De Havilland Aircraft of Canada Limited did not publish any guidance to operators of Dash 8 aircraft on the transmission and reception performance limitations of VHF COM 2 radios for ground-based communications.
On 6 December 2024, De Havilland Aircraft of Canada Limited released 2 flight operations service letters to operators recognising that VHF COM 1 may provide better ground-based signals to other stations either on the ground or in the air. ATSB believes that the proactive release of the flight operations service letters to inform operators of the limitations of the aircraft radio systems is sufficient for ATSB to conclude that the safety action taken by De Havilland Aircraft of Canada Limited was appropriate and timely and considers this safety issue adequately addressed.
De Havilland Aircraft of Canada Limited provided a response on 28 November 2024 stating that:
After reviewing the details of each event, De Havilland Aircraft of Canada Limited believes the root cause of the events to be operational and not aircraft related. However, in order to increase awareness of on ground communication De Havilland released 2 flight operations service letters (FOSLs) highlighting the antenna locations.
The FOSLs were released on 6 December 2024 for the Dash-8-100/200/300 (DH8-SL-23-008A) and Dash-8-400 (DH8-SL-23-020A). Details included a description of the limitations of VHF line of sight communications and the recommendation that VHF COM 1 may provide a better signal (receiving and transmitting) to other stations on the ground, or nearby in the air.
Both FOSLs identified the location of the VHF COM 1 and COM 2 antennas and that the nature of direct line of sight VHF communications can be affected by buildings, terrain or features of the aircraft, such as the vertical stabilizer or landing gear. They also identified that use of the upper fuselage antenna may provide a better line of sight with other aircraft or ground stations, which may result in improved communication in both transmission and reception.
The FOSLs are both located in Appendix D.
