Roy Smith wrote:
Ron Rosenfeld wrote:

If possible, you can also have an overflying a/c relay a cancellation to
ATC.


Have you actually done that? It's my understanding that ATC won't accept
an IFR cancellation via an aircraft relay.


I did this just a few weeks ago, as I was next in line for the approach, the
aircraft on the ground was unable to raise ATC on the radio, and I relayed the
cancellation and was immediately cleared for the approach.

Well, "immediately" is relative. There was a sort of three-way handshake to
verify the cancellation.

Something like:
Me: ATC, Nxxx is trying to call you to cancel IFR.
ATC: Verify you're relaying for Nxxx trying to cancel IFR.
Me: yes
ATC: Please call Nxxx and ask them to verify cancelling IFR.
Me. Nxxx, please verify for ATC that you wish to cancel IFR.
Nxxx: Affirmative cancelling IFR.
Me. ATC, Nxxx confirms cancelling IFR.
ATC: Advise Nxxx cancellation received.
Me; Nxxx, ATC advises cancellation received.
Nxxx: Thank you.
ATC: Nyyy cleared RNAV rwy 21 approach...