of the European airspace development initiative intended to ease the workload of air traffic control with regard to automation processes. The primary objective is to simplify communication and coordination between aircraft.

Highly Complex Projects

Given its complexity, this year’s work on the DC-6 was divided into two projects. One engineering team performed the standard maintenance tasks, while the avionics retrofit was carried out by a different team. A total of around 2,000 man-hours were invested in the avionics retrofit, plus several hundred man-hours by the project team for the preparation of technical documentation, certification documents, and project management in general.

Retaining the original look of the cockpit was a considerable challenge. In spite of the many new features, it is mandatory to maintain the look of historic aircraft such as the DC-6. Therefore, no electronic flight instruments or large screens are in place. The flight instruments remain analogue and the integration of modern systems does not alter the cockpit’s visual design greatly. This resulted in much more tedious planning and installation efforts.

The physical modifications to the DC-6 were completed in June. As part of the second phase of the project, verification flights are being carried out at various airports and under varying conditions, in coordination with the licensing authority, to put the system through its paces in flight mode. The completion of this process is imminent and soon the crown jewel of The Flying Bulls will be able to return to the skies.