Being a little concerned I just ran a quick test on my Icom 8600 and my Whistler TRX-1, both on 123.450MHz AM mode. I did a crude sensitivity measurement as I didn't want to break out audio cables to my SINAD meter and both the Icom and Whistler receive a .1uv AM signal modulated 30% with a 1KHz tone about the same from my IFR 1200S feeding a 10ft RG-142 BNC-BNC cable. At .2uv both receivers have a nice audible tone with some noise but its very listenable.
I squelched both radios with the Icom squelching at 30 and the TRX-1 just barely squelched with its analog knob and the Icom will unsquelch with a weak signal at .12uv and the TRX-1 closer to .11uv. That's splitting hairs, but from what I see the Icom 8600 is working just fine and is in the relm of very sensitive in the AM aircraft band.
Reading this thread concerned me a bit. I never really use my R8600 on VHF air band more than extremely causally, just occasionally going to the local airport Unicom. So I really had not checked out the R8600 in AM and VHF.
I do not have a SINAD meter. I do have a HP 8640B and a software audio power meter (on the soundcard of one of my machines). So, what follows may not be a true 10 dB S+N/N measurement, but should be somewhat close.
R8600 was set to: 124.000 MHz, AM mode, Default FIL 1, AGC OFF, Pre Amp was tried both ON and OFF, NB, NR, ATT, IP+, NOTCH all OFF.
HP 8640B set to: 124.000 MHz, Internal AM modulation, 1000 Hz, 30% modulation.
I took the audio out of the R8600 directly to the line input of the sound card. I set the audio power meter software REFERENCE to 0 dB (raw number was about -36 dB) with Squelch OFF and no RF signal input to the R8600.
R8600 Pre Amp OFF, Squelch set to 30% (just killed static):
-118 dBm, 0.28 uV, broke squelch with usable but somewhat scratchy audio.
R8600 Pre Amp ON, Squelch set to 30% (just killed static):
-130 dBm, 0.07 uV, broke squelch with scratchy audio.
R8600 Pre Amp OFF, Squelch OFF, Audio Power meter REF set to 0 dB with no signal present:
-112 dBm, 0.56 uV, 10 dB increase in Audio Power meter
R8600 Pre Amp ON, Squelch OFF, Audio Power meter REF set to 0 dB with no signal present:
-120 dBm, 0.22 uV, 10 dB increase in Audio Power meter
Again, I am not going to claim this is a 100% valid 10dB S+N/N measurement, but it should be in the ball park.
It looks to me like the R8600, at least my copy, is adequately sensitive in the VHF Air Band.
T!