2
$\begingroup$

A device on top of Cessna 152 A device on top of Cessna 152 (closer look) A device on top of Cessna 152 (only one) A device on top of Cessna 152 (look like there are two)

What is this device? What is it for? Seems that some variants have only one, while some others have two.

Added: As some have two, so what are they? The answers and comments have not explained which antennae they are, especially for the ones with two antennae. As I asked, how does it work? I need an explanation; if the two antennas are for the same purpose, then why do they need two at the same place?

$\endgroup$
  • 1
    $\begingroup$ They are radio antennas. Most airplanes have two radios but small trainers like these often only have one. $\endgroup$ – JScarry Oct 3 '19 at 0:28
  • $\begingroup$ What antenna are they? $\endgroup$ – AirCraft Lover Oct 3 '19 at 1:12
  • 1
    $\begingroup$ Communication radio antenna. 118.00 to 136.975 MHz in 8.33 KHz spacing. Example: aircraftspruce.com/catalog/avpages/domeant.php $\endgroup$ – CrossRoads Oct 3 '19 at 1:32
  • 1
    $\begingroup$ Two antenna for two radios. Pilot can talk/listen on one, copilot can talk/listen on the other. Or pilot can talk/listen on one, and monitor incoming announcements on the other, such as automated weather & traffic advisories for the intended airport of landing. $\endgroup$ – CrossRoads Oct 3 '19 at 1:37
  • 1
    $\begingroup$ Huh? I would have Answered, but that is not a choice. $\endgroup$ – CrossRoads Oct 3 '19 at 12:11
7
$\begingroup$

Short answer: They're antenna(s) for the onboard VHF radio(s).

Airplanes aren't actually required to have radios. But, if you want to fly into certain classes of airspace, you must have at least one VHF radio on board, to communicate with air traffic control. A lot of planes (in fact, I would say the majority of them) actually have two radios installed. Thus, you see planes with zero, one, or two antennas.

Having two radios has several advantages, beyond just the obvious "backup in case one fails" advantage. Most often, one will be used to listen to the ATIS/AWOS/ASOS or other automated information broadcast while the other is used to keep in touch with ATC. You could also use the second one to contact Flight Services, or (if you're charter/commercial) keep in touch with your company (although that last one is getting more and more likely to be done with a cell phone or the internet).

$\endgroup$
  • $\begingroup$ Thank you for your explanation. $\endgroup$ – AirCraft Lover Oct 3 '19 at 3:48

Not the answer you're looking for? Browse other questions tagged or ask your own question.