Many years ago my father dropped me off at Darwin airport, I was catching a red eye special down to Melbourne. My plane was 20 minutes late getting in and as soon as it landed the pilot and copilot climbed out, walked under the left hand wing and opened the engine cowling, both of them stood there pointing and scratching their heads.
I asked my father what was going on and he said they probably had an ibis go through the engine when landing. Then the pilots shrugged their shoulders, closed up the cowling and walked away. I said to the old man "What's going on now then?" and he said "It's not cooked yet.".
That flight ended up leaving an hour and forty minutes late. Half an hour in to the flight I looked out the window and was shocked to be able to see the Stuart Highway and I could see trucks and cars travelling along it. You never fly anywhere near low enough to be able to see such things.
Just as I was starting to get worried about that the pilot spoke over the PA system, he said that he'd found a favourable jet stream at 23,000 feet and we should get to Adelaide on time. We ended up in Adelaide about 15 minutes early, what's normally a 4 hour flight took only 2. And think of how much fuel he saved doing that too.
I think planes should fly at this height. So if there is an emergency they are already almost on the ground so they don't fall 30 000 feet.