Can aviation HF radios receive while transmitting? I was listening to Gander Radio on HF at 5616 kHz today and I've noticed that operator at Gander would often start transmitting reply before the airplane finished transmission, as if trying to interrupt radio operator on the plane.

To me, this was very unusual behavior. From what I've heard and from what I concluded after listening to frequencies, it seems that HF radios in aeronautical mobile service work in traditional simplex mode, so crew normally crew wouldn't be able to hear the part of transmission send before they stop keying their radio. 

So this brings me to these questions: 
Are aviation HF radios capable of receiving while transmitting? If so, how?
Or if not, what's the point of Gander stepping on the plane's transmission?
In general, the HF radios in aviation work in simplex mode.

According to the Annex 10 to the Convention on International Civil Aviation- Aeronautical Telecommunications Volume V Aeronautical Radio Frequency Spectrum Utilization Chapter 3, 


  3.1.1 In the aeronautical mobile service, single channel simplex shall be used in radiotelephone communications utilizing radio frequencies below 30 MHz in the bands allocated exclusively to the aeronautical mobile (R) service.


Though some aviation radios are capable of semi-duplex operation, virtually all aviation services operate on simplex.

I have no idea why the operator was stepping on the aircraft's transmission though.