[Scan-DC] Should aviation use full duplex for tower comms?

[Dewey3]

This is just an opinion and worth exactly what you paid for it :)

As an aviation buff, one of my favorite TV pastimes is Air Disasters (aka
Air Crash Investigation, and Mayday).  There have been a couple episodes
where this was a significant factor, to include aviation's deadlist crash
(not including 9/11), the two 747s that collided on the island of Tenerife
(Air Disasters - Disaster at Tenerife).  Another epsiode that comes to mind
is where a commuter plane was landing and collided on the runway with a
private plane taking off (Air Disasters - Fatal Transmission).  Since the
*1977* Tenerife crash remains the deadliest to this day (again, not
including 9/11), my thoughts are your theory/proposition has been looked
at, probably several times in the past, but maybe just not feasible.  This
invokes the old adage and question, how much is a human life worth?

Dewey

On Thu, Mar 27, 2025 at 10:50 AM Andrew Clegg <andrew_w_clegg at hotmail.com>
wrote:

> I'm listening to the hearing on the DCA crash and air system safety. In
> reading some of the background on this crash, one of the items that came up
> is that the helicopter pilots may have had their radio keyed up to transmit
> to the tower at the same moment the tower was telling them to keep an eye
> out for the passenger plane, so they did not hear the controller. This is
> likely not the direct cause of the accident, but it probably didn't help.
>
> Besides this instance, when I listen to DCA tower, there are frequent
> occurrences when one pilot keys up when the tower is attempting to
> communicate with a different plane, causing the second pilot (and the
> first) not able to hear the tower.
>
> It seems to me that if full duplex was used, in which the frequency that
> the pilots transmit on is different from the one they receive on and they
> can therefore receive and transmit at the same time, then the interference
> caused by pilots keying up at inopportune times could be mitigated.
>
> The current simplex mode of operation in the 118-136 MHz aeronautical band
> reflects decades of established precedent and international agreement, as
> does the aeronautical radio equipment manufactured for this band. But
> switching to full duplex comms would seem to be a fairly straightforward
> option, if not inexpensive. The two frequencies would need to be separated
> by enough frequency that an effective duplex filter could be employed.
> There would be challenges with frequency planning, but if this was
> implemented solely for critical comms, such as tower comms but not
> approach, departure, and enroute frequencies, the frequency planning might
> be workable. For example, the tower could transmit at the low side (say,
> 118-121 MHz), the planes could transmit on the high side (say, 133-136),
> with a duplex gap from 121-133 MHz, which is where the non-tower comms
> could be placed.
>
> In the case of DCA, the tower is already using two frequencies: one for
> communications with planes (119.1) and another with helicopters (134.35).
> The tower side of the conversation is simulcast on both. I actually receive
> the tower on the helicopter frequency at my place better than I do the
> frequency used for airplanes. The antenna patterns might be different
> (lower elevation for the helicopter frequency perhaps).
>
> Just a thought for what it's worth, which probably isn't much.
>
> 73,
> W4JE
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