This is a subject close to my heart. But first, just a jogged memory.
I was pre-flighting a medium weight turboprop prior to a passenger flight. My usual test for O2 first flight of the day, was to turn the oxygen off, then keep breathing until I was sure the valve had actually closed.
One day I just kept breathing. I put my finger in the outlet duct while looking in the mask. I could see my finger! The fleet's masks had been cleaned and some NRVs had never been replaced. They'd been flying like that for some days.
You can imagine the potential danger.
The jogged memory was about a Navajo I used to fly occasionally while training crews on a turboprop for most of the time. It was a nice little break, lovely countryside, and an undemanding schedule. But, I often just didn't feel right as I approached say, 8,000 feet.
It was hard to tell what was wrong, but something was. A feeling that the aircraft was balanced on a needle point. Move, and it would fall. I loved aerobatics, and if no pax, would throw it around as hard as I dared. Nothing. All normal. It was just when trying to maintain a smooth flight with a steady power setting.
Long story short, I had a huge medical, and nothing was found. Rather worrying. Then another pilot reported the same thing. The Air Force did his tests. EEGs, the lot. Nothing found. The aircraft was fitted with CO detectors. Nothing.
I reported that the sensation
Always went away almost as soon as I dropped the nose for the decent. ( Change in engine note perhaps. )
One doc made the remark that up to now, he'd never had sound vibrations affecting crews, but 'it was going to happen one day.' Maybe. I tried different engine settings but it didn't help. Not enough change perhaps.
The thing is, just imagine if the two of us had been in that aircraft at the same time. Major red herring.
That was in 1979, and never happened again in thousands of hours of flying, though one significant factor has just come to mind. Somewhere in the same year, I was treated with Tetracycline for an ear infection. Can't have been too near the time, or it would have been obvious, but I've had tinnitus ever since, so just maybe a connection. Just a hint of the wrong signals going in from the balance circuits, but not enough to give the game away perhaps.
By the way, there is a school of thought that links that antibiotic with tinnitus. Be careful - Tinnitus sucks.
