Unbeknown to him, F/O Bloggs had decided it would be a good idea to detune the ILS in favour of the VOR, and did it saying nothing until after the apparent failure.
Thank you. It was precisely what I was getting at re un-announced navaid frequency changes. Of course I didn't mean the PNF had to ask for the captain's approval every time he wanted to make a radio call. Thinks! I really must edit my contributions to avoid misconceptions..
During my command training on an F28 (first civil jet I'd operated) we were descending into Melbourne from Sydney and I was all at sea trying to work out the descent profile DME versus Altitude.
I was never much good at mental maths and it didn't help that the check captain in the jump seat was jumping down my neck every few miles of the descent demanding to know what height I should be at the next DME check point. "Come on" he said - "you should bloody know this by now - what height should you be at 40 DME and why have you got the speed brake out now - you don't need it - come on now for Christ's sake -smarten up".
The ADF was on Epping NDB and I think in those days we back-tracked from Eildon Weir VOR to a turning point called Kinglake and then at Kinglake you turn a bit right towards EPP NDB which was on the Melbourne 27 localiser.
The F/O kept silent no doubt in sympathy at the squawking from the jump seat. I knew EPP NDB needle should show about 10 degrees right until we were at Kinglake, but I was surprised to see the ADF needle showing dead ahead instead of off to the right. The jump seat check pilot was still impatiently demanding to know what should be the height NOW at 26 DME or some useless figure. It was then I looked across and saw the ADF was actually on Plenty NDB (situated on Essendon extended centre line) and not EPP where it had been.
I asked the F/O if he had changed the ADF to Plenty NDB and he said yes. He said he found it was better to have the NDB on PLE as it gave better tracking than Eildon Weir which was steadily going away from us behind us and that he was only trying to help.
If he had suggested that, I could have either accepted his suggestion or not. But his silent changing to another NDB without asking first, really upset the apple-cart along with the screaming skull in my right ear. I snapped, but that is of no consequence here. That was the point I was originally trying to make about PNF's that change frequencies without reference to the PF. It can be very distracting.