VHF Communications systems on aircraft

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SUMMARY

The VHF communications system on aircraft is powered by the 28Vdc Essential Bus to ensure reliable operation during emergencies and to maintain communication with ground ATC before engine or APU start-up. This design choice prioritizes safety, as VHF radios are essential for instrument flying (IFR) operations. The reliance on the Essential Bus allows for standby power availability, ensuring that communication is not lost in critical situations, such as engine failure in single-engine aircraft.

PREREQUISITES
  • Understanding of aircraft electrical systems, specifically 28Vdc power distribution.
  • Knowledge of VHF communication systems and their role in aviation.
  • Familiarity with instrument flying rules (IFR) and their implications for communication.
  • Awareness of emergency procedures in aviation regarding power sources.
NEXT STEPS
  • Research the design and function of the 28Vdc Essential Bus in aircraft.
  • Study the operational principles of VHF communication systems in aviation.
  • Learn about emergency power systems and their applications in aircraft.
  • Examine the implications of IFR regulations on aircraft communication systems.
USEFUL FOR

Aviation engineers, aircraft maintenance technicians, and pilots seeking to understand the importance of VHF communications systems and their power sources in ensuring safety and compliance with IFR regulations.

qwertyu7
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Homework Statement


Does anyone know why number 1 VHF communications system powered from 28Vdc Battery Bus or 28Vdc Essential Bus and not from another source such as 28Vdc Main Bus or similar power source.

Homework Equations


The Attempt at a Solution


I was struggling to find reasons as to why this maybe so, but i was thinking that it may be because if they do operate on the 28Vdc Essential Bus, they can operate on standby power in case of emergency?
 
Last edited:
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First, I believe radio communication is considered essential equipment, at least on aircrafts that are rated for instrument flying (IFR). Like you said, its not good to loose communication as well if you have engine stop on a single-engine aircraft, for instance.

Secondly, since the main bus is typically is driven by generator that are powered by the engines or APU there is, for larger aircrafts at least, a procedural reason to power the radio stack from the battery so that ground ATC communications can be established before engine or APU start-up.
 

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